From 1d45a52da7b9565ade641b18fba09c8d99c5b891 Mon Sep 17 00:00:00 2001
From: Jamie <113370520+jamiebuilds-signal@users.noreply.github.com>
Date: Thu, 12 Mar 2026 16:24:01 -0700
Subject: [PATCH] Enable tsconfig noUncheckedIndexedAccess

---
 app/attachment_channel.main.ts                |   4 +-
 app/main.main.ts                              |  18 +-
 app/menu.std.ts                               |  11 +-
 build/intl-linter/linter.node.ts              |   3 +-
 build/intl-linter/rules/wrapEmoji.std.ts      |   3 +-
 ts/ConversationController.preload.ts          |   4 +-
 ts/Crypto.node.ts                             |  17 +-
 ts/Curve.node.ts                              |  13 +-
 ts/RemoteConfig.dom.ts                        |   4 +-
 ts/SignalProtocolStore.preload.ts             |  21 +-
 ts/axo/AxoAvatar.dom.stories.tsx              |   3 +-
 ts/axo/AxoTokens.std.ts                       |   6 +-
 ts/calling/VideoSupport.preload.ts            |   2 +-
 ts/calling/findBestMatchingDevice.std.ts      |   9 +-
 .../AddUserToAnotherGroupModal.dom.tsx        |   2 +
 .../AnnouncementsOnlyGroupBanner.dom.tsx      |   3 +-
 ts/components/Avatar.dom.stories.tsx          |   3 +-
 ts/components/BadgeDialog.dom.tsx             |   3 +-
 ts/components/CallManager.dom.stories.tsx     |  46 ++--
 ts/components/CallReactionBurstEmoji.dom.tsx  |   3 +-
 ts/components/CallScreen.dom.stories.tsx      |  16 +-
 ts/components/CallScreen.dom.tsx              |   3 +-
 ts/components/CallingDeviceSelection.dom.tsx  |   3 +-
 ...CallingPendingParticipants.dom.stories.tsx |  12 +-
 ts/components/CallingPip.dom.tsx              |   6 +-
 .../CallingPreCallInfo.dom.stories.tsx        |  12 +-
 ts/components/CallingPreCallInfo.dom.tsx      |  56 ++---
 ts/components/CallingToast.dom.tsx            |   6 +-
 ts/components/ChatColorPicker.dom.tsx         |   3 +-
 ts/components/CompositionArea.dom.stories.tsx |   9 +-
 ts/components/CompositionArea.dom.tsx         |   9 +-
 ts/components/CompositionInput.dom.tsx        |   4 +-
 ts/components/ContactPills.dom.stories.tsx    |  29 ++-
 ts/components/ContextMenu.dom.tsx             |   3 +-
 .../ConversationList.dom.stories.tsx          |   4 +-
 .../EditHistoryMessagesModal.dom.tsx          |   2 +
 .../GroupCallRemoteParticipants.dom.tsx       |  19 +-
 ts/components/GroupMembersNames.dom.tsx       |  44 ++--
 ts/components/IncomingCallBar.dom.tsx         |  17 +-
 ts/components/LeftPane.dom.stories.tsx        |   4 +-
 ts/components/Lightbox.dom.tsx                |   9 +-
 ts/components/MyStories.dom.stories.tsx       |   9 +-
 ts/components/MyStoryButton.dom.tsx           |   9 +-
 ...GroupInvitedContactsDialog.dom.stories.tsx |   4 +-
 ...yCreatedGroupInvitedContactsDialog.dom.tsx |   3 +-
 .../NotificationProfilesMenu.dom.stories.tsx  |  14 +-
 ts/components/PlaybackRateButton.dom.tsx      |   5 +-
 ts/components/PollCreateModal.dom.tsx         |   2 +-
 ts/components/Preferences.dom.stories.tsx     |  12 +-
 .../PreferencesNotificationProfiles.dom.tsx   |   3 +-
 ts/components/ProfileEditor.dom.tsx           |   7 +-
 ts/components/SafetyTipsModal.dom.tsx         |   3 +-
 ts/components/SharedGroupNames.dom.tsx        |  26 ++-
 ts/components/TextAttachment.dom.tsx          |   2 +-
 .../VoiceNotesPlaybackContext.dom.tsx         |   4 +-
 .../conversation/AttachmentList.dom.tsx       |   3 +-
 .../conversation/ContactModal.dom.tsx         |   3 +-
 .../conversation/ConversationView.dom.tsx     |   4 +-
 .../conversation/GroupNotification.dom.tsx    |   6 +-
 .../conversation/GroupV1Migration.dom.tsx     |   3 +-
 ts/components/conversation/ImageGrid.dom.tsx  | 186 ++++++++-------
 ts/components/conversation/Message.dom.tsx    |  19 +-
 .../conversation/ReactionViewer.dom.tsx       |   1 +
 ts/components/conversation/Timeline.dom.tsx   |   4 +
 .../TimelineMessage.dom.stories.tsx           |   3 +-
 .../conversation/TimelineMessage.dom.tsx      |   3 +-
 .../conversation/TypingBubble.dom.tsx         |   6 +-
 .../ChooseGroupMembersModal.dom.tsx           |   1 +
 .../ConversationDetails.dom.stories.tsx       |  11 +-
 .../ConversationDetails.dom.tsx               |   3 +-
 ...ationDetailsMembershipList.dom.stories.tsx |   6 +-
 .../ConversationDetailsMembershipList.dom.tsx |   3 +-
 .../GroupMemberLabelEditor.dom.tsx            |   5 +-
 .../PendingInvites.dom.tsx                    |  42 ++--
 .../conversation-details/util.std.ts          |  12 +-
 .../media-gallery/MediaGallery.dom.tsx        |   3 +-
 .../media-gallery/utils/mocks.std.ts          |  39 ++--
 .../pinned-messages/PinnedMessagesBar.dom.tsx |   3 +-
 ts/components/fun/FunEmoji.dom.stories.tsx    |   3 +-
 ts/components/fun/panels/FunPanelGifs.dom.tsx |   5 +-
 .../fun/panels/FunPanelStickers.dom.tsx       |   1 +
 .../fun/virtual/useFunVirtualGrid.dom.tsx     |  11 +-
 .../LeftPaneChooseGroupMembersHelper.dom.tsx  |   3 +-
 .../leftPane/LeftPaneInboxHelper.dom.tsx      |   6 +-
 .../leftPane/LeftPaneSearchHelper.dom.tsx     |   3 +-
 ts/groups.preload.ts                          |  30 +--
 ts/hooks/useRestoreFocus.dom.ts               |   2 +-
 ts/hooks/useSizeObserver.dom.tsx              |   3 +-
 ts/hooks/useTabs.dom.tsx                      |   3 +-
 ts/jobs/AttachmentBackupManager.preload.ts    |   1 +
 ts/jobs/conversationJobQueue.preload.ts       |   3 +-
 ts/jobs/helpers/sendNormalMessage.preload.ts  |   6 +-
 ts/jobs/helpers/sendPollTerminate.preload.ts  |   3 +-
 ts/jobs/helpers/sendPollVote.preload.ts       |   3 +-
 ts/jobs/helpers/sendReaction.preload.ts       |   3 +-
 ts/jobs/helpers/sendStory.preload.ts          |  59 +++--
 ts/logging/log.std.ts                         |   3 +-
 ts/logging/main_process_logging.main.ts       |   6 +-
 .../MessageReceipts.preload.ts                |   6 +-
 ts/messageModifiers/Polls.preload.ts          |   3 +-
 ts/messages/copyQuote.preload.ts              |   3 +-
 ts/messages/migrateMessageData.preload.ts     |   3 +-
 ts/models/conversations.preload.ts            |  30 ++-
 .../index.dom.tsx                             |   3 +-
 ts/quill/emoji/completion.dom.tsx             |  22 +-
 ts/quill/formatting/matchers.dom.ts           |   4 +-
 ts/quill/mentions/completion.dom.tsx          |  12 +-
 ts/quill/signal-clipboard/util.dom.ts         |   7 +-
 .../build-localized-display-names.node.ts     |  18 +-
 ts/scripts/check-min-os-version.node.ts       |  11 +-
 ts/scripts/constants.std.ts                   |   1 +
 ts/scripts/gen-nsis-script.node.ts            |   3 +-
 ts/scripts/notarize-universal-dmg.node.ts     |   3 +-
 ts/scripts/publish-installer-size.node.ts     |   3 +-
 ts/scripts/remove-strings.node.ts             |   5 +-
 ts/scripts/symbolicate-crash-report.node.ts   |   9 +-
 ts/scripts/update-gha.node.ts                 |   9 +-
 ts/services/BeforeNavigate.std.ts             |   3 +-
 ts/services/LinkPreview.preload.ts            |   3 +-
 ts/services/MessageCache.preload.ts           |   3 +-
 .../addGlobalKeyboardShortcuts.preload.ts     |   2 +
 ts/services/backups/credentials.preload.ts    |   6 +-
 ts/services/backups/import.preload.ts         |   4 +-
 ts/services/calling.preload.ts                |  39 +++-
 ts/services/groupCredentialFetcher.preload.ts |   6 +-
 .../releaseNoteAndMegaphoneFetcher.preload.ts |   8 +-
 ts/services/retryPlaceholders.std.ts          |   4 +-
 ts/services/storage.preload.ts                |   6 +-
 ts/services/storyLoader.preload.ts            |   3 +-
 ts/services/username.preload.ts               |   3 +-
 ts/services/writeProfile.preload.ts           |   3 +-
 ts/sql/Server.node.ts                         |  48 ++--
 ts/sql/hydration.std.ts                       |   3 +-
 ts/sql/main.main.ts                           |   6 +
 .../migrations/1280-blob-unprocessed.std.ts   |   3 +
 ts/sql/migrations/88-service-ids.std.ts       |   6 +-
 ts/sql/migrations/index.node.ts               |  17 +-
 ts/sql/util.std.ts                            |   3 +-
 ts/state/ducks/audioPlayer.preload.ts         |   3 +-
 ts/state/ducks/calling.preload.ts             |   2 +-
 ts/state/ducks/composer.preload.ts            |  17 +-
 ts/state/ducks/conversations.preload.ts       |  41 ++--
 ts/state/ducks/lightbox.preload.ts            |  12 +-
 ts/state/ducks/mediaGallery.preload.ts        |   6 +-
 ts/state/ducks/safetyNumber.preload.ts        |   4 +
 ts/state/ducks/search.preload.ts              |   5 +-
 ts/state/ducks/stickers.preload.ts            |   6 +-
 ts/state/ducks/stories.preload.ts             |  77 +++++--
 .../ducks/storyDistributionLists.preload.ts   |  12 +-
 ts/state/selectors/callHistory.std.ts         |   4 +-
 ts/state/selectors/conversations.dom.ts       |  44 ++--
 ts/state/selectors/message.preload.ts         |  12 +-
 ts/state/selectors/stickers.std.ts            |   2 +-
 ts/state/selectors/stories.preload.ts         |   9 +-
 ts/state/selectors/timeline.preload.ts        |   3 +-
 ts/state/smart/CallManager.preload.tsx        |  16 +-
 ts/state/smart/ToastManager.preload.tsx       |   3 +-
 ts/test-electron/Crypto_test.preload.ts       |  12 +-
 .../MessageReceipts_test.preload.ts           |  28 +--
 .../SignalProtocolStore_test.preload.ts       |   6 +-
 ts/test-electron/backup/helpers.preload.ts    |   3 +-
 .../linkPreviewFetch_test.preload.ts          |  13 +-
 .../models/conversations_test.preload.ts      |   4 +-
 .../models/messages_test.preload.ts           |   4 +-
 .../quill/emoji/completion_test.dom.tsx       |  26 ++-
 .../quill/mentions/matchers_test.std.ts       |   4 +
 .../AttachmentBackupManager_test.preload.ts   |  91 +++++---
 .../AttachmentDownloadManager_test.preload.ts | 212 +++++++++++-------
 ...aseNoteAndMegaphoneFetcher_test.preload.ts |   8 +-
 .../sql/fullTextSearch_test.preload.ts        |  34 +--
 .../sql/getRecentStoryReplies_test.preload.ts |   6 +-
 ts/test-electron/sql/markRead_test.preload.ts |  28 +--
 .../sql/notificationProfiles_test.preload.ts  |   2 +-
 .../sql/pollVoteMarkRead_test.preload.ts      |  12 +-
 ts/test-electron/sql/sendLog_test.preload.ts  |  10 +-
 ts/test-electron/sql/stories_test.preload.ts  |  18 +-
 .../sql/storyDistribution_test.preload.ts     |   5 +-
 .../sql/timelineFetches_test.preload.ts       |  30 +--
 .../state/ducks/calling_test.preload.ts       |  16 +-
 .../state/ducks/conversations_test.preload.ts |  18 +-
 .../textsecure/generate_keys_test.preload.ts  |   6 +-
 .../addAttachmentToMessage_test.preload.ts    |  12 +-
 .../util/migrateMessageData_test.preload.ts   |  10 +-
 ts/test-helpers/expireTimers.std.ts           |  21 +-
 ts/test-helpers/generateBackup.node.ts        |   3 +-
 ts/test-helpers/getRandomColor.std.ts         |   3 +-
 ts/test-mock/backups/backups_test.node.ts     |   7 +-
 .../call_history_search_bench.node.ts         |   3 +-
 .../benchmarks/convo_open_bench.node.ts       |   2 +-
 .../benchmarks/group_send_bench.node.ts       |   6 +-
 ts/test-mock/benchmarks/send_bench.node.ts    |   3 +-
 ts/test-mock/benchmarks/startup_bench.node.ts |   3 +-
 ts/test-mock/bootstrap.node.ts                |   6 +-
 .../messaging/attachments_test.node.ts        |  20 +-
 ts/test-mock/messaging/backfill_test.node.ts  |   2 +-
 ts/test-mock/messaging/edit_test.node.ts      |  33 +--
 ts/test-mock/messaging/lightbox_test.node.ts  |   6 +-
 ts/test-mock/messaging/reaction_test.node.ts  |  24 +-
 ts/test-mock/messaging/readSync_test.node.ts  |   3 +-
 ts/test-mock/messaging/relink_test.node.ts    |  19 +-
 ts/test-mock/messaging/retries_test.node.ts   |   9 +-
 .../messaging/safety_number_test.node.ts      |  19 +-
 .../messaging/sender_key_test.node.ts         |   6 +-
 ts/test-mock/messaging/stories_test.node.ts   |   9 +-
 .../messaging/unknown_contact_test.node.ts    |   2 +-
 .../messaging/unprocessed_test.node.ts        |  13 +-
 .../network/serverAlerts_test.node.ts         |   2 +-
 .../pnp/accept_gv2_invite_test.node.ts        |  17 +-
 ts/test-mock/pnp/change_number_test.node.ts   |   3 +-
 ts/test-mock/pnp/merge_test.node.ts           |   2 +-
 ts/test-mock/pnp/send_gv2_invite_test.node.ts |   2 +-
 ts/test-mock/pnp/username_test.node.ts        |   4 +-
 ts/test-mock/routing/routing_test.node.ts     |   3 +-
 ts/test-mock/storage/archive_test.node.ts     |   3 +-
 ts/test-mock/storage/conflict_test.node.ts    |  14 +-
 ts/test-mock/storage/fixtures.node.ts         |  10 +-
 .../storage/max_read_keys_test.node.ts        |   5 +-
 ts/test-mock/storage/sticker_test.node.ts     |   7 +-
 .../LeftPaneArchiveHelper_test.dom.ts         |  12 +-
 ...ftPaneChooseGroupMembersHelper_test.dom.ts |   8 +-
 .../LeftPaneComposeHelper_test.dom.ts         |  10 +-
 .../leftPane/LeftPaneInboxHelper_test.dom.tsx |  42 ++--
 .../leftPane/LeftPaneSearchHelper_test.dom.ts |  43 ++--
 ...LeftPaneSetGroupMetadataHelper_test.dom.ts |   2 +-
 .../getConversationInDirection_test.dom.ts    |   4 +-
 .../groupMediaItemsByDate.std.ts              |  44 ++--
 ts/test-node/jobs/JobQueue_test.node.ts       |   4 +-
 .../messages/MessageSendState_test.std.ts     |   2 +-
 ts/test-node/reactions/util_test.std.ts       |   2 +-
 ts/test-node/sql/migration_1000_test.node.ts  |   8 +-
 ts/test-node/sql/migration_1040_test.node.ts  |   2 +-
 ts/test-node/sql/migration_1060_test.node.ts  |   4 +-
 ts/test-node/sql/migration_1200_test.node.ts  |   2 +-
 ts/test-node/sql/migration_89_test.preload.ts |  42 ++--
 ts/test-node/sql/migrations_test.node.ts      |  82 ++++---
 .../selectors/conversations_test.preload.ts   |  26 +--
 .../state/selectors/search_test.preload.ts    |   4 +-
 ts/test-node/types/BodyRange_test.std.ts      |   2 +-
 .../types/EmbeddedContact_test.std.ts         |  18 +-
 .../types/NotificationProfile_test.node.ts    |   6 +-
 .../updater/differential_test.node.ts         |  14 +-
 ts/test-node/updater/signature_test.main.ts   |   3 +-
 .../util/getFontNameByTextScript_test.dom.ts  |   2 +
 ts/test-node/util/iterables_test.std.ts       |   4 +-
 ts/test-node/util/logPadding_test.node.ts     |  23 +-
 .../queueAttachmentDownloads_test.preload.ts  | 126 +++++------
 ts/textsecure/Errors.std.ts                   |  10 +-
 ts/textsecure/EventTarget.std.ts              |   2 +-
 ts/textsecure/Helpers.std.ts                  |   3 +-
 ts/textsecure/MessageReceiver.preload.ts      |   5 +-
 ts/textsecure/Provisioner.preload.ts          |  10 +-
 ts/textsecure/SendMessage.preload.ts          |   6 +-
 ts/textsecure/WebAPI.preload.ts               |  28 ++-
 ts/types/AttachmentSize.std.ts                |   3 +-
 ts/types/BodyRange.std.ts                     |   7 +-
 ts/types/Colors.std.ts                        |   5 +-
 ts/types/Megaphone.std.ts                     |   3 +-
 ts/types/Message2.preload.ts                  |   2 +
 ts/types/QualifiedAddress.std.ts              |   8 +-
 ts/types/Stickers.preload.ts                  |  25 +--
 ts/updater/common.main.ts                     |   3 +-
 ts/updater/curve.node.ts                      |   7 +-
 ts/updater/differential.node.ts               |  11 +-
 ts/updater/generateSignature.main.ts          |   4 +-
 ts/util/Attachment.std.ts                     |   5 +-
 ts/util/BackOff.std.ts                        |   3 +-
 ts/util/DelimitedStream.node.ts               |   3 +-
 ts/util/arePinnedConversationsEqual.node.ts   |   2 +-
 ts/util/benchmark/stats.std.ts                |   6 +-
 ts/util/cleanup.preload.ts                    |   6 +-
 ts/util/computeBlurHashUrl.std.ts             |   9 +-
 ts/util/createHTTPSAgent.node.ts              |  12 +-
 ts/util/createIdenticon.preload.tsx           |   2 +
 ts/util/createProxyAgent.node.ts              |   3 +-
 ts/util/createSupportUrl.std.ts               |   4 +-
 ts/util/deleteStoryForEveryone.preload.ts     |   3 +-
 ts/util/deliveryReceipt.preload.ts            |   4 +-
 ts/util/desktopCapturer.preload.ts            |   6 +-
 ts/util/downloadOnboardingStory.preload.ts    |   6 +-
 ts/util/editHelpers.std.ts                    |   6 +-
 ts/util/expirationTimer.std.ts                |   2 +-
 ts/util/exponentialBackoff.std.ts             |   3 +-
 ts/util/filterAndSortConversations.std.ts     |   5 +-
 ...ndDeleteOnboardingStoryIfExists.preload.ts |   3 +-
 ts/util/generateDonationReceipt.dom.ts        |   2 +-
 ts/util/generateMessageId.node.ts             |  12 +-
 ts/util/getColorForCallLink.std.ts            |   7 +-
 ts/util/getCountryData.dom.ts                 |   3 +-
 ts/util/getFontNameByTextScript.std.ts        | 171 +++++++-------
 ts/util/getHSL.std.ts                         |  12 +-
 ts/util/getInitials.std.ts                    |   3 +-
 .../getNotificationDataForMessage.preload.ts  |   9 +-
 ts/util/getQuoteBodyText.std.ts               |   3 +-
 ts/util/graphemeAndLinkAwareSlice.std.ts      |   3 +-
 ts/util/groupAndOrderReactions.dom.ts         |   3 +-
 ts/util/groupSendEndorsements.preload.ts      |   1 +
 ts/util/handleRetry.preload.ts                |   3 +-
 ts/util/lint/license_comments.node.ts         |   6 +-
 ts/util/objectMap.std.ts                      |   3 +-
 ts/util/scaleImageToLevel.preload.ts          |   3 +-
 ts/util/search.std.ts                         |   6 +-
 ts/util/sendStoryMessage.preload.ts           |   3 +-
 ts/util/sendToGroup.preload.ts                |   4 +-
 ts/util/sniffImageMimeType.std.ts             |   7 +-
 ts/util/syncTasks.preload.ts                  |   3 +-
 ts/util/userLanguages.std.ts                  |   3 +-
 ts/util/whitespaceStringUtil.std.ts           |  47 ----
 ts/window.d.ts                                |  30 +++
 ts/windows/main/preload_test.preload.ts       |   6 +-
 ts/windows/main/start.preload.ts              |   2 +-
 tsconfig.json                                 |   3 +-
 311 files changed, 2146 insertions(+), 1589 deletions(-)
 delete mode 100644 ts/util/whitespaceStringUtil.std.ts

diff --git a/app/attachment_channel.main.ts b/app/attachment_channel.main.ts
index 24c059945a..2b70c77e82 100644
--- a/app/attachment_channel.main.ts
+++ b/app/attachment_channel.main.ts
@@ -791,13 +791,15 @@ function handleRangeRequest({
   }
 
   // Chromium only sends open-ended ranges: "start-"
+  type Match = RegExpMatchArray & { 1: string };
   const match = range.match(/^bytes=(\d+)-$/);
   if (match == null) {
     log.error(`invalid range header: ${range}`);
     return create200Response();
   }
 
-  const startParam = safeParseInteger(match[1]);
+  const [startInput] = match as Match;
+  const startParam = safeParseInteger(startInput);
   if (startParam == null) {
     log.error(`invalid range header: ${range}`);
     return create200Response();
diff --git a/app/main.main.ts b/app/main.main.ts
index 60097d4531..da85a29df2 100644
--- a/app/main.main.ts
+++ b/app/main.main.ts
@@ -819,10 +819,14 @@ async function createWindow() {
       maximized: mainWindow.isMaximized(),
       autoHideMenuBar: mainWindow.autoHideMenuBar,
       fullscreen: mainWindow.isFullScreen(),
-      width: size[0],
-      height: size[1],
-      x: position[0],
-      y: position[1],
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      width: size[0]!,
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      height: size[1]!,
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      x: position[0]!,
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      y: position[1]!,
     };
 
     if (
@@ -1565,8 +1569,10 @@ function showPermissionsPopupWindow(forCalling: boolean, forCamera: boolean) {
 
     const size = mainWindow.getSize();
     const options = {
-      width: Math.min(400, size[0]),
-      height: Math.min(150, size[1]),
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      width: Math.min(400, size[0]!),
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      height: Math.min(150, size[1]!),
       resizable: false,
       title: getResolvedMessagesLocale().i18n('icu:allowAccess'),
       titleBarStyle: nonMainTitleBarStyle,
diff --git a/app/menu.std.ts b/app/menu.std.ts
index 0f47420e1d..b854d59915 100644
--- a/app/menu.std.ts
+++ b/app/menu.std.ts
@@ -9,6 +9,7 @@ import type {
   MenuOptionsType,
   MenuActionsType,
 } from '../ts/types/menu.std.js';
+import { strictAssert } from '../ts/util/assert.std.js';
 
 const { isString } = lodash;
 
@@ -220,6 +221,7 @@ export const createTemplate = (
 
   if (includeSetup) {
     const fileMenu = template[0];
+    strictAssert(fileMenu, 'Missing fileMenu');
 
     if (Array.isArray(fileMenu.submenu)) {
       // These are in reverse order, since we're prepending them one at a time
@@ -265,6 +267,7 @@ function updateForMac(
 
   // Remove About item and separator from Help menu, since they're in the app menu
   const aboutMenu = template[4];
+  strictAssert(aboutMenu, 'Missing aboutMenu');
   if (Array.isArray(aboutMenu.submenu)) {
     aboutMenu.submenu.pop();
     aboutMenu.submenu.pop();
@@ -275,6 +278,7 @@ function updateForMac(
   // Remove preferences, separator, and quit from the File menu, since they're
   // in the app menu
   const fileMenu = template[0];
+  strictAssert(fileMenu, 'Missing fileMenu');
   if (Array.isArray(fileMenu.submenu)) {
     fileMenu.submenu.pop();
     fileMenu.submenu.pop();
@@ -343,6 +347,7 @@ function updateForMac(
   });
 
   const editMenu = template[2];
+  strictAssert(editMenu, 'Missing editMenu');
   if (Array.isArray(editMenu.submenu)) {
     editMenu.submenu.push(
       {
@@ -366,9 +371,11 @@ function updateForMac(
     throw new Error('updateForMac: edit.submenu was not an array!');
   }
 
+  const windowMenu = template[4];
+  strictAssert(windowMenu, 'Missing windowMenu');
   // Replace Window menu
-  // eslint-disable-next-line no-param-reassign
-  template[4].submenu = [
+
+  windowMenu.submenu = [
     {
       label: i18n('icu:windowMenuMinimize'),
       accelerator: 'CmdOrCtrl+M',
diff --git a/build/intl-linter/linter.node.ts b/build/intl-linter/linter.node.ts
index eeb0f4ea9f..9183c0d342 100644
--- a/build/intl-linter/linter.node.ts
+++ b/build/intl-linter/linter.node.ts
@@ -174,7 +174,8 @@ async function lintMessages() {
     const key = topProp.key.value;
 
     if (process.argv.includes('--test')) {
-      const test = tests[key];
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      const test = tests[key]!;
       const actualErrors = reports.map(report => report.id);
       deepEqual(actualErrors, test.expectErrors);
       continue;
diff --git a/build/intl-linter/rules/wrapEmoji.std.ts b/build/intl-linter/rules/wrapEmoji.std.ts
index 115bfe3df6..272957c9d1 100644
--- a/build/intl-linter/rules/wrapEmoji.std.ts
+++ b/build/intl-linter/rules/wrapEmoji.std.ts
@@ -37,7 +37,8 @@ export default rule('wrapEmoji', context => {
         return;
       }
 
-      const child = element.children[0];
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      const child = element.children[0]!;
       if (!isLiteralElement(child)) {
         // non-literal
         context.report(
diff --git a/ts/ConversationController.preload.ts b/ts/ConversationController.preload.ts
index ae05b76b4f..0a708450d1 100644
--- a/ts/ConversationController.preload.ts
+++ b/ts/ConversationController.preload.ts
@@ -1587,9 +1587,7 @@ export class ConversationController {
       `forceRerender: Starting to loop through ${conversations.length} conversations`
     );
 
-    for (let i = 0, max = conversations.length; i < max; i += 1) {
-      const conversation = conversations[i];
-
+    for (const conversation of conversations) {
       if (conversation.cachedProps) {
         conversation.oldCachedProps = conversation.cachedProps;
         conversation.cachedProps = null;
diff --git a/ts/Crypto.node.ts b/ts/Crypto.node.ts
index 78f2735fe2..8b588d0fa5 100644
--- a/ts/Crypto.node.ts
+++ b/ts/Crypto.node.ts
@@ -357,8 +357,8 @@ export function verifyHmacSha256(
   let result = 0;
 
   for (let i = 0; i < theirMac.byteLength; i += 1) {
-    // eslint-disable-next-line no-bitwise
-    result |= ourMac[i] ^ theirMac[i];
+    // eslint-disable-next-line no-bitwise, @typescript-eslint/no-non-null-assertion
+    result |= ourMac[i]! ^ theirMac[i]!;
   }
   if (result !== 0) {
     throw new Error('Bad MAC');
@@ -482,8 +482,8 @@ function verifyDigest(data: Uint8Array, theirDigest: Uint8Array): void {
   const ourDigest = sha256(data);
   let result = 0;
   for (let i = 0; i < theirDigest.byteLength; i += 1) {
-    // eslint-disable-next-line no-bitwise
-    result |= ourDigest[i] ^ theirDigest[i];
+    // eslint-disable-next-line no-bitwise, @typescript-eslint/no-non-null-assertion
+    result |= ourDigest[i]! ^ theirDigest[i]!;
   }
   if (result !== 0) {
     throw new Error('Bad digest');
@@ -744,7 +744,8 @@ export function getIdentifierHash({
   }
 
   const digest = hash(HashType.size256, identifier);
-  return digest[0];
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  return digest[0]!;
 }
 
 export function generateAvatarColor({
@@ -761,8 +762,10 @@ export function generateAvatarColor({
   const hashValue = getIdentifierHash({ aci, e164, pni, groupId });
 
   if (hashValue == null) {
-    return sample(AvatarColors) || AvatarColors[0];
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    return sample(AvatarColors) || AvatarColors[0]!;
   }
 
-  return AvatarColors[hashValue % AVATAR_COLOR_COUNT];
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  return AvatarColors[hashValue % AVATAR_COLOR_COUNT]!;
 }
diff --git a/ts/Curve.node.ts b/ts/Curve.node.ts
index 605734c712..dd351e3420 100644
--- a/ts/Curve.node.ts
+++ b/ts/Curve.node.ts
@@ -145,10 +145,11 @@ export function setPublicKeyTypeByte(publicKey: Uint8Array): void {
 }
 
 export function clampPrivateKey(privateKey: Uint8Array): void {
-  // eslint-disable-next-line no-bitwise, no-param-reassign
-  privateKey[0] &= 248;
-  // eslint-disable-next-line no-bitwise, no-param-reassign
-  privateKey[31] &= 127;
-  // eslint-disable-next-line no-bitwise, no-param-reassign
-  privateKey[31] |= 64;
+  /* eslint-disable no-bitwise, no-param-reassign */
+  /* eslint-disable @typescript-eslint/no-non-null-assertion */
+  privateKey[0]! &= 248;
+  privateKey[31]! &= 127;
+  privateKey[31]! |= 64;
+  /* eslint-enable no-bitwise, no-param-reassign */
+  /* eslint-enable @typescript-eslint/no-non-null-assertion */
 }
diff --git a/ts/RemoteConfig.dom.ts b/ts/RemoteConfig.dom.ts
index 18edf9e61d..0de6dba541 100644
--- a/ts/RemoteConfig.dom.ts
+++ b/ts/RemoteConfig.dom.ts
@@ -166,7 +166,9 @@ export function onChange(
   listeners[key] = keyListeners;
 
   return () => {
-    listeners[key] = listeners[key].filter(l => l !== fn);
+    if (listeners[key]) {
+      listeners[key] = listeners[key].filter(l => l !== fn);
+    }
   };
 }
 
diff --git a/ts/SignalProtocolStore.preload.ts b/ts/SignalProtocolStore.preload.ts
index 2a0ff4cf82..dea6fcfc9c 100644
--- a/ts/SignalProtocolStore.preload.ts
+++ b/ts/SignalProtocolStore.preload.ts
@@ -176,8 +176,7 @@ async function _fillCaches<ID, T extends HasIdType<ID>, HydratedType>(
   const items = await itemsPromise;
 
   const cache = new Map<ID, CacheEntryType<T, HydratedType>>();
-  for (let i = 0, max = items.length; i < max; i += 1) {
-    const fromDB = items[i];
+  for (const fromDB of items) {
     const { id } = fromDB;
 
     cache.set(id, {
@@ -304,12 +303,12 @@ export class SignalProtocolStore extends EventEmitter {
           return;
         }
 
-        for (const serviceId of Object.keys(map.value)) {
+        for (const [serviceId, keyPair] of Object.entries(map.value)) {
           strictAssert(
             isServiceIdString(serviceId),
             'Invalid identity key serviceId'
           );
-          const { privKey, pubKey } = map.value[serviceId];
+          const { privKey, pubKey } = keyPair;
           const privateKey = PrivateKey.deserialize(privKey);
           const publicKey = PublicKey.deserialize(pubKey);
           this.#ourIdentityKeys.set(
@@ -327,12 +326,12 @@ export class SignalProtocolStore extends EventEmitter {
           return;
         }
 
-        for (const serviceId of Object.keys(map.value)) {
+        for (const [serviceId, registrationId] of Object.entries(map.value)) {
           strictAssert(
             isServiceIdString(serviceId),
             'Invalid registration id serviceId'
           );
-          this.#ourRegistrationIds.set(serviceId, map.value[serviceId]);
+          this.#ourRegistrationIds.set(serviceId, registrationId);
         }
       })(),
       (async () => {
@@ -1670,10 +1669,7 @@ export class SignalProtocolStore extends EventEmitter {
           `removeSessionsByConversation: Conversation not found: ${identifier}`
         );
 
-        const entries = Array.from(this.sessions.values());
-
-        for (let i = 0, max = entries.length; i < max; i += 1) {
-          const entry = entries[i];
+        for (const entry of this.sessions.values()) {
           if (entry.fromDB.conversationId === id) {
             this.sessions.delete(entry.fromDB.id);
             this.#pendingSessions.delete(entry.fromDB.id);
@@ -1695,10 +1691,7 @@ export class SignalProtocolStore extends EventEmitter {
 
       log.info('removeSessionsByServiceId: deleting sessions for', serviceId);
 
-      const entries = Array.from(this.sessions.values());
-
-      for (let i = 0, max = entries.length; i < max; i += 1) {
-        const entry = entries[i];
+      for (const entry of this.sessions.values()) {
         if (entry.fromDB.serviceId === serviceId) {
           this.sessions.delete(entry.fromDB.id);
           this.#pendingSessions.delete(entry.fromDB.id);
diff --git a/ts/axo/AxoAvatar.dom.stories.tsx b/ts/axo/AxoAvatar.dom.stories.tsx
index 53b2736452..bec32f22a8 100644
--- a/ts/axo/AxoAvatar.dom.stories.tsx
+++ b/ts/axo/AxoAvatar.dom.stories.tsx
@@ -185,7 +185,8 @@ export function Icons(): JSX.Element {
       {size => (
         <AxoAvatar.Root size={size}>
           <AxoAvatar.Content label={null}>
-            <AxoAvatar.Icon symbol={icons[size % icons.length]} />
+            {/* eslint-disable-next-line @typescript-eslint/no-non-null-assertion */}
+            <AxoAvatar.Icon symbol={icons[size % icons.length]!} />
           </AxoAvatar.Content>
         </AxoAvatar.Root>
       )}
diff --git a/ts/axo/AxoTokens.std.ts b/ts/axo/AxoTokens.std.ts
index 570153827e..965e0a7c98 100644
--- a/ts/axo/AxoTokens.std.ts
+++ b/ts/axo/AxoTokens.std.ts
@@ -60,7 +60,8 @@ export namespace AxoTokens {
         Number.isInteger(hash) && hash >= 0,
         'Hash must be positive integer'
       );
-      return ALL_COLOR_NAMES[hash % ALL_COLOR_NAMES.length];
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      return ALL_COLOR_NAMES[hash % ALL_COLOR_NAMES.length]!;
     }
 
     export type GradientValues = Readonly<{
@@ -96,7 +97,8 @@ export namespace AxoTokens {
         Number.isInteger(hash) && hash >= 0,
         'Hash must be positive integer'
       );
-      return Gradients[hash % Gradients.length];
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      return Gradients[hash % Gradients.length]!;
     }
 
     export function getGradientsCount(): number {
diff --git a/ts/calling/VideoSupport.preload.ts b/ts/calling/VideoSupport.preload.ts
index cef7cd9b4c..5878b4a989 100644
--- a/ts/calling/VideoSupport.preload.ts
+++ b/ts/calling/VideoSupport.preload.ts
@@ -92,7 +92,7 @@ export class GumVideoCapturer {
       return;
     }
 
-    const settings = this.mediaStream.getVideoTracks()?.[0].getSettings();
+    const settings = this.mediaStream.getVideoTracks()?.[0]?.getSettings();
     if (!settings?.width || !settings?.height) {
       return;
     }
diff --git a/ts/calling/findBestMatchingDevice.std.ts b/ts/calling/findBestMatchingDevice.std.ts
index 0929085f17..e066878b7f 100644
--- a/ts/calling/findBestMatchingDevice.std.ts
+++ b/ts/calling/findBestMatchingDevice.std.ts
@@ -58,12 +58,5 @@ export function findBestMatchingCameraId(
 
   // By default, pick the first non-IR camera (but allow the user to pick the
   // infrared if they so desire)
-  if (matchingId.length > 0) {
-    return matchingId[0].deviceId;
-  }
-  if (nonInfrared.length > 0) {
-    return nonInfrared[0].deviceId;
-  }
-
-  return undefined;
+  return matchingId[0]?.deviceId ?? nonInfrared[0]?.deviceId;
 }
diff --git a/ts/components/AddUserToAnotherGroupModal.dom.tsx b/ts/components/AddUserToAnotherGroupModal.dom.tsx
index 1e444c153c..954d156e2e 100644
--- a/ts/components/AddUserToAnotherGroupModal.dom.tsx
+++ b/ts/components/AddUserToAnotherGroupModal.dom.tsx
@@ -22,6 +22,7 @@ import { ListView } from './ListView.dom.js';
 import { ListTile } from './ListTile.dom.js';
 import type { ShowToastAction } from '../state/ducks/toast.preload.js';
 import { SizeObserver } from '../hooks/useSizeObserver.dom.js';
+import { strictAssert } from '../util/assert.std.js';
 
 const { pick } = lodash;
 
@@ -111,6 +112,7 @@ export function AddUserToAnotherGroupModal({
   const handleGetRow = React.useCallback(
     (idx: number): GroupListItemConversationType => {
       const convo = filteredConversations[idx];
+      strictAssert(convo, 'Missing conversation');
 
       // these are always populated in the case of a group
       const memberships = convo.memberships ?? [];
diff --git a/ts/components/AnnouncementsOnlyGroupBanner.dom.tsx b/ts/components/AnnouncementsOnlyGroupBanner.dom.tsx
index 2810e10963..fffe766822 100644
--- a/ts/components/AnnouncementsOnlyGroupBanner.dom.tsx
+++ b/ts/components/AnnouncementsOnlyGroupBanner.dom.tsx
@@ -12,11 +12,12 @@ import type { PreferredBadgeSelectorType } from '../state/selectors/badges.prelo
 import { tw } from '../axo/tw.dom.js';
 import type { AdminMembershipType } from '../state/selectors/conversations.dom.js';
 import { UserText } from './UserText.dom.js';
+import type { ContactNameColorType } from '../types/Colors.std.js';
 
 type PropsType = {
   getPreferredBadge: PreferredBadgeSelectorType;
   groupAdmins: Array<AdminMembershipType>;
-  memberColors: Map<string, string>;
+  memberColors: Map<string, ContactNameColorType>;
   i18n: LocalizerType;
   showConversation: ShowConversationType;
   theme: ThemeType;
diff --git a/ts/components/Avatar.dom.stories.tsx b/ts/components/Avatar.dom.stories.tsx
index 45f1be2f37..2e27f69a0d 100644
--- a/ts/components/Avatar.dom.stories.tsx
+++ b/ts/components/Avatar.dom.stories.tsx
@@ -109,7 +109,8 @@ Default.play = async (context: any) => {
   const { args, canvasElement } = context;
   const canvas = within(canvasElement);
   const [avatar] = canvas.getAllByRole('button');
-  await userEvent.click(avatar);
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  await userEvent.click(avatar!);
   await expect(args.onClick).toHaveBeenCalled();
 };
 
diff --git a/ts/components/BadgeDialog.dom.tsx b/ts/components/BadgeDialog.dom.tsx
index 68e2941aed..ded375d167 100644
--- a/ts/components/BadgeDialog.dom.tsx
+++ b/ts/components/BadgeDialog.dom.tsx
@@ -78,7 +78,8 @@ function BadgeDialogWithBadges({
     currentBadgeIndex = 0;
     currentBadge = firstBadge;
   } else {
-    currentBadge = badges[currentBadgeIndex];
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    currentBadge = badges[currentBadgeIndex]!;
   }
 
   const setCurrentBadgeIndex = (index: number): void => {
diff --git a/ts/components/CallManager.dom.stories.tsx b/ts/components/CallManager.dom.stories.tsx
index 5e56bdb7cc..df79b671e0 100644
--- a/ts/components/CallManager.dom.stories.tsx
+++ b/ts/components/CallManager.dom.stories.tsx
@@ -36,6 +36,14 @@ import { allRemoteParticipants } from './CallScreen.dom.stories.js';
 
 const { i18n } = window.SignalContext;
 
+const [participant1, participant2, participant3, participant4] =
+  allRemoteParticipants as [
+    GroupCallRemoteParticipantType,
+    GroupCallRemoteParticipantType,
+    GroupCallRemoteParticipantType,
+    GroupCallRemoteParticipantType,
+  ];
+
 const getConversation = () =>
   getDefaultConversation({
     id: '3051234567',
@@ -344,7 +352,7 @@ export function CallLinkLobbyParticipants1Known1Unknown(): React.JSX.Element {
     <CallManager
       {...createProps({
         activeCall: getActiveCallForCallLink({
-          peekedParticipants: [allRemoteParticipants[0], getUnknownContact()],
+          peekedParticipants: [participant1, getUnknownContact()],
         }),
         callLink: FAKE_CALL_LINK,
       })}
@@ -359,7 +367,7 @@ export function CallLinkLobbyParticipants1Known2Unknown(): React.JSX.Element {
         activeCall: getActiveCallForCallLink({
           peekedParticipants: [
             getUnknownContact(),
-            allRemoteParticipants[0],
+            participant1,
             getUnknownContact(),
           ],
         }),
@@ -370,9 +378,7 @@ export function CallLinkLobbyParticipants1Known2Unknown(): React.JSX.Element {
 }
 
 export function CallLinkLobbyParticipants1Known12Unknown(): React.JSX.Element {
-  const peekedParticipants: Array<ConversationType> = [
-    allRemoteParticipants[0],
-  ];
+  const peekedParticipants: Array<ConversationType> = [participant1];
   for (let n = 12; n > 0; n -= 1) {
     peekedParticipants.push(getUnknownContact());
   }
@@ -412,8 +418,8 @@ export function CallLinkWithJoinRequestsOne(): React.JSX.Element {
         activeCall: getActiveCallForCallLink({
           connectionState: GroupCallConnectionState.Connected,
           joinState: GroupCallJoinState.Joined,
-          peekedParticipants: [allRemoteParticipants[0]],
-          pendingParticipants: [allRemoteParticipants[1]],
+          peekedParticipants: [participant1],
+          pendingParticipants: [participant2],
           showParticipantsList: false,
         }),
         callLink: FAKE_CALL_LINK_WITH_ADMIN_KEY,
@@ -429,7 +435,7 @@ export function CallLinkWithJoinRequestsTwo(): React.JSX.Element {
         activeCall: getActiveCallForCallLink({
           connectionState: GroupCallConnectionState.Connected,
           joinState: GroupCallJoinState.Joined,
-          peekedParticipants: [allRemoteParticipants[0]],
+          peekedParticipants: [participant1],
           pendingParticipants: allRemoteParticipants.slice(1, 3),
           showParticipantsList: false,
         }),
@@ -446,7 +452,7 @@ export function CallLinkWithJoinRequestsMany(): React.JSX.Element {
         activeCall: getActiveCallForCallLink({
           connectionState: GroupCallConnectionState.Connected,
           joinState: GroupCallJoinState.Joined,
-          peekedParticipants: [allRemoteParticipants[0]],
+          peekedParticipants: [participant1],
           pendingParticipants: allRemoteParticipants.slice(1, 11),
           showParticipantsList: false,
         }),
@@ -463,11 +469,11 @@ export function CallLinkWithJoinRequestUnknownContact(): React.JSX.Element {
         activeCall: getActiveCallForCallLink({
           connectionState: GroupCallConnectionState.Connected,
           joinState: GroupCallJoinState.Joined,
-          peekedParticipants: [allRemoteParticipants[0]],
+          peekedParticipants: [participant1],
           pendingParticipants: [
             getUnknownContact(),
-            allRemoteParticipants[1],
-            allRemoteParticipants[2],
+            participant2,
+            participant3,
           ],
           showParticipantsList: false,
         }),
@@ -484,9 +490,9 @@ export function CallLinkWithJoinRequestsSystemContact(): React.JSX.Element {
         activeCall: getActiveCallForCallLink({
           connectionState: GroupCallConnectionState.Connected,
           joinState: GroupCallJoinState.Joined,
-          peekedParticipants: [allRemoteParticipants[0]],
+          peekedParticipants: [participant1],
           pendingParticipants: [
-            { ...allRemoteParticipants[1], name: 'My System Contact Friend' },
+            { ...participant2, name: 'My System Contact Friend' },
           ],
           showParticipantsList: false,
         }),
@@ -503,11 +509,11 @@ export function CallLinkWithJoinRequestsSystemContactMany(): React.JSX.Element {
         activeCall: getActiveCallForCallLink({
           connectionState: GroupCallConnectionState.Connected,
           joinState: GroupCallJoinState.Joined,
-          peekedParticipants: [allRemoteParticipants[0]],
+          peekedParticipants: [participant1],
           pendingParticipants: [
-            { ...allRemoteParticipants[1], name: 'My System Contact Friend' },
-            allRemoteParticipants[2],
-            allRemoteParticipants[3],
+            { ...participant2, name: 'My System Contact Friend' },
+            participant3,
+            participant4,
           ],
           showParticipantsList: false,
         }),
@@ -524,7 +530,7 @@ export function CallLinkWithJoinRequestsParticipantsOpen(): React.JSX.Element {
         activeCall: getActiveCallForCallLink({
           connectionState: GroupCallConnectionState.Connected,
           joinState: GroupCallJoinState.Joined,
-          peekedParticipants: [allRemoteParticipants[0]],
+          peekedParticipants: [participant1],
           pendingParticipants: allRemoteParticipants.slice(1, 4),
         }),
         callLink: FAKE_CALL_LINK_WITH_ADMIN_KEY,
@@ -541,7 +547,7 @@ export function CallLinkWithUnknownContacts(): React.JSX.Element {
           connectionState: GroupCallConnectionState.Connected,
           joinState: GroupCallJoinState.Joined,
           remoteParticipants: [
-            allRemoteParticipants[0],
+            participant1,
             getUnknownParticipant(),
             getUnknownParticipant(),
           ],
diff --git a/ts/components/CallReactionBurstEmoji.dom.tsx b/ts/components/CallReactionBurstEmoji.dom.tsx
index 0efaa641f8..5f4387fd49 100644
--- a/ts/components/CallReactionBurstEmoji.dom.tsx
+++ b/ts/components/CallReactionBurstEmoji.dom.tsx
@@ -40,7 +40,8 @@ export function CallReactionBurstEmoji({
     (index: number) => {
       return {
         key: uuid(),
-        value: values[index % values.length],
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        value: values[index % values.length]!,
         springConfig: {
           mass: random(10, 20),
           tension: random(45, 60),
diff --git a/ts/components/CallScreen.dom.stories.tsx b/ts/components/CallScreen.dom.stories.tsx
index 48f3a58105..955ce67005 100644
--- a/ts/components/CallScreen.dom.stories.tsx
+++ b/ts/components/CallScreen.dom.stories.tsx
@@ -36,6 +36,7 @@ import { fakeGetGroupCallVideoFrameSource } from '../test-helpers/fakeGetGroupCa
 import { CallingToastProvider, useCallingToasts } from './CallingToast.dom.js';
 import type { CallingImageDataCache } from './CallManager.dom.js';
 import { MINUTE } from '../util/durations/index.std.js';
+import { strictAssert } from '../util/assert.std.js';
 
 const { sample, shuffle, times } = lodash;
 
@@ -542,7 +543,7 @@ export const allRemoteParticipants = times(MAX_PARTICIPANTS).map(index => {
           : ''
       } ${index + 1}`,
     }),
-  };
+  } satisfies GroupCallRemoteParticipantType;
 });
 
 export function GroupCallManyPaginated(): React.JSX.Element {
@@ -851,6 +852,7 @@ export function GroupCallReactionsManyInOrder(): React.JSX.Element {
       DEFAULT_PREFERRED_REACTION_EMOJI[
         i % DEFAULT_PREFERRED_REACTION_EMOJI.length
       ];
+    strictAssert(value, 'Missing value');
     return { timestamp, demuxId, value };
   });
   const [props] = React.useState(
@@ -886,7 +888,9 @@ function useReactionsEmitter({
         const participantIndex = Math.floor(
           Math.random() * call.remoteParticipants.length
         );
-        const { demuxId } = call.remoteParticipants[participantIndex];
+        const participant = call.remoteParticipants[participantIndex];
+        strictAssert(participant, 'Missing participant');
+        const { demuxId } = participant;
 
         const reactions: ActiveCallReactionsType = [
           ...(state.reactions ?? []).filter(
@@ -986,9 +990,11 @@ function useHandRaiser(
         );
 
         const raisedHands = new Set(
-          participantIndices.map(
-            index => call.remoteParticipants[index].demuxId
-          )
+          participantIndices.map(index => {
+            const participant = call.remoteParticipants[index];
+            strictAssert(participant, 'Missing participant');
+            return participant.demuxId;
+          })
         );
 
         return {
diff --git a/ts/components/CallScreen.dom.tsx b/ts/components/CallScreen.dom.tsx
index 5c6d6bdcca..ab717b354f 100644
--- a/ts/components/CallScreen.dom.tsx
+++ b/ts/components/CallScreen.dom.tsx
@@ -483,7 +483,8 @@ export function CallScreen({
       isRinging =
         activeCall.outgoingRing &&
         !activeCall.remoteParticipants.length &&
-        !(groupMembers?.length === 1 && groupMembers[0].id === me.id);
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        !(groupMembers?.length === 1 && groupMembers[0]!.id === me.id);
       hasCallStarted = activeCall.joinState !== GroupCallJoinState.NotJoined;
       participantCount = activeCall.remoteParticipants.length + 1;
       conversationsByDemuxId = activeCall.conversationsByDemuxId;
diff --git a/ts/components/CallingDeviceSelection.dom.tsx b/ts/components/CallingDeviceSelection.dom.tsx
index dd2befbd81..cb0c93b769 100644
--- a/ts/components/CallingDeviceSelection.dom.tsx
+++ b/ts/components/CallingDeviceSelection.dom.tsx
@@ -80,7 +80,8 @@ function createAudioChangeHandler(
   return (value: string): void => {
     changeIODevice({
       type,
-      selectedDevice: devices[Number(value)],
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      selectedDevice: devices[Number(value)]!,
     });
   };
 }
diff --git a/ts/components/CallingPendingParticipants.dom.stories.tsx b/ts/components/CallingPendingParticipants.dom.stories.tsx
index 87bc7ad9bc..9e06b97a79 100644
--- a/ts/components/CallingPendingParticipants.dom.stories.tsx
+++ b/ts/components/CallingPendingParticipants.dom.stories.tsx
@@ -7,12 +7,18 @@ import type { Meta } from '@storybook/react';
 import type { PropsType } from './CallingPendingParticipants.dom.js';
 import { CallingPendingParticipants } from './CallingPendingParticipants.dom.js';
 import { allRemoteParticipants } from './CallScreen.dom.stories.js';
+import { strictAssert } from '../util/assert.std.js';
 
 const { i18n } = window.SignalContext;
 
+strictAssert(allRemoteParticipants[0], 'Missing allRemoteParticipants[0]');
+strictAssert(allRemoteParticipants[1], 'Missing allRemoteParticipants[1]');
+const participant1 = allRemoteParticipants[0];
+const participant2 = allRemoteParticipants[1];
+
 const createProps = (storyProps: Partial<PropsType> = {}): PropsType => ({
   i18n,
-  participants: [allRemoteParticipants[0], allRemoteParticipants[1]],
+  participants: [participant1, participant2],
   approveUser: action('approve-user'),
   batchUserAction: action('batch-user-action'),
   denyUser: action('deny-user'),
@@ -32,7 +38,7 @@ export function One(): React.JSX.Element {
   return (
     <CallingPendingParticipants
       {...createProps({
-        participants: [allRemoteParticipants[0]],
+        participants: [participant1],
       })}
     />
   );
@@ -83,7 +89,7 @@ export function ExpandedOne(): React.JSX.Element {
     <CallingPendingParticipants
       {...createProps({
         defaultIsExpanded: true,
-        participants: [allRemoteParticipants[0]],
+        participants: [participant1],
       })}
     />
   );
diff --git a/ts/components/CallingPip.dom.tsx b/ts/components/CallingPip.dom.tsx
index 77c9f45793..368e68d285 100644
--- a/ts/components/CallingPip.dom.tsx
+++ b/ts/components/CallingPip.dom.tsx
@@ -204,7 +204,7 @@ export function CallingPip({
         distanceToRightEdge = innerWidth - (offsetX + width);
       }
 
-      const snapCandidates: Array<SnapCandidate> = [
+      const snapCandidates = [
         {
           mode: PositionMode.SnapToLeft,
           distanceToEdge: distanceToLeftEdge,
@@ -221,7 +221,7 @@ export function CallingPip({
           mode: PositionMode.SnapToBottom,
           distanceToEdge: innerHeight - (offsetY + height),
         },
-      ];
+      ] as const satisfies Array<SnapCandidate>;
 
       // This fallback is mostly for TypeScript, because `minBy` says it can return
       //   `undefined`.
@@ -245,7 +245,7 @@ export function CallingPip({
           });
           break;
         default:
-          throw missingCaseError(snapTo.mode);
+          throw missingCaseError(snapTo);
       }
     }
   }, [height, isRTL, positionState, setPositionState, width]);
diff --git a/ts/components/CallingPreCallInfo.dom.stories.tsx b/ts/components/CallingPreCallInfo.dom.stories.tsx
index 93d385b287..20ba4e2805 100644
--- a/ts/components/CallingPreCallInfo.dom.stories.tsx
+++ b/ts/components/CallingPreCallInfo.dom.stories.tsx
@@ -2,7 +2,6 @@
 // SPDX-License-Identifier: AGPL-3.0-only
 
 import React from 'react';
-import lodash from 'lodash';
 import type { Meta } from '@storybook/react';
 import { getDefaultConversation } from '../test-helpers/getDefaultConversation.std.js';
 import type { PropsType } from './CallingPreCallInfo.dom.js';
@@ -12,8 +11,6 @@ import { generateAci } from '../types/ServiceId.std.js';
 import { FAKE_CALL_LINK } from '../test-helpers/fakeCallLink.std.js';
 import { callLinkToConversation } from '../util/callLinks.std.js';
 
-const { times } = lodash;
-
 const { i18n } = window.SignalContext;
 const getDefaultGroupConversation = () =>
   getDefaultConversation({
@@ -23,7 +20,14 @@ const getDefaultGroupConversation = () =>
     title: 'Tahoe Trip',
     type: 'group',
   });
-const otherMembers = times(6, () => getDefaultConversation());
+const otherMembers = [
+  getDefaultConversation(),
+  getDefaultConversation(),
+  getDefaultConversation(),
+  getDefaultConversation(),
+  getDefaultConversation(),
+  getDefaultConversation(),
+] as const;
 
 const getUnknownContact = (): ConversationType => ({
   acceptedMessageRequest: false,
diff --git a/ts/components/CallingPreCallInfo.dom.tsx b/ts/components/CallingPreCallInfo.dom.tsx
index 8723bec29c..bde9a7c4b4 100644
--- a/ts/components/CallingPreCallInfo.dom.tsx
+++ b/ts/components/CallingPreCallInfo.dom.tsx
@@ -50,7 +50,7 @@ export type PropsType = {
   ringMode: RingMode;
 
   // The following should only be set for group conversations.
-  groupMembers?: Array<
+  groupMembers?: ReadonlyArray<
     Pick<
       ConversationType,
       'id' | 'firstName' | 'systemGivenName' | 'systemNickname' | 'title'
@@ -58,7 +58,7 @@ export type PropsType = {
   >;
   isCallFull?: boolean;
   isConnecting?: boolean;
-  peekedParticipants?: Array<PeekedParticipantType>;
+  peekedParticipants?: ReadonlyArray<PeekedParticipantType>;
 };
 
 export function CallingPreCallInfo({
@@ -110,36 +110,38 @@ export function CallingPreCallInfo({
         }
         return getParticipantName(participant);
       });
+      /* eslint-disable @typescript-eslint/no-non-null-assertion */
       switch (participantNames.length) {
         case 1:
           subtitle = hasYou
             ? i18n('icu:calling__pre-call-info--another-device-in-call')
             : i18n('icu:calling__pre-call-info--1-person-in-call', {
-                first: participantNames[0],
+                first: participantNames[0]!,
               });
           break;
         case 2:
           subtitle = i18n('icu:calling__pre-call-info--2-people-in-call', {
-            first: participantNames[0],
-            second: participantNames[1],
+            first: participantNames[0]!,
+            second: participantNames[1]!,
           });
           break;
         case 3:
           subtitle = i18n('icu:calling__pre-call-info--3-people-in-call', {
-            first: participantNames[0],
-            second: participantNames[1],
-            third: participantNames[2],
+            first: participantNames[0]!,
+            second: participantNames[1]!,
+            third: participantNames[2]!,
           });
           break;
         default:
           subtitle = i18n('icu:calling__pre-call-info--many-people-in-call', {
-            first: participantNames[0],
-            second: participantNames[1],
+            first: participantNames[0]!,
+            second: participantNames[1]!,
             others: participantNames.length - 2,
           });
           break;
       }
     }
+    /* eslint-enable @typescript-eslint/no-non-null-assertion */
   } else {
     let memberNames: Array<string>;
     switch (conversation.type) {
@@ -158,6 +160,7 @@ export function CallingPreCallInfo({
 
     const ring = ringMode === RingMode.WillRing;
 
+    /* eslint-disable @typescript-eslint/no-non-null-assertion */
     switch (memberNames.length) {
       case 0:
         subtitle = i18n('icu:calling__pre-call-info--empty-group');
@@ -165,55 +168,56 @@ export function CallingPreCallInfo({
       case 1: {
         subtitle = ring
           ? i18n('icu:calling__pre-call-info--will-ring-1', {
-              person: memberNames[0],
+              person: memberNames[0]!,
             })
           : i18n('icu:calling__pre-call-info--will-notify-1', {
-              person: memberNames[0],
+              person: memberNames[0]!,
             });
         break;
       }
       case 2: {
         subtitle = ring
           ? i18n('icu:calling__pre-call-info--will-ring-2', {
-              first: memberNames[0],
-              second: memberNames[1],
+              first: memberNames[0]!,
+              second: memberNames[1]!,
             })
           : i18n('icu:calling__pre-call-info--will-notify-2', {
-              first: memberNames[0],
-              second: memberNames[1],
+              first: memberNames[0]!,
+              second: memberNames[1]!,
             });
         break;
       }
       case 3: {
         subtitle = ring
           ? i18n('icu:calling__pre-call-info--will-ring-3', {
-              first: memberNames[0],
-              second: memberNames[1],
-              third: memberNames[2],
+              first: memberNames[0]!,
+              second: memberNames[1]!,
+              third: memberNames[2]!,
             })
           : i18n('icu:calling__pre-call-info--will-notify-3', {
-              first: memberNames[0],
-              second: memberNames[1],
-              third: memberNames[2],
+              first: memberNames[0]!,
+              second: memberNames[1]!,
+              third: memberNames[2]!,
             });
         break;
       }
       default: {
         subtitle = ring
           ? i18n('icu:calling__pre-call-info--will-ring-many', {
-              first: memberNames[0],
-              second: memberNames[1],
+              first: memberNames[0]!,
+              second: memberNames[1]!,
               others: memberNames.length - 2,
             })
           : i18n('icu:calling__pre-call-info--will-notify-many', {
-              first: memberNames[0],
-              second: memberNames[1],
+              first: memberNames[0]!,
+              second: memberNames[1]!,
               others: memberNames.length - 2,
             });
         break;
       }
     }
   }
+  /* eslint-enable @typescript-eslint/no-non-null-assertion */
 
   return (
     <div className="module-CallingPreCallInfo">
diff --git a/ts/components/CallingToast.dom.tsx b/ts/components/CallingToast.dom.tsx
index 4bd9770c41..96f63c8a3f 100644
--- a/ts/components/CallingToast.dom.tsx
+++ b/ts/components/CallingToast.dom.tsx
@@ -235,7 +235,8 @@ export function CallingToastProvider({
         toast => toast.key === item.key
       );
       const isToastReplacingAnExistingOneAtThisPosition = toastsRemoved.has(
-        previousToasts[enteringItemIndex]
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        previousToasts[enteringItemIndex]!
       );
       return {
         ...transitionFrom,
@@ -275,7 +276,8 @@ export function CallingToastProvider({
         toast => toast.key === item.key
       );
       const isToastBeingReplacedByANewOneAtThisPosition = toastsAdded.has(
-        toasts[leavingItemIndex]
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        toasts[leavingItemIndex]!
       );
       return {
         zIndex: 0,
diff --git a/ts/components/ChatColorPicker.dom.tsx b/ts/components/ChatColorPicker.dom.tsx
index 17ff0fb570..c4609b27b9 100644
--- a/ts/components/ChatColorPicker.dom.tsx
+++ b/ts/components/ChatColorPicker.dom.tsx
@@ -196,8 +196,7 @@ export function ChatColorPicker({
               ref={i === 0 ? focusRef : undefined}
             />
           ))}
-          {Object.keys(customColors).map(colorId => {
-            const colorValues = customColors[colorId];
+          {Object.entries(customColors).map(([colorId, colorValues]) => {
             return (
               <CustomColorBubble
                 color={colorValues}
diff --git a/ts/components/CompositionArea.dom.stories.tsx b/ts/components/CompositionArea.dom.stories.tsx
index 4c3d7ae8d0..d89227785a 100644
--- a/ts/components/CompositionArea.dom.stories.tsx
+++ b/ts/components/CompositionArea.dom.stories.tsx
@@ -12,6 +12,7 @@ import { StorybookThemeContext } from '../../.storybook/StorybookThemeContext.st
 import { fakeDraftAttachment } from '../test-helpers/fakeAttachment.std.js';
 import { landscapeGreenUrl } from '../storybook/Fixtures.std.js';
 import { RecordingState } from '../types/AudioRecorder.std.js';
+import type { ContactNameColorType } from '../types/Colors.std.js';
 import { ContactNameColors, ConversationColors } from '../types/Colors.std.js';
 import { getDefaultConversation } from '../test-helpers/getDefaultConversation.std.js';
 import { PaymentEventKind } from '../types/Payment.std.js';
@@ -44,11 +45,15 @@ const groupAdmins = [
 ];
 const memberColors = new Map(
   groupAdmins
-    .map((admin, i): [string, string] | null => {
+    .map((admin, i): [string, ContactNameColorType] | null => {
       if (!admin.member.id) {
         return null;
       }
-      return [admin.member.id?.toString(), ContactNameColors[i]];
+      return [
+        admin.member.id?.toString(),
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        ContactNameColors[i % ContactNameColors.length]!,
+      ];
     })
     .filter(isNotNil)
 );
diff --git a/ts/components/CompositionArea.dom.tsx b/ts/components/CompositionArea.dom.tsx
index 75b33378e6..39b66b532b 100644
--- a/ts/components/CompositionArea.dom.tsx
+++ b/ts/components/CompositionArea.dom.tsx
@@ -91,6 +91,7 @@ import type { PollCreateType } from '../types/Polls.dom.js';
 import { PollCreateModal } from './PollCreateModal.dom.js';
 import { useDocumentKeyDown } from '../hooks/useDocumentKeyDown.dom.js';
 import { hasDraft } from '../util/hasDraft.std.js';
+import type { ContactNameColorType } from '../types/Colors.std.js';
 
 export type OwnProps = Readonly<{
   acceptedMessageRequest: boolean | null;
@@ -139,7 +140,7 @@ export type OwnProps = Readonly<{
   lastEditableMessageId: string | null;
   recordingState: RecordingState;
   messageCompositionId: string;
-  memberColors: Map<string, string>;
+  memberColors: Map<string, ContactNameColorType>;
   shouldHidePopovers: boolean | null;
   isMuted: boolean;
   isSmsOnlyOrUnregistered: boolean | null;
@@ -1101,7 +1102,11 @@ export const CompositionArea = memo(function CompositionArea({
     return renderSmartCompositionRecording();
   }
 
-  if (draftAttachments.length === 1 && isVoiceMessage(draftAttachments[0])) {
+  if (
+    draftAttachments.length === 1 &&
+    draftAttachments[0] != null &&
+    isVoiceMessage(draftAttachments[0])
+  ) {
     const voiceNoteAttachment = draftAttachments[0];
 
     if (!voiceNoteAttachment.pending && voiceNoteAttachment.url) {
diff --git a/ts/components/CompositionInput.dom.tsx b/ts/components/CompositionInput.dom.tsx
index b2628f4e10..65f3af1a8d 100644
--- a/ts/components/CompositionInput.dom.tsx
+++ b/ts/components/CompositionInput.dom.tsx
@@ -934,9 +934,9 @@ export function CompositionInput(props: Props): React.ReactElement {
               key: tabKey,
               handler: () => callbacksRef.current.onTab(),
             });
-            const ourHandler = quill.keyboard.bindings[tabKey].pop();
+            const ourHandler = quill.keyboard.bindings[tabKey]?.pop();
             if (ourHandler) {
-              quill.keyboard.bindings[tabKey].unshift(ourHandler);
+              quill.keyboard.bindings[tabKey]?.unshift(ourHandler);
             }
 
             const emojiCompletion = quill.getModule('emojiCompletion');
diff --git a/ts/components/ContactPills.dom.stories.tsx b/ts/components/ContactPills.dom.stories.tsx
index 74cfd9bb0f..1f75d138bd 100644
--- a/ts/components/ContactPills.dom.stories.tsx
+++ b/ts/components/ContactPills.dom.stories.tsx
@@ -2,7 +2,6 @@
 // SPDX-License-Identifier: AGPL-3.0-only
 
 import React from 'react';
-import lodash from 'lodash';
 
 import { action } from '@storybook/addon-actions';
 
@@ -13,8 +12,6 @@ import { ContactPill } from './ContactPill.dom.js';
 import { gifUrl } from '../storybook/Fixtures.std.js';
 import { getDefaultConversation } from '../test-helpers/getDefaultConversation.std.js';
 
-const { times } = lodash;
-
 const { i18n } = window.SignalContext;
 
 export default {
@@ -23,15 +20,15 @@ export default {
 
 type ContactType = Omit<ContactPillPropsType, 'i18n' | 'onClickRemove'>;
 
-const contacts: Array<ContactType> = times(50, index =>
-  getDefaultConversation({
+function createContact(index: number) {
+  return getDefaultConversation({
     id: `contact-${index}`,
     name: `Contact ${index}`,
     phoneNumber: '(202) 555-0001',
     profileName: `C${index}`,
     title: `Contact ${index}`,
-  })
-);
+  });
+}
 
 const contactPillProps = (
   overrideProps?: ContactType
@@ -67,9 +64,9 @@ export function OneContact(): React.JSX.Element {
 export function ThreeContacts(): React.JSX.Element {
   return (
     <ContactPills>
-      <ContactPill {...contactPillProps(contacts[0])} />
-      <ContactPill {...contactPillProps(contacts[1])} />
-      <ContactPill {...contactPillProps(contacts[2])} />
+      <ContactPill {...contactPillProps(createContact(0))} />
+      <ContactPill {...contactPillProps(createContact(1))} />
+      <ContactPill {...contactPillProps(createContact(2))} />
     </ContactPills>
   );
 }
@@ -77,16 +74,16 @@ export function ThreeContacts(): React.JSX.Element {
 export function FourContactsOneWithALongName(): React.JSX.Element {
   return (
     <ContactPills>
-      <ContactPill {...contactPillProps(contacts[0])} />
+      <ContactPill {...contactPillProps(createContact(0))} />
       <ContactPill
         {...contactPillProps({
-          ...contacts[1],
+          ...createContact(1),
           title:
             'Pablo Diego José Francisco de Paula Juan Nepomuceno María de los Remedios Cipriano de la Santísima Trinidad Ruiz y Picasso',
         })}
       />
-      <ContactPill {...contactPillProps(contacts[2])} />
-      <ContactPill {...contactPillProps(contacts[3])} />
+      <ContactPill {...contactPillProps(createContact(2))} />
+      <ContactPill {...contactPillProps(createContact(3))} />
     </ContactPills>
   );
 }
@@ -94,8 +91,8 @@ export function FourContactsOneWithALongName(): React.JSX.Element {
 export function FiftyContacts(): React.JSX.Element {
   return (
     <ContactPills>
-      {contacts.map(contact => (
-        <ContactPill key={contact.id} {...contactPillProps(contact)} />
+      {Array.from({ length: 50 }, (_, index) => (
+        <ContactPill key={index} {...contactPillProps(createContact(index))} />
       ))}
     </ContactPills>
   );
diff --git a/ts/components/ContextMenu.dom.tsx b/ts/components/ContextMenu.dom.tsx
index 29cb676b42..0f553cbc7e 100644
--- a/ts/components/ContextMenu.dom.tsx
+++ b/ts/components/ContextMenu.dom.tsx
@@ -191,7 +191,8 @@ export function ContextMenu<T>({
 
     if (ev.key === 'Enter') {
       if (focusedIndex !== undefined) {
-        const focusedOption = menuOptions[focusedIndex];
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        const focusedOption = menuOptions[focusedIndex]!;
         focusedOption.onClick(focusedOption.value);
       }
       setIsMenuShowing(false);
diff --git a/ts/components/ConversationList.dom.stories.tsx b/ts/components/ConversationList.dom.stories.tsx
index 179225ae99..c5ed24f28a 100644
--- a/ts/components/ConversationList.dom.stories.tsx
+++ b/ts/components/ConversationList.dom.stories.tsx
@@ -27,7 +27,7 @@ export default {
   args: {},
 } satisfies Meta<PropsType>;
 
-const defaultConversations: Array<ConversationListItemPropsType> = [
+const defaultConversations = [
   getDefaultConversation({
     id: 'fred-convo',
     title: 'Fred Willard',
@@ -48,7 +48,7 @@ const defaultConversations: Array<ConversationListItemPropsType> = [
       'Pablo Diego José Francisco de Paula Juan Nepomuceno María de los Remedios Cipriano de la Santísima Trinidad Ruiz y Picasso',
   }),
   getDefaultConversation(),
-];
+] as const satisfies Array<ConversationListItemPropsType>;
 
 function Wrapper({
   rows,
diff --git a/ts/components/EditHistoryMessagesModal.dom.tsx b/ts/components/EditHistoryMessagesModal.dom.tsx
index 87c64434a7..e7cb976204 100644
--- a/ts/components/EditHistoryMessagesModal.dom.tsx
+++ b/ts/components/EditHistoryMessagesModal.dom.tsx
@@ -23,6 +23,7 @@ import { TimelineDateHeader } from './conversation/TimelineDateHeader.dom.js';
 import { AxoContextMenu } from '../axo/AxoContextMenu.dom.js';
 import { drop } from '../util/drop.std.js';
 import type { AxoMenuBuilder } from '../axo/AxoMenuBuilder.dom.js';
+import { strictAssert } from '../util/assert.std.js';
 
 const { noop } = lodash;
 
@@ -115,6 +116,7 @@ export function EditHistoryMessagesModal({
   >({});
 
   const [currentMessage, ...pastEdits] = editHistoryMessages;
+  strictAssert(currentMessage, 'Missing currentMessage');
   const currentMessageId = `${currentMessage.id}.${currentMessage.timestamp}`;
 
   let previousItem = currentMessage;
diff --git a/ts/components/GroupCallRemoteParticipants.dom.tsx b/ts/components/GroupCallRemoteParticipants.dom.tsx
index 54447c40ef..fed88b54f1 100644
--- a/ts/components/GroupCallRemoteParticipants.dom.tsx
+++ b/ts/components/GroupCallRemoteParticipants.dom.tsx
@@ -192,9 +192,12 @@ export function GroupCallRemoteParticipants({
     }
 
     if (isInSpeakerView) {
+      const firstParticipiant = prioritySortedParticipants[0];
+      strictAssert(firstParticipiant, 'Missing firstParticipiant');
+
       return [
         {
-          rows: [[prioritySortedParticipants[0]]],
+          rows: [[firstParticipiant]],
           hasSpaceRemaining: false,
           numParticipants: 1,
         },
@@ -222,7 +225,7 @@ export function GroupCallRemoteParticipants({
 
   const isSomeonePresenting =
     prioritySortedParticipants.length &&
-    prioritySortedParticipants[0].presenting;
+    prioritySortedParticipants[0]?.presenting;
 
   // Make sure we're not on a page that no longer exists (e.g. if people left the call)
   if (
@@ -750,6 +753,10 @@ function getGridParticipantsByPage({
               PARTICIPANTS_TO_REMOVE_PER_ATTEMPT.length - 1
             )
           ];
+        strictAssert(
+          numLeastPrioritizedParticipantsToRemove,
+          'Missing numLeastPrioritizedParticipantsToRemove'
+        );
 
         const leastPrioritizedParticipantIds = new Set(
           priorityParticipantsOnNextPage
@@ -804,7 +811,9 @@ function getGridParticipantsByPage({
 
     // Add a previous page tile if needed
     if (pages.length > 0) {
-      nextPageTiles.rows[0].unshift({
+      const firstRow = nextPageTiles.rows[0];
+      strictAssert(firstRow, 'Missing firstRow');
+      firstRow.unshift({
         isPaginationButton: true,
         paginationButtonType: 'prev',
         videoAspectRatio: PAGINATION_BUTTON_ASPECT_RATIO,
@@ -877,11 +886,11 @@ function getNextPage({
   // Initialize fresh page with empty first row
   const rows: Array<Array<GroupCallRemoteParticipantType>> = [[]];
   let row = rows[0];
+  strictAssert(row, 'Missing row');
   let numParticipants = 0;
 
   // Start looping through participants and adding them to the rows one-by-one
-  for (let i = 0; i < participants.length; i += 1) {
-    const participant = participants[i];
+  for (const [i, participant] of participants.entries()) {
     const isLastParticipant =
       !isSubsetOfAllParticipants && i === participants.length - 1;
 
diff --git a/ts/components/GroupMembersNames.dom.tsx b/ts/components/GroupMembersNames.dom.tsx
index e16e003540..cb9805fc19 100644
--- a/ts/components/GroupMembersNames.dom.tsx
+++ b/ts/components/GroupMembersNames.dom.tsx
@@ -54,33 +54,35 @@ function MemberList({
   i18n: LocalizerType;
   onOtherMembersClick?: () => void;
 }): React.JSX.Element {
+  const [member1, member2, member3] = firstThreeMemberNames;
+
   if (areWeInGroup) {
-    if (otherMemberNames.length === 0) {
+    if (member1 == null) {
       return (
         <I18n i18n={i18n} id="icu:ConversationHero--group-members-only-you" />
       );
     }
 
-    if (otherMemberNames.length === 1) {
+    if (member2 == null) {
       return (
         <I18n
           i18n={i18n}
           id="icu:ConversationHero--group-members-one-and-you"
           components={{
-            member: firstThreeMemberNames[0],
+            member: member1,
           }}
         />
       );
     }
 
-    if (otherMemberNames.length === 2) {
+    if (member3 == null) {
       return (
         <I18n
           i18n={i18n}
           id="icu:ConversationHero--group-members-two-and-you"
           components={{
-            member1: firstThreeMemberNames[0],
-            member2: firstThreeMemberNames[1],
+            member1,
+            member2,
           }}
         />
       );
@@ -93,9 +95,9 @@ function MemberList({
         i18n={i18n}
         id="icu:ConversationHero--group-members-other-and-you"
         components={{
-          member1: firstThreeMemberNames[0],
-          member2: firstThreeMemberNames[1],
-          member3: firstThreeMemberNames[2],
+          member1,
+          member2,
+          member3,
           clickable: (parts: ReactNode) =>
             renderClickableButton(parts, onOtherMembersClick),
           remainingCount,
@@ -106,30 +108,30 @@ function MemberList({
 
   // When the user is not in the group
 
-  if (otherMemberNames.length === 0) {
+  if (member1 == null) {
     return <I18n i18n={i18n} id="icu:ConversationHero--group-members-zero" />;
   }
 
-  if (otherMemberNames.length === 1) {
+  if (member2 == null) {
     return (
       <I18n
         i18n={i18n}
         id="icu:ConversationHero--group-members-one"
         components={{
-          member: firstThreeMemberNames[0],
+          member: member1,
         }}
       />
     );
   }
 
-  if (otherMemberNames.length === 2) {
+  if (member3 == null) {
     return (
       <I18n
         i18n={i18n}
         id="icu:ConversationHero--group-members-two"
         components={{
-          member1: firstThreeMemberNames[0],
-          member2: firstThreeMemberNames[1],
+          member1,
+          member2,
         }}
       />
     );
@@ -141,9 +143,9 @@ function MemberList({
         i18n={i18n}
         id="icu:ConversationHero--group-members-three"
         components={{
-          member1: firstThreeMemberNames[0],
-          member2: firstThreeMemberNames[1],
-          member3: firstThreeMemberNames[2],
+          member1,
+          member2,
+          member3,
         }}
       />
     );
@@ -156,9 +158,9 @@ function MemberList({
       i18n={i18n}
       id="icu:ConversationHero--group-members-other"
       components={{
-        member1: firstThreeMemberNames[0],
-        member2: firstThreeMemberNames[1],
-        member3: firstThreeMemberNames[2],
+        member1,
+        member2,
+        member3,
         clickable: (parts: ReactNode) =>
           renderClickableButton(parts, onOtherMembersClick),
         remainingCount,
diff --git a/ts/components/IncomingCallBar.dom.tsx b/ts/components/IncomingCallBar.dom.tsx
index 694d06d833..b3e1f99443 100644
--- a/ts/components/IncomingCallBar.dom.tsx
+++ b/ts/components/IncomingCallBar.dom.tsx
@@ -123,6 +123,7 @@ function GroupCallMessage({
     .map(member => <UserText text={getParticipantName(member)} />);
   const ringerNode = <UserText text={getParticipantName(ringer)} />;
 
+  /* eslint-disable @typescript-eslint/no-non-null-assertion */
   switch (otherMembersRung.length) {
     case 0:
       return (
@@ -139,7 +140,8 @@ function GroupCallMessage({
           i18n={i18n}
           components={{
             ringer: ringerNode,
-            otherMember: first,
+
+            otherMember: first!,
           }}
         />
       );
@@ -150,8 +152,8 @@ function GroupCallMessage({
           i18n={i18n}
           components={{
             ringer: ringerNode,
-            first,
-            second,
+            first: first!,
+            second: second!,
           }}
         />
       );
@@ -162,8 +164,8 @@ function GroupCallMessage({
           i18n={i18n}
           components={{
             ringer: ringerNode,
-            first,
-            second,
+            first: first!,
+            second: second!,
           }}
         />
       );
@@ -174,13 +176,14 @@ function GroupCallMessage({
           i18n={i18n}
           components={{
             ringer: ringerNode,
-            first,
-            second,
+            first: first!,
+            second: second!,
             remaining: otherMembersRung.length - 2,
           }}
         />
       );
   }
+  /* eslint-enable @typescript-eslint/no-non-null-assertion */
 }
 
 export function IncomingCallBar(props: PropsType): React.JSX.Element | null {
diff --git a/ts/components/LeftPane.dom.stories.tsx b/ts/components/LeftPane.dom.stories.tsx
index 8ba05b1132..a97fe72f5b 100644
--- a/ts/components/LeftPane.dom.stories.tsx
+++ b/ts/components/LeftPane.dom.stories.tsx
@@ -51,7 +51,7 @@ export default {
   args: {},
 } satisfies Meta<PropsType>;
 
-const defaultConversations: Array<ConversationType> = [
+const defaultConversations = [
   getDefaultConversation({
     id: 'fred-convo',
     title: 'Fred Willard',
@@ -61,7 +61,7 @@ const defaultConversations: Array<ConversationType> = [
     isSelected: true,
     title: 'Marc Barraca',
   }),
-];
+] as const satisfies Array<ConversationType>;
 
 const defaultSearchProps = {
   filterByUnread: false,
diff --git a/ts/components/Lightbox.dom.tsx b/ts/components/Lightbox.dom.tsx
index 2a0ff91f09..0a3b52f72f 100644
--- a/ts/components/Lightbox.dom.tsx
+++ b/ts/components/Lightbox.dom.tsx
@@ -35,6 +35,7 @@ import { formatFileSize } from '../util/formatFileSize.std.js';
 import { SECOND } from '../util/durations/index.std.js';
 import { Toast } from './Toast.dom.js';
 import { isAbortError } from '../util/isAbortError.std.js';
+import { strictAssert } from '../util/assert.std.js';
 
 const { noop } = lodash;
 
@@ -146,6 +147,7 @@ export function Lightbox({
   >();
 
   const currentItem = media[selectedIndex];
+
   const attachment = currentItem?.attachment;
   const url = attachment?.url;
   const incrementalUrl = attachment?.incrementalUrl;
@@ -242,6 +244,7 @@ export function Lightbox({
       event.preventDefault();
 
       const mediaItem = media[selectedIndex];
+      strictAssert(mediaItem, 'Missing mediaItem');
       const { attachment: attachmentToSave, message, index } = mediaItem;
 
       saveAttachment(attachmentToSave, message.sentAt, index + 1);
@@ -261,6 +264,8 @@ export function Lightbox({
 
     closeLightbox();
     const mediaItem = media[selectedIndex];
+    strictAssert(mediaItem, 'Missing mediaItem');
+
     toggleForwardMessagesModal({
       type: ForwardMessagesModalType.Forward,
       messageIds: [mediaItem.message.id],
@@ -473,6 +478,7 @@ export function Lightbox({
   const handleTouchStart = useCallback(
     (ev: TouchEvent) => {
       const [touch] = ev.touches;
+      strictAssert(touch, 'Missing touch');
 
       dragCacheRef.current = {
         startX: touch.clientX,
@@ -493,6 +499,7 @@ export function Lightbox({
       }
 
       const [touch] = ev.touches;
+      strictAssert(touch, 'Missing touch');
 
       const deltaX = touch.clientX - dragCache.startX;
       const deltaY = touch.clientY - dragCache.startY;
@@ -724,7 +731,7 @@ export function Lightbox({
               ref={focusRef}
             >
               <div className="Lightbox__header">
-                {getConversation ? (
+                {getConversation && currentItem != null ? (
                   <LightboxHeader
                     getConversation={getConversation}
                     i18n={i18n}
diff --git a/ts/components/MyStories.dom.stories.tsx b/ts/components/MyStories.dom.stories.tsx
index 18dd43e2eb..afa8e851a8 100644
--- a/ts/components/MyStories.dom.stories.tsx
+++ b/ts/components/MyStories.dom.stories.tsx
@@ -54,7 +54,8 @@ const interactionTest: PlayFunction<ReactRenderer, PropsType> = async ({
 }) => {
   const canvas = within(canvasElement);
   const [btnDownload] = canvas.getAllByLabelText('Download story');
-  await userEvent.click(btnDownload);
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  await userEvent.click(btnDownload!);
   await expect(args.onSave).toHaveBeenCalled();
 
   const btnBack = canvas.getByText('Back');
@@ -63,10 +64,12 @@ const interactionTest: PlayFunction<ReactRenderer, PropsType> = async ({
 
   const [btnCtxMenu] = canvas.getAllByLabelText('Context menu');
 
-  await userEvent.click(btnCtxMenu);
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  await userEvent.click(btnCtxMenu!);
   await sleep(300);
   const [btnFwd] = canvas.getAllByLabelText('Forward');
-  await userEvent.click(btnFwd);
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  await userEvent.click(btnFwd!);
   await expect(args.onForward).toHaveBeenCalled();
 };
 
diff --git a/ts/components/MyStoryButton.dom.tsx b/ts/components/MyStoryButton.dom.tsx
index 9e615e332a..eb6dd8f795 100644
--- a/ts/components/MyStoryButton.dom.tsx
+++ b/ts/components/MyStoryButton.dom.tsx
@@ -28,7 +28,8 @@ export type PropsType = {
 };
 
 function getNewestMyStory(story: MyStoryType): StoryViewType {
-  return story.stories[0];
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  return story.stories[0]!;
 }
 
 export function MyStoryButton({
@@ -45,7 +46,8 @@ export function MyStoryButton({
   const [active, setActive] = useState(false);
 
   const newestStory = myStories.length
-    ? getNewestMyStory(myStories[0])
+    ? // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      getNewestMyStory(myStories[0]!)
     : undefined;
 
   const { avatarUrl, color, profileName, title } = me;
@@ -85,7 +87,8 @@ export function MyStoryButton({
   }
 
   const hasMultiple = myStories.length
-    ? myStories[0].stories.length > 1
+    ? // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      myStories[0]!.stories.length > 1
     : false;
 
   const reducedSendStatus: ResolvedSendStatus = myStories.reduce(
diff --git a/ts/components/NewlyCreatedGroupInvitedContactsDialog.dom.stories.tsx b/ts/components/NewlyCreatedGroupInvitedContactsDialog.dom.stories.tsx
index 2c378461b2..c8c60272dc 100644
--- a/ts/components/NewlyCreatedGroupInvitedContactsDialog.dom.stories.tsx
+++ b/ts/components/NewlyCreatedGroupInvitedContactsDialog.dom.stories.tsx
@@ -14,10 +14,10 @@ import { ThemeType } from '../types/Util.std.js';
 
 const { i18n } = window.SignalContext;
 
-const conversations: Array<ConversationType> = [
+const conversations = [
   getDefaultConversation({ title: 'Fred Willard' }),
   getDefaultConversation({ title: 'Marc Barraca' }),
-];
+] as const satisfies Array<ConversationType>;
 
 export default {
   title: 'Components/NewlyCreatedGroupInvitedContactsDialog',
diff --git a/ts/components/NewlyCreatedGroupInvitedContactsDialog.dom.tsx b/ts/components/NewlyCreatedGroupInvitedContactsDialog.dom.tsx
index ea30a57203..417f2dd71f 100644
--- a/ts/components/NewlyCreatedGroupInvitedContactsDialog.dom.tsx
+++ b/ts/components/NewlyCreatedGroupInvitedContactsDialog.dom.tsx
@@ -29,7 +29,8 @@ export function NewlyCreatedGroupInvitedContactsDialog({
 }: PropsType): React.JSX.Element {
   let body: ReactNode;
   if (contacts.length === 1) {
-    const contact = contacts[0];
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const contact = contacts[0]!;
 
     body = (
       <>
diff --git a/ts/components/NotificationProfilesMenu.dom.stories.tsx b/ts/components/NotificationProfilesMenu.dom.stories.tsx
index 5715047a41..88005db261 100644
--- a/ts/components/NotificationProfilesMenu.dom.stories.tsx
+++ b/ts/components/NotificationProfilesMenu.dom.stories.tsx
@@ -17,6 +17,7 @@ import type { NotificationProfileIdString } from '../types/NotificationProfile.s
 import { HOUR } from '../util/durations/index.std.js';
 import { AxoDropdownMenu } from '../axo/AxoDropdownMenu.dom.js';
 import { AxoButton } from '../axo/AxoButton.dom.js';
+import type { ConversationType } from '../state/ducks/conversations.preload.js';
 
 const { i18n } = window.SignalContext;
 
@@ -25,6 +26,11 @@ const conversations = shuffle([
   ...Array.from(Array(20), getDefaultConversation),
 ]);
 
+const [conversation1, conversation2] = conversations as [
+  ConversationType,
+  ConversationType,
+];
+
 const threeProfiles = [
   {
     id: 'Weekday' as NotificationProfileIdString,
@@ -37,7 +43,7 @@ const threeProfiles = [
     allowAllCalls: true,
     allowAllMentions: true,
 
-    allowedMembers: new Set([conversations[0].id, conversations[1].id]),
+    allowedMembers: new Set([conversation1.id, conversation2.id]),
     scheduleEnabled: true,
 
     scheduleStartTime: 1800,
@@ -66,7 +72,7 @@ const threeProfiles = [
     allowAllCalls: true,
     allowAllMentions: true,
 
-    allowedMembers: new Set([conversations[0].id, conversations[1].id]),
+    allowedMembers: new Set([conversation1.id, conversation2.id]),
     scheduleEnabled: true,
 
     scheduleStartTime: 1800,
@@ -95,7 +101,7 @@ const threeProfiles = [
     allowAllCalls: true,
     allowAllMentions: true,
 
-    allowedMembers: new Set([conversations[0].id, conversations[1].id]),
+    allowedMembers: new Set([conversation1.id, conversation2.id]),
     scheduleEnabled: true,
 
     scheduleStartTime: 1800,
@@ -113,7 +119,7 @@ const threeProfiles = [
     deletedAtTimestampMs: undefined,
     storageNeedsSync: true,
   },
-];
+] as const;
 
 export default {
   title: 'Components/NotificationProfilesMenu',
diff --git a/ts/components/PlaybackRateButton.dom.tsx b/ts/components/PlaybackRateButton.dom.tsx
index f1b5d85e53..f4a7f257ec 100644
--- a/ts/components/PlaybackRateButton.dom.tsx
+++ b/ts/components/PlaybackRateButton.dom.tsx
@@ -76,7 +76,7 @@ export function PlaybackRateButton({
   };
 
   const label = playbackRate
-    ? playbackRateLabels[playbackRate].toString()
+    ? playbackRateLabels[playbackRate]?.toString()
     : undefined;
 
   return (
@@ -105,7 +105,8 @@ const playbackRates = [1, 1.5, 2, 0.5];
 
 PlaybackRateButton.nextPlaybackRate = (currentRate: number): number => {
   // cycle through the rates
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
   return playbackRates[
     (playbackRates.indexOf(currentRate) + 1) % playbackRates.length
-  ];
+  ]!;
 };
diff --git a/ts/components/PollCreateModal.dom.tsx b/ts/components/PollCreateModal.dom.tsx
index f52c5bf90a..7b4377b550 100644
--- a/ts/components/PollCreateModal.dom.tsx
+++ b/ts/components/PollCreateModal.dom.tsx
@@ -75,7 +75,7 @@ export function PollCreateModal({
       const isLastOption = changedIndex === resultOptions.length - 1;
       const isSecondToLast = changedIndex === resultOptions.length - 2;
       const changedOption = resultOptions[changedIndex];
-      const hasText = changedOption?.value.trim().length > 0;
+      const hasText = (changedOption?.value.trim().length ?? 0) > 0;
       const canAddMore = resultOptions.length < POLL_OPTIONS_MAX_COUNT;
       const canRemove = resultOptions.length > POLL_OPTIONS_MIN_COUNT;
       let removedIndex: number | undefined;
diff --git a/ts/components/Preferences.dom.stories.tsx b/ts/components/Preferences.dom.stories.tsx
index 18de3c9b6e..b5cfa6b9a2 100644
--- a/ts/components/Preferences.dom.stories.tsx
+++ b/ts/components/Preferences.dom.stories.tsx
@@ -76,6 +76,10 @@ const conversations = shuffle([
   ...Array.from(Array(20), getDefaultConversation),
 ]);
 
+const [conversation1, conversation2] = conversations;
+strictAssert(conversation1, 'Missing conversation1');
+strictAssert(conversation2, 'Missing conversation2');
+
 function conversationSelector(conversationId?: string) {
   strictAssert(conversationId, 'Missing conversation id');
   const found = conversations.find(conversation => {
@@ -734,7 +738,7 @@ const threeProfiles = [
     allowAllCalls: true,
     allowAllMentions: true,
 
-    allowedMembers: new Set([conversations[0].id, conversations[1].id]),
+    allowedMembers: new Set([conversation1.id, conversation2.id]),
     scheduleEnabled: true,
 
     scheduleStartTime: 1800,
@@ -763,7 +767,7 @@ const threeProfiles = [
     allowAllCalls: true,
     allowAllMentions: true,
 
-    allowedMembers: new Set([conversations[0].id, conversations[1].id]),
+    allowedMembers: new Set([conversation1.id, conversation2.id]),
     scheduleEnabled: true,
 
     scheduleStartTime: 100,
@@ -792,7 +796,7 @@ const threeProfiles = [
     allowAllCalls: true,
     allowAllMentions: true,
 
-    allowedMembers: new Set([conversations[0].id, conversations[1].id]),
+    allowedMembers: new Set([conversation1.id, conversation2.id]),
     scheduleEnabled: true,
 
     scheduleStartTime: 1800,
@@ -810,7 +814,7 @@ const threeProfiles = [
     deletedAtTimestampMs: undefined,
     storageNeedsSync: true,
   },
-];
+] as const;
 
 NotificationsPageWithThreeProfiles.args = {
   settingsLocation: { page: SettingsPage.Notifications },
diff --git a/ts/components/PreferencesNotificationProfiles.dom.tsx b/ts/components/PreferencesNotificationProfiles.dom.tsx
index 985f6bd314..6aa68d7dac 100644
--- a/ts/components/PreferencesNotificationProfiles.dom.tsx
+++ b/ts/components/PreferencesNotificationProfiles.dom.tsx
@@ -243,7 +243,8 @@ const ARGB_BITS = 0xff000000;
 const A100_BACKGROUND_ARGB = 0xffe3e3fe;
 
 function getRandomColor(): number {
-  const colorName = sample(AvatarColors) || AvatarColors[0];
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  const colorName = sample(AvatarColors) || AvatarColors[0]!;
   const color = AvatarColorMap.get(colorName);
   if (!color) {
     return A100_BACKGROUND_ARGB; // A100, background, with bits for ARGB
diff --git a/ts/components/ProfileEditor.dom.tsx b/ts/components/ProfileEditor.dom.tsx
index 86cb7b592c..3440269346 100644
--- a/ts/components/ProfileEditor.dom.tsx
+++ b/ts/components/ProfileEditor.dom.tsx
@@ -29,7 +29,6 @@ import {
   ConversationDetailsIcon,
   IconType,
 } from './conversation/conversation-details/ConversationDetailsIcon.dom.js';
-import { isWhitespace, trim } from '../util/whitespaceStringUtil.std.js';
 import { UserText } from './UserText.dom.js';
 import { Tooltip, TooltipPlacement } from './Tooltip.dom.js';
 import { offsetDistanceModifier } from '../util/popperUtil.std.js';
@@ -294,9 +293,9 @@ export function ProfileEditor({
       onProfileChanged(
         {
           ...stagedProfile,
-          firstName: trim(stagedProfile.firstName),
+          firstName: stagedProfile.firstName.trim(),
           familyName: stagedProfile.familyName
-            ? trim(stagedProfile.familyName)
+            ? stagedProfile.familyName.trim()
             : undefined,
         },
         {
@@ -376,7 +375,7 @@ export function ProfileEditor({
       !stagedProfile.firstName ||
       (stagedProfile.firstName === fullName.firstName &&
         stagedProfile.familyName === fullName.familyName) ||
-      isWhitespace(stagedProfile.firstName);
+      stagedProfile.firstName.trim() === '';
 
     content = (
       <>
diff --git a/ts/components/SafetyTipsModal.dom.tsx b/ts/components/SafetyTipsModal.dom.tsx
index 3405e5adde..6594db3dbe 100644
--- a/ts/components/SafetyTipsModal.dom.tsx
+++ b/ts/components/SafetyTipsModal.dom.tsx
@@ -56,7 +56,8 @@ export function SafetyTipsModal({
   const [cardWrapperId] = useState(() => uuid());
 
   function getCardIdForPage(pageIndex: number) {
-    return `${cardWrapperId}_${pages[pageIndex].key}`;
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    return `${cardWrapperId}_${pages[pageIndex]!.key}`;
   }
 
   const maxPageIndex = pages.length - 1;
diff --git a/ts/components/SharedGroupNames.dom.tsx b/ts/components/SharedGroupNames.dom.tsx
index a7d3fba655..5f2890fd1d 100644
--- a/ts/components/SharedGroupNames.dom.tsx
+++ b/ts/components/SharedGroupNames.dom.tsx
@@ -29,6 +29,7 @@ export function SharedGroupNames({
     </strong>
   ));
 
+  /* eslint-disable @typescript-eslint/no-non-null-assertion */
   if (sharedGroupNames.length >= 5) {
     const remainingCount = sharedGroupNames.length - 3;
     return (
@@ -36,9 +37,9 @@ export function SharedGroupNames({
         i18n={i18n}
         id="icu:member-of-more-than-3-groups--multiple-more"
         components={{
-          group1: firstThreeGroups[0],
-          group2: firstThreeGroups[1],
-          group3: firstThreeGroups[2],
+          group1: firstThreeGroups[0]!,
+          group2: firstThreeGroups[1]!,
+          group3: firstThreeGroups[2]!,
           remainingCount,
         }}
       />
@@ -50,9 +51,9 @@ export function SharedGroupNames({
         i18n={i18n}
         id="icu:member-of-more-than-3-groups--one-more"
         components={{
-          group1: firstThreeGroups[0],
-          group2: firstThreeGroups[1],
-          group3: firstThreeGroups[2],
+          group1: firstThreeGroups[0]!,
+          group2: firstThreeGroups[1]!,
+          group3: firstThreeGroups[2]!,
         }}
       />
     );
@@ -63,9 +64,9 @@ export function SharedGroupNames({
         i18n={i18n}
         id="icu:member-of-3-groups"
         components={{
-          group1: firstThreeGroups[0],
-          group2: firstThreeGroups[1],
-          group3: firstThreeGroups[2],
+          group1: firstThreeGroups[0]!,
+          group2: firstThreeGroups[1]!,
+          group3: firstThreeGroups[2]!,
         }}
       />
     );
@@ -76,8 +77,8 @@ export function SharedGroupNames({
         i18n={i18n}
         id="icu:member-of-2-groups"
         components={{
-          group1: firstThreeGroups[0],
-          group2: firstThreeGroups[1],
+          group1: firstThreeGroups[0]!,
+          group2: firstThreeGroups[1]!,
         }}
       />
     );
@@ -88,11 +89,12 @@ export function SharedGroupNames({
         i18n={i18n}
         id="icu:member-of-1-group"
         components={{
-          group: firstThreeGroups[0],
+          group: firstThreeGroups[0]!,
         }}
       />
     );
   }
+  /* eslint-enable @typescript-eslint/no-non-null-assertion */
 
   return <>{i18n('icu:no-groups-in-common')}</>;
 }
diff --git a/ts/components/TextAttachment.dom.tsx b/ts/components/TextAttachment.dom.tsx
index 7380b07bc6..f519ddc842 100644
--- a/ts/components/TextAttachment.dom.tsx
+++ b/ts/components/TextAttachment.dom.tsx
@@ -75,7 +75,7 @@ function getFont(
   textStyle?: TextAttachmentStyleType | null,
   i18n?: LocalizerType
 ): string {
-  const textStyleIndex = Number(textStyle) || 0;
+  const textStyleIndex = textStyle ?? TextAttachmentStyleType.DEFAULT;
   const fontName = getFontNameByTextScript(text, textStyleIndex, i18n);
 
   let fontSize = FONT_SIZE_SMALL;
diff --git a/ts/components/VoiceNotesPlaybackContext.dom.tsx b/ts/components/VoiceNotesPlaybackContext.dom.tsx
index b9d42be2be..ae0ecbddd9 100644
--- a/ts/components/VoiceNotesPlaybackContext.dom.tsx
+++ b/ts/components/VoiceNotesPlaybackContext.dom.tsx
@@ -122,9 +122,9 @@ async function doComputePeaks(
   ) {
     const channel = data.getChannelData(channelNum);
 
-    for (let sample = 0; sample < channel.length; sample += 1) {
+    for (const [sample, sampleData] of channel.entries()) {
       const i = Math.floor(sample / samplesPerPeak);
-      peaks[i] += channel[sample] ** 2;
+      peaks[i] += sampleData ** 2;
       norms[i] += 1;
     }
   }
diff --git a/ts/components/conversation/AttachmentList.dom.tsx b/ts/components/conversation/AttachmentList.dom.tsx
index ec540af5a3..ff6b417fc4 100644
--- a/ts/components/conversation/AttachmentList.dom.tsx
+++ b/ts/components/conversation/AttachmentList.dom.tsx
@@ -97,7 +97,8 @@ export function AttachmentList<
       <div className="module-attachments__rail">
         {attachments.map((attachment, index) => {
           const url = getUrl(attachment);
-          const forUI = attachmentsForUI[index];
+          // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+          const forUI = attachmentsForUI[index]!;
 
           const key =
             attachment.clientUuid ||
diff --git a/ts/components/conversation/ContactModal.dom.tsx b/ts/components/conversation/ContactModal.dom.tsx
index 51e487df17..2887222321 100644
--- a/ts/components/conversation/ContactModal.dom.tsx
+++ b/ts/components/conversation/ContactModal.dom.tsx
@@ -39,6 +39,7 @@ import { AxoSymbol } from '../../axo/AxoSymbol.dom.js';
 import { tw } from '../../axo/tw.dom.js';
 import { strictAssert } from '../../util/assert.std.js';
 import type { RemoveClientType } from '../../types/Calling.std.js';
+import type { ContactNameColorType } from '../../types/Colors.std.js';
 
 const ACCESS_ENUM = Proto.AccessControl.AccessRequired;
 
@@ -52,7 +53,7 @@ export type PropsDataType = {
   contact?: ConversationType;
   contactLabelEmoji: string | undefined;
   contactLabelString: string | undefined;
-  contactNameColor: string | undefined;
+  contactNameColor: ContactNameColorType | undefined;
   conversation?: ConversationType;
   hasStories?: HasStories;
   readonly i18n: LocalizerType;
diff --git a/ts/components/conversation/ConversationView.dom.tsx b/ts/components/conversation/ConversationView.dom.tsx
index e5432c8610..17454b6e9a 100644
--- a/ts/components/conversation/ConversationView.dom.tsx
+++ b/ts/components/conversation/ConversationView.dom.tsx
@@ -114,8 +114,8 @@ export function ConversationView({
       });
       if (allVisual) {
         const files: Array<File> = [];
-        for (let i = 0; i < items.length; i += 1) {
-          const file = getAsFile(items[i]);
+        for (const item of items) {
+          const file = getAsFile(item);
           if (file) {
             files.push(file);
           }
diff --git a/ts/components/conversation/GroupNotification.dom.tsx b/ts/components/conversation/GroupNotification.dom.tsx
index 32bb8de487..cbcadff62f 100644
--- a/ts/components/conversation/GroupNotification.dom.tsx
+++ b/ts/components/conversation/GroupNotification.dom.tsx
@@ -92,7 +92,8 @@ function GroupNotificationChange({
                 <I18n
                   i18n={i18n}
                   id="icu:joinedTheGroup"
-                  components={{ name: otherPeople[0] }}
+                  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+                  components={{ name: otherPeople[0]! }}
                 />
               ) : (
                 <I18n
@@ -123,7 +124,8 @@ function GroupNotificationChange({
         <I18n
           id="icu:multipleLeftTheGroup"
           i18n={i18n}
-          components={{ name: otherPeople[0] }}
+          // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+          components={{ name: otherPeople[0]! }}
         />
       ) : (
         <I18n
diff --git a/ts/components/conversation/GroupV1Migration.dom.tsx b/ts/components/conversation/GroupV1Migration.dom.tsx
index 6b2d47760c..4e625d3e56 100644
--- a/ts/components/conversation/GroupV1Migration.dom.tsx
+++ b/ts/components/conversation/GroupV1Migration.dom.tsx
@@ -128,7 +128,8 @@ function renderUsers({
   }
 
   if (members && count === 1) {
-    const contact = <ContactName title={members[0].title} />;
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const contact = <ContactName title={members[0]!.title} />;
     return (
       <p>
         {kind === 'invited' && (
diff --git a/ts/components/conversation/ImageGrid.dom.tsx b/ts/components/conversation/ImageGrid.dom.tsx
index c1e3bb0a48..3420a4951e 100644
--- a/ts/components/conversation/ImageGrid.dom.tsx
+++ b/ts/components/conversation/ImageGrid.dom.tsx
@@ -23,6 +23,7 @@ import { Image, CurveType } from './Image.dom.js';
 
 import type { LocalizerType, ThemeType } from '../../types/Util.std.js';
 import { AttachmentDetailPill } from './AttachmentDetailPill.dom.js';
+import { strictAssert } from '../../util/assert.std.js';
 
 export type DirectionType = 'incoming' | 'outgoing';
 
@@ -158,10 +159,13 @@ export function ImageGrid({
   );
 
   const showAttachmentOrNoLongerAvailableToast = React.useCallback(
-    (attachmentIndex: number) =>
-      attachments[attachmentIndex].isPermanentlyUndownloadable
+    (attachmentIndex: number) => {
+      const attachment = attachments[attachmentIndex];
+      strictAssert(attachment, 'Missing attachment');
+      return attachment.isPermanentlyUndownloadable
         ? showMediaNoLongerAvailableToast
-        : showVisualAttachment,
+        : showVisualAttachment;
+    },
     [attachments, showVisualAttachment, showMediaNoLongerAvailableToast]
   );
 
@@ -189,8 +193,10 @@ export function ImageGrid({
   });
 
   if (attachments.length === 1 || !areAllAttachmentsVisual(attachments)) {
+    const [attachment] = attachments;
+    strictAssert(attachment, 'Missing attachment');
     const { height, width } = getImageDimensionsForTimeline(
-      attachments[0],
+      attachment,
       isSticker ? stickerSize : undefined
     );
 
@@ -203,10 +209,10 @@ export function ImageGrid({
         )}
       >
         <Image
-          alt={getAlt(attachments[0], i18n)}
+          alt={getAlt(attachment, i18n)}
           i18n={i18n}
           theme={theme}
-          blurHash={attachments[0].blurHash}
+          blurHash={attachment.blurHash}
           bottomOverlay={withBottomOverlay}
           noBorder={isSticker}
           noBackground={isSticker}
@@ -214,13 +220,11 @@ export function ImageGrid({
           curveTopRight={curveTopRight}
           curveBottomLeft={curveBottomLeft}
           curveBottomRight={curveBottomRight}
-          attachment={attachments[0]}
-          playIconOverlay={isVideoAttachment(attachments[0])}
+          attachment={attachment}
+          playIconOverlay={isVideoAttachment(attachment)}
           height={height}
           width={width}
-          url={
-            getUrl(attachments[0]) ?? attachments[0].thumbnailFromBackup?.url
-          }
+          url={getUrl(attachment) ?? attachment.thumbnailFromBackup?.url}
           tabIndex={tabIndex}
           showMediaNoLongerAvailableToast={showMediaNoLongerAvailableToast}
           showVisualAttachment={showAttachmentOrNoLongerAvailableToast(0)}
@@ -234,23 +238,26 @@ export function ImageGrid({
   }
 
   if (attachments.length === 2) {
+    const [attachment1, attachment2] = attachments;
+    strictAssert(attachment1, 'Missing attachment 1');
+    strictAssert(attachment2, 'Missing attachment 2');
     return (
       <div className="module-image-grid">
         <Image
-          alt={getAlt(attachments[0], i18n)}
+          alt={getAlt(attachment1, i18n)}
           i18n={i18n}
           theme={theme}
-          attachment={attachments[0]}
-          blurHash={attachments[0].blurHash}
+          attachment={attachment1}
+          blurHash={attachment1.blurHash}
           bottomOverlay={withBottomOverlay}
           noBorder={false}
           curveTopLeft={curveTopLeft}
           curveBottomLeft={curveBottomLeft}
-          playIconOverlay={isVideoAttachment(attachments[0])}
+          playIconOverlay={isVideoAttachment(attachment1)}
           height={150}
           width={150}
           cropWidth={GAP}
-          url={getThumbnailUrl(attachments[0])}
+          url={getThumbnailUrl(attachment1)}
           showMediaNoLongerAvailableToast={showMediaNoLongerAvailableToast}
           showVisualAttachment={showAttachmentOrNoLongerAvailableToast(0)}
           cancelDownload={cancelDownload}
@@ -258,19 +265,19 @@ export function ImageGrid({
           onError={onError}
         />
         <Image
-          alt={getAlt(attachments[1], i18n)}
+          alt={getAlt(attachment2, i18n)}
           i18n={i18n}
           theme={theme}
-          blurHash={attachments[1].blurHash}
+          blurHash={attachment2.blurHash}
           bottomOverlay={withBottomOverlay}
           noBorder={false}
           curveTopRight={curveTopRight}
           curveBottomRight={curveBottomRight}
-          playIconOverlay={isVideoAttachment(attachments[1])}
+          playIconOverlay={isVideoAttachment(attachment2)}
           height={150}
           width={150}
-          attachment={attachments[1]}
-          url={getThumbnailUrl(attachments[1])}
+          attachment={attachment2}
+          url={getThumbnailUrl(attachment2)}
           showMediaNoLongerAvailableToast={showMediaNoLongerAvailableToast}
           showVisualAttachment={showAttachmentOrNoLongerAvailableToast(1)}
           cancelDownload={cancelDownload}
@@ -284,23 +291,27 @@ export function ImageGrid({
   }
 
   if (attachments.length === 3) {
+    const [attachment1, attachment2, attachment3] = attachments;
+    strictAssert(attachment1, 'Missing attachment 1');
+    strictAssert(attachment2, 'Missing attachment 2');
+    strictAssert(attachment3, 'Missing attachment 3');
     return (
       <div className="module-image-grid">
         <Image
-          alt={getAlt(attachments[0], i18n)}
+          alt={getAlt(attachment1, i18n)}
           i18n={i18n}
           theme={theme}
-          blurHash={attachments[0].blurHash}
+          blurHash={attachment1.blurHash}
           bottomOverlay={withBottomOverlay}
           noBorder={false}
           curveTopLeft={curveTopLeft}
           curveBottomLeft={curveBottomLeft}
-          attachment={attachments[0]}
-          playIconOverlay={isVideoAttachment(attachments[0])}
+          attachment={attachment1}
+          playIconOverlay={isVideoAttachment(attachment1)}
           height={200}
           width={200}
           cropWidth={GAP}
-          url={getUrl(attachments[0])}
+          url={getUrl(attachment1)}
           showMediaNoLongerAvailableToast={showMediaNoLongerAvailableToast}
           showVisualAttachment={showAttachmentOrNoLongerAvailableToast(0)}
           cancelDownload={cancelDownload}
@@ -309,17 +320,17 @@ export function ImageGrid({
         />
         <div className="module-image-grid__column">
           <Image
-            alt={getAlt(attachments[1], i18n)}
+            alt={getAlt(attachment2, i18n)}
             i18n={i18n}
             theme={theme}
-            blurHash={attachments[1].blurHash}
+            blurHash={attachment2.blurHash}
             curveTopRight={curveTopRight}
             height={100}
             width={100}
             cropHeight={GAP}
-            attachment={attachments[1]}
-            playIconOverlay={isVideoAttachment(attachments[1])}
-            url={getThumbnailUrl(attachments[1])}
+            attachment={attachment2}
+            playIconOverlay={isVideoAttachment(attachment2)}
+            url={getThumbnailUrl(attachment2)}
             showMediaNoLongerAvailableToast={showMediaNoLongerAvailableToast}
             showVisualAttachment={showAttachmentOrNoLongerAvailableToast(1)}
             cancelDownload={cancelDownload}
@@ -327,18 +338,18 @@ export function ImageGrid({
             onError={onError}
           />
           <Image
-            alt={getAlt(attachments[2], i18n)}
+            alt={getAlt(attachment3, i18n)}
             i18n={i18n}
             theme={theme}
-            blurHash={attachments[2].blurHash}
+            blurHash={attachment3.blurHash}
             bottomOverlay={withBottomOverlay}
             noBorder={false}
             curveBottomRight={curveBottomRight}
             height={100}
             width={100}
-            attachment={attachments[2]}
-            playIconOverlay={isVideoAttachment(attachments[2])}
-            url={getThumbnailUrl(attachments[2])}
+            attachment={attachment3}
+            playIconOverlay={isVideoAttachment(attachment3)}
+            url={getThumbnailUrl(attachment3)}
             showMediaNoLongerAvailableToast={showMediaNoLongerAvailableToast}
             showVisualAttachment={showAttachmentOrNoLongerAvailableToast(2)}
             cancelDownload={cancelDownload}
@@ -353,24 +364,29 @@ export function ImageGrid({
   }
 
   if (attachments.length === 4) {
+    const [attachment1, attachment2, attachment3, attachment4] = attachments;
+    strictAssert(attachment1, 'Missing attachment 1');
+    strictAssert(attachment2, 'Missing attachment 2');
+    strictAssert(attachment3, 'Missing attachment 3');
+    strictAssert(attachment4, 'Missing attachment 4');
     return (
       <div className="module-image-grid">
         <div className="module-image-grid__column">
           <div className="module-image-grid__row">
             <Image
-              alt={getAlt(attachments[0], i18n)}
+              alt={getAlt(attachment1, i18n)}
               i18n={i18n}
               theme={theme}
-              blurHash={attachments[0].blurHash}
+              blurHash={attachment1.blurHash}
               curveTopLeft={curveTopLeft}
               noBorder={false}
-              attachment={attachments[0]}
-              playIconOverlay={isVideoAttachment(attachments[0])}
+              attachment={attachment1}
+              playIconOverlay={isVideoAttachment(attachment1)}
               height={150}
               width={150}
               cropHeight={GAP}
               cropWidth={GAP}
-              url={getThumbnailUrl(attachments[0])}
+              url={getThumbnailUrl(attachment1)}
               showMediaNoLongerAvailableToast={showMediaNoLongerAvailableToast}
               showVisualAttachment={showAttachmentOrNoLongerAvailableToast(0)}
               cancelDownload={cancelDownload}
@@ -378,18 +394,18 @@ export function ImageGrid({
               onError={onError}
             />
             <Image
-              alt={getAlt(attachments[1], i18n)}
+              alt={getAlt(attachment2, i18n)}
               i18n={i18n}
               theme={theme}
-              blurHash={attachments[1].blurHash}
+              blurHash={attachment2.blurHash}
               curveTopRight={curveTopRight}
-              playIconOverlay={isVideoAttachment(attachments[1])}
+              playIconOverlay={isVideoAttachment(attachment2)}
               noBorder={false}
               height={150}
               width={150}
               cropHeight={GAP}
-              attachment={attachments[1]}
-              url={getThumbnailUrl(attachments[1])}
+              attachment={attachment2}
+              url={getThumbnailUrl(attachment2)}
               showMediaNoLongerAvailableToast={showMediaNoLongerAvailableToast}
               showVisualAttachment={showAttachmentOrNoLongerAvailableToast(1)}
               cancelDownload={cancelDownload}
@@ -399,19 +415,19 @@ export function ImageGrid({
           </div>
           <div className="module-image-grid__row">
             <Image
-              alt={getAlt(attachments[2], i18n)}
+              alt={getAlt(attachment3, i18n)}
               i18n={i18n}
               theme={theme}
-              blurHash={attachments[2].blurHash}
+              blurHash={attachment3.blurHash}
               bottomOverlay={withBottomOverlay}
               noBorder={false}
               curveBottomLeft={curveBottomLeft}
-              playIconOverlay={isVideoAttachment(attachments[2])}
+              playIconOverlay={isVideoAttachment(attachment3)}
               height={150}
               width={150}
               cropWidth={GAP}
-              attachment={attachments[2]}
-              url={getThumbnailUrl(attachments[2])}
+              attachment={attachment3}
+              url={getThumbnailUrl(attachment3)}
               showMediaNoLongerAvailableToast={showMediaNoLongerAvailableToast}
               showVisualAttachment={showAttachmentOrNoLongerAvailableToast(2)}
               cancelDownload={cancelDownload}
@@ -419,18 +435,18 @@ export function ImageGrid({
               onError={onError}
             />
             <Image
-              alt={getAlt(attachments[3], i18n)}
+              alt={getAlt(attachment4, i18n)}
               i18n={i18n}
               theme={theme}
-              blurHash={attachments[3].blurHash}
+              blurHash={attachment4.blurHash}
               bottomOverlay={withBottomOverlay}
               noBorder={false}
               curveBottomRight={curveBottomRight}
-              playIconOverlay={isVideoAttachment(attachments[3])}
+              playIconOverlay={isVideoAttachment(attachment4)}
               height={150}
               width={150}
-              attachment={attachments[3]}
-              url={getThumbnailUrl(attachments[3])}
+              attachment={attachment4}
+              url={getThumbnailUrl(attachment4)}
               showMediaNoLongerAvailableToast={showMediaNoLongerAvailableToast}
               showVisualAttachment={showAttachmentOrNoLongerAvailableToast(3)}
               cancelDownload={cancelDownload}
@@ -450,22 +466,30 @@ export function ImageGrid({
     ? `+${attachments.length - 5}`
     : undefined;
 
+  const [attachment1, attachment2, attachment3, attachment4, attachment5] =
+    attachments;
+  strictAssert(attachment1, 'Missing attachment 1');
+  strictAssert(attachment2, 'Missing attachment 2');
+  strictAssert(attachment3, 'Missing attachment 3');
+  strictAssert(attachment4, 'Missing attachment 4');
+  strictAssert(attachment5, 'Missing attachment 4');
+
   return (
     <div className="module-image-grid">
       <div className="module-image-grid__column">
         <div className="module-image-grid__row">
           <Image
-            alt={getAlt(attachments[0], i18n)}
+            alt={getAlt(attachment1, i18n)}
             i18n={i18n}
             theme={theme}
-            blurHash={attachments[0].blurHash}
+            blurHash={attachment1.blurHash}
             curveTopLeft={curveTopLeft}
-            attachment={attachments[0]}
-            playIconOverlay={isVideoAttachment(attachments[0])}
+            attachment={attachment1}
+            playIconOverlay={isVideoAttachment(attachment1)}
             height={150}
             width={150}
             cropWidth={GAP}
-            url={getThumbnailUrl(attachments[0])}
+            url={getThumbnailUrl(attachment1)}
             showMediaNoLongerAvailableToast={showMediaNoLongerAvailableToast}
             showVisualAttachment={showVisualAttachment}
             cancelDownload={cancelDownload}
@@ -473,16 +497,16 @@ export function ImageGrid({
             onError={onError}
           />
           <Image
-            alt={getAlt(attachments[1], i18n)}
+            alt={getAlt(attachment2, i18n)}
             i18n={i18n}
             theme={theme}
-            blurHash={attachments[1].blurHash}
+            blurHash={attachment2.blurHash}
             curveTopRight={curveTopRight}
-            playIconOverlay={isVideoAttachment(attachments[1])}
+            playIconOverlay={isVideoAttachment(attachment2)}
             height={150}
             width={150}
-            attachment={attachments[1]}
-            url={getThumbnailUrl(attachments[1])}
+            attachment={attachment2}
+            url={getThumbnailUrl(attachment2)}
             showMediaNoLongerAvailableToast={showMediaNoLongerAvailableToast}
             showVisualAttachment={showVisualAttachment}
             cancelDownload={cancelDownload}
@@ -492,19 +516,19 @@ export function ImageGrid({
         </div>
         <div className="module-image-grid__row">
           <Image
-            alt={getAlt(attachments[2], i18n)}
+            alt={getAlt(attachment3, i18n)}
             i18n={i18n}
             theme={theme}
-            blurHash={attachments[2].blurHash}
+            blurHash={attachment3.blurHash}
             bottomOverlay={withBottomOverlay}
             noBorder={isSticker}
             curveBottomLeft={curveBottomLeft}
-            playIconOverlay={isVideoAttachment(attachments[2])}
+            playIconOverlay={isVideoAttachment(attachment3)}
             height={100}
             width={100}
             cropWidth={GAP}
-            attachment={attachments[2]}
-            url={getThumbnailUrl(attachments[2])}
+            attachment={attachment3}
+            url={getThumbnailUrl(attachment3)}
             showMediaNoLongerAvailableToast={showMediaNoLongerAvailableToast}
             showVisualAttachment={showVisualAttachment}
             cancelDownload={cancelDownload}
@@ -512,18 +536,18 @@ export function ImageGrid({
             onError={onError}
           />
           <Image
-            alt={getAlt(attachments[3], i18n)}
+            alt={getAlt(attachment4, i18n)}
             i18n={i18n}
             theme={theme}
-            blurHash={attachments[3].blurHash}
+            blurHash={attachment4.blurHash}
             bottomOverlay={withBottomOverlay}
             noBorder={isSticker}
-            playIconOverlay={isVideoAttachment(attachments[3])}
+            playIconOverlay={isVideoAttachment(attachment4)}
             height={100}
             width={100}
             cropWidth={GAP}
-            attachment={attachments[3]}
-            url={getThumbnailUrl(attachments[3])}
+            attachment={attachment4}
+            url={getThumbnailUrl(attachment4)}
             showMediaNoLongerAvailableToast={showMediaNoLongerAvailableToast}
             showVisualAttachment={showVisualAttachment}
             cancelDownload={cancelDownload}
@@ -531,20 +555,20 @@ export function ImageGrid({
             onError={onError}
           />
           <Image
-            alt={getAlt(attachments[4], i18n)}
+            alt={getAlt(attachment5, i18n)}
             i18n={i18n}
             theme={theme}
-            blurHash={attachments[4].blurHash}
+            blurHash={attachment5.blurHash}
             bottomOverlay={withBottomOverlay}
             noBorder={isSticker}
             curveBottomRight={curveBottomRight}
-            playIconOverlay={isVideoAttachment(attachments[4])}
+            playIconOverlay={isVideoAttachment(attachment5)}
             height={100}
             width={100}
             darkOverlay={moreMessagesOverlay}
             overlayText={moreMessagesOverlayText}
-            attachment={attachments[4]}
-            url={getThumbnailUrl(attachments[4])}
+            attachment={attachment5}
+            url={getThumbnailUrl(attachment5)}
             showMediaNoLongerAvailableToast={showMediaNoLongerAvailableToast}
             showVisualAttachment={showVisualAttachment}
             cancelDownload={undefined}
diff --git a/ts/components/conversation/Message.dom.tsx b/ts/components/conversation/Message.dom.tsx
index f3b18a9795..6d34a75078 100644
--- a/ts/components/conversation/Message.dom.tsx
+++ b/ts/components/conversation/Message.dom.tsx
@@ -108,7 +108,7 @@ import { getColorForCallLink } from '../../util/getColorForCallLink.std.js';
 import { getKeyFromCallLink } from '../../util/callLinks.std.js';
 import { InAnotherCallTooltip } from './InAnotherCallTooltip.dom.js';
 import { formatFileSize } from '../../util/formatFileSize.std.js';
-import { assertDev } from '../../util/assert.std.js';
+import { assertDev, strictAssert } from '../../util/assert.std.js';
 import { AttachmentStatusIcon } from './AttachmentStatusIcon.dom.js';
 import { TapToViewNotAvailableType } from '../TapToViewNotAvailableModal.dom.js';
 import type { DataPropsType as TapToViewNotAvailablePropsType } from '../TapToViewNotAvailableModal.dom.js';
@@ -491,17 +491,19 @@ const MessageReactions = forwardRef(function MessageReactions(
   const reactionsContainerRefMerger = useRef(createRefMerger());
 
   // Take the first three groups for rendering
-  const toRender = take(ordered, 3).map(res => {
-    const isMe = res.some(re => Boolean(re.from.isMe));
-    const count = res.length;
-    const { emoji } = res[0];
+  const toRender = take(ordered, 3).map(group => {
+    const isMe = group.some(re => Boolean(re.from.isMe));
+    const count = group.length;
+    const firstReaction = group[0];
+    strictAssert(firstReaction, 'Missing firstReaction');
+    const { emoji } = firstReaction;
 
     let label: string;
     if (isMe) {
       label = i18n('icu:Message__reaction-emoji-label--you', { emoji });
     } else if (count === 1) {
       label = i18n('icu:Message__reaction-emoji-label--single', {
-        title: res[0].from.title,
+        title: firstReaction.from.title,
         emoji,
       });
     } else {
@@ -2543,6 +2545,7 @@ export class Message extends React.PureComponent<Props, State> {
     }
 
     const onlyPreview = previews[0];
+    strictAssert(onlyPreview, 'Missing onlyPreview');
     return Boolean(onlyPreview.isCallLink);
   }
 
@@ -2551,6 +2554,7 @@ export class Message extends React.PureComponent<Props, State> {
 
     if (this.#shouldShowJoinButton()) {
       const firstPreview = previews[0];
+      strictAssert(firstPreview, 'Missing firstPreview');
       const inAnotherCall = Boolean(
         activeCallConversationId &&
         (!firstPreview.callLinkRoomId ||
@@ -2672,6 +2676,7 @@ export class Message extends React.PureComponent<Props, State> {
 
     if (previews && previews.length) {
       const first = previews[0];
+      strictAssert(first, 'Missing first');
       const { image } = first;
 
       return isImageAttachment(image);
@@ -2688,6 +2693,7 @@ export class Message extends React.PureComponent<Props, State> {
     }
 
     const first = attachments[0];
+    strictAssert(first, 'Missing first');
 
     return Boolean(first.pending);
   }
@@ -3216,6 +3222,7 @@ export class Message extends React.PureComponent<Props, State> {
       event.stopPropagation();
 
       const attachment = attachments[0];
+      strictAssert(attachment, 'Missing attachment');
 
       showLightbox({ attachment, messageId: id });
     }
diff --git a/ts/components/conversation/ReactionViewer.dom.tsx b/ts/components/conversation/ReactionViewer.dom.tsx
index e3925f3ebb..345a577ce5 100644
--- a/ts/components/conversation/ReactionViewer.dom.tsx
+++ b/ts/components/conversation/ReactionViewer.dom.tsx
@@ -168,6 +168,7 @@ export const ReactionViewer = React.forwardRef<HTMLDivElement, Props>(
               // Find the local user's reaction first, then fall back to most recent
               const localUserReaction = groupedReactions.find(r => r.from.isMe);
               const firstReaction = localUserReaction || groupedReactions[0];
+              strictAssert(firstReaction, 'Missing firstReaction');
               return {
                 id: firstReaction.parentKey,
                 index: DEFAULT_EMOJI_ORDER.includes(firstReaction.parentKey)
diff --git a/ts/components/conversation/Timeline.dom.tsx b/ts/components/conversation/Timeline.dom.tsx
index 823e819f6e..b7d2270d18 100644
--- a/ts/components/conversation/Timeline.dom.tsx
+++ b/ts/components/conversation/Timeline.dom.tsx
@@ -260,6 +260,7 @@ export class Timeline extends React.Component<
     if (setFocus && items && items.length > 0) {
       const lastIndex = items.length - 1;
       const lastMessageId = items[lastIndex];
+      strictAssert(lastMessageId, 'Missing lastMessageId');
       targetMessage(lastMessageId, id);
     } else {
       const containerEl = this.#containerRef.current;
@@ -307,6 +308,7 @@ export class Timeline extends React.Component<
     ) {
       if (setFocus) {
         const messageId = items[oldestUnseenIndex];
+        strictAssert(messageId, 'Missing messageId');
         targetMessage(messageId, id);
       } else {
         this.#lastSeenIndicatorRef.current?.scrollIntoView();
@@ -824,6 +826,7 @@ export class Timeline extends React.Component<
       }
 
       const messageId = items[targetIndex];
+      strictAssert(messageId, 'Missing messageId');
       targetMessage(messageId, id);
 
       event.preventDefault();
@@ -851,6 +854,7 @@ export class Timeline extends React.Component<
       }
 
       const messageId = items[targetIndex];
+      strictAssert(messageId, 'Missing messageId');
       targetMessage(messageId, id);
 
       event.preventDefault();
diff --git a/ts/components/conversation/TimelineMessage.dom.stories.tsx b/ts/components/conversation/TimelineMessage.dom.stories.tsx
index 4bdffe6a92..c9c5cd9916 100644
--- a/ts/components/conversation/TimelineMessage.dom.stories.tsx
+++ b/ts/components/conversation/TimelineMessage.dom.stories.tsx
@@ -3424,7 +3424,8 @@ export const EmbeddedContactWithSendMessage = Template.bind({});
 EmbeddedContactWithSendMessage.args = {
   contact: {
     ...fullContact,
-    firstNumber: fullContact.number[0].value,
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    firstNumber: fullContact.number[0]!.value,
     serviceId: generateAci(),
   },
   direction: 'incoming',
diff --git a/ts/components/conversation/TimelineMessage.dom.tsx b/ts/components/conversation/TimelineMessage.dom.tsx
index 5f812252cf..99ba4d446a 100644
--- a/ts/components/conversation/TimelineMessage.dom.tsx
+++ b/ts/components/conversation/TimelineMessage.dom.tsx
@@ -250,7 +250,8 @@ export function TimelineMessage(props: Props): React.JSX.Element {
       if (attachments.length !== 1) {
         saveAttachments(attachments, timestamp);
       } else {
-        saveAttachment(attachments[0], timestamp);
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        saveAttachment(attachments[0]!, timestamp);
       }
     },
     [
diff --git a/ts/components/conversation/TypingBubble.dom.tsx b/ts/components/conversation/TypingBubble.dom.tsx
index cb752e6e24..671b00e945 100644
--- a/ts/components/conversation/TypingBubble.dom.tsx
+++ b/ts/components/conversation/TypingBubble.dom.tsx
@@ -341,8 +341,10 @@ export function TypingBubble({
       return;
     }
 
-    const lastTypingContactId = typingContactIds[0];
-    const lastTypingTimestamp = typingContactIdTimestamps[lastTypingContactId];
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const lastTypingContactId = typingContactIds[0]!;
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const lastTypingTimestamp = typingContactIdTimestamps[lastTypingContactId]!;
     if (
       lastItemAuthorId === lastTypingContactId &&
       lastItemTimestamp > lastTypingTimestamp
diff --git a/ts/components/conversation/conversation-details/AddGroupMembersModal/ChooseGroupMembersModal.dom.tsx b/ts/components/conversation/conversation-details/AddGroupMembersModal/ChooseGroupMembersModal.dom.tsx
index 0100dff7d9..8916e04f75 100644
--- a/ts/components/conversation/conversation-details/AddGroupMembersModal/ChooseGroupMembersModal.dom.tsx
+++ b/ts/components/conversation/conversation-details/AddGroupMembersModal/ChooseGroupMembersModal.dom.tsx
@@ -216,6 +216,7 @@ export function ChooseGroupMembersModal({
 
     if (virtualIndex < filteredContacts.length) {
       const contact = filteredContacts[virtualIndex];
+      strictAssert(contact, 'Missing contact');
 
       const isSelected = selectedConversationIdsSet.has(contact.id);
       const isAlreadyInGroup = conversationIdsAlreadyInGroup.has(contact.id);
diff --git a/ts/components/conversation/conversation-details/ConversationDetails.dom.stories.tsx b/ts/components/conversation/conversation-details/ConversationDetails.dom.stories.tsx
index c750c85253..f3dddc00ee 100644
--- a/ts/components/conversation/conversation-details/ConversationDetails.dom.stories.tsx
+++ b/ts/components/conversation/conversation-details/ConversationDetails.dom.stories.tsx
@@ -18,6 +18,7 @@ import { ThemeType } from '../../../types/Util.std.js';
 import { DurationInSeconds } from '../../../util/durations/index.std.js';
 import { NavTab } from '../../../types/Nav.std.js';
 import { getFakeCallHistoryGroup } from '../../../test-helpers/getFakeCallHistoryGroup.std.js';
+import type { ContactNameColorType } from '../../../types/Colors.std.js';
 import { ContactNameColors } from '../../../types/Colors.std.js';
 import { isNotNil } from '../../../util/isNotNil.std.js';
 
@@ -52,16 +53,20 @@ const createProps = (
       isMe: i === 2,
     }),
   }));
-  const memberColors = new Map<string, string>(
+  const memberColors = new Map<string, ContactNameColorType>(
     memberships
-      .map((membership, i): [string, string] | null => {
+      .map((membership, i): [string, ContactNameColorType] | null => {
         const { serviceId } = membership.member;
 
         if (!serviceId) {
           return null;
         }
 
-        return [serviceId.toString(), ContactNameColors[i]];
+        return [
+          serviceId.toString(),
+          // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+          ContactNameColors[i % ContactNameColors.length]!,
+        ];
       })
       .filter(isNotNil)
   );
diff --git a/ts/components/conversation/conversation-details/ConversationDetails.dom.tsx b/ts/components/conversation/conversation-details/ConversationDetails.dom.tsx
index cc8fbe3260..62b9f4675c 100644
--- a/ts/components/conversation/conversation-details/ConversationDetails.dom.tsx
+++ b/ts/components/conversation/conversation-details/ConversationDetails.dom.tsx
@@ -68,6 +68,7 @@ import { BadgeSustainerInstructionsDialog } from '../../BadgeSustainerInstructio
 import type { ContactModalStateType } from '../../../types/globalModals.std.js';
 import type { ShowToastAction } from '../../../state/ducks/toast.preload.js';
 import { ToastType } from '../../../types/Toast.dom.js';
+import type { ContactNameColorType } from '../../../types/Colors.std.js';
 
 enum ModalState {
   AddingGroupMembers,
@@ -101,7 +102,7 @@ export type StateProps = {
   maxGroupSize: number;
   maxRecommendedGroupSize: number;
   memberships: ReadonlyArray<GroupV2Membership>;
-  memberColors: Map<string, string>;
+  memberColors: Map<string, ContactNameColorType>;
   pendingApprovalMemberships: ReadonlyArray<GroupV2RequestingMembership>;
   pendingAvatarDownload?: boolean;
   pendingMemberships: ReadonlyArray<GroupV2PendingMembership>;
diff --git a/ts/components/conversation/conversation-details/ConversationDetailsMembershipList.dom.stories.tsx b/ts/components/conversation/conversation-details/ConversationDetailsMembershipList.dom.stories.tsx
index f652f30044..ae34ba22d8 100644
--- a/ts/components/conversation/conversation-details/ConversationDetailsMembershipList.dom.stories.tsx
+++ b/ts/components/conversation/conversation-details/ConversationDetailsMembershipList.dom.stories.tsx
@@ -12,6 +12,7 @@ import type {
   GroupV2Membership,
 } from './ConversationDetailsMembershipList.dom.js';
 import { ConversationDetailsMembershipList } from './ConversationDetailsMembershipList.dom.js';
+import type { ContactNameColorType } from '../../../types/Colors.std.js';
 import { ContactNameColors } from '../../../types/Colors.std.js';
 
 const { i18n } = window.SignalContext;
@@ -33,11 +34,12 @@ const createMemberships = (
 
 const getMemberColors = (
   memberships: Array<GroupV2Membership>
-): Map<string, string> =>
+): Map<string, ContactNameColorType> =>
   new Map(
     memberships.map((membership, i) => [
       membership.member.id,
-      ContactNameColors[i],
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      ContactNameColors[i % ContactNameColors.length]!,
     ])
   );
 
diff --git a/ts/components/conversation/conversation-details/ConversationDetailsMembershipList.dom.tsx b/ts/components/conversation/conversation-details/ConversationDetailsMembershipList.dom.tsx
index 6b1789a6dd..ec550ef00d 100644
--- a/ts/components/conversation/conversation-details/ConversationDetailsMembershipList.dom.tsx
+++ b/ts/components/conversation/conversation-details/ConversationDetailsMembershipList.dom.tsx
@@ -19,6 +19,7 @@ import { PanelSection } from './PanelSection.dom.js';
 import { GroupMemberLabel } from '../ContactName.dom.js';
 import { AriaClickable } from '../../../axo/AriaClickable.dom.js';
 import type { ContactModalStateType } from '../../../types/globalModals.std.js';
+import type { ContactNameColorType } from '../../../types/Colors.std.js';
 
 export type GroupV2Membership = {
   isAdmin: boolean;
@@ -36,7 +37,7 @@ export type Props = {
   isEditMemberLabelEnabled: boolean;
   maxShownMemberCount?: number;
   memberships: ReadonlyArray<GroupV2Membership>;
-  memberColors: Map<string, string>;
+  memberColors: Map<string, ContactNameColorType>;
   showContactModal: (payload: ContactModalStateType) => void;
   showLabelEditor: () => void;
   startAddingNewMembers?: () => void;
diff --git a/ts/components/conversation/conversation-details/GroupMemberLabelEditor.dom.tsx b/ts/components/conversation/conversation-details/GroupMemberLabelEditor.dom.tsx
index b3315dd061..eb5f2cc12b 100644
--- a/ts/components/conversation/conversation-details/GroupMemberLabelEditor.dom.tsx
+++ b/ts/components/conversation/conversation-details/GroupMemberLabelEditor.dom.tsx
@@ -23,6 +23,7 @@ import {
   MessageInteractivity,
   TextDirection,
 } from '../Message.dom.js';
+import type { ContactNameColorType } from '../../../types/Colors.std.js';
 import { ConversationColors } from '../../../types/Colors.std.js';
 import { WidthBreakpoint } from '../../_util.std.js';
 import { AxoAlertDialog } from '../../../axo/AxoAlertDialog.dom.js';
@@ -52,13 +53,13 @@ export type PropsDataType = {
   isActive: boolean;
   me: ConversationType;
   membersWithLabel: Array<{
-    contactNameColor: string;
+    contactNameColor: ContactNameColorType;
     isAdmin: boolean;
     labelEmoji: string | undefined;
     labelString: string;
     member: ConversationType;
   }>;
-  ourColor: string | undefined;
+  ourColor: ContactNameColorType | undefined;
   theme: ThemeType;
 };
 
diff --git a/ts/components/conversation/conversation-details/PendingInvites.dom.tsx b/ts/components/conversation/conversation-details/PendingInvites.dom.tsx
index 833f744a96..43d3d72c66 100644
--- a/ts/components/conversation/conversation-details/PendingInvites.dom.tsx
+++ b/ts/components/conversation/conversation-details/PendingInvites.dom.tsx
@@ -18,7 +18,6 @@ import {
 } from './ConversationDetailsIcon.dom.js';
 import { isAccessControlEnabled } from '../../../groups/util.std.js';
 import { Tabs } from '../../Tabs.dom.js';
-import { assertDev } from '../../../util/assert.std.js';
 
 export type PropsDataType = {
   readonly conversation?: ConversationType;
@@ -197,11 +196,13 @@ function MembershipActionConfirmation({
     }
     approvePendingMembershipFromGroupV2(
       conversation.id,
-      stagedMemberships[0].membership.member.id
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      stagedMemberships[0]!.membership.member.id
     );
   };
 
-  const membershipType = stagedMemberships[0].type;
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  const membershipType = stagedMemberships[0]!.type;
 
   const modalAction =
     membershipType === StageType.APPROVE_REQUEST
@@ -255,12 +256,13 @@ function getConfirmationMessage({
   ourAci: AciString;
   stagedMemberships: ReadonlyArray<StagedMembershipType>;
 }>): string {
-  if (!stagedMemberships || !stagedMemberships.length) {
+  const [stagedMembership] = stagedMemberships;
+  if (stagedMembership == null) {
     return '';
   }
 
-  const membershipType = stagedMemberships[0].type;
-  const firstMembership = stagedMemberships[0].membership;
+  const membershipType = stagedMembership.type;
+  const firstMembership = stagedMembership.membership;
 
   // Requesting a membership since they weren't added by anyone
   if (membershipType === StageType.DENY_REQUEST) {
@@ -419,19 +421,23 @@ function MembersPendingProfileKey({
   const { [ourAci]: ourPendingMemberships, ...otherPendingMembershipGroups } =
     groupedPendingMemberships;
 
-  const otherPendingMemberships = Object.keys(otherPendingMembershipGroups)
-    .map(id => members.find(member => member.serviceId === id))
-    .filter((member): member is ConversationType => member !== undefined)
-    .map(member => {
-      assertDev(
-        member.serviceId,
-        'We just verified that member has serviceId above'
-      );
-      return {
-        member,
-        pendingMemberships: otherPendingMembershipGroups[member.serviceId],
-      };
+  const otherPendingMemberships: Array<{
+    member: ConversationType;
+    pendingMemberships: Array<GroupV2PendingMembership>;
+  }> = [];
+
+  for (const [id, pendingMemberships] of Object.entries(
+    otherPendingMembershipGroups
+  )) {
+    const member = members.find(m => m.serviceId === id);
+    if (member == null) {
+      continue;
+    }
+    otherPendingMemberships.push({
+      member,
+      pendingMemberships,
     });
+  }
 
   return (
     <PanelSection>
diff --git a/ts/components/conversation/conversation-details/util.std.ts b/ts/components/conversation/conversation-details/util.std.ts
index c98f6022eb..c7cb2602a5 100644
--- a/ts/components/conversation/conversation-details/util.std.ts
+++ b/ts/components/conversation/conversation-details/util.std.ts
@@ -15,19 +15,15 @@ export const bemGenerator =
     const base = `${block}__${element}`;
     const classes = [base];
 
-    let conditionals: Record<string, boolean> = {};
+    const conditionals: Record<string, boolean> = {};
 
     if (modifier) {
       if (typeof modifier === 'string') {
         classes.push(`${base}--${modifier}`);
       } else {
-        conditionals = Object.keys(modifier).reduce(
-          (acc, key) => ({
-            ...acc,
-            [`${base}--${key}`]: modifier[key],
-          }),
-          {} as Record<string, boolean>
-        );
+        for (const [key, value] of Object.entries(modifier)) {
+          conditionals[`${base}--${key}`] = value;
+        }
       }
     }
 
diff --git a/ts/components/conversation/media-gallery/MediaGallery.dom.tsx b/ts/components/conversation/media-gallery/MediaGallery.dom.tsx
index 7f642ed3af..740b16e9d3 100644
--- a/ts/components/conversation/media-gallery/MediaGallery.dom.tsx
+++ b/ts/components/conversation/media-gallery/MediaGallery.dom.tsx
@@ -180,7 +180,8 @@ function MediaSection({
 
   const sections = groupedItems.map((section, index) => {
     const isLast = index === groupedItems.length - 1;
-    const first = section.mediaItems[0];
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const first = section.mediaItems[0]!;
     const { message } = first;
     const date = moment(message.receivedAtMs || message.receivedAt);
 
diff --git a/ts/components/conversation/media-gallery/utils/mocks.std.ts b/ts/components/conversation/media-gallery/utils/mocks.std.ts
index 65588ba39b..927b785e39 100644
--- a/ts/components/conversation/media-gallery/utils/mocks.std.ts
+++ b/ts/components/conversation/media-gallery/utils/mocks.std.ts
@@ -2,7 +2,7 @@
 // SPDX-License-Identifier: AGPL-3.0-only
 
 import lodash from 'lodash';
-import { type MIMEType, IMAGE_JPEG } from '../../../../types/MIME.std.js';
+import { IMAGE_JPEG, stringToMIMEType } from '../../../../types/MIME.std.js';
 import type {
   MediaItemType,
   ContactMediaItemType,
@@ -21,17 +21,22 @@ export const days = (n: number): number => n * DAY_MS;
 const tokens = ['foo', 'bar', 'baz', 'qux', 'quux'];
 
 const contentTypes = {
-  gif: 'image/gif',
-  jpg: 'image/jpeg',
-  png: 'image/png',
-  mp4: 'video/mp4',
-  docx: 'application/text',
-  pdf: 'application/pdf',
-  exe: 'application/exe',
-  txt: 'application/text',
-} as unknown as Record<string, MIMEType>;
+  gif: stringToMIMEType('image/gif'),
+  jpg: stringToMIMEType('image/jpeg'),
+  png: stringToMIMEType('image/png'),
+  mp3: stringToMIMEType('audio/mp3'),
+  mp4: stringToMIMEType('video/mp4'),
+  docx: stringToMIMEType('application/text'),
+  pdf: stringToMIMEType('application/pdf'),
+  exe: stringToMIMEType('application/exe'),
+  txt: stringToMIMEType('application/text'),
+} as const;
 
-function createRandomAttachment(fileExtension: string): AttachmentForUIType {
+type FileExtension = keyof typeof contentTypes;
+
+function createRandomAttachment(
+  fileExtension: FileExtension
+): AttachmentForUIType {
   const contentType = contentTypes[fileExtension];
   const fileName = `${sample(tokens)}${sample(tokens)}.${fileExtension}`;
 
@@ -101,7 +106,7 @@ function createRandomFile(
   type: 'media' | 'document' | 'audio',
   startTime: number,
   timeWindow: number,
-  fileExtension: string
+  fileExtension: FileExtension
 ): MediaItemType {
   return {
     type,
@@ -154,15 +159,11 @@ function createRandomFiles(
   type: 'media' | 'document' | 'audio',
   startTime: number,
   timeWindow: number,
-  fileExtensions: Array<string>
+  fileExtensions: Array<FileExtension>
 ): Array<MediaItemType> {
   return range(random(5, 20)).map(() =>
-    createRandomFile(
-      type,
-      startTime,
-      timeWindow,
-      sample(fileExtensions) as string
-    )
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    createRandomFile(type, startTime, timeWindow, sample(fileExtensions)!)
   );
 }
 export function createRandomDocuments(
diff --git a/ts/components/conversation/pinned-messages/PinnedMessagesBar.dom.tsx b/ts/components/conversation/pinned-messages/PinnedMessagesBar.dom.tsx
index 3da4991d37..f7e598c98a 100644
--- a/ts/components/conversation/pinned-messages/PinnedMessagesBar.dom.tsx
+++ b/ts/components/conversation/pinned-messages/PinnedMessagesBar.dom.tsx
@@ -105,8 +105,7 @@ export const PinnedMessagesBar = memo(function PinnedMessagesBar(
       return null;
     }
 
-    for (let index = 0; index < pins.length; index += 1) {
-      const value = pins[index];
+    for (const [index, value] of pins.entries()) {
       if (value.id === current) {
         return { index, value };
       }
diff --git a/ts/components/fun/FunEmoji.dom.stories.tsx b/ts/components/fun/FunEmoji.dom.stories.tsx
index fa1290575a..103b57fed6 100644
--- a/ts/components/fun/FunEmoji.dom.stories.tsx
+++ b/ts/components/fun/FunEmoji.dom.stories.tsx
@@ -77,7 +77,8 @@ export function All(props: AllProps): React.JSX.Element {
         }}
       >
         {rowVirtualizer.getVirtualItems().map(rowItem => {
-          const row = rows[rowItem.index];
+          // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+          const row = rows[rowItem.index]!;
           return (
             <div
               key={rowItem.index}
diff --git a/ts/components/fun/panels/FunPanelGifs.dom.tsx b/ts/components/fun/panels/FunPanelGifs.dom.tsx
index ec45e0a4aa..bd3ba4a1ef 100644
--- a/ts/components/fun/panels/FunPanelGifs.dom.tsx
+++ b/ts/components/fun/panels/FunPanelGifs.dom.tsx
@@ -319,6 +319,7 @@ export function FunPanelGifs({
   const estimateSize = useCallback(
     (index: number) => {
       const gif = items[index];
+      strictAssert(gif, 'Missing gif');
       const aspectRatio = gif.previewMedia.width / gif.previewMedia.height;
       const baseHeight = GIF_WATERFALL_ITEM_WIDTH / aspectRatio;
       return baseHeight + GIF_WATERFALL_ITEM_MARGIN + GIF_WATERFALL_ITEM_MARGIN;
@@ -350,7 +351,8 @@ export function FunPanelGifs({
 
   const getItemKey = useCallback(
     (index: number) => {
-      return items[index].id;
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      return items[index]!.id;
     },
     [items]
   );
@@ -578,6 +580,7 @@ export function FunPanelGifs({
                 <FunWaterfallContainer totalSize={virtualizer.getTotalSize()}>
                   {virtualizer.getVirtualItems().map(item => {
                     const gif = items[item.index];
+                    strictAssert(gif, 'Missing gif');
                     const key = String(item.key);
                     const isTabbable =
                       selectedItemKey != null
diff --git a/ts/components/fun/panels/FunPanelStickers.dom.tsx b/ts/components/fun/panels/FunPanelStickers.dom.tsx
index 1b83dd18be..7608cd4d2f 100644
--- a/ts/components/fun/panels/FunPanelStickers.dom.tsx
+++ b/ts/components/fun/panels/FunPanelStickers.dom.tsx
@@ -605,6 +605,7 @@ const Cell = memo(function Cell(props: {
 }): React.JSX.Element {
   const { onClickSticker, onClickTimeSticker } = props;
   const stickerLookupItem = props.stickerLookup[props.value];
+  strictAssert(stickerLookupItem, 'Missing stickerLookupItem');
 
   const handleClick = useCallback(
     (event: PointerEvent) => {
diff --git a/ts/components/fun/virtual/useFunVirtualGrid.dom.tsx b/ts/components/fun/virtual/useFunVirtualGrid.dom.tsx
index c19f1510d7..ce8cf54700 100644
--- a/ts/components/fun/virtual/useFunVirtualGrid.dom.tsx
+++ b/ts/components/fun/virtual/useFunVirtualGrid.dom.tsx
@@ -207,11 +207,15 @@ function buildLayout(
   totalHeight: number
 ): Layout {
   const groups = groupBy(virtualItems, virtualItem => {
-    return list.listItems[virtualItem.index].sectionMeta.sectionKey;
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    return list.listItems[virtualItem.index]!.sectionMeta.sectionKey;
   });
 
   const sections = Object.keys(groups).map((sectionKey): SectionLayoutNode => {
-    const [headerVirtualItem, ...rowVirtualItems] = groups[sectionKey];
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const [maybeHeaderVirtualItem, ...rowVirtualItems] = groups[sectionKey]!;
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const headerVirtualItem = maybeHeaderVirtualItem!;
     const headerListItem = list.listItems.at(headerVirtualItem.index);
 
     strictAssert(
@@ -446,7 +450,8 @@ export function useFunVirtualGrid({
 
   const getItemKey = useCallback(
     (index: number) => {
-      return list.listItems[index].key;
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      return list.listItems[index]!.key;
     },
     [list]
   );
diff --git a/ts/components/leftPane/LeftPaneChooseGroupMembersHelper.dom.tsx b/ts/components/leftPane/LeftPaneChooseGroupMembersHelper.dom.tsx
index f2c3270dd4..fb803629d3 100644
--- a/ts/components/leftPane/LeftPaneChooseGroupMembersHelper.dom.tsx
+++ b/ts/components/leftPane/LeftPaneChooseGroupMembersHelper.dom.tsx
@@ -315,7 +315,8 @@ export class LeftPaneChooseGroupMembersHelper extends LeftPaneHelper<LeftPaneCho
       }
 
       if (virtualRowIndex <= this.#candidateContacts.length) {
-        const contact = this.#candidateContacts[virtualRowIndex - 1];
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        const contact = this.#candidateContacts[virtualRowIndex - 1]!;
 
         const isChecked = this.#selectedConversationIdsSet.has(contact.id);
         const disabledReason =
diff --git a/ts/components/leftPane/LeftPaneInboxHelper.dom.tsx b/ts/components/leftPane/LeftPaneInboxHelper.dom.tsx
index cc9ab76888..2a816a1b9a 100644
--- a/ts/components/leftPane/LeftPaneInboxHelper.dom.tsx
+++ b/ts/components/leftPane/LeftPaneInboxHelper.dom.tsx
@@ -239,7 +239,8 @@ export class LeftPaneInboxHelper extends LeftPaneHelper<LeftPaneInboxPropsType>
       if (index < pinnedConversations.length) {
         return {
           type: RowType.Conversation,
-          conversation: pinnedConversations[index],
+          // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+          conversation: pinnedConversations[index]!,
         };
       }
       index -= pinnedConversations.length;
@@ -259,7 +260,8 @@ export class LeftPaneInboxHelper extends LeftPaneHelper<LeftPaneInboxPropsType>
     if (index < conversations.length) {
       return {
         type: RowType.Conversation,
-        conversation: conversations[index],
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        conversation: conversations[index]!,
       };
     }
     index -= conversations.length;
diff --git a/ts/components/leftPane/LeftPaneSearchHelper.dom.tsx b/ts/components/leftPane/LeftPaneSearchHelper.dom.tsx
index 2be6f1abb6..bf9ec6d1f4 100644
--- a/ts/components/leftPane/LeftPaneSearchHelper.dom.tsx
+++ b/ts/components/leftPane/LeftPaneSearchHelper.dom.tsx
@@ -18,7 +18,7 @@ import type {
 import { LeftPaneSearchInput } from '../LeftPaneSearchInput.dom.js';
 
 import { I18n } from '../I18n.dom.js';
-import { assertDev } from '../../util/assert.std.js';
+import { assertDev, strictAssert } from '../../util/assert.std.js';
 import { UserText } from '../UserText.dom.js';
 
 // The "correct" thing to do is to measure the size of the left pane and render enough
@@ -381,6 +381,7 @@ export class LeftPaneSearchHelper extends LeftPaneHelper<LeftPaneSearchPropsType
       }
       if (pointer < list.results.length) {
         const result = list.results[pointer];
+        strictAssert(result, 'Missing result');
         return result.type === 'incoming' || result.type === 'outgoing' // message
           ? {
               conversationId: result.conversationId,
diff --git a/ts/groups.preload.ts b/ts/groups.preload.ts
index 0359c9c4e0..f5faa46931 100644
--- a/ts/groups.preload.ts
+++ b/ts/groups.preload.ts
@@ -3356,6 +3356,10 @@ export function _mergeGroupChangeMessages(
 
   const [firstDetail] = firstChange.details;
   const [secondDetail] = secondChange.details;
+
+  strictAssert(firstDetail, 'Missing firstDetail');
+  strictAssert(secondDetail, 'Missing secondDetail');
+
   let isApprovalPending: boolean;
   if (secondDetail.type === 'admin-approval-add-one') {
     isApprovalPending = true;
@@ -3428,6 +3432,7 @@ export function _isGroupChangeMessageBounceable(
   }
 
   const [first] = groupV2Change.details;
+  strictAssert(first, 'Missing first');
   if (
     first.type === 'admin-approval-add-one' ||
     first.type === 'admin-approval-bounce'
@@ -4267,18 +4272,14 @@ async function integrateGroupChanges({
   const finalMessages: Array<Array<GroupChangeMessageType>> = [];
   const finalNewProfileKeys = new Map<AciString, string>();
 
-  const imax = changes.length;
-  for (let i = 0; i < imax; i += 1) {
-    const { groupChanges } = changes[i];
+  for (const change of changes) {
+    const { groupChanges } = change;
 
     if (!groupChanges) {
       continue;
     }
 
-    const jmax = groupChanges.length;
-    for (let j = 0; j < jmax; j += 1) {
-      const changeState = groupChanges[j];
-
+    for (const changeState of groupChanges) {
       const { groupChange, groupState } = changeState;
 
       if (!groupChange && !groupState) {
@@ -4323,8 +4324,8 @@ async function integrateGroupChanges({
   if (isFirstFetch && moreThanOneVersion) {
     // The first array in finalMessages is from the first revision we could process. It
     //   should contain a message about how we joined the group.
-    const joinMessages = finalMessages[0];
-    const alreadyHaveJoinMessage = joinMessages && joinMessages.length > 0;
+    const joinMessage = finalMessages[0]?.[0];
+    const alreadyHaveJoinMessage = joinMessage != null;
 
     // There have been other changes since that first revision, so we generate diffs for
     //   the whole of the change since then, likely without the initial join message.
@@ -4334,9 +4335,8 @@ async function integrateGroupChanges({
       dropInitialJoinMessage: alreadyHaveJoinMessage,
     });
 
-    const groupChangeMessages = alreadyHaveJoinMessage
-      ? [joinMessages[0], ...otherMessages]
-      : otherMessages;
+    const groupChangeMessages =
+      joinMessage != null ? [joinMessage, ...otherMessages] : otherMessages;
 
     return {
       newAttributes: attributes,
@@ -4897,6 +4897,7 @@ function extractDiffs({
   const removedPendingMemberIds = Array.from(oldPendingMemberLookup.keys());
   if (removedPendingMemberIds.length > 1) {
     const firstUuid = removedPendingMemberIds[0];
+    strictAssert(firstUuid, 'Missing firstUuid');
     const firstRemovedMember = oldPendingMemberLookup.get(firstUuid);
     strictAssert(
       firstRemovedMember !== undefined,
@@ -4913,6 +4914,7 @@ function extractDiffs({
     });
   } else if (removedPendingMemberIds.length === 1) {
     const serviceId = removedPendingMemberIds[0];
+    strictAssert(serviceId, 'Missing serviceId');
     const removedMember = oldPendingMemberLookup.get(serviceId);
     strictAssert(removedMember !== undefined, 'Removed member not found');
 
@@ -5434,7 +5436,7 @@ async function applyGroupChange({
       members[aci] = {
         aci,
         joinedAtVersion: version,
-        role: previousRecord.role || MemberRole.DEFAULT,
+        role: previousRecord?.role || MemberRole.DEFAULT,
       };
 
       newProfileKeys.push({
@@ -5478,7 +5480,7 @@ async function applyGroupChange({
       members[aci] = {
         aci,
         joinedAtVersion: version,
-        role: previousRecord.role || MemberRole.DEFAULT,
+        role: previousRecord?.role || MemberRole.DEFAULT,
       };
 
       newProfileKeys.push({
diff --git a/ts/hooks/useRestoreFocus.dom.ts b/ts/hooks/useRestoreFocus.dom.ts
index a5d92fe5ee..1f8e88cfbd 100644
--- a/ts/hooks/useRestoreFocus.dom.ts
+++ b/ts/hooks/useRestoreFocus.dom.ts
@@ -6,7 +6,7 @@ import * as React from 'react';
 type CallbackType = (toFocus: HTMLElement | null | undefined) => void;
 
 // Restore focus on teardown
-export const useRestoreFocus = (): Array<CallbackType> => {
+export const useRestoreFocus = (): [CallbackType] => {
   const toFocusRef = React.useRef<HTMLElement | null>(null);
   const lastFocusedRef = React.useRef<HTMLElement | null>(null);
 
diff --git a/ts/hooks/useSizeObserver.dom.tsx b/ts/hooks/useSizeObserver.dom.tsx
index b61be5467b..91a24b85f4 100644
--- a/ts/hooks/useSizeObserver.dom.tsx
+++ b/ts/hooks/useSizeObserver.dom.tsx
@@ -52,7 +52,8 @@ export function useSizeObserver<T extends Element = Element>(
       // We're only ever observing one element, and `ResizeObserver` for some
       // reason is an array of exactly one rect (I assume to support wrapped
       // inline elements in the future)
-      const borderBoxSize = entries[0].borderBoxSize[0];
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      const borderBoxSize = entries[0]!.borderBoxSize[0]!;
       // We are assuming a horizontal writing-mode here, we could call
       // `getBoundingClientRect()` here but MDN says not to. In the future if
       // we are adding support for a vertical locale we may need to change this
diff --git a/ts/hooks/useTabs.dom.tsx b/ts/hooks/useTabs.dom.tsx
index 78dd2cc1a8..2bdae93683 100644
--- a/ts/hooks/useTabs.dom.tsx
+++ b/ts/hooks/useTabs.dom.tsx
@@ -52,7 +52,8 @@ export function useTabs(options: TabsOptionsType): TabsProps {
     // This is enforced by the type system.
     // eslint-disable-next-line react-hooks/rules-of-hooks
     const [tabState, setTabState] = useState<string>(
-      options.initialSelectedTab || options.tabs[0].id
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      options.initialSelectedTab || options.tabs[0]!.id
     );
 
     selectedTab = tabState;
diff --git a/ts/jobs/AttachmentBackupManager.preload.ts b/ts/jobs/AttachmentBackupManager.preload.ts
index 66dc41a69a..6e21b906d8 100644
--- a/ts/jobs/AttachmentBackupManager.preload.ts
+++ b/ts/jobs/AttachmentBackupManager.preload.ts
@@ -604,6 +604,7 @@ async function copyToBackupTier({
   });
 
   const response = responses[0];
+  strictAssert(response, 'Missing response');
   if (!response.isSuccess) {
     if (response.status === FILE_NOT_FOUND_ON_TRANSIT_TIER_STATUS) {
       throw new FileNotFoundOnTransitTierError();
diff --git a/ts/jobs/conversationJobQueue.preload.ts b/ts/jobs/conversationJobQueue.preload.ts
index c43a085997..f348eb27c2 100644
--- a/ts/jobs/conversationJobQueue.preload.ts
+++ b/ts/jobs/conversationJobQueue.preload.ts
@@ -615,7 +615,8 @@ export class ConversationJobQueue extends JobQueue<ConversationQueueJobData> {
   #getRetryWithBackoff(attempts: number) {
     return (
       Date.now() +
-      MINUTE * (FIBONACCI[attempts] ?? FIBONACCI[FIBONACCI.length - 1])
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      MINUTE * (FIBONACCI[attempts] ?? FIBONACCI[FIBONACCI.length - 1]!)
     );
   }
 
diff --git a/ts/jobs/helpers/sendNormalMessage.preload.ts b/ts/jobs/helpers/sendNormalMessage.preload.ts
index ddabbfc051..6dc84b0df0 100644
--- a/ts/jobs/helpers/sendNormalMessage.preload.ts
+++ b/ts/jobs/helpers/sendNormalMessage.preload.ts
@@ -392,7 +392,8 @@ export async function sendNormalMessage(
 
         log.info('sending direct message');
         innerPromise = messaging.sendMessageToServiceId({
-          serviceId: recipientServiceIdsWithoutMe[0],
+          // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+          serviceId: recipientServiceIdsWithoutMe[0]!,
           messageOptions: {
             attachments,
             body,
@@ -951,7 +952,8 @@ async function uploadMessageQuote({
       );
 
       const attachmentAfterThumbnailUpload =
-        attachmentsAfterThumbnailUpload[index];
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        attachmentsAfterThumbnailUpload[index]!;
       return {
         ...attachment,
         thumbnail: {
diff --git a/ts/jobs/helpers/sendPollTerminate.preload.ts b/ts/jobs/helpers/sendPollTerminate.preload.ts
index 3dec46e289..48ae804648 100644
--- a/ts/jobs/helpers/sendPollTerminate.preload.ts
+++ b/ts/jobs/helpers/sendPollTerminate.preload.ts
@@ -137,7 +137,8 @@ export async function sendPollTerminate(
         return;
       }
 
-      const recipientServiceId = recipients[0];
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      const recipientServiceId = recipients[0]!;
 
       jobLog.info(
         `${logId}: Sending direct poll terminate for poll timestamp ${targetTimestamp}`
diff --git a/ts/jobs/helpers/sendPollVote.preload.ts b/ts/jobs/helpers/sendPollVote.preload.ts
index b920530b2b..18b37cc0d3 100644
--- a/ts/jobs/helpers/sendPollVote.preload.ts
+++ b/ts/jobs/helpers/sendPollVote.preload.ts
@@ -242,7 +242,8 @@ export async function sendPollVote(
 
         promise = messaging.sendMessageProtoAndWait({
           timestamp: currentTimestamp,
-          recipients: [recipientServiceIdsWithoutMe[0]],
+          // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+          recipients: [recipientServiceIdsWithoutMe[0]!],
           proto: contentMessage,
           contentHint: ContentHint.Resendable,
           groupId: undefined,
diff --git a/ts/jobs/helpers/sendReaction.preload.ts b/ts/jobs/helpers/sendReaction.preload.ts
index d210250d36..21be9c264b 100644
--- a/ts/jobs/helpers/sendReaction.preload.ts
+++ b/ts/jobs/helpers/sendReaction.preload.ts
@@ -231,7 +231,8 @@ export async function sendReaction(
 
         log.info('sending direct reaction message');
         promise = messaging.sendMessageToServiceId({
-          serviceId: recipientServiceIdsWithoutMe[0],
+          // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+          serviceId: recipientServiceIdsWithoutMe[0]!,
           messageOptions: {
             reaction: reactionForSend,
             timestamp: pendingReaction.timestamp,
diff --git a/ts/jobs/helpers/sendStory.preload.ts b/ts/jobs/helpers/sendStory.preload.ts
index cd1f14f062..3e3eebb257 100644
--- a/ts/jobs/helpers/sendStory.preload.ts
+++ b/ts/jobs/helpers/sendStory.preload.ts
@@ -52,6 +52,7 @@ import {
   saveErrorsOnMessage,
 } from '../../test-node/util/messageFailures.preload.js';
 import { send } from '../../messages/send.preload.js';
+import { strictAssert } from '../../util/assert.std.js';
 
 const { isEqual } = lodash;
 
@@ -167,9 +168,9 @@ export async function sendStory(
           preview: undefined,
         };
       } else {
-        const hydratedPreview = (
-          await loadPreviewData([localAttachment.preview])
-        )[0];
+        const previewData = await loadPreviewData([localAttachment.preview]);
+        const hydratedPreview = previewData[0];
+        strictAssert(hydratedPreview, 'Missing hydratedPreview');
 
         textAttachment = {
           ...localAttachment,
@@ -495,57 +496,48 @@ export async function sendStory(
 
       let hasFailedSends = false;
 
-      const newSendStateByConversationId = Object.keys(
-        oldSendStateByConversationId
-      ).reduce((acc, conversationId) => {
-        const sendState = sentConversationIds.get(conversationId);
-        if (sendState) {
-          return {
-            ...acc,
-            [conversationId]: sendState,
-          };
-        }
+      const newSendStateByConversationId: SendStateByConversationId = {};
 
-        const oldSendState = {
-          ...oldSendStateByConversationId[conversationId],
-        };
-        if (!oldSendState) {
-          return acc;
+      for (const [conversationId, oldSendState] of Object.entries(
+        oldSendStateByConversationId
+      )) {
+        const sendState = sentConversationIds.get(conversationId);
+
+        if (sendState) {
+          newSendStateByConversationId[conversationId] = sendState;
+          continue;
         }
 
         const recipient = window.ConversationController.get(conversationId);
         if (!recipient) {
-          return acc;
+          continue;
         }
 
         if (isMe(recipient.attributes)) {
-          return acc;
+          continue;
         }
 
         if (recipient.isEverUnregistered()) {
           if (!isSent(oldSendState.status)) {
             // We should have filtered this out on initial send, but we'll drop them from
             //   send list here if needed.
-            return acc;
+            continue;
           }
 
           // If a previous send to them did succeed, we'll keep that status around
-          return {
-            ...acc,
-            [conversationId]: oldSendState,
-          };
+          newSendStateByConversationId[conversationId] = oldSendState;
         }
 
         hasFailedSends = true;
 
-        return {
-          ...acc,
-          [conversationId]: sendStateReducer(oldSendState, {
+        newSendStateByConversationId[conversationId] = sendStateReducer(
+          oldSendState,
+          {
             type: SendActionType.Failed,
             updatedAt: Date.now(),
-          }),
-        };
-      }, {} as SendStateByConversationId);
+          }
+        );
+      }
 
       if (hasFailedSends) {
         notifyStorySendFailed(message);
@@ -609,8 +601,9 @@ export async function sendStory(
       sendErrors.push(result);
     }
   });
-  if (sendErrors.length) {
-    throw sendErrors[0].reason;
+  const [firstError] = sendErrors;
+  if (firstError != null) {
+    throw firstError.reason;
   }
 }
 
diff --git a/ts/logging/log.std.ts b/ts/logging/log.std.ts
index b08d06f5c8..cac658b719 100644
--- a/ts/logging/log.std.ts
+++ b/ts/logging/log.std.ts
@@ -69,7 +69,8 @@ function getSubsystemColor(name: string): string {
   hash >>>= 0;
   /* eslint-enable no-bitwise */
 
-  const result = COLORS[hash % COLORS.length];
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  const result = COLORS[hash % COLORS.length]!;
   SUBSYSTEM_COLORS.set(name, result);
 
   return result;
diff --git a/ts/logging/main_process_logging.main.ts b/ts/logging/main_process_logging.main.ts
index cf31913e78..616ef4d434 100644
--- a/ts/logging/main_process_logging.main.ts
+++ b/ts/logging/main_process_logging.main.ts
@@ -210,8 +210,10 @@ export function eliminateOutOfDateFiles(
             path: target,
             start: isLineAfterDate(start, date),
             end:
-              isLineAfterDate(end[end.length - 1], date) ||
-              isLineAfterDate(end[end.length - 2], date),
+              // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+              isLineAfterDate(end[end.length - 1]!, date) ||
+              // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+              isLineAfterDate(end[end.length - 2]!, date),
           };
 
           if (!file.start && !file.end) {
diff --git a/ts/messageModifiers/MessageReceipts.preload.ts b/ts/messageModifiers/MessageReceipts.preload.ts
index f550c6fa2f..8f00e9be0e 100644
--- a/ts/messageModifiers/MessageReceipts.preload.ts
+++ b/ts/messageModifiers/MessageReceipts.preload.ts
@@ -105,7 +105,8 @@ const processReceiptBatcher = createWaitBatcher({
         continue;
       }
       // All receipts have the same sentAt, so we can grab it from the first
-      const sentAt = receiptsForMessageSentAt[0].receiptSync.messageSentAt;
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      const sentAt = receiptsForMessageSentAt[0]!.receiptSync.messageSentAt;
 
       const messagesMatchingTimestamp =
         // eslint-disable-next-line no-await-in-loop
@@ -374,7 +375,8 @@ function getTargetMessage({
     `);
   }
 
-  const message = matchingMessages[0];
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  const message = matchingMessages[0]!;
   return window.MessageCache.register(new MessageModel(message));
 }
 const wasDeliveredWithSealedSender = (
diff --git a/ts/messageModifiers/Polls.preload.ts b/ts/messageModifiers/Polls.preload.ts
index 267a86af37..20e48640ad 100644
--- a/ts/messageModifiers/Polls.preload.ts
+++ b/ts/messageModifiers/Polls.preload.ts
@@ -436,7 +436,8 @@ export async function handlePollVote(
     );
 
     if (existingVoteIndex !== -1) {
-      const existingVote = currentVotes[existingVoteIndex];
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      const existingVote = currentVotes[existingVoteIndex]!;
 
       if (newVote.voteCount > existingVote.voteCount) {
         updatedVotes = [...currentVotes];
diff --git a/ts/messages/copyQuote.preload.ts b/ts/messages/copyQuote.preload.ts
index ba70d9130c..04dd28541b 100644
--- a/ts/messages/copyQuote.preload.ts
+++ b/ts/messages/copyQuote.preload.ts
@@ -185,7 +185,8 @@ export const copyQuoteContentFromOriginal = async (
   }
 
   if (queryPreview.length > 0) {
-    const { image: quotedPreviewImage } = queryPreview[0];
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const { image: quotedPreviewImage } = queryPreview[0]!;
     if (quotedPreviewImage && quotedPreviewImage.path) {
       quoteAttachment.thumbnail = {
         ...quotedPreviewImage,
diff --git a/ts/messages/migrateMessageData.preload.ts b/ts/messages/migrateMessageData.preload.ts
index 1ada5cd422..1a221a28b7 100644
--- a/ts/messages/migrateMessageData.preload.ts
+++ b/ts/messages/migrateMessageData.preload.ts
@@ -129,7 +129,8 @@ export async function _migrateMessageData({
   );
 
   const failedToSaveMessageIds = failedToSaveIndices.map(
-    idx => upgradedMessages[idx].id
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    idx => upgradedMessages[idx]!.id
   );
 
   if (failedToUpgradeMessageIds.length || failedToSaveMessageIds.length) {
diff --git a/ts/models/conversations.preload.ts b/ts/models/conversations.preload.ts
index 108fbffde9..2cf39c9e3b 100644
--- a/ts/models/conversations.preload.ts
+++ b/ts/models/conversations.preload.ts
@@ -3111,7 +3111,7 @@ export class ConversationModel {
       return false;
     }
 
-    if (contacts.length === 1 && isMe(contacts[0]?.attributes)) {
+    if (contacts.length === 1 && contacts[0] && isMe(contacts[0].attributes)) {
       return false;
     }
 
@@ -4514,7 +4514,8 @@ export class ConversationModel {
       preview = window.MessageCache.register(
         new MessageModel(previewAttributes)
       );
-      const updates = (await this.cleanAttributes([preview.attributes]))?.[0];
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      const updates = (await this.cleanAttributes([preview.attributes]))[0]!;
       preview.set(updates);
     }
 
@@ -4522,7 +4523,8 @@ export class ConversationModel {
       activity = window.MessageCache.register(
         new MessageModel(activityAttributes)
       );
-      const updates = (await this.cleanAttributes([activity.attributes]))?.[0];
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      const updates = (await this.cleanAttributes([activity.attributes]))[0]!;
       activity.set(updates);
     }
 
@@ -5809,18 +5811,22 @@ export class ConversationModel {
     }
 
     if (isTyping) {
-      this.contactTypingTimers[typingToken] = this.contactTypingTimers[
-        typingToken
-      ] || {
-        timestamp: Date.now(),
-        senderId,
-        senderDevice,
-      };
-
-      this.contactTypingTimers[typingToken].timer = setTimeout(
+      const timer = setTimeout(
         this.clearContactTypingTimer.bind(this, typingToken),
         15 * 1000
       );
+
+      const prev = this.contactTypingTimers[typingToken];
+      if (prev != null) {
+        prev.timer = timer;
+      } else {
+        this.contactTypingTimers[typingToken] ??= {
+          timestamp: Date.now(),
+          senderId,
+          timer,
+        };
+      }
+
       // User was not previously typing before. State change!
       if (!record) {
         window.ConversationController.conversationUpdated(
diff --git a/ts/quill/auto-substitute-ascii-emojis/index.dom.tsx b/ts/quill/auto-substitute-ascii-emojis/index.dom.tsx
index 9218b31159..4467beaa6b 100644
--- a/ts/quill/auto-substitute-ascii-emojis/index.dom.tsx
+++ b/ts/quill/auto-substitute-ascii-emojis/index.dom.tsx
@@ -48,6 +48,7 @@ function buildRegexp(obj: EmojiShortcutMap): RegExp {
   return new RegExp(`(${sanitizedKeys.join('|')})$`);
 }
 
+type EmojiRegExpMatch = RegExpExecArray & { 1: string };
 const EMOJI_REGEXP = buildRegexp(emojiShortcutMap);
 
 let isEnabled = true;
@@ -108,7 +109,7 @@ export class AutoSubstituteAsciiEmojis {
       return;
     }
 
-    const [, textEmoji] = match;
+    const [, textEmoji] = match as EmojiRegExpMatch;
     const emojiParentKey = emojiShortcutMap[textEmoji];
 
     if (emojiParentKey != null) {
diff --git a/ts/quill/emoji/completion.dom.tsx b/ts/quill/emoji/completion.dom.tsx
index a0a1137e64..0eaf27ccb6 100644
--- a/ts/quill/emoji/completion.dom.tsx
+++ b/ts/quill/emoji/completion.dom.tsx
@@ -26,6 +26,7 @@ import type {
 } from '../../components/fun/useFunEmojiSearch.dom.js';
 import { type FunEmojiLocalizer } from '../../components/fun/useFunEmojiLocalizer.dom.js';
 import type { FunEmojiSelection } from '../../components/fun/panels/FunPanelEmojis.dom.js';
+import { strictAssert } from '../../util/assert.std.js';
 
 const { isNumber, debounce } = lodash;
 
@@ -164,8 +165,12 @@ export class EmojiCompletion {
       /^([-+0-9\p{Alpha}_]*):/iu
     );
 
+    type LeftTokenMatch = RegExpMatchArray & { 1: string; 2: string };
+    type RightTokenMatch = RegExpMatchArray & { 1: string };
+
     if (leftTokenTextMatch) {
-      const [, leftTokenText, isSelfClosing] = leftTokenTextMatch;
+      const [, leftTokenText, isSelfClosing] =
+        leftTokenTextMatch as LeftTokenMatch;
 
       if (isSelfClosing || justPressedColon) {
         const parentKey =
@@ -186,7 +191,7 @@ export class EmojiCompletion {
       }
 
       if (rightTokenTextMatch) {
-        const [, rightTokenText] = rightTokenTextMatch;
+        const [, rightTokenText] = rightTokenTextMatch as RightTokenMatch;
         const tokenText = leftTokenText + rightTokenText;
         const parentKey =
           this.options.emojiLocalizer.getParentKeyForText(tokenText);
@@ -240,15 +245,20 @@ export class EmojiCompletion {
     }
 
     const result = this.results[this.index];
+    if (result == null) {
+      return;
+    }
+
     const [leafText] = this.getCurrentLeafTextPartitions();
 
     const tokenTextMatch = /:([-+0-9\p{Alpha}_]*)(:?)$/iu.exec(leafText);
+    type TokenTextMatch = RegExpExecArray & { 1: string };
 
     if (tokenTextMatch == null) {
       return;
     }
 
-    const [, tokenText] = tokenTextMatch;
+    const [, tokenText] = tokenTextMatch as TokenTextMatch;
 
     this.insertEmoji({
       emojiParentKey: result.parentKey,
@@ -355,7 +365,9 @@ export class EmojiCompletion {
               `Could not find the beginning of the emoji word to be completed. startOfEmojiText=${startOfEmojiText}, textBeforeCursor.length=${textBeforeCursor?.length}, range.offsets=${range.startOffset}-${range.endOffset}`
             );
           }
-          return range.getClientRects()[0];
+          const [clientRect] = range.getClientRects();
+          strictAssert(clientRect, 'Missing clientRect');
+          return clientRect;
         }
         log.warn('No selection range when auto-completing emoji');
         return new DOMRect(); // don't crash just because we couldn't get a rectangle
@@ -373,7 +385,7 @@ export class EmojiCompletion {
             aria-expanded
             aria-activedescendant={`emoji-result--${
               emojiResults.length
-                ? emojiResults[emojiResultsIndex].parentKey
+                ? emojiResults[emojiResultsIndex]?.parentKey
                 : ''
             }`}
             tabIndex={0}
diff --git a/ts/quill/formatting/matchers.dom.ts b/ts/quill/formatting/matchers.dom.ts
index f1529f1b11..9a7b2178b6 100644
--- a/ts/quill/formatting/matchers.dom.ts
+++ b/ts/quill/formatting/matchers.dom.ts
@@ -72,7 +72,7 @@ export const matchMonospace: Matcher = (
   const classes = [
     'MessageTextRenderer__formatting--monospace',
     'quill--monospace',
-  ];
+  ] as const;
   // Note: This is defined as $monospace in _variables.scss
   const fontFamily =
     'font-family: "SF Mono", SFMono-Regular, ui-monospace, "DejaVu Sans Mono", Menlo, Consolas, monospace;';
@@ -99,7 +99,7 @@ export const matchSpoiler: Matcher = (
     'quill--spoiler',
     'MessageTextRenderer__formatting--spoiler',
     'MessageTextRenderer__formatting--spoiler--revealed',
-  ];
+  ] as const;
 
   if (
     delta.length() > 0 &&
diff --git a/ts/quill/mentions/completion.dom.tsx b/ts/quill/mentions/completion.dom.tsx
index 6e1170e3f7..f234ad1c82 100644
--- a/ts/quill/mentions/completion.dom.tsx
+++ b/ts/quill/mentions/completion.dom.tsx
@@ -31,6 +31,7 @@ export type MentionCompletionOptions = {
 };
 
 const MENTION_REGEX = /(?:^|\W)@([-+\p{L}\p{M}\p{N}]*)$/u;
+type MentionRegexMatch = RegExpMatchArray & { 1: string };
 
 export class MentionCompletion {
   results: ReadonlyArray<MemberType>;
@@ -126,7 +127,7 @@ export class MentionCompletion {
       );
 
       if (leftTokenTextMatch) {
-        const [, leftTokenText] = leftTokenTextMatch;
+        const [, leftTokenText] = leftTokenTextMatch as MentionRegexMatch;
 
         let results: ReadonlyArray<MemberType> = [];
 
@@ -175,6 +176,9 @@ export class MentionCompletion {
     }
 
     const member = this.results[resultIndex];
+    if (member == null) {
+      return;
+    }
 
     const [blot, index] = this.quill.getLeaf(range.index);
 
@@ -185,7 +189,7 @@ export class MentionCompletion {
     );
 
     if (leftTokenTextMatch) {
-      const [, leftTokenText] = leftTokenTextMatch;
+      const [, leftTokenText] = leftTokenTextMatch as MentionRegexMatch;
 
       this.insertMention(
         member,
@@ -267,7 +271,9 @@ export class MentionCompletion {
             role="listbox"
             aria-expanded
             aria-activedescendant={`mention-result--${
-              memberResults.length ? memberResults[memberResultsIndex].name : ''
+              memberResults.length
+                ? (memberResults[memberResultsIndex]?.name ?? '')
+                : ''
             }`}
             tabIndex={0}
           >
diff --git a/ts/quill/signal-clipboard/util.dom.ts b/ts/quill/signal-clipboard/util.dom.ts
index 4ef2ef1d78..150d3096ed 100644
--- a/ts/quill/signal-clipboard/util.dom.ts
+++ b/ts/quill/signal-clipboard/util.dom.ts
@@ -97,7 +97,8 @@ function getStringFromNode(
   }
   let result = '';
   for (let i = 0; i < childCount; i += 1) {
-    const child = element.childNodes[i];
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const child = element.childNodes[i]!;
     const nextChild = element.childNodes[i + 1];
     result += getStringFromNode(child, node, nextChild);
   }
@@ -122,12 +123,12 @@ const STRIKETHROUGH_TAG = 's';
 const MONOSPACE_CLASSES = [
   'quill--monospace',
   'MessageTextRenderer__formatting--monospace',
-];
+] as const;
 const SPOILER_CLASSES = [
   'quill--spoiler',
   'MessageTextRenderer__formatting--spoiler',
   'MessageTextRenderer__formatting--spoiler--revealed',
-];
+] as const;
 
 // When the user cuts/copies single-line text which don't cross any mentions/emojo or
 // formatting boundaries, we don't get the surrounding formatting nodes in our selection.
diff --git a/ts/scripts/build-localized-display-names.node.ts b/ts/scripts/build-localized-display-names.node.ts
index c36ea0a3ce..c4c34a51a9 100644
--- a/ts/scripts/build-localized-display-names.node.ts
+++ b/ts/scripts/build-localized-display-names.node.ts
@@ -12,14 +12,15 @@ if (type !== 'countries' && type !== 'locales') {
   throw new Error('Invalid first argument, expceted "countries" or "locales"');
 }
 
-const localeDisplayNamesDataPath = process.argv[3];
-if (!localeDisplayNamesDataPath) {
+if (!process.argv[3]) {
   throw new Error('Missing second argument: source csv file');
 }
-const localeDisplayNamesBuildPath = process.argv[4];
-if (!localeDisplayNamesBuildPath) {
+const localeDisplayNamesDataPath = process.argv[3];
+
+if (!process.argv[4]) {
   throw new Error('Missing third argument: output json file');
 }
+const localeDisplayNamesBuildPath = process.argv[4];
 
 const availableLocales = _getAvailableLocales();
 
@@ -68,7 +69,8 @@ function convertData(
 
       result[subKey] = {};
       for (const [index, message] of messages.entries()) {
-        result[subKey][keys[index]] = message;
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        result[subKey][keys[index]!] = message;
       }
     }
   } else {
@@ -81,7 +83,8 @@ function convertData(
       const [subKey, ...messages] = row;
 
       for (const [index, message] of messages.entries()) {
-        result[keys[index]][subKey] = message;
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        result[keys[index]!]![subKey] = message;
       }
     }
   }
@@ -103,7 +106,8 @@ function assertValuesForAllLocales(result: LocaleDisplayNamesResult) {
 }
 
 function assertValuesForAllCountries(result: LocaleDisplayNamesResult) {
-  const availableCountries = Object.keys(result.en);
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  const availableCountries = Object.keys(result.en!);
   for (const locale of availableLocales) {
     const values = result[locale];
     if (values == null) {
diff --git a/ts/scripts/check-min-os-version.node.ts b/ts/scripts/check-min-os-version.node.ts
index 7e5d6acd02..b9ba96807b 100644
--- a/ts/scripts/check-min-os-version.node.ts
+++ b/ts/scripts/check-min-os-version.node.ts
@@ -62,12 +62,13 @@ async function macosVersionCheck(file: string) {
 
   const { stdout } = await execFile('otool', ['-l', file]);
 
+  type MacosMatch = RegExpMatchArray & { 1: string };
   const match = stdout.match(/minos\s+([\d.]+)/);
   if (match == null) {
     throw new Error(`Failed to detect min OS version of ${file}`);
   }
 
-  const [, macosVersion] = match;
+  const [, macosVersion] = match as MacosMatch;
   const darwinVersion = MACOS_TO_DARWIN_VERSIONS.get(macosVersion);
   if (darwinVersion == null) {
     throw new Error(`No matching darwin version for macOS ${macosVersion}`);
@@ -108,7 +109,9 @@ async function linuxVersionCheck(file: string) {
   });
 
   let minGlibcVersion: string | undefined;
-  for (const [, unpaddedVersion] of stdout.matchAll(/GLIBC_([\d.]+)/g)) {
+  type GlibcMatch = RegExpExecArray & { 1: string };
+  for (const match of stdout.matchAll(/GLIBC_([\d.]+)/g)) {
+    const [, unpaddedVersion] = match as GlibcMatch;
     const glibcVersion = padGlibcVersion(unpaddedVersion);
     if (minGlibcVersion == null || gte(glibcVersion, minGlibcVersion)) {
       minGlibcVersion = glibcVersion;
@@ -126,6 +129,7 @@ async function linuxVersionCheck(file: string) {
     throw new Error('Missing libc6 dependency in package.json');
   }
 
+  type Libc6Match = RegExpMatchArray & { 1: string };
   const match = libc6Dependency.match(/^libc6 \(>= ([\d.]+)\)$/);
   if (match == null) {
     throw new Error(
@@ -133,7 +137,8 @@ async function linuxVersionCheck(file: string) {
     );
   }
 
-  const minSupported = padGlibcVersion(match[1]);
+  const [, unpaddedVersion] = match as Libc6Match;
+  const minSupported = padGlibcVersion(unpaddedVersion);
   if (gte(minSupported, minGlibcVersion)) {
     console.log(`${file}: required version ${minGlibcVersion}`);
     return;
diff --git a/ts/scripts/constants.std.ts b/ts/scripts/constants.std.ts
index 273b1f5756..7abd6ded08 100644
--- a/ts/scripts/constants.std.ts
+++ b/ts/scripts/constants.std.ts
@@ -1,4 +1,5 @@
 // Copyright 2024 Signal Messenger, LLC
 // SPDX-License-Identifier: AGPL-3.0-only
 
+export type DeletedMatch = RegExpMatchArray & { 1: string };
 export const DELETED_REGEXP = /\(\s*deleted\s+(\d{2,4}\/\d{2}\/\d{2,4})\s*\)/i;
diff --git a/ts/scripts/gen-nsis-script.node.ts b/ts/scripts/gen-nsis-script.node.ts
index efe3193e35..8dbc806d3f 100644
--- a/ts/scripts/gen-nsis-script.node.ts
+++ b/ts/scripts/gen-nsis-script.node.ts
@@ -46,7 +46,8 @@ const fallbackMessages = JSON.parse(
 
 const nsisStrings = new Array<string>();
 for (const lang of REQUIRED_LANGUAGES) {
-  const langId = LCID[lang] ?? LCID.en_US;
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  const langId = LCID[lang] ?? LCID.en_US!;
   if (USED.has(langId)) {
     continue;
   }
diff --git a/ts/scripts/notarize-universal-dmg.node.ts b/ts/scripts/notarize-universal-dmg.node.ts
index 5c6856b7ef..0035b26bae 100644
--- a/ts/scripts/notarize-universal-dmg.node.ts
+++ b/ts/scripts/notarize-universal-dmg.node.ts
@@ -63,7 +63,8 @@ export async function afterAllArtifactBuild({
     return;
   }
 
-  const [dmgPath] = artifactsToStaple;
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  const dmgPath = artifactsToStaple[0]!;
   console.log(`Notarizing dmg: ${dmgPath}`);
 
   await notarize({
diff --git a/ts/scripts/publish-installer-size.node.ts b/ts/scripts/publish-installer-size.node.ts
index 0f13d3220a..1f0c9c3e21 100644
--- a/ts/scripts/publish-installer-size.node.ts
+++ b/ts/scripts/publish-installer-size.node.ts
@@ -18,7 +18,8 @@ const RELEASE_DIR = join(__dirname, '..', '..', 'release');
 
 // TODO: DESKTOP-9836
 async function main(): Promise<void> {
-  const config = process.argv[2];
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  const config = process.argv[2]!;
   if (!SUPPORT_CONFIG.has(config)) {
     throw new Error(`Invalid argument: ${config}`);
   }
diff --git a/ts/scripts/remove-strings.node.ts b/ts/scripts/remove-strings.node.ts
index 46ba85cdc4..bb1fbaf08d 100644
--- a/ts/scripts/remove-strings.node.ts
+++ b/ts/scripts/remove-strings.node.ts
@@ -9,7 +9,7 @@ import path from 'node:path';
 
 import { MONTH } from '../util/durations/index.std.js';
 import { isOlderThan } from '../util/timestamp.std.js';
-import { DELETED_REGEXP } from './constants.std.js';
+import { DELETED_REGEXP, type DeletedMatch } from './constants.std.js';
 
 const ROOT_DIR = path.join(__dirname, '..', '..');
 const MESSAGES_FILE = path.join(ROOT_DIR, '_locales', 'en', 'messages.json');
@@ -33,7 +33,8 @@ async function main() {
           return;
         }
 
-        const deletedAt = new Date(match[1]).getTime();
+        const [deletedAtStr] = match as DeletedMatch;
+        const deletedAt = new Date(deletedAtStr).getTime();
         if (!isOlderThan(deletedAt, MONTH)) {
           return;
         }
diff --git a/ts/scripts/symbolicate-crash-report.node.ts b/ts/scripts/symbolicate-crash-report.node.ts
index ae00052f42..460e49801e 100644
--- a/ts/scripts/symbolicate-crash-report.node.ts
+++ b/ts/scripts/symbolicate-crash-report.node.ts
@@ -11,11 +11,10 @@ import pMap from 'p-map';
 
 const gunzip = promisify(gunzipCb);
 
-const INPUT_FILE = process.argv[2];
-
-if (!INPUT_FILE) {
+if (!process.argv[2]) {
   throw new Error('Usage: node symbolicate-crash-report.js <input>');
 }
+const INPUT_FILE = process.argv[2];
 
 async function main(): Promise<void> {
   let file = await readFile(INPUT_FILE);
@@ -30,6 +29,7 @@ async function main(): Promise<void> {
     .matchAll(
       /WARN[^\n]*crashReports:\s+dump=\[REDACTED\]([0-9a-z]+).dmp\s+mtime="([\d\-T:.Z]+)"\s+({(\n|.)*?\n})/g
     );
+  type CrashDumpMatch = RegExpExecArray & { 1: string; 2: string; 3: string };
 
   function moduleName(filename: string | undefined): string {
     if (!filename) {
@@ -47,7 +47,8 @@ async function main(): Promise<void> {
   }
 
   const dumps = new Array<string>();
-  for (const [, dump, mtime, json] of matches) {
+  for (const match of matches) {
+    const [, dump, mtime, json] = match as CrashDumpMatch;
     const out = [];
 
     let info;
diff --git a/ts/scripts/update-gha.node.ts b/ts/scripts/update-gha.node.ts
index 9079b0b4b7..41241d5fca 100644
--- a/ts/scripts/update-gha.node.ts
+++ b/ts/scripts/update-gha.node.ts
@@ -16,6 +16,12 @@ const WORKFLOWS_DIR = join(__dirname, '..', '..', '.github', 'workflows');
 const REGEXP =
   /uses:\s*(?<path>[^\s]+)@(?<ref>[^\s#]+)(?:\s*#\s*(?<originalRef>[^\n]+))?/g;
 
+type RegexGroups = {
+  path: string;
+  ref: string;
+  originalRef?: string;
+};
+
 const CACHE = new Map<string, string>();
 
 const TagsSchema = z
@@ -32,7 +38,7 @@ async function updateAction(fullPath: string): Promise<void> {
 
   for (const { groups } of source.matchAll(REGEXP)) {
     strictAssert(groups != null, 'Expected regexp to fully match');
-    const { path, ref, originalRef } = groups;
+    const { path, ref, originalRef } = groups as RegexGroups;
 
     // Skip local actions
     if (path.startsWith('.')) {
@@ -50,6 +56,7 @@ async function updateAction(fullPath: string): Promise<void> {
     }
 
     const [org, repo] = path.split('/', 2);
+    strictAssert(repo, 'Missing repo');
 
     const url =
       `https://api.github.com/repos/${encodeURIComponent(org)}/` +
diff --git a/ts/services/BeforeNavigate.std.ts b/ts/services/BeforeNavigate.std.ts
index 0d95b5261f..8766a68f2b 100644
--- a/ts/services/BeforeNavigate.std.ts
+++ b/ts/services/BeforeNavigate.std.ts
@@ -83,8 +83,7 @@ export class BeforeNavigateService {
     const logId = `shouldCancelNavigation/${context}`;
     const entries = Array.from(this.#beforeNavigateCallbacks);
 
-    for (let i = 0, max = entries.length; i < max; i += 1) {
-      const entry = entries[i];
+    for (const entry of entries) {
       // eslint-disable-next-line no-await-in-loop
       const response = await Promise.race([
         entry.callback({ existingLocation, newLocation }),
diff --git a/ts/services/LinkPreview.preload.ts b/ts/services/LinkPreview.preload.ts
index 6aa52e244b..2f0cac0bb9 100644
--- a/ts/services/LinkPreview.preload.ts
+++ b/ts/services/LinkPreview.preload.ts
@@ -475,7 +475,8 @@ async function getStickerPackPreview(
     }
 
     const { title, coverStickerId } = pack;
-    const sticker = pack.stickers[coverStickerId];
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const sticker = pack.stickers[coverStickerId]!;
     const data =
       pack.status === 'ephemeral'
         ? await readTempData(sticker)
diff --git a/ts/services/MessageCache.preload.ts b/ts/services/MessageCache.preload.ts
index a3e2c9913c..5afada0f11 100644
--- a/ts/services/MessageCache.preload.ts
+++ b/ts/services/MessageCache.preload.ts
@@ -163,7 +163,8 @@ export class MessageCache {
       }
       const { [obsoleteId]: obsoleteSendState, ...rest } = sendState;
       return {
-        [conversationId]: obsoleteSendState,
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        [conversationId]: obsoleteSendState!,
         ...rest,
       };
     };
diff --git a/ts/services/addGlobalKeyboardShortcuts.preload.ts b/ts/services/addGlobalKeyboardShortcuts.preload.ts
index 123612860c..49debba08d 100644
--- a/ts/services/addGlobalKeyboardShortcuts.preload.ts
+++ b/ts/services/addGlobalKeyboardShortcuts.preload.ts
@@ -11,6 +11,7 @@ import { getQuotedMessageSelector } from '../state/selectors/composer.preload.js
 import { removeLinkPreview } from './LinkPreview.preload.js';
 import { ForwardMessagesModalType } from '../components/ForwardMessagesModal.dom.js';
 import { getSelectedConversationId } from '../state/selectors/nav.std.js';
+import { strictAssert } from '../util/assert.std.js';
 
 const log = createLogger('addGlobalKeyboardShortcuts');
 
@@ -96,6 +97,7 @@ export function addGlobalKeyboardShortcuts(): void {
       }
 
       const node = targets[index];
+      strictAssert(node, 'Missing node');
       const firstFocusableElement = matchOrQueryFocusable(node);
 
       if (firstFocusableElement) {
diff --git a/ts/services/backups/credentials.preload.ts b/ts/services/backups/credentials.preload.ts
index edbb7df389..99c8e6774d 100644
--- a/ts/services/backups/credentials.preload.ts
+++ b/ts/services/backups/credentials.preload.ts
@@ -359,8 +359,10 @@ export class BackupCredentials {
     result.sort((a, b) => a.redemptionTimeMs - b.redemptionTimeMs);
     await this.#updateCache(result);
 
-    const startMs = result[0].redemptionTimeMs;
-    const endMs = result[result.length - 1].redemptionTimeMs;
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const startMs = result[0]!.redemptionTimeMs;
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const endMs = result[result.length - 1]!.redemptionTimeMs;
     log.info(`saved [${startMs}, ${endMs}]`);
 
     strictAssert(result.length === 14, 'Expected one week of credentials');
diff --git a/ts/services/backups/import.preload.ts b/ts/services/backups/import.preload.ts
index d0b5e531ab..c51e78902f 100644
--- a/ts/services/backups/import.preload.ts
+++ b/ts/services/backups/import.preload.ts
@@ -3425,7 +3425,7 @@ export class BackupImportStream extends Writable {
         if (Bytes.isNotEmpty(updaterAci)) {
           from = fromAciObject(Aci.fromUuidBytes(updaterAci));
         }
-        if (!invitees || invitees.length === 0) {
+        if (!invitees || invitees[0] == null) {
           throw new Error(
             `${logId}: groupInvitationRevokedUpdate had missing invitees list!`
           );
@@ -3707,7 +3707,7 @@ export class BackupImportStream extends Writable {
       additionalMessages.push(migrationMessage);
     }
 
-    if (finalDetails.length === 0 && additionalMessages.length > 0) {
+    if (finalDetails.length === 0 && additionalMessages[0] != null) {
       return {
         message: additionalMessages[0],
         additionalMessages: additionalMessages.slice(1),
diff --git a/ts/services/calling.preload.ts b/ts/services/calling.preload.ts
index c26ffe5327..7ac97bd6e8 100644
--- a/ts/services/calling.preload.ts
+++ b/ts/services/calling.preload.ts
@@ -2814,27 +2814,38 @@ export class CallingClass {
       return false;
     }
     for (let i = 0; i < a.availableCameras.length; i += 1) {
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      const aCamera = a.availableCameras[i]!;
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      const bCamera = a.availableCameras[i]!;
       if (
-        a.availableCameras[i].deviceId !== b.availableCameras[i].deviceId ||
-        a.availableCameras[i].groupId !== b.availableCameras[i].groupId ||
-        a.availableCameras[i].label !== b.availableCameras[i].label
+        aCamera.deviceId !== bCamera.deviceId ||
+        aCamera.groupId !== bCamera.groupId ||
+        aCamera.label !== bCamera.label
       ) {
         return false;
       }
     }
     for (let i = 0; i < a.availableMicrophones.length; i += 1) {
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      const aMicrophone = a.availableMicrophones[i]!;
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      const bMicrophone = b.availableMicrophones[i]!;
       if (
-        a.availableMicrophones[i].name !== b.availableMicrophones[i].name ||
-        a.availableMicrophones[i].uniqueId !==
-          b.availableMicrophones[i].uniqueId
+        aMicrophone.name !== bMicrophone.name ||
+        aMicrophone.uniqueId !== bMicrophone.uniqueId
       ) {
         return false;
       }
     }
     for (let i = 0; i < a.availableSpeakers.length; i += 1) {
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      const aSpeaker = a.availableSpeakers[i]!;
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      const bSpeaker = b.availableSpeakers[i]!;
       if (
-        a.availableSpeakers[i].name !== b.availableSpeakers[i].name ||
-        a.availableSpeakers[i].uniqueId !== b.availableSpeakers[i].uniqueId
+        aSpeaker.name !== bSpeaker.name ||
+        aSpeaker.uniqueId !== bSpeaker.uniqueId
       ) {
         return false;
       }
@@ -3875,11 +3886,15 @@ export class CallingClass {
     if (this._iceServerOverride) {
       if (typeof this._iceServerOverride === 'string') {
         if (ICE_SERVER_IS_IP_LIKE.test(this._iceServerOverride)) {
-          iceServers[0].urls = [this._iceServerOverride];
-          iceServers = [iceServers[0]];
+          const iceServer = iceServers[0];
+          strictAssert(iceServer, 'Missing iceServers[0]');
+          iceServer.urls = [this._iceServerOverride];
+          iceServers = [iceServer];
         } else {
-          iceServers[1].urls = [this._iceServerOverride];
-          iceServers = [iceServers[1]];
+          const iceServer = iceServers[1];
+          strictAssert(iceServer, 'Missing iceServers[1]');
+          iceServer.urls = [this._iceServerOverride];
+          iceServers = [iceServer];
         }
       } else {
         iceServers = iceServerConfigToList(this._iceServerOverride);
diff --git a/ts/services/groupCredentialFetcher.preload.ts b/ts/services/groupCredentialFetcher.preload.ts
index 6684d417bc..50b92eb499 100644
--- a/ts/services/groupCredentialFetcher.preload.ts
+++ b/ts/services/groupCredentialFetcher.preload.ts
@@ -135,8 +135,10 @@ function getCredentialsForToday(
   }
 
   return {
-    today: credentials[todayIndex],
-    tomorrow: credentials[todayIndex + 1],
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    today: credentials[todayIndex]!,
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    tomorrow: credentials[todayIndex + 1]!,
   };
 }
 
diff --git a/ts/services/releaseNoteAndMegaphoneFetcher.preload.ts b/ts/services/releaseNoteAndMegaphoneFetcher.preload.ts
index dd89b1a277..f8598423f2 100644
--- a/ts/services/releaseNoteAndMegaphoneFetcher.preload.ts
+++ b/ts/services/releaseNoteAndMegaphoneFetcher.preload.ts
@@ -474,19 +474,23 @@ export class ReleaseNoteAndMegaphoneFetcher {
               range.length == null ||
               range.start == null ||
               range.style == null ||
-              !STYLE_MAPPING[range.style] ||
               range.start + range.length - 1 >= body.length
             ) {
               return null;
             }
 
+            const style = STYLE_MAPPING[range.style];
+            if (style == null) {
+              return null;
+            }
+
             const relativeStart =
               range.start + title.length + titleBodySeparator.length;
 
             return {
               start: relativeStart,
               length: range.length,
-              style: STYLE_MAPPING[range.style],
+              style,
             };
           })
           .filter(isNotNil);
diff --git a/ts/services/retryPlaceholders.std.ts b/ts/services/retryPlaceholders.std.ts
index a7a253f56c..876bffa7da 100644
--- a/ts/services/retryPlaceholders.std.ts
+++ b/ts/services/retryPlaceholders.std.ts
@@ -161,11 +161,9 @@ export class RetryPlaceholders {
       throw new Error('RetryPlaceholders: not started');
     }
     const expiration = getDeltaIntoPast(this.#retryReceiptLifespan);
-    const max = this.#items.length;
     const result: Array<RetryItemType> = [];
 
-    for (let i = 0; i < max; i += 1) {
-      const item = this.#items[i];
+    for (const item of this.#items) {
       if (item.receivedAt <= expiration) {
         result.push(item);
       } else {
diff --git a/ts/services/storage.preload.ts b/ts/services/storage.preload.ts
index b1d3a83945..5c550a2fce 100644
--- a/ts/services/storage.preload.ts
+++ b/ts/services/storage.preload.ts
@@ -269,10 +269,7 @@ async function generateManifest(
     };
   }
 
-  const conversations = window.ConversationController.getAll();
-  for (let i = 0; i < conversations.length; i += 1) {
-    const conversation = conversations[i];
-
+  for (const conversation of window.ConversationController.getAll()) {
     let identifierType;
     let storageRecord: Proto.StorageRecord.Params | undefined;
 
@@ -2334,6 +2331,7 @@ async function upload({
     uploadBucket.push(Date.now());
     if (uploadBucket.length >= 3) {
       const [firstMostRecentWrite] = uploadBucket;
+      strictAssert(firstMostRecentWrite, 'Missing firstMostRecentWrite');
 
       if (isMoreRecentThan(5 * durations.MINUTE, firstMostRecentWrite)) {
         throw new Error(`${logId}: too many writes too soon.`);
diff --git a/ts/services/storyLoader.preload.ts b/ts/services/storyLoader.preload.ts
index e0d1ca327f..647e1cf267 100644
--- a/ts/services/storyLoader.preload.ts
+++ b/ts/services/storyLoader.preload.ts
@@ -63,7 +63,8 @@ export function getStoryDataFromMessageAttributes(
       message.preview.length === 1,
       'getStoryDataFromMessageAttributes: story can have only one preview'
     );
-    [preview] = message.preview;
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    preview = message.preview[0]!;
 
     strictAssert(
       attachment?.textAttachment,
diff --git a/ts/services/username.preload.ts b/ts/services/username.preload.ts
index 8fc7aa030b..a19469338a 100644
--- a/ts/services/username.preload.ts
+++ b/ts/services/username.preload.ts
@@ -129,7 +129,8 @@ export async function reserveUsername(
       return { ok: false, error: ReserveUsernameError.Unprocessable };
     }
 
-    const username = candidates[index];
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const username = candidates[index]!;
 
     return {
       ok: true,
diff --git a/ts/services/writeProfile.preload.ts b/ts/services/writeProfile.preload.ts
index dc67ccb29f..d2d5b6ab01 100644
--- a/ts/services/writeProfile.preload.ts
+++ b/ts/services/writeProfile.preload.ts
@@ -15,7 +15,6 @@ import {
   writeNewAttachmentData,
   maybeDeleteAttachmentFile,
 } from '../util/migrations.preload.js';
-import { isWhitespace } from '../util/whitespaceStringUtil.std.js';
 import { imagePathToBytes } from '../util/imagePathToBytes.dom.js';
 import { getLocalAvatarUrl } from '../util/avatarUtils.preload.js';
 import type {
@@ -55,7 +54,7 @@ export async function writeProfile(
   } = conversation;
 
   strictAssert(
-    !isWhitespace(String(conversation.firstName)),
+    conversation.firstName != null && conversation.firstName.trim() !== '',
     'writeProfile: Cannot set an empty profile name'
   );
 
diff --git a/ts/sql/Server.node.ts b/ts/sql/Server.node.ts
index 3e28ea5e0d..104c3633f9 100644
--- a/ts/sql/Server.node.ts
+++ b/ts/sql/Server.node.ts
@@ -1415,13 +1415,11 @@ function insertSentProto(
       `
     );
 
-    const recipientServiceIds = Object.keys(recipients);
-    for (const recipientServiceId of recipientServiceIds) {
+    for (const [recipientServiceId, deviceIds] of Object.entries(recipients)) {
       strictAssert(
         isServiceIdString(recipientServiceId),
         'Recipient must be a service id'
       );
-      const deviceIds = recipients[recipientServiceId];
 
       for (const deviceId of deviceIds) {
         recipientStatement.run({
@@ -1550,18 +1548,24 @@ function deleteSentProtoRecipient(
           sendLogRecipients.deviceId = $deviceId;
        `
         )
-        .all({ timestamp, recipientServiceId, deviceId });
-      if (!rows.length) {
+        .all<{ id: string; hasPniSignatureMessage: string }>({
+          timestamp,
+          recipientServiceId,
+          deviceId,
+        });
+
+      const [row, ...others] = rows;
+      if (row == null) {
         continue;
       }
-      if (rows.length > 1) {
+      if (others.length > 0) {
         logger.warn(
           'deleteSentProtoRecipient: More than one payload matches ' +
             `recipient and timestamp ${timestamp}. Using the first.`
         );
       }
 
-      const { id, hasPniSignatureMessage } = rows[0];
+      const { id, hasPniSignatureMessage } = row;
 
       // 2. Delete the recipient/device combination in question.
       db.prepare(
@@ -2309,9 +2313,11 @@ function searchMessages(
       `
     );
     const hydrated = hydrateMessages(db, queryResult);
-    return queryResult.map((row, idx) => {
+    return queryResult.map((row, idx): ServerSearchResultMessageType => {
+      const message = hydrated[idx];
+      strictAssert(message, 'Missing message');
       return {
-        ...hydrated[idx],
+        ...message,
         ftsSnippet: row.ftsSnippet,
         mentionAci: row.mentionAci,
         mentionStart: row.mentionStart,
@@ -3530,17 +3536,19 @@ function getMessageByAuthorAciAndSentAt(
 
     const rows = db.prepare(query).all<MessageTypeUnhydrated>(params);
 
-    if (rows.length > 1) {
+    const [row, ...others] = rows;
+
+    if (others.length > 0) {
       logger.warn(
         `getMessageByAuthorAciAndSentAt(${authorAci}, ${sentAtTimestamp}): More than one message found`
       );
     }
 
-    if (rows.length < 1) {
+    if (row == null) {
       return null;
     }
 
-    return hydrateMessage(db, rows[0]);
+    return hydrateMessage(db, row);
   })();
 }
 
@@ -5784,28 +5792,30 @@ function getSortedNonAttachmentMedia(
     };
 
     if (type === 'links') {
+      const preview = row.preview?.[0];
       strictAssert(
-        row.preview != null && row.preview.length >= 1,
+        preview,
         `getSortedNonAttachmentMedia: got message without preview ${row.id}`
       );
 
       return {
         type: 'link',
         message,
-        preview: row.preview[0],
+        preview,
       };
     }
 
     if (type === 'contacts') {
+      const contact = row.contact?.[0];
       strictAssert(
-        row.contact != null && row.contact.length >= 1,
+        contact,
         `getSortedNonAttachmentMedia: got message without contact ${row.id}`
       );
 
       return {
         type: 'contact',
         message,
-        contact: row.contact[0],
+        contact,
       };
     }
 
@@ -9431,8 +9441,10 @@ function getUnreadEditedMessagesAndMarkRead(
       .prepare(selectQuery)
       .all<MessageTypeUnhydrated>(selectParams);
 
-    if (rows.length) {
-      const newestSentAt = rows[0].sent_at;
+    const [first] = rows;
+
+    if (first != null) {
+      const newestSentAt = first.sent_at;
 
       const [updateStatusQuery, updateStatusParams] = sql`
         UPDATE edited_messages
diff --git a/ts/sql/hydration.std.ts b/ts/sql/hydration.std.ts
index 8b90b2246a..d9264ac883 100644
--- a/ts/sql/hydration.std.ts
+++ b/ts/sql/hydration.std.ts
@@ -50,7 +50,8 @@ export function hydrateMessage(
   db: ReadableDB,
   row: MessageTypeUnhydrated
 ): MessageType {
-  return hydrateMessages(db, [row])[0];
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  return hydrateMessages(db, [row])[0]!;
 }
 
 export function hydrateMessages(
diff --git a/ts/sql/main.main.ts b/ts/sql/main.main.ts
index d22ff99070..74927a7271 100644
--- a/ts/sql/main.main.ts
+++ b/ts/sql/main.main.ts
@@ -171,6 +171,7 @@ export class MainSQL {
 
     this.#onReady = (async () => {
       const primary = this.#pool[0];
+      strictAssert(primary, 'Missing primary');
       const rest = this.#pool.slice(1);
 
       await this.#send(primary, {
@@ -319,6 +320,7 @@ export class MainSQL {
     }
 
     const primary = this.#pool[0];
+    strictAssert(primary, 'Missing primary');
 
     const { result, duration } = await this.#send<SqlCallResult>(primary, {
       type: 'sqlCall:write',
@@ -393,6 +395,8 @@ export class MainSQL {
 
   async #terminate(request: WorkerRequest): Promise<void> {
     const primary = this.#pool[0];
+    strictAssert(primary, 'Missing primary');
+
     const rest = this.#pool.slice(1);
 
     // Terminate non-primary workers first
@@ -532,6 +536,8 @@ export class MainSQL {
   // Find first pool entry with minimal load
   #getWorker(): PoolEntry {
     let min = this.#pool[0];
+    strictAssert(min, 'Missing min');
+
     for (const entry of this.#pool) {
       if (min && min.load < entry.load) {
         continue;
diff --git a/ts/sql/migrations/1280-blob-unprocessed.std.ts b/ts/sql/migrations/1280-blob-unprocessed.std.ts
index f337b57fc9..0844959507 100644
--- a/ts/sql/migrations/1280-blob-unprocessed.std.ts
+++ b/ts/sql/migrations/1280-blob-unprocessed.std.ts
@@ -14,6 +14,7 @@ import { Migrations as Proto } from '../../protobuf/index.std.js';
 import { sql } from '../util.std.js';
 import type { WritableDB } from '../Interface.std.js';
 import { getOurUuid } from './41-uuid-keys.std.js';
+import { strictAssert } from '../../util/assert.std.js';
 
 export default function updateToSchemaVersion1280(
   db: WritableDB,
@@ -118,6 +119,8 @@ export default function updateToSchemaVersion1280(
         ? Buffer.from(String(decrypted), 'base64')
         : decoded.content;
 
+      strictAssert(id != null, 'Missing id');
+
       insertStmt.run({
         ...rest,
         id,
diff --git a/ts/sql/migrations/88-service-ids.std.ts b/ts/sql/migrations/88-service-ids.std.ts
index 68b1090792..9038e6807f 100644
--- a/ts/sql/migrations/88-service-ids.std.ts
+++ b/ts/sql/migrations/88-service-ids.std.ts
@@ -594,6 +594,7 @@ function migrateSessions(
 
   logger.info(`updating ${sessions.length} sessions`);
   for (const { id, serviceId, ourServiceId, json } of sessions) {
+    type Match = RegExpMatchArray & { 1: string; 2: string; 3: string };
     const match = id.match(/^(.*):(.*)\.(.*)$/);
     if (!match) {
       logger.warn(`invalid session id ${id}`);
@@ -607,7 +608,7 @@ function migrateSessions(
       continue;
     }
 
-    const [, from, to, device] = match;
+    const [, from, to, device] = match as Match;
 
     const newId =
       `${migrateServiceId(from, ourServiceIds, logger)}:` +
@@ -844,6 +845,7 @@ function migratePreKeys(
 
   logger.info(`updating ${preKeys.length} ${table}`);
   for (const { id, json } of preKeys) {
+    type Match = RegExpMatchArray & { 1: string; 2: string };
     const match = id.match(/^(.*):(.*)$/);
     if (!match) {
       logger.warn(`invalid ${table} id ${id}`);
@@ -858,7 +860,7 @@ function migratePreKeys(
       continue;
     }
 
-    const [, ourUuid, keyId] = match;
+    const [, ourUuid, keyId] = match as Match;
 
     const ourServiceId = migrateServiceId(ourUuid, ourServiceIds, logger);
     const newId = `${ourServiceId}:${keyId}`;
diff --git a/ts/sql/migrations/index.node.ts b/ts/sql/migrations/index.node.ts
index a17bed3f44..0668af4079 100644
--- a/ts/sql/migrations/index.node.ts
+++ b/ts/sql/migrations/index.node.ts
@@ -147,6 +147,7 @@ import updateToSchemaVersion1670 from './1670-drop-call-link-epoch.std.js';
 import updateToSchemaVersion1680 from './1680-cleanup-empty-strings.std.js';
 
 import { DataWriter } from '../Server.node.js';
+import { strictAssert } from '../../util/assert.std.js';
 
 const { keyBy } = lodash;
 
@@ -775,7 +776,8 @@ function updateToSchemaVersion20(db: Database): void {
   for (const row of allConversations) {
     const oldId = row.id;
     const newId = generateUuid();
-    allConversationsByOldId[oldId].id = newId;
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    allConversationsByOldId[oldId]!.id = newId;
     const patchObj: { id: string; e164?: string; groupId?: string } = {
       id: newId,
     };
@@ -1687,11 +1689,14 @@ export function updateSchema(db: WritableDB, logger: LoggerType): void {
   const startingVersion = getUserVersion(db);
   const schemaVersion = getSchemaVersion(db);
 
-  const MAX_VERSION = SCHEMA_VERSIONS[SCHEMA_VERSIONS.length - 1].version;
+  const MAX_VERSION = SCHEMA_VERSIONS[SCHEMA_VERSIONS.length - 1]?.version;
+  strictAssert(MAX_VERSION, 'Missing MAX_VERSION');
 
   for (let i = 1; i < SCHEMA_VERSIONS.length; i += 1) {
-    const prev = SCHEMA_VERSIONS[i - 1].version;
-    const next = SCHEMA_VERSIONS[i].version;
+    const prev = SCHEMA_VERSIONS[i - 1]?.version;
+    const next = SCHEMA_VERSIONS[i]?.version;
+    strictAssert(prev, 'Missing prev');
+    strictAssert(next, 'Missing next');
     if (prev >= next) {
       throw new Error(
         `Migration versions are not monotonic: ${prev} >= ${next}`
@@ -1722,7 +1727,9 @@ export function updateSchema(db: WritableDB, logger: LoggerType): void {
     // eslint-disable-next-line no-loop-func
     const needsVacuum = db.transaction(() => {
       for (; i < SCHEMA_VERSIONS.length; i += 1) {
-        const { version, update } = SCHEMA_VERSIONS[i];
+        const schema = SCHEMA_VERSIONS[i];
+        strictAssert(schema, 'Missing schema');
+        const { version, update } = schema;
         if (version <= startingVersion) {
           continue;
         }
diff --git a/ts/sql/util.std.ts b/ts/sql/util.std.ts
index 3cc53f9bfe..79f5276401 100644
--- a/ts/sql/util.std.ts
+++ b/ts/sql/util.std.ts
@@ -73,7 +73,8 @@ export function sqlFragment(
   const params: Array<QueryTemplateParam> = [];
 
   strings.forEach((string, index) => {
-    const value = values[index];
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const value = values[index]!;
 
     query += string;
 
diff --git a/ts/state/ducks/audioPlayer.preload.ts b/ts/state/ducks/audioPlayer.preload.ts
index 28765086e9..fa7ceb5f0c 100644
--- a/ts/state/ducks/audioPlayer.preload.ts
+++ b/ts/state/ducks/audioPlayer.preload.ts
@@ -110,7 +110,8 @@ async function getNextVoiceNote({
     return undefined;
   }
 
-  const { message, attachment } = results[0];
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  const { message, attachment } = results[0]!;
   return extractVoiceNoteForPlayback(
     {
       ...message,
diff --git a/ts/state/ducks/calling.preload.ts b/ts/state/ducks/calling.preload.ts
index e16f4804bc..374cee7738 100644
--- a/ts/state/ducks/calling.preload.ts
+++ b/ts/state/ducks/calling.preload.ts
@@ -3398,7 +3398,7 @@ export function reducer(
                 rootKey:
                   callLinks[conversationId]?.rootKey ??
                   action.payload.callLinkRootKey,
-                adminKey: callLinks[conversationId]?.adminKey,
+                adminKey: callLinks[conversationId]?.adminKey ?? null,
                 storageNeedsSync: false,
               },
             }
diff --git a/ts/state/ducks/composer.preload.ts b/ts/state/ducks/composer.preload.ts
index 34005e8bbe..f31f94292a 100644
--- a/ts/state/ducks/composer.preload.ts
+++ b/ts/state/ducks/composer.preload.ts
@@ -1206,8 +1206,7 @@ function processAttachments({
       file: File;
       pendingAttachment: AttachmentDraftType;
     }> = [];
-    for (let i = 0; i < files.length; i += 1) {
-      const file = files[i];
+    for (const file of files) {
       const processingResult = preProcessAttachment(file, nextDraftAttachments);
       if (processingResult != null) {
         toastToShow = processingResult;
@@ -1374,6 +1373,8 @@ function removeAttachment(
     }
 
     const targetAttachment = attachments[targetAttachmentIndex];
+    strictAssert(targetAttachment, 'Missing targetAttachment');
+
     const nextAttachments = attachments
       .slice(0, targetAttachmentIndex)
       .concat(attachments.slice(targetAttachmentIndex + 1));
@@ -1734,13 +1735,11 @@ export function reducer(
   if (action.type === CONVERSATION_UNLOADED) {
     const nextConversations: Record<string, ComposerStateByConversationType> =
       {};
-    Object.keys(state.conversations).forEach(conversationId => {
-      if (conversationId === action.payload.conversationId) {
-        return;
-      }
-
-      nextConversations[conversationId] = state.conversations[conversationId];
-    });
+    for (const [conversationId, conversation] of Object.entries(
+      state.conversations
+    )) {
+      nextConversations[conversationId] = conversation;
+    }
 
     return {
       ...state,
diff --git a/ts/state/ducks/conversations.preload.ts b/ts/state/ducks/conversations.preload.ts
index bcff03d583..103edc75ba 100644
--- a/ts/state/ducks/conversations.preload.ts
+++ b/ts/state/ducks/conversations.preload.ts
@@ -1624,7 +1624,7 @@ async function getAvatarsAndUpdateConversation(
   const { conversationLookup } = conversations;
   const conversationAttrs = conversationLookup[conversationId];
   const avatars =
-    conversationAttrs.avatars || getAvatarData(conversation.attributes);
+    conversationAttrs?.avatars || getAvatarData(conversation.attributes);
 
   const nextAvatarId = getNextAvatarId(avatars);
   const nextAvatars = getNextAvatarsData(avatars, nextAvatarId);
@@ -3224,6 +3224,8 @@ function toggleSelectMessage(
         [toggledMessage, conversations.lastSelectedMessage],
         message => message
       );
+      strictAssert(after, 'Missing after');
+      strictAssert(before, 'Missing before');
 
       const betweenIds = await DataReader.getMessagesBetween(conversationId, {
         after: {
@@ -3738,6 +3740,7 @@ function revokePendingMembershipsFromGroupV2(
     }
 
     const [memberId] = memberIds;
+    strictAssert(memberId, 'Missing memberId');
 
     const pendingMember = window.ConversationController.get(memberId);
     if (!pendingMember) {
@@ -5700,9 +5703,9 @@ function maybeDropMessageIdsFromMessagesLookup(
   }
 
   const updatedMessagesLookup: Record<string, MessageWithUIFieldsType> = {};
-  for (const messageId of Object.keys(messagesLookup)) {
+  for (const [messageId, message] of Object.entries(messagesLookup)) {
     if (!messageIdsToRemove.has(messageId)) {
-      updatedMessagesLookup[messageId] = messagesLookup[messageId];
+      updatedMessagesLookup[messageId] = message;
     }
   }
 
@@ -6334,6 +6337,7 @@ export function reducer(
     }
 
     const conversationAttrs = state.conversationLookup[conversationId];
+    strictAssert(conversationAttrs, 'Missing conversationAttrs');
     const isGroupStoryReply = isGroup(conversationAttrs) && data.storyId;
     if (isGroupStoryReply) {
       return dropPreloadData(state);
@@ -6563,13 +6567,15 @@ export function reducer(
       const lastId = oldIds[oldIds.length - 1];
 
       if (oldest && oldest.id === firstId && firstId === id) {
-        const second = messagesLookup[oldIds[1]];
+        const secondId = oldIds[1];
+        const second = secondId && messagesLookup[secondId];
         oldest = second
           ? pick(second, ['id', 'received_at', 'sent_at'])
           : undefined;
       }
       if (newest && newest.id === lastId && lastId === id) {
-        const penultimate = messagesLookup[oldIds[oldIds.length - 2]];
+        const secondLastId = oldIds[oldIds.length - 2];
+        const penultimate = secondLastId && messagesLookup[secondLastId];
         newest = penultimate
           ? pick(penultimate, ['id', 'received_at', 'sent_at'])
           : undefined;
@@ -6708,7 +6714,11 @@ export function reducer(
       existingConversation.metrics;
 
     const lookup = fromPairs(
-      existingConversation.messageIds.map(id => [id, messagesLookup[id]])
+      existingConversation.messageIds.map(id => {
+        const message = messagesLookup[id];
+        strictAssert(message, 'Missing message');
+        return [id, message];
+      })
     );
     messages.forEach(message => {
       lookup[message.id] = message;
@@ -6724,10 +6734,10 @@ export function reducer(
     const first = sorted[0];
     const last = sorted[sorted.length - 1];
 
-    if (!newest) {
+    if (!newest && first != null) {
       newest = pick(first, ['id', 'received_at', 'sent_at']);
     }
-    if (!oldest) {
+    if (!oldest && last != null) {
       oldest = pick(last, ['id', 'received_at', 'sent_at']);
     }
 
@@ -6801,7 +6811,7 @@ export function reducer(
           ...existingConversation,
           messageIds,
           messageLoadingState: undefined,
-          scrollToMessageId: isJustSent ? last.id : undefined,
+          scrollToMessageId: isJustSent ? last?.id : undefined,
           metrics: {
             ...existingConversation.metrics,
             newest,
@@ -7372,8 +7382,7 @@ export function reducer(
       ...state,
     };
 
-    Object.keys(conversationLookup).forEach(id => {
-      const existing = conversationLookup[id];
+    for (const [id, existing] of Object.entries(conversationLookup)) {
       const added = {
         ...existing,
         conversationColor,
@@ -7391,7 +7400,7 @@ export function reducer(
           },
         }
       );
-    });
+    }
 
     return nextState;
   }
@@ -7431,11 +7440,9 @@ export function reducer(
       ...state,
     };
 
-    Object.keys(conversationLookup).forEach(id => {
-      const existing = conversationLookup[id];
-
+    for (const [id, existing] of Object.entries(conversationLookup)) {
       if (existing.customColorId !== colorId) {
-        return;
+        continue;
       }
 
       const changed = {
@@ -7455,7 +7462,7 @@ export function reducer(
           },
         }
       );
-    });
+    }
 
     return nextState;
   }
diff --git a/ts/state/ducks/lightbox.preload.ts b/ts/state/ducks/lightbox.preload.ts
index 7c6f516423..703a6fc386 100644
--- a/ts/state/ducks/lightbox.preload.ts
+++ b/ts/state/ducks/lightbox.preload.ts
@@ -404,9 +404,9 @@ function showLightbox(opts: {
         media,
         selectedIndex: index === -1 ? 0 : index,
         hasPrevMessage:
-          older.length > 0 && filterValidAttachments(older[0]).length > 0,
+          older[0] != null && filterValidAttachments(older[0]).length > 0,
         hasNextMessage:
-          newer.length > 0 && filterValidAttachments(newer[0]).length > 0,
+          newer[0] != null && filterValidAttachments(newer[0]).length > 0,
         playbackDisabled: false,
       },
     });
@@ -429,7 +429,7 @@ function showLightboxForAdjacentMessage(
   return async (dispatch, getState) => {
     const { lightbox } = getState();
 
-    if (!lightbox.isShowingLightbox || lightbox.media.length === 0) {
+    if (!lightbox.isShowingLightbox || lightbox.media[0] == null) {
       log.warn('showLightboxForAdjacentMessage: empty lightbox');
       return;
     }
@@ -502,8 +502,10 @@ function showLightboxForAdjacentMessage(
       showLightbox({
         attachment:
           direction === AdjacentMessageDirection.Previous
-            ? attachments[attachments.length - 1]
-            : attachments[0],
+            ? // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+              attachments[attachments.length - 1]!
+            : // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+              attachments[0]!,
         messageId: adjacent.id,
       })
     );
diff --git a/ts/state/ducks/mediaGallery.preload.ts b/ts/state/ducks/mediaGallery.preload.ts
index 1e619afdf4..a96bf4a6a4 100644
--- a/ts/state/ducks/mediaGallery.preload.ts
+++ b/ts/state/ducks/mediaGallery.preload.ts
@@ -660,7 +660,8 @@ export function reducer(
         ? [
             {
               type: 'link',
-              preview: message.preview[0],
+              // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+              preview: message.preview[0]!,
               message: _cleanMessage(message),
             },
           ]
@@ -675,7 +676,8 @@ export function reducer(
       newDocuments = newDocuments.concat(
         _cleanContact({
           type: 'contact',
-          contact: message.contact[0],
+          // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+          contact: message.contact[0]!,
           message: _cleanMessage(message),
         })
       );
diff --git a/ts/state/ducks/safetyNumber.preload.ts b/ts/state/ducks/safetyNumber.preload.ts
index dcce2b77af..47c9fbb839 100644
--- a/ts/state/ducks/safetyNumber.preload.ts
+++ b/ts/state/ducks/safetyNumber.preload.ts
@@ -17,6 +17,7 @@ import * as Errors from '../../types/errors.std.js';
 import type { StateType as RootStateType } from '../reducer.preload.js';
 import type { BoundActionCreatorsMapObject } from '../../hooks/useBoundActions.std.js';
 import { useBoundActions } from '../../hooks/useBoundActions.std.js';
+import { strictAssert } from '../../util/assert.std.js';
 
 const { omit } = lodash;
 
@@ -205,6 +206,7 @@ export function reducer(
     const { contact } = action.payload;
     const { id } = contact;
     const record = state.contacts[id];
+    strictAssert(record, 'Missing record');
     return {
       contacts: {
         ...state.contacts,
@@ -221,6 +223,7 @@ export function reducer(
     const { contact, ...restProps } = action.payload;
     const { id } = contact;
     const record = state.contacts[id];
+    strictAssert(record, 'Missing record');
     return {
       contacts: {
         ...state.contacts,
@@ -237,6 +240,7 @@ export function reducer(
     const { contact, safetyNumber } = action.payload;
     const { id } = contact;
     const record = state.contacts[id];
+    strictAssert(record, 'Missing record');
     return {
       contacts: {
         ...state.contacts,
diff --git a/ts/state/ducks/search.preload.ts b/ts/state/ducks/search.preload.ts
index 97c0313b03..83cabf58a3 100644
--- a/ts/state/ducks/search.preload.ts
+++ b/ts/state/ducks/search.preload.ts
@@ -624,10 +624,7 @@ async function queryConversationsAndContacts(
   // Split into two groups - active conversations and items just from address book
   let conversationIds: Array<string> = [];
   let contactIds: Array<string> = [];
-  const max = searchResults.length;
-  for (let i = 0; i < max; i += 1) {
-    const conversation = searchResults[i];
-
+  for (const conversation of searchResults) {
     if (conversation.type === 'direct' && !conversation.lastMessage) {
       contactIds.push(conversation.id);
     } else {
diff --git a/ts/state/ducks/stickers.preload.ts b/ts/state/ducks/stickers.preload.ts
index 200c15913f..de355e31af 100644
--- a/ts/state/ducks/stickers.preload.ts
+++ b/ts/state/ducks/stickers.preload.ts
@@ -27,6 +27,7 @@ import type { EraseStorageServiceStateAction } from './user.preload.js';
 import type { NoopActionType } from './noop.std.js';
 import type { BoundActionCreatorsMapObject } from '../../hooks/useBoundActions.std.js';
 import { useBoundActions } from '../../hooks/useBoundActions.std.js';
+import { strictAssert } from '../../util/assert.std.js';
 
 const { omit, reject } = lodash;
 
@@ -419,6 +420,7 @@ export function reducer(
   if (action.type === 'stickers/STICKER_ADDED') {
     const { payload } = action;
     const packToUpdate = state.packs[payload.packId];
+    strictAssert(packToUpdate, 'Missing packToUpdate');
 
     return {
       ...state,
@@ -438,6 +440,7 @@ export function reducer(
   if (action.type === 'stickers/STICKER_PACK_UPDATED') {
     const { payload } = action;
     const packToUpdate = state.packs[payload.packId];
+    strictAssert(packToUpdate, 'Missing packToUpdate');
 
     return {
       ...state,
@@ -480,7 +483,7 @@ export function reducer(
       packs: {
         ...packs,
         [packId]: {
-          ...packs[packId],
+          ...existingPack,
           status,
           installedAt,
         },
@@ -515,6 +518,7 @@ export function reducer(
       item => item.packId === packId && item.stickerId === stickerId
     );
     const pack = packs[packId];
+    strictAssert(pack, 'Missing pack');
     const sticker = pack.stickers[stickerId];
 
     return {
diff --git a/ts/state/ducks/stories.preload.ts b/ts/state/ducks/stories.preload.ts
index 265559302e..f5656fcdca 100644
--- a/ts/state/ducks/stories.preload.ts
+++ b/ts/state/ducks/stories.preload.ts
@@ -916,6 +916,7 @@ const viewUserStories: ViewUserStoriesActionCreatorType = ({
       });
 
     const story = storiesByConversationId[currentIndex];
+    strictAssert(story, 'Missing story');
     const state = getState();
 
     const hiddenConversationIds = new Set(getHideStoryConversationIds(state));
@@ -1081,6 +1082,7 @@ const viewStory: ViewStoryActionCreatorType = (
       const currentDistributionListIndex = myStories.findIndex(item => {
         for (let i = item.stories.length - 1; i >= 0; i -= 1) {
           const myStory = item.stories[i];
+          strictAssert(myStory, 'Missing myStory');
           if (myStory.messageId === storyId) {
             // [1] reversed
             currentStoryIndex = item.stories.length - 1 - i;
@@ -1107,37 +1109,51 @@ const viewStory: ViewStoryActionCreatorType = (
       let nextSentStoryIndex = -1;
       let nextNumStories = numStories;
 
+      const currentSentStoryContainer = myStories[currentDistributionListIndex];
+      strictAssert(
+        currentSentStoryContainer,
+        'Missing currentSentStoryContainer'
+      );
+
       // [2] reversed
-      const currentStories = myStories[currentDistributionListIndex].stories
+      const currentStories = currentSentStoryContainer.stories
         .slice()
         .reverse();
 
       if (viewDirection === StoryViewDirectionType.Next) {
         if (currentStoryIndex < currentStories.length - 1) {
           nextSentStoryIndex = currentStoryIndex + 1;
-          nextSentStoryId = currentStories[nextSentStoryIndex].messageId;
+          nextSentStoryId = currentStories[nextSentStoryIndex]?.messageId;
         } else if (currentDistributionListIndex < myStories.length - 1) {
           const nextSentStoryContainer =
             myStories[currentDistributionListIndex + 1];
+          strictAssert(
+            nextSentStoryContainer,
+            'Missing nextSentStoryContainer'
+          );
 
           nextNumStories = nextSentStoryContainer.stories.length;
           nextSentStoryIndex = 0;
           nextSentStoryId =
-            nextSentStoryContainer.stories[nextNumStories - 1].messageId;
+            nextSentStoryContainer.stories[nextNumStories - 1]?.messageId;
         }
       }
 
       if (viewDirection === StoryViewDirectionType.Previous) {
         if (currentStoryIndex > 0) {
           nextSentStoryIndex = currentStoryIndex - 1;
-          nextSentStoryId = currentStories[nextSentStoryIndex].messageId;
+          nextSentStoryId = currentStories[nextSentStoryIndex]?.messageId;
         } else if (currentDistributionListIndex > 0) {
           const nextSentStoryContainer =
             myStories[currentDistributionListIndex - 1];
+          strictAssert(
+            nextSentStoryContainer,
+            'Missing nextSentStoryContainer'
+          );
 
           nextNumStories = nextSentStoryContainer.stories.length;
           nextSentStoryIndex = nextNumStories - 1;
-          nextSentStoryId = nextSentStoryContainer.stories[0].messageId;
+          nextSentStoryId = nextSentStoryContainer.stories[0]?.messageId;
         }
       }
 
@@ -1169,6 +1185,7 @@ const viewStory: ViewStoryActionCreatorType = (
     ) {
       const nextIndex = currentIndex + 1;
       const nextStory = storiesByConversationId[nextIndex];
+      strictAssert(nextStory, 'Missing nextStory');
 
       dispatch({
         type: VIEW_STORY,
@@ -1187,6 +1204,7 @@ const viewStory: ViewStoryActionCreatorType = (
     if (viewDirection === StoryViewDirectionType.Previous && currentIndex > 0) {
       const nextIndex = currentIndex - 1;
       const nextStory = storiesByConversationId[nextIndex];
+      strictAssert(nextStory, 'Missing nextStory');
 
       dispatch({
         type: VIEW_STORY,
@@ -1245,15 +1263,17 @@ const viewStory: ViewStoryActionCreatorType = (
             onlyFromSelf: false,
           }
         );
+        const nextStory =
+          nextSelectedStoryData.storiesByConversationId[
+            nextSelectedStoryData.currentIndex
+          ];
+        strictAssert(nextStory, 'Missing nextStory');
 
         dispatch({
           type: VIEW_STORY,
           payload: {
             currentIndex: nextSelectedStoryData.currentIndex,
-            messageId:
-              nextSelectedStoryData.storiesByConversationId[
-                nextSelectedStoryData.currentIndex
-              ].messageId,
+            messageId: nextStory.messageId,
             numStories: nextSelectedStoryData.numStories,
             storyViewMode,
             unviewedStoryConversationIdsSorted,
@@ -1298,6 +1318,7 @@ const viewStory: ViewStoryActionCreatorType = (
       // Touch area for tapping right should be 80% of width of the screen
       const nextConversationStoryIndex = conversationStoryIndex + 1;
       const conversationStory = conversationStories[nextConversationStoryIndex];
+      strictAssert(conversationStory, 'Missing conversationStory');
 
       const nextSelectedStoryData = getSelectedStoryDataForConversationId(
         dispatch,
@@ -1308,11 +1329,14 @@ const viewStory: ViewStoryActionCreatorType = (
         }
       );
 
+      const nextStory = nextSelectedStoryData.storiesByConversationId[0];
+      strictAssert(nextStory, 'Missing nextStory');
+
       dispatch({
         type: VIEW_STORY,
         payload: {
           currentIndex: 0,
-          messageId: nextSelectedStoryData.storiesByConversationId[0].messageId,
+          messageId: nextStory.messageId,
           numStories: nextSelectedStoryData.numStories,
           storyViewMode,
           unviewedStoryConversationIdsSorted,
@@ -1336,6 +1360,7 @@ const viewStory: ViewStoryActionCreatorType = (
       // Touch area for tapping left should be 20% of width of the screen
       const nextConversationStoryIndex = conversationStoryIndex - 1;
       const conversationStory = conversationStories[nextConversationStoryIndex];
+      strictAssert(conversationStory, 'Missing conversationStory');
 
       const nextSelectedStoryData = getSelectedStoryDataForConversationId(
         dispatch,
@@ -1346,11 +1371,14 @@ const viewStory: ViewStoryActionCreatorType = (
         }
       );
 
+      const nextStory = nextSelectedStoryData.storiesByConversationId[0];
+      strictAssert(nextStory, 'Missing nextStory');
+
       dispatch({
         type: VIEW_STORY,
         payload: {
           currentIndex: 0,
-          messageId: nextSelectedStoryData.storiesByConversationId[0].messageId,
+          messageId: nextStory.messageId,
           numStories: nextSelectedStoryData.numStories,
           storyViewMode,
           unviewedStoryConversationIdsSorted,
@@ -1558,6 +1586,7 @@ export function reducer(
     );
     if (prevStoryIndex >= 0) {
       const prevStory = state.stories[prevStoryIndex];
+      strictAssert(prevStory, 'Missing prevStory');
 
       // Stories rarely need to change, here are the following exceptions...
 
@@ -1708,17 +1737,20 @@ export function reducer(
         story => story.messageId === replyState.messageId
       );
 
-      const stories =
-        storyIndex >= 0
-          ? replaceIndex(state.stories, storyIndex, {
-              ...state.stories[storyIndex],
-              hasReplies: true,
-              hasRepliesFromSelf:
-                state.stories[storyIndex].hasRepliesFromSelf ||
-                state.stories[storyIndex].conversationId ===
-                  action.payload.conversationId,
-            })
-          : state.stories;
+      let stories: ReadonlyArray<StoryDataType>;
+      if (storyIndex >= 0) {
+        const currentStory = state.stories[storyIndex];
+        strictAssert(currentStory, 'Missing currentStory');
+        stories = replaceIndex(state.stories, storyIndex, {
+          ...currentStory,
+          hasReplies: true,
+          hasRepliesFromSelf:
+            currentStory.hasRepliesFromSelf ||
+            currentStory.conversationId === action.payload.conversationId,
+        });
+      } else {
+        stories = state.stories;
+      }
 
       return {
         ...state,
@@ -1775,6 +1807,7 @@ export function reducer(
     }
 
     const existingStory = state.stories[storyIndex];
+    strictAssert(existingStory, 'Missing existingStory');
 
     return {
       ...state,
diff --git a/ts/state/ducks/storyDistributionLists.preload.ts b/ts/state/ducks/storyDistributionLists.preload.ts
index 1293c6274b..46a6f34df3 100644
--- a/ts/state/ducks/storyDistributionLists.preload.ts
+++ b/ts/state/ducks/storyDistributionLists.preload.ts
@@ -19,6 +19,7 @@ import { storageServiceUploadJob } from '../../services/storage.preload.js';
 import type { BoundActionCreatorsMapObject } from '../../hooks/useBoundActions.std.js';
 import { useBoundActions } from '../../hooks/useBoundActions.std.js';
 import { itemStorage } from '../../textsecure/Storage.preload.js';
+import { strictAssert } from '../../util/assert.std.js';
 
 const { omit } = lodash;
 
@@ -530,9 +531,11 @@ function replaceDistributionListData(
     return;
   }
 
+  const list = distributionLists[listIndex];
+  strictAssert(list, 'Missing list');
   return replaceIndex(distributionLists, listIndex, {
-    ...distributionLists[listIndex],
-    ...getNextDistributionListData(distributionLists[listIndex]),
+    ...list,
+    ...getNextDistributionListData(list),
   });
 }
 
@@ -551,6 +554,11 @@ export function reducer(
     );
     if (listIndex >= 0) {
       const existingDistributionList = state.distributionLists[listIndex];
+      strictAssert(
+        existingDistributionList,
+        'Missing existingDistributionList'
+      );
+
       const memberServiceIds = new Set<ServiceIdString>(
         existingDistributionList.memberServiceIds
       );
diff --git a/ts/state/selectors/callHistory.std.ts b/ts/state/selectors/callHistory.std.ts
index b2c3c0f928..e52d442779 100644
--- a/ts/state/selectors/callHistory.std.ts
+++ b/ts/state/selectors/callHistory.std.ts
@@ -46,9 +46,7 @@ export const getCallHistoryLatestCall = createSelector(
   callHistory => {
     let latestCall = null;
 
-    for (const callId of Object.keys(callHistory.callHistoryByCallId)) {
-      const call = callHistory.callHistoryByCallId[callId];
-
+    for (const call of Object.values(callHistory.callHistoryByCallId)) {
       // Skip unused call links
       if (
         call.type === CallType.Adhoc &&
diff --git a/ts/state/selectors/conversations.dom.ts b/ts/state/selectors/conversations.dom.ts
index 08d3607f9b..959d747c15 100644
--- a/ts/state/selectors/conversations.dom.ts
+++ b/ts/state/selectors/conversations.dom.ts
@@ -456,11 +456,7 @@ export const _getLeftPaneLists = ({
   const archivedConversations: Array<ConversationType> = [];
   const pinnedConversations: Array<ConversationType> = [];
 
-  const values = Object.values(conversationLookup);
-  const max = values.length;
-  for (let i = 0; i < max; i += 1) {
-    let conversation = values[i];
-
+  for (let conversation of Object.values(conversationLookup)) {
     if (
       isChatFoldersEnabled(window.SignalContext.getVersion()) &&
       !_shouldIncludeInChatFolder(
@@ -1180,7 +1176,8 @@ export const getCachedConversationMemberColorsSelector = createSelector(
 
             contactNameColors.set(
               conversation.id,
-              ContactNameColors[i % ContactNameColors.length]
+              // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+              ContactNameColors[i % ContactNameColors.length]!
             );
           });
 
@@ -1211,9 +1208,9 @@ export const getContactNameColorSelector = createSelector(
 );
 
 export const getContactNameColor = (
-  contactNameColors: Map<string, string>,
+  contactNameColors: Map<string, ContactNameColorType>,
   contactId: string | undefined
-): string => {
+): ContactNameColorType => {
   if (!contactId) {
     log.warn('No color generated for missing contactId');
     return ContactNameColors[0];
@@ -1460,10 +1457,17 @@ export const getConversationsStoppingSend = createSelector(
 
 export const getHideStoryConversationIds = createSelector(
   getConversationLookup,
-  (conversationLookup): Array<string> =>
-    Object.keys(conversationLookup).filter(
-      conversationId => conversationLookup[conversationId].hideStory
-    )
+  (conversationLookup): Array<string> => {
+    const result: Array<string> = [];
+    for (const [conversationId, conversation] of Object.entries(
+      conversationLookup
+    )) {
+      if (conversation.hideStory) {
+        result.push(conversationId);
+      }
+    }
+    return result;
+  }
 );
 
 export const getStoriesState = (state: StateType): StoriesStateType =>
@@ -1546,20 +1550,10 @@ export const getLastEditableMessageId = createSelector(
       return;
     }
 
-    for (let i = conversationMessages.messageIds.length - 1; i >= 0; i -= 1) {
-      const messageId = conversationMessages.messageIds[i];
+    return conversationMessages.messageIds.findLast(messageId => {
       const message = messagesLookup[messageId];
-
-      if (!message) {
-        continue;
-      }
-
-      if (isOutgoing(message)) {
-        return canEditMessage(message) ? message.id : undefined;
-      }
-    }
-
-    return undefined;
+      return message != null && isOutgoing(message) && canEditMessage(message);
+    });
   }
 );
 
diff --git a/ts/state/selectors/message.preload.ts b/ts/state/selectors/message.preload.ts
index 74a6f70de5..dce3096329 100644
--- a/ts/state/selectors/message.preload.ts
+++ b/ts/state/selectors/message.preload.ts
@@ -72,7 +72,10 @@ import {
   defaultBlurHash,
 } from '../../util/Attachment.std.js';
 import type { MessageAttachmentType } from '../../types/AttachmentDownload.std.js';
-import { type DefaultConversationColorType } from '../../types/Colors.std.js';
+import type {
+  ContactNameColorType,
+  DefaultConversationColorType,
+} from '../../types/Colors.std.js';
 import { ReadStatus } from '../../messages/MessageReadStatus.std.js';
 
 import type { CallingNotificationType } from '../../util/callingNotification.std.js';
@@ -212,7 +215,7 @@ export type GetPropsForBubbleOptions = Readonly<{
   callHistorySelector: CallHistorySelectorType;
   activeCall?: CallStateType;
   accountSelector: AccountSelectorType;
-  contactNameColors: Map<string, string>;
+  contactNameColors: Map<string, ContactNameColorType>;
   defaultConversationColor: DefaultConversationColorType;
 }>;
 
@@ -2115,7 +2118,7 @@ function getDeletedForEveryoneByAdmin(
   message: MessageWithUIFieldsType,
   options: {
     conversationSelector: GetConversationByIdType;
-    contactNameColors: Map<string, string>;
+    contactNameColors: Map<string, ContactNameColorType>;
     ourAci: AciString | undefined;
   }
 ): PropsData['deletedForEveryoneByAdmin'] {
@@ -2157,7 +2160,8 @@ export function getPropsForEmbeddedContact(
     return undefined;
   }
 
-  const firstContact = contacts[0];
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  const firstContact = contacts[0]!;
   const numbers = firstContact?.number;
   const firstNumber = numbers && numbers[0] ? numbers[0].value : undefined;
 
diff --git a/ts/state/selectors/stickers.std.ts b/ts/state/selectors/stickers.std.ts
index eca1e08bcf..5dc3352d5c 100644
--- a/ts/state/selectors/stickers.std.ts
+++ b/ts/state/selectors/stickers.std.ts
@@ -185,7 +185,7 @@ export const getBlessedStickerPacks = createSelector(
   ): Array<StickerPackType> => {
     return filterAndTransformPacks(
       packs,
-      pack => blessedPacks[pack.id] && pack.status !== 'installed',
+      pack => blessedPacks[pack.id] != null && pack.status !== 'installed',
       pack => pack.createdAt,
       blessedPacks
     );
diff --git a/ts/state/selectors/stories.preload.ts b/ts/state/selectors/stories.preload.ts
index 4e1a6fd4b9..0f801b3d18 100644
--- a/ts/state/selectors/stories.preload.ts
+++ b/ts/state/selectors/stories.preload.ts
@@ -113,15 +113,18 @@ function sortMyStories(storyA: MyStoryType, storyB: MyStoryType): number {
     return 1;
   }
 
-  if (!storyA.stories.length) {
+  const a = storyA.stories[0];
+  const b = storyB.stories[0];
+
+  if (a == null) {
     return 1;
   }
 
-  if (!storyB.stories.length) {
+  if (b == null) {
     return -1;
   }
 
-  return storyA.stories[0].timestamp > storyB.stories[0].timestamp ? -1 : 1;
+  return b.timestamp - a.timestamp;
 }
 
 function getAvatarData(
diff --git a/ts/state/selectors/timeline.preload.ts b/ts/state/selectors/timeline.preload.ts
index 26a260ca02..8b46a31bc4 100644
--- a/ts/state/selectors/timeline.preload.ts
+++ b/ts/state/selectors/timeline.preload.ts
@@ -41,11 +41,12 @@ import {
 import type { ConversationType } from '../ducks/conversations.preload.js';
 import { missingCaseError } from '../../util/missingCaseError.std.js';
 import { getGroupMemberships } from '../../util/getGroupMemberships.dom.js';
+import type { ContactNameColorType } from '../../types/Colors.std.js';
 
 const getTimelineItem = (
   state: StateType,
   messageId: string | undefined,
-  contactNameColors: Map<string, string>
+  contactNameColors: Map<string, ContactNameColorType>
 ): TimelineItemType | undefined => {
   if (messageId === undefined) {
     return undefined;
diff --git a/ts/state/smart/CallManager.preload.tsx b/ts/state/smart/CallManager.preload.tsx
index d17d10adce..67937d5343 100644
--- a/ts/state/smart/CallManager.preload.tsx
+++ b/ts/state/smart/CallManager.preload.tsx
@@ -194,8 +194,8 @@ const mapStateToActiveCallProp = (
         },
       } = call;
 
-      for (let i = 0; i < memberships.length; i += 1) {
-        const { aci } = memberships[i];
+      for (const membership of memberships) {
+        const { aci } = membership;
 
         const member = conversationSelector(aci);
         if (!member) {
@@ -206,9 +206,7 @@ const mapStateToActiveCallProp = (
         groupMembers.push(member);
       }
 
-      for (let i = 0; i < call.remoteParticipants.length; i += 1) {
-        const remoteParticipant = call.remoteParticipants[i];
-
+      for (const remoteParticipant of call.remoteParticipants) {
         const remoteConversation = conversationSelectorByAci(
           remoteParticipant.aci
         );
@@ -248,9 +246,7 @@ const mapStateToActiveCallProp = (
         }
       });
 
-      for (let i = 0; i < peekInfo.acis.length; i += 1) {
-        const peekedParticipantAci = peekInfo.acis[i];
-
+      for (const peekedParticipantAci of peekInfo.acis) {
         const peekedConversation =
           conversationSelectorByAci(peekedParticipantAci);
         if (!peekedConversation) {
@@ -261,9 +257,7 @@ const mapStateToActiveCallProp = (
         peekedParticipants.push(peekedConversation);
       }
 
-      for (let i = 0; i < peekInfo.pendingAcis.length; i += 1) {
-        const aci = peekInfo.pendingAcis[i];
-
+      for (const aci of peekInfo.pendingAcis) {
         // In call links, pending users may be unknown until they share profile keys.
         // conversationSelectorByAci should create conversations for new contacts.
         const pendingConversation = conversationSelectorByAci(aci);
diff --git a/ts/state/smart/ToastManager.preload.tsx b/ts/state/smart/ToastManager.preload.tsx
index 2e39729af3..c9c28180e4 100644
--- a/ts/state/smart/ToastManager.preload.tsx
+++ b/ts/state/smart/ToastManager.preload.tsx
@@ -104,7 +104,8 @@ export const SmartToastManager = memo(function SmartToastManager({
     };
   } else if (megaphones.length > 0) {
     megaphone = {
-      ...megaphones[0],
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      ...megaphones[0]!,
       type: MegaphoneType.Remote,
       onInteractWithMegaphone: interactWithMegaphone,
     };
diff --git a/ts/test-electron/Crypto_test.preload.ts b/ts/test-electron/Crypto_test.preload.ts
index 9276f2f5a9..61494f4d93 100644
--- a/ts/test-electron/Crypto_test.preload.ts
+++ b/ts/test-electron/Crypto_test.preload.ts
@@ -305,7 +305,8 @@ describe('Crypto', () => {
       const key = getRandomBytes(32);
 
       const encrypted = encryptSymmetric(key, plaintext);
-      encrypted[2] += 2;
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      encrypted[2]! += 2;
 
       try {
         decryptSymmetric(key, encrypted);
@@ -326,7 +327,8 @@ describe('Crypto', () => {
       const key = getRandomBytes(32);
 
       const encrypted = encryptSymmetric(key, plaintext);
-      encrypted[encrypted.length - 3] += 2;
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      encrypted[encrypted.length - 3]! += 2;
 
       try {
         decryptSymmetric(key, encrypted);
@@ -347,7 +349,8 @@ describe('Crypto', () => {
       const key = getRandomBytes(32);
 
       const encrypted = encryptSymmetric(key, plaintext);
-      encrypted[35] += 9;
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      encrypted[35]! += 9;
 
       try {
         decryptSymmetric(key, encrypted);
@@ -751,7 +754,8 @@ describe('Crypto', () => {
             isNumber(macLength) &&
             encryptedAttachment.incrementalMac
           ) {
-            encryptedAttachment.incrementalMac[macLength / 2] += 1;
+            // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+            encryptedAttachment.incrementalMac[macLength / 2]! += 1;
           }
 
           // Decrypt it via plaintextHash first
diff --git a/ts/test-electron/MessageReceipts_test.preload.ts b/ts/test-electron/MessageReceipts_test.preload.ts
index 613a1bba91..580d13d126 100644
--- a/ts/test-electron/MessageReceipts_test.preload.ts
+++ b/ts/test-electron/MessageReceipts_test.preload.ts
@@ -106,10 +106,10 @@ describe('MessageReceipts', () => {
     const messageFromDatabase = await DataReader.getMessageById(id);
     const savedSendState = messageFromDatabase?.sendStateByConversationId;
 
-    assert.equal(savedSendState?.aaaa.status, SendStatus.Read, 'aaaa');
-    assert.equal(savedSendState?.bbbb.status, SendStatus.Delivered, 'bbbb');
-    assert.equal(savedSendState?.cccc.status, SendStatus.Read, 'cccc');
-    assert.equal(savedSendState?.dddd.status, SendStatus.Sent, 'dddd');
+    assert.equal(savedSendState?.aaaa?.status, SendStatus.Read, 'aaaa');
+    assert.equal(savedSendState?.bbbb?.status, SendStatus.Delivered, 'bbbb');
+    assert.equal(savedSendState?.cccc?.status, SendStatus.Read, 'cccc');
+    assert.equal(savedSendState?.dddd?.status, SendStatus.Sent, 'dddd');
   });
 
   it('updates sendStateByConversationId for edits', async () => {
@@ -221,34 +221,34 @@ describe('MessageReceipts', () => {
 
     assert.deepEqual(
       rootSendState,
-      messageFromDatabase?.editHistory?.[0].sendStateByConversationId,
+      messageFromDatabase?.editHistory?.[0]?.sendStateByConversationId,
       'edit history version should match root version'
     );
-    assert.equal(rootSendState?.aaaa.status, SendStatus.Delivered, 'aaaa');
-    assert.equal(rootSendState?.bbbb.status, SendStatus.Read, 'bbbb');
-    assert.equal(rootSendState?.cccc.status, SendStatus.Read, 'cccc');
-    assert.equal(rootSendState?.dddd.status, SendStatus.Sent, 'dddd');
+    assert.equal(rootSendState?.aaaa?.status, SendStatus.Delivered, 'aaaa');
+    assert.equal(rootSendState?.bbbb?.status, SendStatus.Read, 'bbbb');
+    assert.equal(rootSendState?.cccc?.status, SendStatus.Read, 'cccc');
+    assert.equal(rootSendState?.dddd?.status, SendStatus.Sent, 'dddd');
 
     const originalMessageSendState =
-      messageFromDatabase?.editHistory?.[1].sendStateByConversationId;
+      messageFromDatabase?.editHistory?.[1]?.sendStateByConversationId;
 
     assert.equal(
-      originalMessageSendState?.aaaa.status,
+      originalMessageSendState?.aaaa?.status,
       SendStatus.Read,
       'original-aaaa'
     );
     assert.equal(
-      originalMessageSendState?.bbbb.status,
+      originalMessageSendState?.bbbb?.status,
       SendStatus.Delivered,
       'original-bbbb'
     );
     assert.equal(
-      originalMessageSendState?.cccc.status,
+      originalMessageSendState?.cccc?.status,
       SendStatus.Read,
       'original-cccc'
     );
     assert.equal(
-      originalMessageSendState?.dddd.status,
+      originalMessageSendState?.dddd?.status,
       SendStatus.Sent,
       'original-dddd'
     );
diff --git a/ts/test-electron/SignalProtocolStore_test.preload.ts b/ts/test-electron/SignalProtocolStore_test.preload.ts
index 3494edf479..d2fcdc76d0 100644
--- a/ts/test-electron/SignalProtocolStore_test.preload.ts
+++ b/ts/test-electron/SignalProtocolStore_test.preload.ts
@@ -1527,9 +1527,9 @@ describe('SignalProtocolStore', () => {
 
       // they are in the proper order because the collection comparator is
       // 'receivedAtCounter'
-      assert.strictEqual(Bytes.toString(items[0].content || ZERO), 'first');
-      assert.strictEqual(Bytes.toString(items[1].content || ZERO), 'second');
-      assert.strictEqual(Bytes.toString(items[2].content || ZERO), 'third');
+      assert.strictEqual(Bytes.toString(items[0]?.content || ZERO), 'first');
+      assert.strictEqual(Bytes.toString(items[1]?.content || ZERO), 'second');
+      assert.strictEqual(Bytes.toString(items[2]?.content || ZERO), 'third');
     });
 
     it('removeUnprocessed successfully deletes item', async () => {
diff --git a/ts/test-electron/backup/helpers.preload.ts b/ts/test-electron/backup/helpers.preload.ts
index 94890c95fd..f02cfbe586 100644
--- a/ts/test-electron/backup/helpers.preload.ts
+++ b/ts/test-electron/backup/helpers.preload.ts
@@ -267,7 +267,8 @@ export async function asymmetricRoundtripHarness(
     if (options.comparator) {
       assert.strictEqual(actual.length, expected.length);
       for (let i = 0; i < actual.length; i += 1) {
-        options.comparator(expected[i], actual[i]);
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        options.comparator(expected[i]!, actual[i]!);
       }
     } else {
       assert.deepEqual(actual, expected);
diff --git a/ts/test-electron/linkPreviews/linkPreviewFetch_test.preload.ts b/ts/test-electron/linkPreviews/linkPreviewFetch_test.preload.ts
index b6f4802aa7..7d69d292cc 100644
--- a/ts/test-electron/linkPreviews/linkPreviewFetch_test.preload.ts
+++ b/ts/test-electron/linkPreviews/linkPreviewFetch_test.preload.ts
@@ -157,8 +157,11 @@ describe('link preview fetching', () => {
           tag: '<link rel="icon" href="https://example.com/icon.jpg">',
           expectedHref: 'https://example.com/icon.jpg',
         },
-      ];
-      for (let i = orderedImageHrefSources.length - 1; i >= 0; i -= 1) {
+      ] as const;
+      for (const [i, orderedImageHrefSource] of orderedImageHrefSources
+        .entries()
+        .toArray()
+        .toReversed()) {
         const imageTags = orderedImageHrefSources
           .slice(i)
           .map(({ tag }) => tag)
@@ -180,11 +183,7 @@ describe('link preview fetching', () => {
           'https://example.com',
           new AbortController().signal
         );
-        assert.propertyVal(
-          val,
-          'image',
-          orderedImageHrefSources[i].expectedHref
-        );
+        assert.propertyVal(val, 'image', orderedImageHrefSource.expectedHref);
       }
     });
 
diff --git a/ts/test-electron/models/conversations_test.preload.ts b/ts/test-electron/models/conversations_test.preload.ts
index e273f41fcc..b1419955d2 100644
--- a/ts/test-electron/models/conversations_test.preload.ts
+++ b/ts/test-electron/models/conversations_test.preload.ts
@@ -163,8 +163,8 @@ describe('Conversations', () => {
       ]
     );
 
-    assert.equal(resultWithImage.contentType, 'image/png');
-    assert.equal(resultWithImage.fileName, null);
+    assert.equal(resultWithImage?.contentType, 'image/png');
+    assert.equal(resultWithImage?.fileName, null);
   });
 
   describe('updateExpirationTimer', () => {
diff --git a/ts/test-electron/models/messages_test.preload.ts b/ts/test-electron/models/messages_test.preload.ts
index 18df7d81a1..10723e718f 100644
--- a/ts/test-electron/models/messages_test.preload.ts
+++ b/ts/test-electron/models/messages_test.preload.ts
@@ -184,7 +184,7 @@ describe('Message', () => {
 
       const errors = message.get('errors') || [];
       assert.lengthOf(errors, 1);
-      assert.strictEqual(errors[0].message, 'foo bar');
+      assert.strictEqual(errors[0]?.message, 'foo bar');
     });
 
     it('saves errors from promise rejections with objects', async () => {
@@ -201,7 +201,7 @@ describe('Message', () => {
 
       const errors = message.get('errors') || [];
       assert.lengthOf(errors, 1);
-      assert.strictEqual(errors[0].message, 'baz qux');
+      assert.strictEqual(errors[0]?.message, 'baz qux');
     });
   });
 
diff --git a/ts/test-electron/quill/emoji/completion_test.dom.tsx b/ts/test-electron/quill/emoji/completion_test.dom.tsx
index a25e4f50a3..bdfff0c016 100644
--- a/ts/test-electron/quill/emoji/completion_test.dom.tsx
+++ b/ts/test-electron/quill/emoji/completion_test.dom.tsx
@@ -252,7 +252,10 @@ describe('emojiCompletion', () => {
         });
 
         it('inserts the emoji at the current cursor position', () => {
-          const [{ emojiParentKey, index, range }] = insertEmojiStub.args[0];
+          const firstArgs = insertEmojiStub.args[0];
+          assert.exists(firstArgs);
+
+          const [{ emojiParentKey, index, range }] = firstArgs;
 
           assert.equal(emojiParentKey, PARENT_KEYS.SMILE);
           assert.equal(index, 0);
@@ -281,7 +284,10 @@ describe('emojiCompletion', () => {
         });
 
         it('inserts the emoji at the current cursor position', () => {
-          const [{ emojiParentKey, index, range }] = insertEmojiStub.args[0];
+          const firstArgs = insertEmojiStub.args[0];
+          assert.exists(firstArgs);
+
+          const [{ emojiParentKey, index, range }] = firstArgs;
 
           assert.equal(emojiParentKey, PARENT_KEYS.SMILE);
           assert.equal(index, 7);
@@ -341,7 +347,10 @@ describe('emojiCompletion', () => {
         });
 
         it('inserts the emoji at the current cursor position', () => {
-          const [{ emojiParentKey, index, range }] = insertEmojiStub.args[0];
+          const firstArgs = insertEmojiStub.args[0];
+          assert.exists(firstArgs);
+
+          const [{ emojiParentKey, index, range }] = firstArgs;
 
           assert.equal(emojiParentKey, PARENT_KEYS.SMILE);
           assert.equal(index, 0);
@@ -390,7 +399,10 @@ describe('emojiCompletion', () => {
         });
 
         it('inserts the emoji at the current cursor position', () => {
-          const [{ emojiParentKey, index, range }] = insertEmojiStub.args[0];
+          const firstArgs = insertEmojiStub.args[0];
+          assert.exists(firstArgs);
+
+          const [{ emojiParentKey, index, range }] = firstArgs;
 
           assert.equal(emojiParentKey, PARENT_KEYS.SMILE);
           assert.equal(index, 0);
@@ -435,8 +447,10 @@ describe('emojiCompletion', () => {
       });
 
       it('inserts the currently selected emoji at the current cursor position', () => {
-        const [{ emojiParentKey, index: insertIndex, range }] =
-          insertEmojiStub.args[0];
+        const firstArgs = insertEmojiStub.args[0];
+        assert.exists(firstArgs);
+
+        const [{ emojiParentKey, index: insertIndex, range }] = firstArgs;
 
         assert.equal(emojiParentKey, PARENT_KEYS.SMILE_CAT);
         assert.equal(insertIndex, 0);
diff --git a/ts/test-electron/quill/mentions/matchers_test.std.ts b/ts/test-electron/quill/mentions/matchers_test.std.ts
index b37e678b3c..a2366967ad 100644
--- a/ts/test-electron/quill/mentions/matchers_test.std.ts
+++ b/ts/test-electron/quill/mentions/matchers_test.std.ts
@@ -109,6 +109,7 @@ describe('matchMention', () => {
     assert.isNotEmpty(ops);
 
     const [op] = ops;
+    assert.exists(op);
     const { insert, attributes } = op;
 
     if (isMention(insert)) {
@@ -138,6 +139,7 @@ describe('matchMention', () => {
     assert.isNotEmpty(ops);
 
     const [op] = ops;
+    assert.exists(op);
     const { insert } = op;
 
     if (isMention(insert)) {
@@ -165,6 +167,7 @@ describe('matchMention', () => {
     assert.isNotEmpty(ops);
 
     const [op] = ops;
+    assert.exists(op);
     const { insert } = op;
 
     if (isMention(insert)) {
@@ -189,6 +192,7 @@ describe('matchMention', () => {
     assert.isNotEmpty(ops);
 
     const [op] = ops;
+    assert.exists(op);
     const { insert } = op;
 
     if (isMention(insert)) {
diff --git a/ts/test-electron/services/AttachmentBackupManager_test.preload.ts b/ts/test-electron/services/AttachmentBackupManager_test.preload.ts
index 944fe0f00c..1cc4a72b5b 100644
--- a/ts/test-electron/services/AttachmentBackupManager_test.preload.ts
+++ b/ts/test-electron/services/AttachmentBackupManager_test.preload.ts
@@ -175,6 +175,15 @@ describe('AttachmentBackupManager/JobManager', function attachmentBackupManager(
     await itemStorage.fetch();
   });
 
+  function assertAt<T>(array: Array<T>, index: number): T {
+    assert.ok(
+      index >= 0 && index < array.length,
+      `index out of bounds: ${index}`
+    );
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    return array[index]!;
+  }
+
   async function addJobs(
     num: number,
     overrides: Partial<StandardAttachmentBackupJobType['data']> = {}
@@ -240,37 +249,47 @@ describe('AttachmentBackupManager/JobManager', function attachmentBackupManager(
     assert.strictEqual(allJobs.length, 10, 'initial setup');
 
     await backupManager?.start();
-    await waitForJobToBeStarted(jobs[2]);
+    await waitForJobToBeStarted(assertAt(jobs, 2));
 
     assert.strictEqual(runJob.callCount, 3);
-    assertRunJobCalledWith([jobs[4], jobs[3], jobs[2]]);
+    assertRunJobCalledWith([
+      assertAt(jobs, 4),
+      assertAt(jobs, 3),
+      assertAt(jobs, 2),
+    ]);
 
-    await waitForJobToBeStarted(jobs[0]);
+    await waitForJobToBeStarted(assertAt(jobs, 0));
     assert.strictEqual(runJob.callCount, 5, 'first calls');
-    assertRunJobCalledWith([jobs[4], jobs[3], jobs[2], jobs[1], jobs[0]]);
+    assertRunJobCalledWith([
+      assertAt(jobs, 4),
+      assertAt(jobs, 3),
+      assertAt(jobs, 2),
+      assertAt(jobs, 1),
+      assertAt(jobs, 0),
+    ]);
 
-    await waitForJobToBeCompleted(thumbnailJobs[0]);
+    await waitForJobToBeCompleted(assertAt(thumbnailJobs, 0));
     assert.strictEqual(runJob.callCount, 10, 'all calls');
 
     assertRunJobCalledWith([
-      jobs[4],
-      jobs[3],
-      jobs[2],
-      jobs[1],
-      jobs[0],
-      thumbnailJobs[4],
-      thumbnailJobs[3],
-      thumbnailJobs[2],
-      thumbnailJobs[1],
-      thumbnailJobs[0],
+      assertAt(jobs, 4),
+      assertAt(jobs, 3),
+      assertAt(jobs, 2),
+      assertAt(jobs, 1),
+      assertAt(jobs, 0),
+      assertAt(thumbnailJobs, 4),
+      assertAt(thumbnailJobs, 3),
+      assertAt(thumbnailJobs, 2),
+      assertAt(thumbnailJobs, 1),
+      assertAt(thumbnailJobs, 0),
     ]);
     assert.strictEqual((await getAllSavedJobs()).length, 0);
   });
 
   it('with transitCdnInfo, will copy to backup tier', async () => {
-    const [job] = await addJobs(1);
+    const jobs = await addJobs(1);
     await backupManager?.start();
-    await waitForJobToBeCompleted(job);
+    await waitForJobToBeCompleted(assertAt(jobs, 0));
     assert.strictEqual(backupMediaBatch.callCount, 1);
     assert.strictEqual(encryptAndUploadAttachment.callCount, 0);
 
@@ -295,9 +314,9 @@ describe('AttachmentBackupManager/JobManager', function attachmentBackupManager(
       })
     );
 
-    const [job] = await addJobs(1);
+    const jobs = await addJobs(1);
     await backupManager?.start();
-    await waitForJobToBeCompleted(job);
+    await waitForJobToBeCompleted(assertAt(jobs, 0));
     assert.strictEqual(encryptAndUploadAttachment.callCount, 1);
     assert.strictEqual(backupMediaBatch.callCount, 2);
 
@@ -315,10 +334,10 @@ describe('AttachmentBackupManager/JobManager', function attachmentBackupManager(
   });
 
   it('without transitCdnInfo, will upload then copy', async () => {
-    const [job] = await addJobs(1, { transitCdnInfo: undefined });
+    const jobs = await addJobs(1, { transitCdnInfo: undefined });
 
     await backupManager?.start();
-    await waitForJobToBeCompleted(job);
+    await waitForJobToBeCompleted(assertAt(jobs, 0));
 
     assert.strictEqual(backupMediaBatch.callCount, 1);
     assert.strictEqual(encryptAndUploadAttachment.callCount, 1);
@@ -329,13 +348,13 @@ describe('AttachmentBackupManager/JobManager', function attachmentBackupManager(
   });
 
   it('without transitCdnInfo, will permanently remove job if file not found at path', async () => {
-    const [job] = await addJobs(1, {
+    const jobs = await addJobs(1, {
       transitCdnInfo: undefined,
       path: 'nothing/here',
     });
 
     await backupManager?.start();
-    await waitForJobToBeCompleted(job);
+    await waitForJobToBeCompleted(assertAt(jobs, 0));
 
     assert.strictEqual(backupMediaBatch.callCount, 0);
     assert.strictEqual(encryptAndUploadAttachment.callCount, 0);
@@ -355,10 +374,14 @@ describe('AttachmentBackupManager/JobManager', function attachmentBackupManager(
       })
     );
     await backupManager?.start();
-    await waitForJobToBeStarted(jobs[2]);
+    await waitForJobToBeStarted(assertAt(jobs, 2));
 
     assert.strictEqual(runJob.callCount, 3);
-    assertRunJobCalledWith([jobs[4], jobs[3], jobs[2]]);
+    assertRunJobCalledWith([
+      assertAt(jobs, 4),
+      assertAt(jobs, 3),
+      assertAt(jobs, 2),
+    ]);
 
     // no jobs have occurred
     await clock.tickAsync(50000);
@@ -370,17 +393,17 @@ describe('AttachmentBackupManager/JobManager', function attachmentBackupManager(
     });
 
     await clock.tickAsync(100000);
-    await waitForJobToBeStarted(jobs[0]);
+    await waitForJobToBeStarted(assertAt(jobs, 0));
     assert.strictEqual(runJob.callCount, 8);
     assertRunJobCalledWith([
-      jobs[4],
-      jobs[3],
-      jobs[2],
-      jobs[4],
-      jobs[3],
-      jobs[2],
-      jobs[1],
-      jobs[0],
+      assertAt(jobs, 4),
+      assertAt(jobs, 3),
+      assertAt(jobs, 2),
+      assertAt(jobs, 4),
+      assertAt(jobs, 3),
+      assertAt(jobs, 2),
+      assertAt(jobs, 1),
+      assertAt(jobs, 0),
     ]);
   });
 
diff --git a/ts/test-electron/services/AttachmentDownloadManager_test.preload.ts b/ts/test-electron/services/AttachmentDownloadManager_test.preload.ts
index bd3b6e46b8..bc9b3d4062 100644
--- a/ts/test-electron/services/AttachmentDownloadManager_test.preload.ts
+++ b/ts/test-electron/services/AttachmentDownloadManager_test.preload.ts
@@ -180,6 +180,15 @@ describe('AttachmentDownloadManager', () => {
     await itemStorage.fetch();
   });
 
+  function assertAt<T>(array: ReadonlyArray<T>, index: number): T {
+    assert.ok(
+      index >= 0 && index < array.length,
+      `index out of bounds: ${index}`
+    );
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    return array[index]!;
+  }
+
   async function addJob(
     job: AttachmentDownloadJobType,
     urgency: AttachmentDownloadUrgency
@@ -306,14 +315,24 @@ describe('AttachmentDownloadManager', () => {
     );
 
     await downloadManager?.start();
-    await waitForJobToBeStarted(jobs[2]);
+    await waitForJobToBeStarted(assertAt(jobs, 2));
 
     assert.strictEqual(runJob.callCount, 3);
-    assertRunJobCalledWith([jobs[4], jobs[3], jobs[2]]);
+    assertRunJobCalledWith([
+      assertAt(jobs, 4),
+      assertAt(jobs, 3),
+      assertAt(jobs, 2),
+    ]);
 
-    await waitForJobToBeStarted(jobs[0]);
+    await waitForJobToBeStarted(assertAt(jobs, 0));
     assert.strictEqual(runJob.callCount, 5);
-    assertRunJobCalledWith([jobs[4], jobs[3], jobs[2], jobs[1], jobs[0]]);
+    assertRunJobCalledWith([
+      assertAt(jobs, 4),
+      assertAt(jobs, 3),
+      assertAt(jobs, 2),
+      assertAt(jobs, 1),
+      assertAt(jobs, 0),
+    ]);
   });
 
   it('runs a job immediately if urgency is IMMEDIATE', async () => {
@@ -330,18 +349,23 @@ describe('AttachmentDownloadManager', () => {
     await waitForJobToBeStarted(urgentJobForOldMessage);
 
     assert.strictEqual(runJob.callCount, 4);
-    assertRunJobCalledWith([jobs[5], jobs[4], jobs[3], urgentJobForOldMessage]);
+    assertRunJobCalledWith([
+      assertAt(jobs, 5),
+      assertAt(jobs, 4),
+      assertAt(jobs, 3),
+      urgentJobForOldMessage,
+    ]);
 
-    await waitForJobToBeStarted(jobs[0]);
+    await waitForJobToBeStarted(assertAt(jobs, 0));
     assert.strictEqual(runJob.callCount, 7);
     assertRunJobCalledWith([
-      jobs[5],
-      jobs[4],
-      jobs[3],
+      assertAt(jobs, 5),
+      assertAt(jobs, 4),
+      assertAt(jobs, 3),
       urgentJobForOldMessage,
-      jobs[2],
-      jobs[1],
-      jobs[0],
+      assertAt(jobs, 2),
+      assertAt(jobs, 1),
+      assertAt(jobs, 0),
     ]);
   });
 
@@ -352,13 +376,23 @@ describe('AttachmentDownloadManager', () => {
 
     await downloadManager?.start();
 
-    await waitForJobToBeStarted(jobs[4]);
+    await waitForJobToBeStarted(assertAt(jobs, 4));
     assert.strictEqual(runJob.callCount, 3);
-    assertRunJobCalledWith([jobs[0], jobs[1], jobs[4]]);
+    assertRunJobCalledWith([
+      assertAt(jobs, 0),
+      assertAt(jobs, 1),
+      assertAt(jobs, 4),
+    ]);
 
-    await waitForJobToBeStarted(jobs[2]);
+    await waitForJobToBeStarted(assertAt(jobs, 2));
     assert.strictEqual(runJob.callCount, 5);
-    assertRunJobCalledWith([jobs[0], jobs[1], jobs[4], jobs[3], jobs[2]]);
+    assertRunJobCalledWith([
+      assertAt(jobs, 0),
+      assertAt(jobs, 1),
+      assertAt(jobs, 4),
+      assertAt(jobs, 3),
+      assertAt(jobs, 2),
+    ]);
   });
 
   it("does not start a job if we're in a call", async () => {
@@ -373,7 +407,7 @@ describe('AttachmentDownloadManager', () => {
     isInCall.callsFake(() => false);
 
     await advanceTime(2 * MINUTE);
-    await waitForJobToBeStarted(jobs[0]);
+    await waitForJobToBeStarted(assertAt(jobs, 0));
     assert.strictEqual(runJob.callCount, 5);
   });
 
@@ -382,12 +416,12 @@ describe('AttachmentDownloadManager', () => {
       source: AttachmentDownloadSource.BACKUP_IMPORT_WITH_MEDIA,
     }));
 
-    const jobAttempts = getPromisesForAttempts(jobs[0], 2);
+    const jobAttempts = getPromisesForAttempts(assertAt(jobs, 0), 2);
 
     statfs.callsFake(() => Promise.resolve({ bavail: 0, bsize: 8 }));
 
     await downloadManager?.start();
-    await jobAttempts[0].completed;
+    await assertAt(jobAttempts, 0).completed;
 
     assert.strictEqual(runJob.callCount, 0);
     assert.strictEqual(onLowDiskSpaceBackupImport.callCount, 1);
@@ -400,18 +434,18 @@ describe('AttachmentDownloadManager', () => {
 
     await advanceTime(2 * MINUTE);
     assert.strictEqual(runJob.callCount, 1);
-    await jobAttempts[1].completed;
+    await assertAt(jobAttempts, 1).completed;
   });
 
   it('handles retries for failed', async () => {
     const jobs = await addJobs(2);
-    const job0Attempts = getPromisesForAttempts(jobs[0], 1);
-    const job1Attempts = getPromisesForAttempts(jobs[1], 5);
+    const job0Attempts = getPromisesForAttempts(assertAt(jobs, 0), 1);
+    const job1Attempts = getPromisesForAttempts(assertAt(jobs, 1), 5);
 
     runJob.callsFake(async ({ job }: { job: AttachmentDownloadJobType }) => {
       return new Promise<{ status: 'finished' | 'retry' }>(resolve => {
         Promise.resolve().then(() => {
-          if (job.messageId === jobs[0].messageId) {
+          if (job.messageId === assertAt(jobs, 0).messageId) {
             resolve({ status: 'finished' });
           } else {
             resolve({ status: 'retry' });
@@ -422,12 +456,16 @@ describe('AttachmentDownloadManager', () => {
 
     await downloadManager?.start();
 
-    await job0Attempts[0].completed;
+    await assertAt(job0Attempts, 0).completed;
     assert.strictEqual(runJob.callCount, 2);
-    assertRunJobCalledWith([jobs[1], jobs[0]]);
+    assertRunJobCalledWith([assertAt(jobs, 1), assertAt(jobs, 0)]);
 
-    const retriedJob = await DataReader._getAttachmentDownloadJob(jobs[1]);
-    const finishedJob = await DataReader._getAttachmentDownloadJob(jobs[0]);
+    const retriedJob = await DataReader._getAttachmentDownloadJob(
+      assertAt(jobs, 1)
+    );
+    const finishedJob = await DataReader._getAttachmentDownloadJob(
+      assertAt(jobs, 0)
+    );
 
     assert.isUndefined(finishedJob);
     assert.strictEqual(retriedJob?.attempts, 1);
@@ -435,32 +473,34 @@ describe('AttachmentDownloadManager', () => {
 
     await advanceTime(MINUTE);
 
-    await job1Attempts[1].completed;
+    await assertAt(job1Attempts, 1).completed;
     assert.strictEqual(runJob.callCount, 3);
     await advanceTime(2 * MINUTE);
 
-    await job1Attempts[2].completed;
+    await assertAt(job1Attempts, 2).completed;
     assert.strictEqual(runJob.callCount, 4);
 
     await advanceTime(4 * MINUTE);
-    await job1Attempts[3].completed;
+    await assertAt(job1Attempts, 3).completed;
     assert.strictEqual(runJob.callCount, 5);
 
     await advanceTime(8 * MINUTE);
-    await job1Attempts[4].completed;
+    await assertAt(job1Attempts, 4).completed;
 
     assert.strictEqual(runJob.callCount, 6);
     assertRunJobCalledWith([
-      jobs[1],
-      jobs[0],
-      jobs[1],
-      jobs[1],
-      jobs[1],
-      jobs[1],
+      assertAt(jobs, 1),
+      assertAt(jobs, 0),
+      assertAt(jobs, 1),
+      assertAt(jobs, 1),
+      assertAt(jobs, 1),
+      assertAt(jobs, 1),
     ]);
 
     // Ensure it's been removed after completed
-    assert.isUndefined(await DataReader._getAttachmentDownloadJob(jobs[1]));
+    assert.isUndefined(
+      await DataReader._getAttachmentDownloadJob(assertAt(jobs, 1))
+    );
   });
 
   it('will reset attempts if addJob is called again', async () => {
@@ -473,47 +513,49 @@ describe('AttachmentDownloadManager', () => {
       });
     });
 
-    let attempts = getPromisesForAttempts(jobs[0], 4);
+    let attempts = getPromisesForAttempts(assertAt(jobs, 0), 4);
     await downloadManager?.start();
 
-    await attempts[0].completed;
+    await assertAt(attempts, 0).completed;
     assert.strictEqual(runJob.callCount, 1);
 
     await advanceTime(1 * MINUTE);
-    await attempts[1].completed;
+    await assertAt(attempts, 1).completed;
     assert.strictEqual(runJob.callCount, 2);
 
     await advanceTime(5 * MINUTE);
-    await attempts[2].completed;
+    await assertAt(attempts, 2).completed;
     assert.strictEqual(runJob.callCount, 3);
 
     // add the same job again and it should retry ASAP and reset attempts
-    attempts = getPromisesForAttempts(jobs[0], 5);
+    attempts = getPromisesForAttempts(assertAt(jobs, 0), 5);
     await downloadManager?.addJob({
-      ...jobs[0],
-      isManualDownload: Boolean(jobs[0].isManualDownload),
+      ...assertAt(jobs, 0),
+      isManualDownload: Boolean(assertAt(jobs, 0).isManualDownload),
     });
-    await attempts[0].completed;
+    await assertAt(attempts, 0).completed;
     assert.strictEqual(runJob.callCount, 4);
 
     await advanceTime(1 * MINUTE);
-    await attempts[1].completed;
+    await assertAt(attempts, 1).completed;
     assert.strictEqual(runJob.callCount, 5);
 
     await advanceTime(2 * MINUTE);
-    await attempts[2].completed;
+    await assertAt(attempts, 2).completed;
     assert.strictEqual(runJob.callCount, 6);
 
     await advanceTime(4 * MINUTE);
-    await attempts[3].completed;
+    await assertAt(attempts, 3).completed;
     assert.strictEqual(runJob.callCount, 7);
 
     await advanceTime(8 * MINUTE);
-    await attempts[4].completed;
+    await assertAt(attempts, 4).completed;
     assert.strictEqual(runJob.callCount, 8);
 
     // Ensure it's been removed
-    assert.isUndefined(await DataReader._getAttachmentDownloadJob(jobs[0]));
+    assert.isUndefined(
+      await DataReader._getAttachmentDownloadJob(assertAt(jobs, 0))
+    );
   });
 
   it('only selects backup_import jobs if the mediaDownload is not paused', async () => {
@@ -528,21 +570,29 @@ describe('AttachmentDownloadManager', () => {
     // make one of the backup job messages visible to test that code path as well
     downloadManager?.updateVisibleTimelineMessages(['message-0', 'message-1']);
     await downloadManager?.start();
-    await waitForJobToBeCompleted(jobs[3]);
-    assertRunJobCalledWith([jobs[1], jobs[5], jobs[3]]);
+    await waitForJobToBeCompleted(assertAt(jobs, 3));
+    assertRunJobCalledWith([
+      assertAt(jobs, 1),
+      assertAt(jobs, 5),
+      assertAt(jobs, 3),
+    ]);
     await advanceTime((downloadManager?.tickInterval ?? MINUTE) * 5);
-    assertRunJobCalledWith([jobs[1], jobs[5], jobs[3]]);
+    assertRunJobCalledWith([
+      assertAt(jobs, 1),
+      assertAt(jobs, 5),
+      assertAt(jobs, 3),
+    ]);
 
     // resume backups
     await itemStorage.put('backupMediaDownloadPaused', false);
     await advanceTime((downloadManager?.tickInterval ?? MINUTE) * 5);
     assertRunJobCalledWith([
-      jobs[1],
-      jobs[5],
-      jobs[3],
-      jobs[0],
-      jobs[4],
-      jobs[2],
+      assertAt(jobs, 1),
+      assertAt(jobs, 5),
+      assertAt(jobs, 3),
+      assertAt(jobs, 0),
+      assertAt(jobs, 4),
+      assertAt(jobs, 2),
     ]);
   });
 
@@ -551,7 +601,7 @@ describe('AttachmentDownloadManager', () => {
     const jobs = await addJobs(1, {
       source: AttachmentDownloadSource.BACKUP_IMPORT_WITH_MEDIA,
     });
-    const jobAttempts = getPromisesForAttempts(jobs[0], 2);
+    const jobAttempts = getPromisesForAttempts(assertAt(jobs, 0), 2);
 
     runJob.callsFake(async () => {
       return new Promise<{ status: 'finished' | 'retry' }>(resolve => {
@@ -562,22 +612,21 @@ describe('AttachmentDownloadManager', () => {
     });
 
     await downloadManager?.start();
-    await jobAttempts[0].completed;
-    assertRunJobCalledWith([jobs[0]]);
+    await assertAt(jobAttempts, 0).completed;
+    assertRunJobCalledWith([assertAt(jobs, 0)]);
 
     await DataWriter.resetBackupAttachmentDownloadJobsRetryAfter();
     await downloadManager.start();
 
-    await jobAttempts[1].completed;
+    await assertAt(jobAttempts, 1).completed;
   });
 
   it('retries job with updated job if provided', async () => {
     strictAssert(downloadManager, 'must exist');
-    const job = (
-      await addJobs(1, {
-        source: AttachmentDownloadSource.BACKUP_IMPORT_WITH_MEDIA,
-      })
-    )[0];
+    const jobs = await addJobs(1, {
+      source: AttachmentDownloadSource.BACKUP_IMPORT_WITH_MEDIA,
+    });
+    const job = assertAt(jobs, 0);
     const jobAttempts = getPromisesForAttempts(job, 3);
 
     runJob.callsFake(async args => {
@@ -595,9 +644,9 @@ describe('AttachmentDownloadManager', () => {
     });
 
     await downloadManager?.start();
-    await jobAttempts[0].completed;
+    await assertAt(jobAttempts, 0).completed;
     assertRunJobCalledWith([job]);
-    await jobAttempts[1].completed;
+    await assertAt(jobAttempts, 1).completed;
     assert.deepStrictEqual(
       runJob.getCall(0).args[0].job.attachment,
       job.attachment
@@ -651,42 +700,47 @@ describe('AttachmentDownloadManager', () => {
     });
     it('will retry a job when aborted b/c of shutdown', async () => {
       const jobs = await addJobs(1);
-      const jobAttempts = getPromisesForAttempts(jobs[0], 2);
+      const jobAttempts = getPromisesForAttempts(assertAt(jobs, 0), 2);
 
       await downloadManager?.start();
-      await jobAttempts[0].started;
+      await assertAt(jobAttempts, 0).started;
       await downloadStarted.promise;
 
       // Shutdown behavior
       downloadManager?.stop();
       inflightRequestAbortController.abort();
 
-      await jobAttempts[0].completed;
+      await assertAt(jobAttempts, 0).completed;
       // Ensure it will be retried
       assert.strictEqual(
-        (await DataReader._getAttachmentDownloadJob(jobs[0]))?.attempts,
+        (await DataReader._getAttachmentDownloadJob(assertAt(jobs, 0)))
+          ?.attempts,
         1
       );
       assert.strictEqual(runJob.callCount, 1);
     });
     it('will not retry a job if manually canceled', async () => {
       const jobs = await addJobs(1);
-      const jobAttempts = getPromisesForAttempts(jobs[0], 2);
+      const jobAttempts = getPromisesForAttempts(assertAt(jobs, 0), 2);
 
       await downloadManager?.start();
       const downloadManagerIdled = downloadManager?.waitForIdle();
 
-      await jobAttempts[0].started;
+      await assertAt(jobAttempts, 0).started;
       await downloadStarted.promise;
 
       // user-canceled behavior
       downloadManager?.cancelJobs(JobCancelReason.UserInitiated, () => true);
 
-      await assert.isRejected(jobAttempts[0].completed as Promise<void>);
+      await assert.isRejected(
+        assertAt(jobAttempts, 0).completed as Promise<void>
+      );
       await downloadManagerIdled;
 
       // Ensure it will not be retried
-      assert.isUndefined(await DataReader._getAttachmentDownloadJob(jobs[0]));
+      assert.isUndefined(
+        await DataReader._getAttachmentDownloadJob(assertAt(jobs, 0))
+      );
       assert.strictEqual(runJob.callCount, 1);
     });
   });
diff --git a/ts/test-electron/services/ReleaseNoteAndMegaphoneFetcher_test.preload.ts b/ts/test-electron/services/ReleaseNoteAndMegaphoneFetcher_test.preload.ts
index dfe8326ac6..e749774e11 100644
--- a/ts/test-electron/services/ReleaseNoteAndMegaphoneFetcher_test.preload.ts
+++ b/ts/test-electron/services/ReleaseNoteAndMegaphoneFetcher_test.preload.ts
@@ -508,7 +508,7 @@ describe('ReleaseNoteAndMegaphoneFetcher', () => {
       const dbMegaphones = await getAllMegaphones();
       const dbMegaphone = dbMegaphones[0];
       assert.strictEqual(dbMegaphones.length, 1);
-      assert.strictEqual(dbMegaphone.id, myMegaphone.uuid);
+      assert.strictEqual(dbMegaphone?.id, myMegaphone.uuid);
       assert.strictEqual(
         dbMegaphone.dontShowBeforeEpochMs,
         myMegaphone.dontShowBeforeEpochSeconds * 1000
@@ -588,8 +588,8 @@ describe('ReleaseNoteAndMegaphoneFetcher', () => {
 
       const dbMegaphones = await getAllMegaphones();
       assert.strictEqual(dbMegaphones.length, 2);
-      assert.strictEqual(dbMegaphones[0].id, megaphoneForMyCountry.uuid);
-      assert.strictEqual(dbMegaphones[1].id, wildcardMegaphone.uuid);
+      assert.strictEqual(dbMegaphones[0]?.id, megaphoneForMyCountry.uuid);
+      assert.strictEqual(dbMegaphones[1]?.id, wildcardMegaphone.uuid);
     });
   });
 
@@ -616,7 +616,7 @@ describe('ReleaseNoteAndMegaphoneFetcher', () => {
     const dbMegaphones = await getAllMegaphones();
     assert.strictEqual(dbMegaphones.length, 1);
     const dbMegaphone = dbMegaphones[0];
-    assert.strictEqual(dbMegaphone.id, fakeMegaphoneUuid);
+    assert.strictEqual(dbMegaphone?.id, fakeMegaphoneUuid);
   });
 
   it('deletes saved megaphones if the manifest has empty megaphones', async () => {
diff --git a/ts/test-electron/sql/fullTextSearch_test.preload.ts b/ts/test-electron/sql/fullTextSearch_test.preload.ts
index 016b042be4..da1faf4208 100644
--- a/ts/test-electron/sql/fullTextSearch_test.preload.ts
+++ b/ts/test-electron/sql/fullTextSearch_test.preload.ts
@@ -62,15 +62,15 @@ describe('sql/searchMessages', () => {
 
     const searchResults = await searchMessages({ query: 'unique' });
     assert.lengthOf(searchResults, 1);
-    assert.strictEqual(searchResults[0].id, message2.id);
+    assert.strictEqual(searchResults[0]?.id, message2.id);
 
     message3.body = 'message 3 - unique string';
     await saveMessage(message3, { ourAci, postSaveUpdates });
 
     const searchResults2 = await searchMessages({ query: 'unique' });
     assert.lengthOf(searchResults2, 2);
-    assert.strictEqual(searchResults2[0].id, message3.id);
-    assert.strictEqual(searchResults2[1].id, message2.id);
+    assert.strictEqual(searchResults2[0]?.id, message3.id);
+    assert.strictEqual(searchResults2[1]?.id, message2.id);
   });
 
   it('excludes messages with isViewOnce = true', async () => {
@@ -119,14 +119,14 @@ describe('sql/searchMessages', () => {
 
     const searchResults = await searchMessages({ query: 'unique' });
     assert.lengthOf(searchResults, 1);
-    assert.strictEqual(searchResults[0].id, message1.id);
+    assert.strictEqual(searchResults[0]?.id, message1.id);
 
     message1.body = 'message 3 - unique string';
     await saveMessage(message3, { ourAci, postSaveUpdates });
 
     const searchResults2 = await searchMessages({ query: 'unique' });
     assert.lengthOf(searchResults2, 1);
-    assert.strictEqual(searchResults2[0].id, message1.id);
+    assert.strictEqual(searchResults2[0]?.id, message1.id);
   });
 
   it('excludes messages with storyId !== null', async () => {
@@ -175,14 +175,14 @@ describe('sql/searchMessages', () => {
 
     const searchResults = await searchMessages({ query: 'unique' });
     assert.lengthOf(searchResults, 1);
-    assert.strictEqual(searchResults[0].id, message1.id);
+    assert.strictEqual(searchResults[0]?.id, message1.id);
 
     message1.body = 'message 3 - unique string';
     await saveMessage(message3, { ourAci, postSaveUpdates });
 
     const searchResults2 = await searchMessages({ query: 'unique' });
     assert.lengthOf(searchResults2, 1);
-    assert.strictEqual(searchResults2[0].id, message1.id);
+    assert.strictEqual(searchResults2[0]?.id, message1.id);
   });
 
   it('limits messages returned to a specific conversation if specified', async () => {
@@ -228,7 +228,7 @@ describe('sql/searchMessages', () => {
       conversationId: otherConversationId,
     });
     assert.lengthOf(searchResultsWithConversationId, 1);
-    assert.strictEqual(searchResultsWithConversationId[0].id, message2.id);
+    assert.strictEqual(searchResultsWithConversationId[0]?.id, message2.id);
   });
 });
 
@@ -262,7 +262,7 @@ describe('sql/searchMessages/withMentions', () => {
   }
 
   it('includes messages with mentions', async () => {
-    const mentionedAcis = [generateAci(), generateAci()];
+    const mentionedAcis = [generateAci(), generateAci()] as const;
     const messages = await storeMessages([
       {
         bodyRanges: [{ start: 0, length: 1, mentionAci: mentionedAcis[0] }],
@@ -286,7 +286,7 @@ describe('sql/searchMessages/withMentions', () => {
 
     assert.sameOrderedMembers(
       searchResults.map(res => res.id),
-      [messages[0].id, messages[2].id]
+      [messages[0]?.id, messages[2]?.id]
     );
 
     const searchResultsForMultipleMatchingUuids = await searchMessages({
@@ -297,12 +297,12 @@ describe('sql/searchMessages/withMentions', () => {
     assert.sameOrderedMembers(
       searchResultsForMultipleMatchingUuids.map(res => res.id),
       // TODO: should only return unique messages
-      [messages[0].id, messages[1].id, messages[2].id]
+      [messages[0]?.id, messages[1]?.id, messages[2]?.id]
     );
   });
 
   it('includes messages with mentions and those that match the body text', async () => {
-    const mentionedAcis = [generateAci(), generateAci()];
+    const mentionedAcis = [generateAci(), generateAci()] as const;
     const messages = await storeMessages([
       {
         body: 'cat',
@@ -326,7 +326,7 @@ describe('sql/searchMessages/withMentions', () => {
 
     assert.sameOrderedMembers(
       searchResults.map(res => res.id),
-      [messages[0].id, messages[1].id]
+      [messages[0]?.id, messages[1]?.id]
     );
 
     // check that results get returned in the right order, independent of whether they
@@ -337,11 +337,11 @@ describe('sql/searchMessages/withMentions', () => {
     });
     assert.sameOrderedMembers(
       searchResultsForDog.map(res => res.id),
-      [messages[1].id, messages[2].id]
+      [messages[1]?.id, messages[2]?.id]
     );
   });
   it('respects conversationId for mention matches', async () => {
-    const mentionedAcis = [generateAci(), generateAci()];
+    const mentionedAcis = [generateAci(), generateAci()] as const;
     const conversationId = generateUuid();
     const messages = await storeMessages([
       {
@@ -370,7 +370,7 @@ describe('sql/searchMessages/withMentions', () => {
 
     assert.sameOrderedMembers(
       searchResults.map(res => res.id),
-      [messages[0].id, messages[1].id]
+      [messages[0]?.id, messages[1]?.id]
     );
 
     const searchResultsWithoutConversationid = await searchMessages({
@@ -380,7 +380,7 @@ describe('sql/searchMessages/withMentions', () => {
 
     assert.sameOrderedMembers(
       searchResultsWithoutConversationid.map(res => res.id),
-      [messages[0].id, messages[1].id, messages[2].id, messages[3].id]
+      [messages[0]?.id, messages[1]?.id, messages[2]?.id, messages[3]?.id]
     );
   });
 });
diff --git a/ts/test-electron/sql/getRecentStoryReplies_test.preload.ts b/ts/test-electron/sql/getRecentStoryReplies_test.preload.ts
index f0a0a5596f..79b0eb4067 100644
--- a/ts/test-electron/sql/getRecentStoryReplies_test.preload.ts
+++ b/ts/test-electron/sql/getRecentStoryReplies_test.preload.ts
@@ -102,8 +102,8 @@ describe('sql/getRecentStoryReplies', () => {
       limit: 2,
     });
     assert.lengthOf(searchResultsPage1, 2, 'page 1');
-    assert.strictEqual(searchResultsPage1[0].body, message3.body);
-    assert.strictEqual(searchResultsPage1[1].body, message2.body);
+    assert.strictEqual(searchResultsPage1[0]?.body, message3.body);
+    assert.strictEqual(searchResultsPage1[1]?.body, message2.body);
 
     const searchResultsPage2 = await getRecentStoryReplies(storyId, {
       messageId: message2.id,
@@ -111,6 +111,6 @@ describe('sql/getRecentStoryReplies', () => {
       limit: 2,
     });
     assert.lengthOf(searchResultsPage2, 1, 'page 2');
-    assert.strictEqual(searchResultsPage2[0].body, message1.body);
+    assert.strictEqual(searchResultsPage2[0]?.body, message1.body);
   });
 });
diff --git a/ts/test-electron/sql/markRead_test.preload.ts b/ts/test-electron/sql/markRead_test.preload.ts
index ab7df8b0b8..973d5e234f 100644
--- a/ts/test-electron/sql/markRead_test.preload.ts
+++ b/ts/test-electron/sql/markRead_test.preload.ts
@@ -160,12 +160,12 @@ describe('sql/markRead', () => {
 
     // Sorted in descending order
     assert.strictEqual(
-      markedRead[0].id,
+      markedRead[0]?.id,
       unread.id,
       'no stories/first should be "unread" message'
     );
     assert.strictEqual(
-      markedRead[1].id,
+      markedRead[1]?.id,
       oldestUnread.id,
       'no stories/second should be oldestUnread'
     );
@@ -180,12 +180,12 @@ describe('sql/markRead', () => {
     assert.lengthOf(markedRead2, 2, 'with stories/two messages marked read');
 
     assert.strictEqual(
-      markedRead2[0].id,
+      markedRead2[0]?.id,
       newestUnread.id,
       'with stories/should be newestUnread'
     );
     assert.strictEqual(
-      markedRead2[1].id,
+      markedRead2[1]?.id,
       unreadStoryReply.id,
       'with stories/should be unreadStoryReply'
     );
@@ -310,17 +310,17 @@ describe('sql/markRead', () => {
 
     // Sorted in descending order
     assert.strictEqual(
-      markedRead[0].id,
+      markedRead[0]?.id,
       message7.id,
       'first should be message7'
     );
     assert.strictEqual(
-      markedRead[1].id,
+      markedRead[1]?.id,
       message4.id,
       'first should be message4'
     );
     assert.strictEqual(
-      markedRead[2].id,
+      markedRead[2]?.id,
       message2.id,
       'second should be message2'
     );
@@ -418,7 +418,7 @@ describe('sql/markRead', () => {
 
     assert.lengthOf(markedRead, 1, 'one message marked read');
     assert.strictEqual(
-      markedRead[0].id,
+      markedRead[0]?.id,
       message4.id,
       'first should be message4'
     );
@@ -436,21 +436,21 @@ describe('sql/markRead', () => {
       (left, right) => left.timestamp - right.timestamp
     );
 
-    assert.strictEqual(sorted[0].id, message1.id, 'checking message 1');
+    assert.strictEqual(sorted[0]?.id, message1.id, 'checking message 1');
     assert.strictEqual(
       sorted[0].expirationStartTimestamp,
       now,
       "message1's expirationStartTimestamp was moved earlier"
     );
 
-    assert.strictEqual(sorted[1].id, message2.id, 'checking message 2');
+    assert.strictEqual(sorted[1]?.id, message2.id, 'checking message 2');
     assert.strictEqual(
       sorted[1].expirationStartTimestamp,
       now,
       'checking message 2 expirationStartTimestamp'
     );
 
-    assert.strictEqual(sorted[3].id, message4.id, 'checking message 4');
+    assert.strictEqual(sorted[3]?.id, message4.id, 'checking message 4');
     assert.strictEqual(
       sorted[3].expirationStartTimestamp,
       now,
@@ -610,7 +610,7 @@ describe('sql/markRead', () => {
 
     assert.lengthOf(markedRead2, 1);
     assert.strictEqual(
-      markedRead2[0].messageId,
+      markedRead2[0]?.messageId,
       reaction5.messageId,
       'should be reaction5'
     );
@@ -760,7 +760,7 @@ describe('sql/markRead', () => {
 
     assert.lengthOf(markedRead2, 1);
     assert.strictEqual(
-      markedRead2[0].messageId,
+      markedRead2[0]?.messageId,
       reaction5.messageId,
       'should be reaction5'
     );
@@ -837,7 +837,7 @@ describe('sql/markRead', () => {
 
     // Sorted in descending order
     assert.strictEqual(
-      markedRead[0].id,
+      markedRead[0]?.id,
       message3.id,
       'first should be message3'
     );
diff --git a/ts/test-electron/sql/notificationProfiles_test.preload.ts b/ts/test-electron/sql/notificationProfiles_test.preload.ts
index c2cff10356..decebb4d85 100644
--- a/ts/test-electron/sql/notificationProfiles_test.preload.ts
+++ b/ts/test-electron/sql/notificationProfiles_test.preload.ts
@@ -170,7 +170,7 @@ describe('sql/notificationProfiles', () => {
 
     const twoProfiles = await getAllNotificationProfiles();
     assert.lengthOf(twoProfiles, 2);
-    assert.strictEqual(twoProfiles[1].deletedAtTimestampMs, timestamp);
+    assert.strictEqual(twoProfiles[1]?.deletedAtTimestampMs, timestamp);
   });
 
   it('can update a profile', async () => {
diff --git a/ts/test-electron/sql/pollVoteMarkRead_test.preload.ts b/ts/test-electron/sql/pollVoteMarkRead_test.preload.ts
index 3195b47531..38319c797c 100644
--- a/ts/test-electron/sql/pollVoteMarkRead_test.preload.ts
+++ b/ts/test-electron/sql/pollVoteMarkRead_test.preload.ts
@@ -110,7 +110,7 @@ describe('sql/pollVoteMarkRead', () => {
       });
 
       assert.lengthOf(markedRead2, 1, 'only one poll vote remains unread');
-      assert.strictEqual(markedRead2[0].id, pollMessage3.id);
+      assert.strictEqual(markedRead2[0]?.id, pollMessage3.id);
     });
 
     it('respects received_at cutoff', async () => {
@@ -167,7 +167,7 @@ describe('sql/pollVoteMarkRead', () => {
       });
 
       assert.lengthOf(markedRead, 1, 'only one poll vote within cutoff');
-      assert.strictEqual(markedRead[0].id, pollMessage1.id);
+      assert.strictEqual(markedRead[0]?.id, pollMessage1.id);
     });
 
     it('filters by conversationId correctly', async () => {
@@ -224,7 +224,7 @@ describe('sql/pollVoteMarkRead', () => {
       });
 
       assert.lengthOf(markedRead, 1, 'only polls from conversationId1');
-      assert.strictEqual(markedRead[0].id, pollMessage1.id);
+      assert.strictEqual(markedRead[0]?.id, pollMessage1.id);
     });
 
     it('only returns messages with hasUnreadPollVotes = true', async () => {
@@ -280,7 +280,7 @@ describe('sql/pollVoteMarkRead', () => {
       });
 
       assert.lengthOf(markedRead, 1, 'only unread poll votes');
-      assert.strictEqual(markedRead[0].id, pollMessage1.id);
+      assert.strictEqual(markedRead[0]?.id, pollMessage1.id);
     });
 
     it('marks multiple poll votes as read in single call', async () => {
@@ -536,7 +536,7 @@ describe('sql/pollVoteMarkRead', () => {
       });
 
       assert.lengthOf(markedRead, 1, 'second poll still unread');
-      assert.strictEqual(markedRead[0].id, pollMessage2.id);
+      assert.strictEqual(markedRead[0]?.id, pollMessage2.id);
     });
 
     it('returns full MessageAttributesType on success', async () => {
@@ -626,7 +626,7 @@ describe('sql/pollVoteMarkRead', () => {
       const result = await markPollVoteAsRead(start + 2000);
 
       assert.isNotNull(result);
-      assert.strictEqual(result?.id, pollMessages[2].id);
+      assert.strictEqual(result?.id, pollMessages[2]?.id);
 
       // Other polls should still be unread
       const markedRead = await getUnreadPollVotesAndMarkRead({
diff --git a/ts/test-electron/sql/sendLog_test.preload.ts b/ts/test-electron/sql/sendLog_test.preload.ts
index 650ed8432b..25a0064d2a 100644
--- a/ts/test-electron/sql/sendLog_test.preload.ts
+++ b/ts/test-electron/sql/sendLog_test.preload.ts
@@ -56,7 +56,7 @@ describe('sql/sendLog', () => {
     assert.lengthOf(allProtos, 1);
     const actual = allProtos[0];
 
-    assert.strictEqual(actual.contentHint, proto.contentHint);
+    assert.strictEqual(actual?.contentHint, proto.contentHint);
     assert.isTrue(constantTimeEqual(actual.proto, proto.proto));
     assert.strictEqual(actual.timestamp, proto.timestamp);
     assert.strictEqual(actual.urgent, proto.urgent);
@@ -96,7 +96,7 @@ describe('sql/sendLog', () => {
     assert.lengthOf(allProtos, 1);
     const actual = allProtos[0];
 
-    assert.strictEqual(actual.contentHint, proto.contentHint);
+    assert.strictEqual(actual?.contentHint, proto.contentHint);
     assert.isTrue(constantTimeEqual(actual.proto, proto.proto));
     assert.strictEqual(actual.timestamp, proto.timestamp);
     assert.strictEqual(actual.urgent, proto.urgent);
@@ -153,7 +153,7 @@ describe('sql/sendLog', () => {
     assert.lengthOf(allProtos, 1);
     const actual = allProtos[0];
 
-    assert.strictEqual(actual.timestamp, proto.timestamp);
+    assert.strictEqual(actual?.timestamp, proto.timestamp);
 
     await removeMessageById(id, { cleanupMessages });
 
@@ -294,12 +294,12 @@ describe('sql/sendLog', () => {
       assert.lengthOf(allProtos, 2);
 
       const actual1 = allProtos[0];
-      assert.strictEqual(actual1.contentHint, proto1.contentHint);
+      assert.strictEqual(actual1?.contentHint, proto1.contentHint);
       assert.isTrue(constantTimeEqual(actual1.proto, proto1.proto));
       assert.strictEqual(actual1.timestamp, proto1.timestamp);
 
       const actual2 = allProtos[1];
-      assert.strictEqual(actual2.contentHint, proto2.contentHint);
+      assert.strictEqual(actual2?.contentHint, proto2.contentHint);
       assert.isTrue(constantTimeEqual(actual2.proto, proto2.proto));
       assert.strictEqual(actual2.timestamp, proto2.timestamp);
     });
diff --git a/ts/test-electron/sql/stories_test.preload.ts b/ts/test-electron/sql/stories_test.preload.ts
index f0704c35e7..32605a27fb 100644
--- a/ts/test-electron/sql/stories_test.preload.ts
+++ b/ts/test-electron/sql/stories_test.preload.ts
@@ -91,12 +91,12 @@ describe('sql/stories', () => {
 
       // They are in ASC order
       assert.strictEqual(
-        stories[0].id,
+        stories[0]?.id,
         story1.id,
         'stories first should be story5'
       );
       assert.strictEqual(
-        stories[3].id,
+        stories[3]?.id,
         story5.id,
         'stories last should be story1'
       );
@@ -112,12 +112,12 @@ describe('sql/stories', () => {
 
       // They are in ASC order
       assert.strictEqual(
-        storiesInConversation[0].id,
+        storiesInConversation[0]?.id,
         story1.id,
         'storiesInConversation first should be story4'
       );
       assert.strictEqual(
-        storiesInConversation[1].id,
+        storiesInConversation[1]?.id,
         story4.id,
         'storiesInConversation last should be story1'
       );
@@ -129,12 +129,12 @@ describe('sql/stories', () => {
 
       // They are in ASC order
       assert.strictEqual(
-        storiesByAuthor[0].id,
+        storiesByAuthor[0]?.id,
         story2.id,
         'storiesByAuthor first should be story5'
       );
       assert.strictEqual(
-        storiesByAuthor[1].id,
+        storiesByAuthor[1]?.id,
         story5.id,
         'storiesByAuthor last should be story2'
       );
@@ -230,12 +230,12 @@ describe('sql/stories', () => {
 
       // They are in ASC order
       assert.strictEqual(
-        stories[0].id,
+        stories[0]?.id,
         story1.id,
         'stories first should be story1'
       );
       assert.strictEqual(
-        stories[2].id,
+        stories[2]?.id,
         story3.id,
         'stories last should be story3'
       );
@@ -243,7 +243,7 @@ describe('sql/stories', () => {
       assert.strictEqual(stories[0].hasReplies, true);
       assert.strictEqual(stories[0].hasRepliesFromSelf, true);
 
-      assert.strictEqual(stories[1].hasReplies, true);
+      assert.strictEqual(stories[1]?.hasReplies, true);
       assert.strictEqual(stories[1].hasRepliesFromSelf, false);
 
       assert.strictEqual(stories[2].hasReplies, false);
diff --git a/ts/test-electron/sql/storyDistribution_test.preload.ts b/ts/test-electron/sql/storyDistribution_test.preload.ts
index 6f883f6ddf..4d36c482fa 100644
--- a/ts/test-electron/sql/storyDistribution_test.preload.ts
+++ b/ts/test-electron/sql/storyDistribution_test.preload.ts
@@ -233,6 +233,9 @@ describe('sql/storyDistribution', () => {
 
     const allHydratedLists = await getAllStoryDistributionsWithMembers();
     assert.lengthOf(allHydratedLists, 1);
-    assert.deepEqual(allHydratedLists[0].members, [SERVICE_ID_1, SERVICE_ID_2]);
+    assert.deepEqual(allHydratedLists[0]?.members, [
+      SERVICE_ID_1,
+      SERVICE_ID_2,
+    ]);
   });
 });
diff --git a/ts/test-electron/sql/timelineFetches_test.preload.ts b/ts/test-electron/sql/timelineFetches_test.preload.ts
index 9c49a914ed..7b39d4b66e 100644
--- a/ts/test-electron/sql/timelineFetches_test.preload.ts
+++ b/ts/test-electron/sql/timelineFetches_test.preload.ts
@@ -101,8 +101,8 @@ describe('sql/timelineFetches', () => {
       assert.lengthOf(messages, 3);
 
       // Fetched with DESC query, but with reverse() call afterwards
-      assert.strictEqual(messages[0].id, message1.id);
-      assert.strictEqual(messages[1].id, message2.id);
+      assert.strictEqual(messages[0]?.id, message1.id);
+      assert.strictEqual(messages[1]?.id, message2.id);
     });
 
     it('returns N most recent messages for a given story', async () => {
@@ -158,7 +158,7 @@ describe('sql/timelineFetches', () => {
         storyId,
       });
       assert.lengthOf(messages, 1);
-      assert.strictEqual(messages[0].id, message2.id);
+      assert.strictEqual(messages[0]?.id, message2.id);
     });
 
     it('returns N most recent messages excluding group story replies', async () => {
@@ -214,7 +214,7 @@ describe('sql/timelineFetches', () => {
         storyId: undefined,
       });
       assert.lengthOf(messages, 1);
-      assert.strictEqual(messages[0].id, message3.id);
+      assert.strictEqual(messages[0]?.id, message3.id);
     });
 
     it('returns N messages older than provided received_at', async () => {
@@ -269,7 +269,7 @@ describe('sql/timelineFetches', () => {
         storyId: undefined,
       });
       assert.lengthOf(messages, 1);
-      assert.strictEqual(messages[0].id, message1.id);
+      assert.strictEqual(messages[0]?.id, message1.id);
     });
 
     it('returns N older messages with received_at, lesser sent_at', async () => {
@@ -327,8 +327,8 @@ describe('sql/timelineFetches', () => {
       assert.lengthOf(messages, 2);
 
       // Fetched with DESC query, but with reverse() call afterwards
-      assert.strictEqual(messages[0].id, message1.id, 'checking message 1');
-      assert.strictEqual(messages[1].id, message2.id, 'checking message 2');
+      assert.strictEqual(messages[0]?.id, message1.id, 'checking message 1');
+      assert.strictEqual(messages[1]?.id, message2.id, 'checking message 2');
     });
 
     it('returns N older messages, same received_at/sent_at but excludes messageId', async () => {
@@ -385,7 +385,7 @@ describe('sql/timelineFetches', () => {
       });
 
       assert.lengthOf(messages, 1);
-      assert.strictEqual(messages[0].id, message1.id);
+      assert.strictEqual(messages[0]?.id, message1.id);
     });
   });
 
@@ -462,8 +462,8 @@ describe('sql/timelineFetches', () => {
       });
 
       assert.lengthOf(messages, 3);
-      assert.strictEqual(messages[0].id, message3.id, 'checking message 3');
-      assert.strictEqual(messages[1].id, message4.id, 'checking message 4');
+      assert.strictEqual(messages[0]?.id, message3.id, 'checking message 3');
+      assert.strictEqual(messages[1]?.id, message4.id, 'checking message 4');
     });
 
     it('returns N oldest messages for a given story with no parameters', async () => {
@@ -520,7 +520,7 @@ describe('sql/timelineFetches', () => {
       });
 
       assert.lengthOf(messages, 1);
-      assert.strictEqual(messages[0].id, message2.id);
+      assert.strictEqual(messages[0]?.id, message2.id);
     });
 
     it('returns N messages newer than provided received_at', async () => {
@@ -575,7 +575,7 @@ describe('sql/timelineFetches', () => {
         storyId: undefined,
       });
       assert.lengthOf(messages, 1);
-      assert.strictEqual(messages[0].id, message3.id);
+      assert.strictEqual(messages[0]?.id, message3.id);
     });
 
     it('returns N messages excluding group story replies', async () => {
@@ -632,7 +632,7 @@ describe('sql/timelineFetches', () => {
         sentAt: target,
       });
       assert.lengthOf(messages, 1);
-      assert.strictEqual(messages[0].id, message2.id);
+      assert.strictEqual(messages[0]?.id, message2.id);
     });
 
     it('returns N newer messages with same received_at, greater sent_at', async () => {
@@ -689,8 +689,8 @@ describe('sql/timelineFetches', () => {
 
       assert.lengthOf(messages, 2);
       // They are not in DESC order because MessageCollection is sorting them
-      assert.strictEqual(messages[0].id, message2.id);
-      assert.strictEqual(messages[1].id, message3.id);
+      assert.strictEqual(messages[0]?.id, message2.id);
+      assert.strictEqual(messages[1]?.id, message3.id);
     });
   });
 
diff --git a/ts/test-electron/state/ducks/calling_test.preload.ts b/ts/test-electron/state/ducks/calling_test.preload.ts
index 327979a4f1..d01c71d954 100644
--- a/ts/test-electron/state/ducks/calling_test.preload.ts
+++ b/ts/test-electron/state/ducks/calling_test.preload.ts
@@ -117,7 +117,7 @@ describe('calling duck', () => {
   const remoteAci = generateAci();
   const ringerAci = generateAci();
 
-  const stateWithGroupCall: CallingStateType = {
+  const stateWithGroupCall = {
     ...getEmptyState(),
     callsByConversation: {
       'fake-group-call-conversation-id': {
@@ -148,9 +148,9 @@ describe('calling duck', () => {
         ],
       } satisfies GroupCallStateType,
     },
-  };
+  } as const satisfies CallingStateType;
 
-  const stateWithNotJoinedGroupCall: CallingStateType = {
+  const stateWithNotJoinedGroupCall = {
     ...getEmptyState(),
     callsByConversation: {
       'fake-group-call-conversation-id': {
@@ -170,9 +170,9 @@ describe('calling duck', () => {
         remoteParticipants: [],
       } satisfies GroupCallStateType,
     },
-  };
+  } as const satisfies CallingStateType;
 
-  const stateWithIncomingGroupCall: CallingStateType = {
+  const stateWithIncomingGroupCall = {
     ...stateWithGroupCall,
     callsByConversation: {
       ...stateWithGroupCall.callsByConversation,
@@ -184,7 +184,7 @@ describe('calling duck', () => {
         ringerAci: generateAci(),
       },
     },
-  };
+  } as const satisfies CallingStateType;
 
   const groupCallActiveCallState: ActiveCallStateType = {
     state: 'Active',
@@ -202,10 +202,10 @@ describe('calling duck', () => {
     joinedAt: null,
   };
 
-  const stateWithActiveGroupCall: CallingStateTypeWithActiveCall = {
+  const stateWithActiveGroupCall = {
     ...stateWithGroupCall,
     activeCallState: groupCallActiveCallState,
-  };
+  } as const satisfies CallingStateTypeWithActiveCall;
 
   const ourAci = generateAci();
 
diff --git a/ts/test-electron/state/ducks/conversations_test.preload.ts b/ts/test-electron/state/ducks/conversations_test.preload.ts
index f321ae8983..a8b03af357 100644
--- a/ts/test-electron/state/ducks/conversations_test.preload.ts
+++ b/ts/test-electron/state/ducks/conversations_test.preload.ts
@@ -2217,19 +2217,21 @@ describe('both/state/ducks/conversations', () => {
         const nextState = reducer(getState().conversations, action);
 
         sinon.assert.calledOnce(dispatch);
-        assert.isUndefined(nextState.conversationLookup.abc.conversationColor);
-        assert.isUndefined(nextState.conversationLookup.def.conversationColor);
-        assert.isUndefined(nextState.conversationLookup.ghi.conversationColor);
-        assert.isUndefined(nextState.conversationLookup.jkl.conversationColor);
+        assert.isUndefined(nextState.conversationLookup.abc?.conversationColor);
+        assert.isUndefined(nextState.conversationLookup.def?.conversationColor);
+        assert.isUndefined(nextState.conversationLookup.ghi?.conversationColor);
+        assert.isUndefined(nextState.conversationLookup.jkl?.conversationColor);
         assert.isUndefined(
-          nextState.conversationsByServiceId[abc.serviceId].conversationColor
+          nextState.conversationsByServiceId[abc.serviceId]?.conversationColor
         );
         assert.isUndefined(
-          nextState.conversationsByServiceId[def.serviceId].conversationColor
+          nextState.conversationsByServiceId[def.serviceId]?.conversationColor
         );
-        assert.isUndefined(nextState.conversationsByE164.ghi.conversationColor);
         assert.isUndefined(
-          nextState.conversationsByGroupId.jkl.conversationColor
+          nextState.conversationsByE164.ghi?.conversationColor
+        );
+        assert.isUndefined(
+          nextState.conversationsByGroupId.jkl?.conversationColor
         );
         await itemStorage.remove('defaultConversationColor');
       });
diff --git a/ts/test-electron/textsecure/generate_keys_test.preload.ts b/ts/test-electron/textsecure/generate_keys_test.preload.ts
index 61507ac8f2..415ef17ff8 100644
--- a/ts/test-electron/textsecure/generate_keys_test.preload.ts
+++ b/ts/test-electron/textsecure/generate_keys_test.preload.ts
@@ -116,7 +116,7 @@ describe('Key generation', function (this: Mocha.Suite) {
     it('result contains the correct keyIds', () => {
       const preKeys = result.preKeys || [];
       for (let i = 0; i < count; i += 1) {
-        assert.strictEqual(preKeys[i].keyId, i + 1);
+        assert.strictEqual(preKeys[i]?.keyId, i + 1);
       }
     });
     it('result contains the correct public keys', async () => {
@@ -153,7 +153,7 @@ describe('Key generation', function (this: Mocha.Suite) {
     it('result contains the correct keyIds', () => {
       const preKeys = result.preKeys || [];
       for (let i = 1; i <= count; i += 1) {
-        assert.strictEqual(preKeys[i - 1].keyId, i + count);
+        assert.strictEqual(preKeys[i - 1]?.keyId, i + count);
       }
     });
     it('result contains the correct public keys', async () => {
@@ -194,7 +194,7 @@ describe('Key generation', function (this: Mocha.Suite) {
     it('result contains the correct keyIds', () => {
       const preKeys = result.preKeys || [];
       for (let i = 1; i <= count; i += 1) {
-        assert.strictEqual(preKeys[i - 1].keyId, i + 2 * count);
+        assert.strictEqual(preKeys[i - 1]?.keyId, i + 2 * count);
       }
     });
     it('result contains the correct public keys', async () => {
diff --git a/ts/test-electron/util/addAttachmentToMessage_test.preload.ts b/ts/test-electron/util/addAttachmentToMessage_test.preload.ts
index e7eff9aea3..bb293bda3e 100644
--- a/ts/test-electron/util/addAttachmentToMessage_test.preload.ts
+++ b/ts/test-electron/util/addAttachmentToMessage_test.preload.ts
@@ -147,7 +147,7 @@ describe('addAttachmentToMessage', () => {
     );
 
     const message = await getMessageById(messageId);
-    assert.deepStrictEqual(message?.attributes.preview?.[0].image, {
+    assert.deepStrictEqual(message?.attributes.preview?.[0]?.image, {
       ...attachment,
       path: '/path/to/attachment',
     });
@@ -181,7 +181,7 @@ describe('addAttachmentToMessage', () => {
 
     const message = await getMessageById(messageId);
     assert.deepStrictEqual(
-      message?.attributes.editHistory?.[0].preview?.[0].image,
+      message?.attributes.editHistory?.[0]?.preview?.[0]?.image,
       {
         ...attachment,
         path: '/path/to/attachment',
@@ -215,7 +215,7 @@ describe('addAttachmentToMessage', () => {
 
     const message = await getMessageById(messageId);
     assert.deepStrictEqual(
-      message?.attributes.quote?.attachments[0].thumbnail,
+      message?.attributes.quote?.attachments[0]?.thumbnail,
       {
         ...attachment,
         path: '/path/to/attachment',
@@ -258,7 +258,7 @@ describe('addAttachmentToMessage', () => {
 
     const message = await getMessageById(messageId);
     assert.deepStrictEqual(
-      message?.attributes.editHistory?.[0].quote?.attachments[0].thumbnail,
+      message?.attributes.editHistory?.[0]?.quote?.attachments[0]?.thumbnail,
       {
         ...attachment,
         path: '/path/to/attachment',
@@ -394,11 +394,11 @@ describe('addAttachmentToMessage', () => {
 
     const message = await getMessageById(messageId);
     assert.deepStrictEqual(
-      message?.attributes.editHistory?.[0].body,
+      message?.attributes.editHistory?.[0]?.body,
       'attachmenttext'
     );
     assert.deepStrictEqual(
-      message?.attributes.editHistory?.[0].bodyAttachment,
+      message?.attributes.editHistory?.[0]?.bodyAttachment,
       {
         ...attachment,
         path: 'bodyAttachmentPath',
diff --git a/ts/test-electron/util/migrateMessageData_test.preload.ts b/ts/test-electron/util/migrateMessageData_test.preload.ts
index 4524cf8b31..91609d4bc3 100644
--- a/ts/test-electron/util/migrateMessageData_test.preload.ts
+++ b/ts/test-electron/util/migrateMessageData_test.preload.ts
@@ -34,9 +34,13 @@ describe('utils/migrateMessageData', async () => {
     await itemStorage.fetch();
   });
   it('increments attempts for messages which fail to save', async () => {
-    const messages = new Array(5)
-      .fill(null)
-      .map((_, idx) => composeMessage(idx + 1));
+    const messages = [
+      composeMessage(1),
+      composeMessage(2),
+      composeMessage(3),
+      composeMessage(4),
+      composeMessage(5),
+    ] as const;
 
     const CANNOT_UPGRADE_MESSAGE_ID = messages[1].id;
     const CANNOT_SAVE_MESSAGE_ID = messages[2].id;
diff --git a/ts/test-helpers/expireTimers.std.ts b/ts/test-helpers/expireTimers.std.ts
index 8668216bd3..439537384b 100644
--- a/ts/test-helpers/expireTimers.std.ts
+++ b/ts/test-helpers/expireTimers.std.ts
@@ -4,20 +4,17 @@
 import * as durations from '../util/durations/index.std.js';
 import { DurationInSeconds } from '../util/durations/index.std.js';
 
+const { fromMillis } = DurationInSeconds;
+
 export type TestExpireTimer = Readonly<{
   value: DurationInSeconds;
   label: string;
 }>;
 
-export const EXPIRE_TIMERS: ReadonlyArray<TestExpireTimer> = [
-  { value: 42 * durations.SECOND, label: '42 seconds' },
-  { value: 5 * durations.MINUTE, label: '5 minutes' },
-  { value: 1 * durations.HOUR, label: '1 hour' },
-  { value: 6 * durations.DAY, label: '6 days' },
-  { value: 3 * durations.WEEK, label: '3 weeks' },
-].map(({ value, label }) => {
-  return {
-    value: DurationInSeconds.fromMillis(value),
-    label,
-  };
-});
+export const EXPIRE_TIMERS = [
+  { value: fromMillis(42 * durations.SECOND), label: '42 seconds' },
+  { value: fromMillis(5 * durations.MINUTE), label: '5 minutes' },
+  { value: fromMillis(1 * durations.HOUR), label: '1 hour' },
+  { value: fromMillis(6 * durations.DAY), label: '6 days' },
+  { value: fromMillis(3 * durations.WEEK), label: '3 weeks' },
+] as const satisfies ReadonlyArray<TestExpireTimer>;
diff --git a/ts/test-helpers/generateBackup.node.ts b/ts/test-helpers/generateBackup.node.ts
index 526d7c4fa5..2a91a8a632 100644
--- a/ts/test-helpers/generateBackup.node.ts
+++ b/ts/test-helpers/generateBackup.node.ts
@@ -253,7 +253,8 @@ function* createRecords({
   }
 
   for (let i = 0; i < messages; i += 1) {
-    const chat = chats[i % chats.length];
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const chat = chats[i % chats.length]!;
 
     const isIncoming = i % 2 === 0;
 
diff --git a/ts/test-helpers/getRandomColor.std.ts b/ts/test-helpers/getRandomColor.std.ts
index f4913309bb..5cdf33a500 100644
--- a/ts/test-helpers/getRandomColor.std.ts
+++ b/ts/test-helpers/getRandomColor.std.ts
@@ -8,5 +8,6 @@ import { AvatarColors } from '../types/Colors.std.js';
 const { sample } = lodash;
 
 export function getRandomColor(): AvatarColorType {
-  return sample(AvatarColors) || AvatarColors[0];
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  return sample(AvatarColors) || AvatarColors[0]!;
 }
diff --git a/ts/test-mock/backups/backups_test.node.ts b/ts/test-mock/backups/backups_test.node.ts
index d90c6e396d..763544f63d 100644
--- a/ts/test-mock/backups/backups_test.node.ts
+++ b/ts/test-mock/backups/backups_test.node.ts
@@ -6,6 +6,7 @@ import { randomBytes } from 'node:crypto';
 import { join } from 'node:path';
 import os from 'node:os';
 import createDebug from 'debug';
+import type { PrimaryDevice } from '@signalapp/mock-server';
 import { Proto, StorageState } from '@signalapp/mock-server';
 import { assert } from 'chai';
 import { expect } from 'playwright/test';
@@ -74,7 +75,7 @@ describe('backups', function (this: Mocha.Suite) {
     let state = StorageState.getEmpty();
 
     const { phone, contacts } = bootstrap;
-    const [friend, pinned] = contacts;
+    const [friend, pinned] = contacts as [PrimaryDevice, PrimaryDevice];
 
     state = state.updateAccount({
       profileKey: phone.profileKey.serialize(),
@@ -289,7 +290,7 @@ describe('backups', function (this: Mocha.Suite) {
         .waitFor();
 
       const [catMessage] = await app.getMessagesBySentAt(catTimestamp);
-      const [image] = catMessage.attachments ?? [];
+      const [image] = catMessage?.attachments ?? [];
       strictAssert(image.plaintextHash, 'plaintextHash was calculated');
       strictAssert(image.digest, 'digest was calculated at download time');
       strictAssert(
@@ -395,7 +396,7 @@ describe('backups', function (this: Mocha.Suite) {
 
     {
       const [catMessage] = await app.getMessagesBySentAt(catTimestamp);
-      const [image] = catMessage.attachments ?? [];
+      const [image] = catMessage?.attachments ?? [];
       if (!bootstrapLinkParams.localBackup) {
         strictAssert(
           image.digest,
diff --git a/ts/test-mock/benchmarks/call_history_search_bench.node.ts b/ts/test-mock/benchmarks/call_history_search_bench.node.ts
index 0f9b091458..cfd63129c3 100644
--- a/ts/test-mock/benchmarks/call_history_search_bench.node.ts
+++ b/ts/test-mock/benchmarks/call_history_search_bench.node.ts
@@ -166,7 +166,8 @@ Bootstrap.benchmark(async (bootstrap: Bootstrap): Promise<void> => {
 
   async function measure(runId: number): Promise<number> {
     // setup
-    const searchContact = contacts[runId % contacts.length];
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const searchContact = contacts[runId % contacts.length]!;
     const OtherCallListItems = CallListItem.filter({
       hasNotText: searchContact.profileName,
     });
diff --git a/ts/test-mock/benchmarks/convo_open_bench.node.ts b/ts/test-mock/benchmarks/convo_open_bench.node.ts
index 1af2cd57c0..3092d96902 100644
--- a/ts/test-mock/benchmarks/convo_open_bench.node.ts
+++ b/ts/test-mock/benchmarks/convo_open_bench.node.ts
@@ -17,7 +17,7 @@ Bootstrap.benchmark(async (bootstrap: Bootstrap): Promise<void> => {
   const app = await bootstrap.link();
   const { server, contacts, phone, desktop } = bootstrap;
 
-  const [first, second] = contacts;
+  const [first, second] = contacts as [PrimaryDevice, PrimaryDevice];
 
   const messages = new Array<Buffer>();
   debug('encrypting');
diff --git a/ts/test-mock/benchmarks/group_send_bench.node.ts b/ts/test-mock/benchmarks/group_send_bench.node.ts
index 0de6310ae0..afe92afeb2 100644
--- a/ts/test-mock/benchmarks/group_send_bench.node.ts
+++ b/ts/test-mock/benchmarks/group_send_bench.node.ts
@@ -4,6 +4,7 @@
 
 import assert from 'node:assert';
 
+import type { PrimaryDevice } from '@signalapp/mock-server';
 import {
   StorageState,
   EnvelopeType,
@@ -46,7 +47,7 @@ Bootstrap.benchmark(async (bootstrap: Bootstrap): Promise<void> => {
   const app = await bootstrap.link();
 
   const { server, desktop } = bootstrap;
-  const [first] = members;
+  const [first] = members as [PrimaryDevice];
 
   const messages = new Array<Buffer>();
   debug('encrypting');
@@ -94,7 +95,8 @@ Bootstrap.benchmark(async (bootstrap: Bootstrap): Promise<void> => {
 
   // Fill group
   for (let i = 0; i < CONVERSATION_SIZE; i += 1) {
-    const contact = unblockedMembers[i % unblockedMembers.length];
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const contact = unblockedMembers[i % unblockedMembers.length]!;
     const messageTimestamp = bootstrap.getTimestamp();
 
     const isLast = i === CONVERSATION_SIZE - 1;
diff --git a/ts/test-mock/benchmarks/send_bench.node.ts b/ts/test-mock/benchmarks/send_bench.node.ts
index 567212659b..c94f78b4b7 100644
--- a/ts/test-mock/benchmarks/send_bench.node.ts
+++ b/ts/test-mock/benchmarks/send_bench.node.ts
@@ -4,6 +4,7 @@
 
 import assert from 'node:assert';
 
+import type { PrimaryDevice } from '@signalapp/mock-server';
 import { ReceiptType } from '@signalapp/mock-server';
 
 import { Bootstrap, debug, RUN_COUNT, DISCARD_COUNT } from './fixtures.node.js';
@@ -19,7 +20,7 @@ Bootstrap.benchmark(async (bootstrap: Bootstrap): Promise<void> => {
 
   const { server, contacts, phone, desktop } = bootstrap;
 
-  const [first] = contacts;
+  const [first] = contacts as [PrimaryDevice];
 
   const messages = new Array<Buffer>();
   debug('encrypting');
diff --git a/ts/test-mock/benchmarks/startup_bench.node.ts b/ts/test-mock/benchmarks/startup_bench.node.ts
index fb96a0fe2b..aca8bbd025 100644
--- a/ts/test-mock/benchmarks/startup_bench.node.ts
+++ b/ts/test-mock/benchmarks/startup_bench.node.ts
@@ -25,7 +25,8 @@ Bootstrap.regressionBenchmark(
     debug('started generating messages');
 
     for (let i = 0; i < messageCount; i += 1) {
-      const contact = contacts[Math.floor(i / 2) % contacts.length];
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      const contact = contacts[Math.floor(i / 2) % contacts.length]!;
       const direction = i % 2 ? 'message' : 'reply';
 
       const messageTimestamp = bootstrap.getTimestamp();
diff --git a/ts/test-mock/bootstrap.node.ts b/ts/test-mock/bootstrap.node.ts
index cb89c967a0..5cce73f693 100644
--- a/ts/test-mock/bootstrap.node.ts
+++ b/ts/test-mock/bootstrap.node.ts
@@ -888,7 +888,8 @@ export class Bootstrap {
       }
 
       const result: Record<string, number> = Object.create(null);
-      const keys = Object.keys(samples[0].data).filter(
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      const keys = Object.keys(samples[0]!.data).filter(
         (key: string): key is `${string}Duration` => key.endsWith('Duration')
       );
       const human = new Array<string>();
@@ -896,7 +897,8 @@ export class Bootstrap {
       let worstError = 0;
       for (const key of keys) {
         const { yIntercept, slope, confidence, outliers, severeOutliers } =
-          regress(samples.map(s => ({ y: s.value, x: s.data[key] })));
+          // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+          regress(samples.map(s => ({ y: s.value, x: s.data[key]! })));
 
         const delay = -yIntercept / slope;
         const perSecond = slope * SECOND;
diff --git a/ts/test-mock/messaging/attachments_test.node.ts b/ts/test-mock/messaging/attachments_test.node.ts
index 193bbee22d..af9232eba1 100644
--- a/ts/test-mock/messaging/attachments_test.node.ts
+++ b/ts/test-mock/messaging/attachments_test.node.ts
@@ -60,7 +60,7 @@ describe('attachments', function (this: Mocha.Suite) {
     let state = StorageState.getEmpty();
 
     const { phone, contacts } = bootstrap;
-    [pinned] = contacts;
+    [pinned] = contacts as [PrimaryDevice];
 
     state = state.addContact(pinned, {
       identityKey: pinned.publicKey.serialize(),
@@ -94,6 +94,7 @@ describe('attachments', function (this: Mocha.Suite) {
     } = await sendMessageWithAttachments(page, pinned, 'This is my cat', [
       CAT_PATH,
     ]);
+    strictAssert(attachmentCat, 'attachment must exist');
 
     const Message = getTimelineMessageWithText(page, 'This is my cat');
     const MessageSent = Message.locator(
@@ -278,12 +279,15 @@ describe('attachments', function (this: Mocha.Suite) {
     strictAssert(sentTimestamp, 'outgoing timestamp must exist');
 
     const phoneDBMessage = (await app.getMessagesBySentAt(phoneTimestamp))[0];
-    const phoneDBAttachment: AttachmentType = phoneDBMessage.attachments?.[0];
-
     const friendDBMessage = (await app.getMessagesBySentAt(friendTimestamp))[0];
-    const friendDBAttachment: AttachmentType = friendDBMessage.attachments?.[0];
-
     const sentDBMessage = (await app.getMessagesBySentAt(sentTimestamp))[0];
+
+    strictAssert(phoneDBMessage, 'outgoing sync message exists in DB');
+    strictAssert(friendDBMessage, 'incoming message exists in DB');
+    strictAssert(sentDBMessage, 'sent message exists in DB');
+
+    const phoneDBAttachment: AttachmentType = phoneDBMessage.attachments?.[0];
+    const friendDBAttachment: AttachmentType = friendDBMessage.attachments?.[0];
     const sentDBAttachment: AttachmentType = sentDBMessage.attachments?.[0];
 
     strictAssert(phoneDBAttachment, 'outgoing sync message exists in DB');
@@ -383,11 +387,11 @@ describe('attachments', function (this: Mocha.Suite) {
 
     const firstAttachment: AttachmentType = (
       await app.getMessagesBySentAt(firstTimestamp)
-    )[0].attachments?.[0];
+    )[0]?.attachments?.[0];
 
     const secondAttachment: AttachmentType = (
       await app.getMessagesBySentAt(secondTimestamp)
-    )[0].attachments?.[0];
+    )[0]?.attachments?.[0];
 
     strictAssert(firstAttachment, 'firstAttachment exists in DB');
     strictAssert(secondAttachment, 'secondAttachment exists in DB');
@@ -470,6 +474,7 @@ describe('attachments', function (this: Mocha.Suite) {
       ]);
 
     const sentVideo = sentVideoAttachments[0];
+    assert.exists(sentVideo);
     assert.deepStrictEqual(
       sentVideo.attachmentIdentifier,
       recentPointer.attachmentIdentifier
@@ -486,6 +491,7 @@ describe('attachments', function (this: Mocha.Suite) {
     assert.notDeepEqual(sentVideo.fileName, recentPointer.fileName);
 
     const sentCat = sentCatAttachments[0];
+    assert.exists(sentCat);
     assert.notDeepEqual(
       sentCat.attachmentIdentifier,
       stalePointer.attachmentIdentifier
diff --git a/ts/test-mock/messaging/backfill_test.node.ts b/ts/test-mock/messaging/backfill_test.node.ts
index 431e11f36f..856fdfb104 100644
--- a/ts/test-mock/messaging/backfill_test.node.ts
+++ b/ts/test-mock/messaging/backfill_test.node.ts
@@ -66,7 +66,7 @@ describe('attachment backfill', function (this: Mocha.Suite) {
     page = await app.getWindow();
 
     const { unknownContacts } = bootstrap;
-    [unknownContact] = unknownContacts;
+    [unknownContact] = unknownContacts as [PrimaryDevice];
 
     textAttachment = await bootstrap.encryptAndStoreAttachmentOnCDN(
       Buffer.from('look at this pic, it is gorgeous!'),
diff --git a/ts/test-mock/messaging/edit_test.node.ts b/ts/test-mock/messaging/edit_test.node.ts
index 9d5826ed04..19436c57f1 100644
--- a/ts/test-mock/messaging/edit_test.node.ts
+++ b/ts/test-mock/messaging/edit_test.node.ts
@@ -3,6 +3,7 @@
 
 // `window` use below is actually executed in the browser.
 // eslint-disable-next-line local-rules/file-suffix
+import type { PrimaryDevice } from '@signalapp/mock-server';
 import { Proto, EMPTY_DATA_MESSAGE } from '@signalapp/mock-server';
 import { Aci } from '@signalapp/libsignal-client';
 import { assert } from 'chai';
@@ -250,7 +251,7 @@ describe('editing', function (this: Mocha.Suite) {
 
       const window = await app.getWindow();
 
-      const [friend] = contacts;
+      const [friend] = contacts as [PrimaryDevice];
 
       const initialMessageBody = 'hey yhere';
       const originalMessage = createMessage(initialMessageBody);
@@ -341,7 +342,7 @@ describe('editing', function (this: Mocha.Suite) {
 
       const window = await app.getWindow();
 
-      const [friend] = contacts;
+      const [friend] = contacts as [PrimaryDevice];
 
       debug('incoming message');
       await friend.sendText(desktop, 'hello', {
@@ -562,14 +563,14 @@ describe('editing', function (this: Mocha.Suite) {
           originalMessageTimestamp
         );
         strictAssert(messages, 'messages does not exist');
-        strictAssert(messages.length === 1, 'message does not exist');
+        strictAssert(messages[0], 'message does not exist');
 
         return messages[0];
       }
 
       const { contacts, desktop } = bootstrap;
 
-      const [friend] = contacts;
+      const [friend] = contacts as [PrimaryDevice];
 
       const page = await app.getWindow();
 
@@ -660,7 +661,7 @@ describe('editing', function (this: Mocha.Suite) {
           'sendStateByConversationId'
         );
         assert.strictEqual(
-          message.sendStateByConversationId[conversationId].status,
+          message.sendStateByConversationId[conversationId]?.status,
           SendStatus.Delivered,
           'send state is delivered for main message'
         );
@@ -706,12 +707,12 @@ describe('editing', function (this: Mocha.Suite) {
         // eslint-disable-next-line @typescript-eslint/no-unused-vars
         const [_v2, v1] = message.editHistory;
         assert.strictEqual(
-          message.sendStateByConversationId?.[conversationId].status,
+          message.sendStateByConversationId?.[conversationId]?.status,
           SendStatus.Sent,
           'send state is reverted back to sent for main message'
         );
         assert.strictEqual(
-          v1.sendStateByConversationId?.[conversationId].status,
+          v1?.sendStateByConversationId?.[conversationId]?.status,
           SendStatus.Read,
           'original message is marked read'
         );
@@ -806,7 +807,7 @@ describe('editing', function (this: Mocha.Suite) {
           'sendStateByConversationId'
         );
         assert.strictEqual(
-          message.sendStateByConversationId[conversationId].status,
+          message.sendStateByConversationId[conversationId]?.status,
           SendStatus.Sent,
           'original message send state is sent (v4)'
         );
@@ -814,30 +815,30 @@ describe('editing', function (this: Mocha.Suite) {
         strictAssert(message.editHistory, 'edit history exists');
         const [v4, v3, v2, v1] = message.editHistory;
 
-        strictAssert(v1.sendStateByConversationId, 'v1 has send state');
+        strictAssert(v1?.sendStateByConversationId, 'v1 has send state');
         assert.strictEqual(
-          v1.sendStateByConversationId[conversationId].status,
+          v1.sendStateByConversationId[conversationId]?.status,
           SendStatus.Read,
           'send state for first message is read'
         );
 
-        strictAssert(v2.sendStateByConversationId, 'v2 has send state');
+        strictAssert(v2?.sendStateByConversationId, 'v2 has send state');
         assert.strictEqual(
-          v2.sendStateByConversationId[conversationId].status,
+          v2.sendStateByConversationId[conversationId]?.status,
           SendStatus.Sent,
           'send state for v2 message is sent'
         );
 
-        strictAssert(v3.sendStateByConversationId, 'v3 has send state');
+        strictAssert(v3?.sendStateByConversationId, 'v3 has send state');
         assert.strictEqual(
-          v3.sendStateByConversationId[conversationId].status,
+          v3.sendStateByConversationId[conversationId]?.status,
           SendStatus.Read,
           'send state for v3 message is read'
         );
 
-        strictAssert(v4.sendStateByConversationId, 'v4 has send state');
+        strictAssert(v4?.sendStateByConversationId, 'v4 has send state');
         assert.strictEqual(
-          v4.sendStateByConversationId[conversationId].status,
+          v4.sendStateByConversationId[conversationId]?.status,
           SendStatus.Sent,
           'send state for v4 message is sent'
         );
diff --git a/ts/test-mock/messaging/lightbox_test.node.ts b/ts/test-mock/messaging/lightbox_test.node.ts
index 0bd09d7010..ac39011ff7 100644
--- a/ts/test-mock/messaging/lightbox_test.node.ts
+++ b/ts/test-mock/messaging/lightbox_test.node.ts
@@ -37,7 +37,7 @@ describe('lightbox', function (this: Mocha.Suite) {
     let state = StorageState.getEmpty();
 
     const { phone, contacts } = bootstrap;
-    [pinned] = contacts;
+    [pinned] = contacts as [PrimaryDevice];
 
     state = state.addContact(pinned, {
       identityKey: pinned.publicKey.serialize(),
@@ -114,6 +114,10 @@ describe('lightbox', function (this: Mocha.Suite) {
       imageWaterfall,
     ]);
 
+    strictAssert(attachmentCat, 'attachmentCat exists');
+    strictAssert(attachmentSnow, 'attachmentSnow exists');
+    strictAssert(attachmentWaterfall, 'attachmentWaterfall exists');
+
     await sendAttachmentsBack('Message3', [attachmentCat]);
     await sendAttachmentsBack('Message4', [
       attachmentSnow,
diff --git a/ts/test-mock/messaging/reaction_test.node.ts b/ts/test-mock/messaging/reaction_test.node.ts
index 38becb8645..d643f2f3bb 100644
--- a/ts/test-mock/messaging/reaction_test.node.ts
+++ b/ts/test-mock/messaging/reaction_test.node.ts
@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: AGPL-3.0-only
 
 import createDebug from 'debug';
+import type { PrimaryDevice } from '@signalapp/mock-server';
 import { StorageState } from '@signalapp/mock-server';
 import { type Page } from 'playwright';
 import { expect } from 'playwright/test';
@@ -80,7 +81,11 @@ describe('reactions', function (this: Mocha.Suite) {
     await bootstrap.init();
 
     const { phone, contacts } = bootstrap;
-    const [alice, bob, charlie] = contacts;
+    const [alice, bob, charlie] = contacts as [
+      PrimaryDevice,
+      PrimaryDevice,
+      PrimaryDevice,
+    ];
     let state = StorageState.getEmpty();
 
     state = state.addContact(alice, {
@@ -114,7 +119,11 @@ describe('reactions', function (this: Mocha.Suite) {
   it('should correctly match on participant, timestamp, and author in 1:1 conversation', async () => {
     this.timeout(10000);
     const { contacts, phone, desktop } = bootstrap;
-    const [alice, bob, charlie] = contacts;
+    const [alice, bob, charlie] = contacts as [
+      PrimaryDevice,
+      PrimaryDevice,
+      PrimaryDevice,
+    ];
 
     const window = await app.getWindow();
 
@@ -237,7 +246,12 @@ describe('reactions', function (this: Mocha.Suite) {
     this.timeout(10000);
 
     const { contacts, phone, desktop } = bootstrap;
-    const [alice, bob, charlie, danielle] = contacts;
+    const [alice, bob, charlie, danielle] = contacts as [
+      PrimaryDevice,
+      PrimaryDevice,
+      PrimaryDevice,
+      PrimaryDevice,
+    ];
 
     const groupMembers = [alice, bob, charlie];
     const groupForSending = {
@@ -357,7 +371,7 @@ describe('reactions', function (this: Mocha.Suite) {
     this.timeout(30_000);
 
     const { contacts, phone, desktop } = bootstrap;
-    const [alice, bob] = contacts;
+    const [alice, bob] = contacts as [PrimaryDevice, PrimaryDevice];
 
     // Create a group that includes both Alice and Bob
     const groupForSending = {
@@ -421,6 +435,7 @@ describe('reactions', function (this: Mocha.Suite) {
 
     // First row: Bob's 👍🏿
     const firstReaction = reactionRows[0];
+    strictAssert(firstReaction, 'firstReaction exists');
     await expect(
       firstReaction.locator('.module-reaction-viewer__body__row__name')
     ).toHaveText(bob.profileName);
@@ -431,6 +446,7 @@ describe('reactions', function (this: Mocha.Suite) {
 
     // Second row: local user's 👍🏽
     const secondReaction = reactionRows[1];
+    strictAssert(secondReaction, 'secondReaction exists');
     await expect(
       secondReaction.locator('.module-reaction-viewer__body__row__name')
     ).toHaveText('You');
diff --git a/ts/test-mock/messaging/readSync_test.node.ts b/ts/test-mock/messaging/readSync_test.node.ts
index ad07da9a3f..31f015b76f 100644
--- a/ts/test-mock/messaging/readSync_test.node.ts
+++ b/ts/test-mock/messaging/readSync_test.node.ts
@@ -3,6 +3,7 @@
 
 import createDebug from 'debug';
 
+import type { PrimaryDevice } from '@signalapp/mock-server';
 import type { App } from '../playwright.node.js';
 import * as durations from '../../util/durations/index.std.js';
 import { Bootstrap } from '../bootstrap.node.js';
@@ -33,7 +34,7 @@ describe('readSync', function (this: Mocha.Suite) {
 
   it('applies out of order read syncs', async () => {
     const { contacts, desktop, phone } = bootstrap;
-    const [friend] = contacts;
+    const [friend] = contacts as [PrimaryDevice];
 
     const page = await app.getWindow();
 
diff --git a/ts/test-mock/messaging/relink_test.node.ts b/ts/test-mock/messaging/relink_test.node.ts
index 3dbd584e5f..d2f3916403 100644
--- a/ts/test-mock/messaging/relink_test.node.ts
+++ b/ts/test-mock/messaging/relink_test.node.ts
@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: AGPL-3.0-only
 
 import createDebug from 'debug';
+import type { PrimaryDevice } from '@signalapp/mock-server';
 import { Proto, StorageState } from '@signalapp/mock-server';
 
 import * as durations from '../../util/durations/index.std.js';
@@ -21,10 +22,12 @@ describe('messaging/relink', function (this: Mocha.Suite) {
     bootstrap = new Bootstrap();
     await bootstrap.init();
 
-    const {
-      phone,
-      contacts: [first, second, third],
-    } = bootstrap;
+    const { phone, contacts } = bootstrap;
+    const [first, second, third] = contacts as [
+      PrimaryDevice,
+      PrimaryDevice,
+      PrimaryDevice,
+    ];
 
     let state = StorageState.getEmpty();
 
@@ -68,12 +71,8 @@ describe('messaging/relink', function (this: Mocha.Suite) {
   });
 
   it('updates pin state on relink', async () => {
-    const {
-      contacts: [first, second],
-      desktop,
-      phone,
-      server,
-    } = bootstrap;
+    const { contacts, desktop, phone, server } = bootstrap;
+    const [first, second] = contacts as [PrimaryDevice, PrimaryDevice];
 
     {
       const window = await app.getWindow();
diff --git a/ts/test-mock/messaging/retries_test.node.ts b/ts/test-mock/messaging/retries_test.node.ts
index d05a9fce2a..4003db6b7d 100644
--- a/ts/test-mock/messaging/retries_test.node.ts
+++ b/ts/test-mock/messaging/retries_test.node.ts
@@ -3,6 +3,7 @@
 
 import { assert } from 'chai';
 import createDebug from 'debug';
+import type { PrimaryDevice } from '@signalapp/mock-server';
 import { EnvelopeType, StorageState } from '@signalapp/mock-server';
 
 import type { App } from '../playwright.node.js';
@@ -24,7 +25,7 @@ describe('retries', function (this: Mocha.Suite) {
     app = await bootstrap.link();
 
     const { contacts, phone } = bootstrap;
-    const [first] = contacts;
+    const [first] = contacts as [PrimaryDevice];
 
     let state = StorageState.getEmpty();
 
@@ -50,7 +51,7 @@ describe('retries', function (this: Mocha.Suite) {
 
   it('sends a retry request on a missing sender key error', async () => {
     const { desktop, contacts } = bootstrap;
-    const [first] = contacts;
+    const [first] = contacts as [PrimaryDevice];
 
     debug('send a sender key message without sending skdm first');
     const distributionId = await first.sendSenderKey(desktop, {
@@ -75,7 +76,7 @@ describe('retries', function (this: Mocha.Suite) {
 
   it('does not send a retry request if message succeeded later', async () => {
     const { desktop, contacts } = bootstrap;
-    const [first] = contacts;
+    const [first] = contacts as [PrimaryDevice];
 
     await app.close();
 
@@ -132,7 +133,7 @@ describe('retries', function (this: Mocha.Suite) {
 
   it('sends only one retry request if many failures with same timestamp', async () => {
     const { desktop, contacts } = bootstrap;
-    const [first] = contacts;
+    const [first] = contacts as [PrimaryDevice];
 
     debug('send a sender key message without sending skdm first');
     const firstDistributionId = await first.sendSenderKey(desktop, {
diff --git a/ts/test-mock/messaging/safety_number_test.node.ts b/ts/test-mock/messaging/safety_number_test.node.ts
index 76b57f06e7..efdaacf66f 100644
--- a/ts/test-mock/messaging/safety_number_test.node.ts
+++ b/ts/test-mock/messaging/safety_number_test.node.ts
@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: AGPL-3.0-only
 
 import createDebug from 'debug';
+import type { PrimaryDevice } from '@signalapp/mock-server';
 import { StorageState, Proto } from '@signalapp/mock-server';
 import { assert } from 'chai';
 
@@ -31,7 +32,7 @@ describe('safety number', function (this: Mocha.Suite) {
     await bootstrap.init();
 
     const { phone, contacts } = bootstrap;
-    const [alice] = contacts;
+    const [alice] = contacts as [PrimaryDevice];
     let state = StorageState.getEmpty();
 
     state = state.updateAccount({
@@ -77,10 +78,8 @@ describe('safety number', function (this: Mocha.Suite) {
   });
 
   async function changeIdentityKey(): Promise<void> {
-    const {
-      phone,
-      contacts: [alice, bob],
-    } = bootstrap;
+    const { phone, contacts } = bootstrap;
+    const [alice, bob] = contacts as [PrimaryDevice, PrimaryDevice];
 
     await app.waitForStorageService();
 
@@ -101,9 +100,8 @@ describe('safety number', function (this: Mocha.Suite) {
   }
 
   it('show safety number change UI on regular send', async () => {
-    const {
-      contacts: [alice],
-    } = bootstrap;
+    const { contacts } = bootstrap;
+    const [alice] = contacts as [PrimaryDevice];
 
     const window = await app.getWindow();
 
@@ -141,9 +139,8 @@ describe('safety number', function (this: Mocha.Suite) {
   });
 
   it('show safety number change UI on story send', async () => {
-    const {
-      contacts: [alice],
-    } = bootstrap;
+    const { contacts } = bootstrap;
+    const [alice] = contacts as [PrimaryDevice];
     const window = await app.getWindow();
 
     const storiesPane = window.locator('.Stories');
diff --git a/ts/test-mock/messaging/sender_key_test.node.ts b/ts/test-mock/messaging/sender_key_test.node.ts
index adf5022a94..1e114e3091 100644
--- a/ts/test-mock/messaging/sender_key_test.node.ts
+++ b/ts/test-mock/messaging/sender_key_test.node.ts
@@ -3,7 +3,7 @@
 
 import createDebug from 'debug';
 import { StorageState } from '@signalapp/mock-server';
-import type { Group } from '@signalapp/mock-server';
+import type { Group, PrimaryDevice } from '@signalapp/mock-server';
 
 import * as durations from '../../util/durations/index.std.js';
 import type { App } from '../playwright.node.js';
@@ -23,7 +23,7 @@ describe('senderKey', function (this: Mocha.Suite) {
     await bootstrap.init();
 
     const { contacts, phone } = bootstrap;
-    const [first] = contacts;
+    const [first] = contacts as [PrimaryDevice];
 
     group = await first.createGroup({
       title: 'Group',
@@ -60,7 +60,7 @@ describe('senderKey', function (this: Mocha.Suite) {
 
   it('handles incoming senderKey distributions and messages', async () => {
     const { desktop, contacts } = bootstrap;
-    const [first] = contacts;
+    const [first] = contacts as [PrimaryDevice];
 
     const window = await app.getWindow();
 
diff --git a/ts/test-mock/messaging/stories_test.node.ts b/ts/test-mock/messaging/stories_test.node.ts
index 779db3d790..8a3052feeb 100644
--- a/ts/test-mock/messaging/stories_test.node.ts
+++ b/ts/test-mock/messaging/stories_test.node.ts
@@ -7,7 +7,7 @@ import {
   StorageState,
   EMPTY_DATA_MESSAGE,
 } from '@signalapp/mock-server';
-import type { Group } from '@signalapp/mock-server';
+import type { Group, PrimaryDevice } from '@signalapp/mock-server';
 
 import * as durations from '../../util/durations/index.std.js';
 import { uuidToBytes } from '../../util/uuidToBytes.std.js';
@@ -35,7 +35,7 @@ describe('story/messaging', function (this: Mocha.Suite) {
     await bootstrap.init();
 
     const { phone, contacts } = bootstrap;
-    const [first, second] = contacts;
+    const [first, second] = contacts as [PrimaryDevice, PrimaryDevice];
 
     let state = StorageState.getEmpty();
 
@@ -130,7 +130,7 @@ describe('story/messaging', function (this: Mocha.Suite) {
 
   it('allows replies on multiple distribution lists', async () => {
     const { phone, desktop, contacts } = bootstrap;
-    const [first, second] = contacts;
+    const [first, second] = contacts as [PrimaryDevice, PrimaryDevice];
 
     const window = await app.getWindow();
     const sentAt = Date.now();
@@ -254,6 +254,7 @@ describe('story/messaging', function (this: Mocha.Suite) {
 
   it('allows replies to groups', async () => {
     const { desktop, contacts } = bootstrap;
+    const [first] = contacts as [PrimaryDevice];
 
     const window = await app.getWindow();
 
@@ -286,7 +287,7 @@ describe('story/messaging', function (this: Mocha.Suite) {
       story: sentAt,
       reply: sentAt + 1,
     });
-    await contacts[0].sendRaw(
+    await first.sendRaw(
       desktop,
       {
         content: {
diff --git a/ts/test-mock/messaging/unknown_contact_test.node.ts b/ts/test-mock/messaging/unknown_contact_test.node.ts
index eef18c2fe8..9efa672260 100644
--- a/ts/test-mock/messaging/unknown_contact_test.node.ts
+++ b/ts/test-mock/messaging/unknown_contact_test.node.ts
@@ -28,7 +28,7 @@ describe('unknown contacts', function (this: Mocha.Suite) {
     page = await app.getWindow();
 
     const { unknownContacts } = bootstrap;
-    [unknownContact] = unknownContacts;
+    [unknownContact] = unknownContacts as [PrimaryDevice];
   });
 
   afterEach(async function (this: Mocha.Context) {
diff --git a/ts/test-mock/messaging/unprocessed_test.node.ts b/ts/test-mock/messaging/unprocessed_test.node.ts
index 6a80474384..a7ac4e8ec3 100644
--- a/ts/test-mock/messaging/unprocessed_test.node.ts
+++ b/ts/test-mock/messaging/unprocessed_test.node.ts
@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: AGPL-3.0-only
 
 import createDebug from 'debug';
+import type { PrimaryDevice } from '@signalapp/mock-server';
 import { StorageState } from '@signalapp/mock-server';
 
 import * as durations from '../../util/durations/index.std.js';
@@ -23,10 +24,8 @@ describe('unprocessed', function (this: Mocha.Suite) {
 
     let state = StorageState.getEmpty();
 
-    const {
-      phone,
-      contacts: [alice],
-    } = bootstrap;
+    const { phone, contacts } = bootstrap;
+    const [alice] = contacts as [PrimaryDevice];
 
     state = state.addContact(alice, {
       identityKey: alice.publicKey.serialize(),
@@ -51,10 +50,8 @@ describe('unprocessed', function (this: Mocha.Suite) {
   });
 
   it('generates and loads unprocessed envelopes', async () => {
-    const {
-      desktop,
-      contacts: [alice],
-    } = bootstrap;
+    const { desktop, contacts } = bootstrap;
+    const [alice] = contacts as [PrimaryDevice];
 
     debug('closing');
     await app.close();
diff --git a/ts/test-mock/network/serverAlerts_test.node.ts b/ts/test-mock/network/serverAlerts_test.node.ts
index 2cf7f403a6..53eb95a719 100644
--- a/ts/test-mock/network/serverAlerts_test.node.ts
+++ b/ts/test-mock/network/serverAlerts_test.node.ts
@@ -24,7 +24,7 @@ describe('serverAlerts', function (this: Mocha.Suite) {
     // Set up a pinned contact to trigger profile fetch to test unauth socket
     let state = StorageState.getEmpty();
     const { phone, contacts } = bootstrap;
-    [pinned] = contacts;
+    [pinned] = contacts as [PrimaryDevice];
 
     state = state.addContact(pinned, {
       identityKey: pinned.publicKey.serialize(),
diff --git a/ts/test-mock/pnp/accept_gv2_invite_test.node.ts b/ts/test-mock/pnp/accept_gv2_invite_test.node.ts
index 7d1e643dad..1223167980 100644
--- a/ts/test-mock/pnp/accept_gv2_invite_test.node.ts
+++ b/ts/test-mock/pnp/accept_gv2_invite_test.node.ts
@@ -34,8 +34,11 @@ describe('pnp/accept gv2 invite', function (this: Mocha.Suite) {
     await bootstrap.init();
 
     const { phone, contacts, unknownContacts } = bootstrap;
-    const [first, second] = contacts;
-    [unknownContact, unknownPniContact] = unknownContacts;
+    const [first, second] = contacts as [PrimaryDevice, PrimaryDevice];
+    [unknownContact, unknownPniContact] = unknownContacts as [
+      PrimaryDevice,
+      PrimaryDevice,
+    ];
 
     group = await first.createGroup({
       title: 'Invited Desktop PNI',
@@ -96,7 +99,7 @@ describe('pnp/accept gv2 invite', function (this: Mocha.Suite) {
 
   it('should accept PNI invite and modify the group state', async () => {
     const { phone, contacts, desktop } = bootstrap;
-    const [first, second] = contacts;
+    const [first, second] = contacts as [PrimaryDevice, PrimaryDevice];
 
     const window = await app.getWindow();
 
@@ -237,7 +240,7 @@ describe('pnp/accept gv2 invite', function (this: Mocha.Suite) {
 
   it('should accept ACI invite with extra PNI on the invite list', async () => {
     const { phone, contacts, desktop } = bootstrap;
-    const [first, second] = contacts;
+    const [first, second] = contacts as [PrimaryDevice, PrimaryDevice];
 
     const window = await app.getWindow();
 
@@ -300,7 +303,7 @@ describe('pnp/accept gv2 invite', function (this: Mocha.Suite) {
 
   it('should decline ACI invite with extra PNI on the invite list', async () => {
     const { phone, contacts, desktop } = bootstrap;
-    const [, second] = contacts;
+    const [, second] = contacts as [PrimaryDevice, PrimaryDevice];
 
     const window = await app.getWindow();
 
@@ -333,7 +336,7 @@ describe('pnp/accept gv2 invite', function (this: Mocha.Suite) {
   it('should display a single notification for remote PNI accept', async () => {
     const { phone, contacts, desktop } = bootstrap;
 
-    const [first, second] = contacts;
+    const [first, second] = contacts as [PrimaryDevice, PrimaryDevice];
 
     debug('Creating new group with Desktop');
     group = await phone.createGroup({
@@ -380,7 +383,7 @@ describe('pnp/accept gv2 invite', function (this: Mocha.Suite) {
   it('should display a e164 for a PNI invite', async () => {
     const { phone, contacts, desktop } = bootstrap;
 
-    const [first] = contacts;
+    const [first] = contacts as [PrimaryDevice];
 
     debug('Creating new group with Desktop');
     group = await phone.createGroup({
diff --git a/ts/test-mock/pnp/change_number_test.node.ts b/ts/test-mock/pnp/change_number_test.node.ts
index a397bd962e..cb82137ce9 100644
--- a/ts/test-mock/pnp/change_number_test.node.ts
+++ b/ts/test-mock/pnp/change_number_test.node.ts
@@ -1,6 +1,7 @@
 // Copyright 2022 Signal Messenger, LLC
 // SPDX-License-Identifier: AGPL-3.0-only
 
+import type { PrimaryDevice } from '@signalapp/mock-server';
 import { ServiceIdKind } from '@signalapp/mock-server';
 import createDebug from 'debug';
 
@@ -31,7 +32,7 @@ describe('pnp/change number', function (this: Mocha.Suite) {
   it('should accept sync message and update keys', async () => {
     const { server, phone, desktop, contacts } = bootstrap;
 
-    const [first] = contacts;
+    const [first] = contacts as [PrimaryDevice];
 
     const window = await app.getWindow();
 
diff --git a/ts/test-mock/pnp/merge_test.node.ts b/ts/test-mock/pnp/merge_test.node.ts
index 92b116746b..aaa42061de 100644
--- a/ts/test-mock/pnp/merge_test.node.ts
+++ b/ts/test-mock/pnp/merge_test.node.ts
@@ -427,7 +427,7 @@ describe('pnp/merge', function (this: Mocha.Suite) {
       }
       assert.strictEqual(aciContacts, 1);
       assert.strictEqual(pniContacts, 1);
-      assert.ok(removed[0].contact != null);
+      assert.ok(removed[0]?.contact != null);
 
       assert.deepEqual(
         removed[0].contact.pniBinary,
diff --git a/ts/test-mock/pnp/send_gv2_invite_test.node.ts b/ts/test-mock/pnp/send_gv2_invite_test.node.ts
index 001bc45bf7..eaf523a053 100644
--- a/ts/test-mock/pnp/send_gv2_invite_test.node.ts
+++ b/ts/test-mock/pnp/send_gv2_invite_test.node.ts
@@ -152,7 +152,7 @@ describe('pnp/send gv2 invite', function (this: Mocha.Suite) {
       const groups = await phone.getAllGroups(state);
       assert.strictEqual(groups.length, 1);
 
-      [group] = groups;
+      [group] = groups as [Group];
       assert.strictEqual(group.title, 'My group');
       assert.strictEqual(group.revision, 0);
       assert.strictEqual(group.state.members?.length, 2);
diff --git a/ts/test-mock/pnp/username_test.node.ts b/ts/test-mock/pnp/username_test.node.ts
index f36e3dbc96..4e9c23e33a 100644
--- a/ts/test-mock/pnp/username_test.node.ts
+++ b/ts/test-mock/pnp/username_test.node.ts
@@ -147,14 +147,14 @@ describe('pnp/username', function (this: Mocha.Suite) {
           'only one record must be removed'
         );
 
-        assert.ok(added[0].contact != null);
+        assert.ok(added[0]?.contact != null);
         assert.deepEqual(
           added[0].contact.aciBinary,
           usernameContact.device.aciRawUuid
         );
         assert.strictEqual(added[0].contact.username, '');
 
-        assert.ok(removed[0].contact != null);
+        assert.ok(removed[0]?.contact != null);
         assert.deepEqual(
           removed[0].contact.aciBinary,
           usernameContact.device.aciRawUuid
diff --git a/ts/test-mock/routing/routing_test.node.ts b/ts/test-mock/routing/routing_test.node.ts
index 1300040072..bb87262adb 100644
--- a/ts/test-mock/routing/routing_test.node.ts
+++ b/ts/test-mock/routing/routing_test.node.ts
@@ -5,6 +5,7 @@
 // eslint-disable-next-line local-rules/file-suffix
 import { assert } from 'chai';
 
+import type { PrimaryDevice } from '@signalapp/mock-server';
 import * as durations from '../../util/durations/index.std.js';
 import type { Bootstrap, App } from '../bootstrap.node.js';
 import {
@@ -54,7 +55,7 @@ describe('routing', function (this: Mocha.Suite) {
 
   it('showConversationRoute', async () => {
     const { contacts } = bootstrap;
-    const [friend] = contacts;
+    const [friend] = contacts as [PrimaryDevice];
     const page = await app.getWindow();
     await page.locator('#LeftPane').waitFor();
     const token = await page.evaluate(
diff --git a/ts/test-mock/storage/archive_test.node.ts b/ts/test-mock/storage/archive_test.node.ts
index d8b450d659..c04c6558bb 100644
--- a/ts/test-mock/storage/archive_test.node.ts
+++ b/ts/test-mock/storage/archive_test.node.ts
@@ -3,6 +3,7 @@
 
 import { assert } from 'chai';
 
+import type { PrimaryDevice } from '@signalapp/mock-server';
 import * as durations from '../../util/durations/index.std.js';
 import type { App, Bootstrap } from './fixtures.node.js';
 import { initStorage, debug } from './fixtures.node.js';
@@ -29,7 +30,7 @@ describe('storage service', function (this: Mocha.Suite) {
 
   it('should archive/unarchive contacts', async () => {
     const { phone, contacts } = bootstrap;
-    const [firstContact] = contacts;
+    const [firstContact] = contacts as [PrimaryDevice];
 
     const window = await app.getWindow();
 
diff --git a/ts/test-mock/storage/conflict_test.node.ts b/ts/test-mock/storage/conflict_test.node.ts
index c4abdfd48b..cfe0fe7247 100644
--- a/ts/test-mock/storage/conflict_test.node.ts
+++ b/ts/test-mock/storage/conflict_test.node.ts
@@ -5,6 +5,7 @@ import { assert } from 'chai';
 import { expect } from 'playwright/test';
 import type {
   Group,
+  PrimaryDevice,
   StorageState,
   StorageStateRecord,
 } from '@signalapp/mock-server';
@@ -45,10 +46,8 @@ describe('storage service', function (this: Mocha.Suite) {
   for (const kind of ['contact', 'group']) {
     // eslint-disable-next-line no-loop-func
     it(`should handle ${kind} conflicts`, async () => {
-      const {
-        phone,
-        contacts: [first],
-      } = bootstrap;
+      const { phone, contacts } = bootstrap;
+      const [first] = contacts as [PrimaryDevice];
 
       const window = await app.getWindow();
 
@@ -132,11 +131,8 @@ describe('storage service', function (this: Mocha.Suite) {
   }
 
   it('should handle account conflicts', async () => {
-    const {
-      phone,
-      desktop,
-      contacts: [first, second],
-    } = bootstrap;
+    const { phone, desktop, contacts } = bootstrap;
+    const [first, second] = contacts as [PrimaryDevice, PrimaryDevice];
 
     const window = await app.getWindow();
 
diff --git a/ts/test-mock/storage/fixtures.node.ts b/ts/test-mock/storage/fixtures.node.ts
index e6f92924bf..4913b17e0f 100644
--- a/ts/test-mock/storage/fixtures.node.ts
+++ b/ts/test-mock/storage/fixtures.node.ts
@@ -61,7 +61,7 @@ export async function initStorage(
     // Populate storage service
     const { contacts, phone } = bootstrap;
 
-    const [firstContact] = contacts;
+    const [firstContact] = contacts as [PrimaryDevice];
 
     const members = [...contacts].slice(0, GROUP_SIZE);
 
@@ -137,12 +137,12 @@ export async function initStorage(
     const { desktop } = bootstrap;
 
     // Send a message to the group and the first contact
-    const contactSend = contacts[0].sendText(desktop, 'hello from contact', {
+    const contactSend = contacts[0]?.sendText(desktop, 'hello from contact', {
       timestamp: bootstrap.getTimestamp(),
       sealed: true,
     });
 
-    const groupSend = members[0].sendText(desktop, 'hello in group', {
+    const groupSend = members[0]?.sendText(desktop, 'hello in group', {
       timestamp: bootstrap.getTimestamp(),
       sealed: true,
       group,
@@ -167,7 +167,7 @@ export type StickerPackType = Readonly<{
   stickerCount: number;
 }>;
 
-export const STICKER_PACKS: ReadonlyArray<StickerPackType> = [
+export const STICKER_PACKS = [
   {
     id: Buffer.from('c40ed069cdc2b91eccfccf25e6bcddfc', 'hex'),
     key: Buffer.from(
@@ -184,7 +184,7 @@ export const STICKER_PACKS: ReadonlyArray<StickerPackType> = [
     ),
     stickerCount: 1,
   },
-];
+] as const satisfies ReadonlyArray<StickerPackType>;
 
 export function getStickerPackLink(pack: StickerPackType): string {
   return artAddStickersRoute
diff --git a/ts/test-mock/storage/max_read_keys_test.node.ts b/ts/test-mock/storage/max_read_keys_test.node.ts
index 6f7aeb41d6..39cdd217c1 100644
--- a/ts/test-mock/storage/max_read_keys_test.node.ts
+++ b/ts/test-mock/storage/max_read_keys_test.node.ts
@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: AGPL-3.0-only
 
 import { assert } from 'chai';
+import type { PrimaryDevice } from '@signalapp/mock-server';
 import { Proto } from '@signalapp/mock-server';
 
 import * as durations from '../../util/durations/index.std.js';
@@ -37,8 +38,8 @@ describe('storage service', function (this: Mocha.Suite) {
     debug('prepare for a slow test');
 
     const { phone, contacts } = bootstrap;
-    const firstContact = contacts[0];
-    const lastContact = contacts[contacts.length - 1];
+    const firstContact = contacts[0] as PrimaryDevice;
+    const lastContact = contacts[contacts.length - 1] as PrimaryDevice;
 
     const window = await app.getWindow();
 
diff --git a/ts/test-mock/storage/sticker_test.node.ts b/ts/test-mock/storage/sticker_test.node.ts
index 90b6a240ac..a80ac717e9 100644
--- a/ts/test-mock/storage/sticker_test.node.ts
+++ b/ts/test-mock/storage/sticker_test.node.ts
@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: AGPL-3.0-only
 
 import { assert } from 'chai';
+import type { PrimaryDevice } from '@signalapp/mock-server';
 import { Proto } from '@signalapp/mock-server';
 import * as durations from '../../util/durations/index.std.js';
 import type { App, Bootstrap } from './fixtures.node.js';
@@ -47,7 +48,7 @@ describe('stickers', function (this: Mocha.Suite) {
 
   it('should install/uninstall stickers', async () => {
     const { phone, desktop, contacts } = bootstrap;
-    const [firstContact] = contacts;
+    const [firstContact] = contacts as [PrimaryDevice];
 
     const window = await app.getWindow();
 
@@ -303,10 +304,10 @@ describe('stickers', function (this: Mocha.Suite) {
       .waitFor();
 
     const firstStickerData = (await app.getMessagesBySentAt(firstTimestamp))[0]
-      .sticker?.data;
+      ?.sticker?.data;
     const secondStickerData = (
       await app.getMessagesBySentAt(secondTimestamp)
-    )[0].sticker?.data;
+    )[0]?.sticker?.data;
 
     strictAssert(firstStickerData?.path, 'path exists');
     strictAssert(firstStickerData?.localKey, 'localKey exists');
diff --git a/ts/test-node/components/leftPane/LeftPaneArchiveHelper_test.dom.ts b/ts/test-node/components/leftPane/LeftPaneArchiveHelper_test.dom.ts
index 9d907036ee..20852829fd 100644
--- a/ts/test-node/components/leftPane/LeftPaneArchiveHelper_test.dom.ts
+++ b/ts/test-node/components/leftPane/LeftPaneArchiveHelper_test.dom.ts
@@ -101,7 +101,7 @@ describe('LeftPaneArchiveHelper', () => {
       const archivedConversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
       const helper = new LeftPaneArchiveHelper({
         ...defaults,
         archivedConversations,
@@ -125,7 +125,7 @@ describe('LeftPaneArchiveHelper', () => {
       const archivedConversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
       const helper = new LeftPaneArchiveHelper(searchingDefaults);
 
       assert.strictEqual(
@@ -140,7 +140,7 @@ describe('LeftPaneArchiveHelper', () => {
       const archivedConversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
       const helper = new LeftPaneArchiveHelper({
         ...defaults,
         archivedConversations,
@@ -174,7 +174,7 @@ describe('LeftPaneArchiveHelper', () => {
       const archivedConversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
       const helper = new LeftPaneArchiveHelper({
         ...defaults,
         archivedConversations,
@@ -194,7 +194,7 @@ describe('LeftPaneArchiveHelper', () => {
       const archivedConversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
       const helper = new LeftPaneArchiveHelper({
         ...defaults,
         archivedConversations,
@@ -246,7 +246,7 @@ describe('LeftPaneArchiveHelper', () => {
       const archivedConversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
       const helper = new LeftPaneArchiveHelper({
         ...defaults,
         archivedConversations,
diff --git a/ts/test-node/components/leftPane/LeftPaneChooseGroupMembersHelper_test.dom.ts b/ts/test-node/components/leftPane/LeftPaneChooseGroupMembersHelper_test.dom.ts
index 684cd529b7..14eb9add99 100644
--- a/ts/test-node/components/leftPane/LeftPaneChooseGroupMembersHelper_test.dom.ts
+++ b/ts/test-node/components/leftPane/LeftPaneChooseGroupMembersHelper_test.dom.ts
@@ -119,7 +119,7 @@ describe('LeftPaneChooseGroupMembersHelper', () => {
       const candidateContacts = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
       const helper = new LeftPaneChooseGroupMembersHelper({
         ...defaults,
         candidateContacts,
@@ -145,7 +145,11 @@ describe('LeftPaneChooseGroupMembersHelper', () => {
     });
 
     it("disables non-selected contact checkboxes if you've selected the maximum number of contacts", () => {
-      const candidateContacts = times(50, () => getDefaultConversation());
+      const candidateContacts = [
+        getDefaultConversation(),
+        getDefaultConversation(),
+        ...times(48, () => getDefaultConversation()),
+      ] as const;
       const helper = new LeftPaneChooseGroupMembersHelper({
         ...defaults,
         candidateContacts,
diff --git a/ts/test-node/components/leftPane/LeftPaneComposeHelper_test.dom.ts b/ts/test-node/components/leftPane/LeftPaneComposeHelper_test.dom.ts
index 102e53c25a..048e40d320 100644
--- a/ts/test-node/components/leftPane/LeftPaneComposeHelper_test.dom.ts
+++ b/ts/test-node/components/leftPane/LeftPaneComposeHelper_test.dom.ts
@@ -244,7 +244,7 @@ describe('LeftPaneComposeHelper', () => {
       const composeContacts = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
       const helper = new LeftPaneComposeHelper({
         composeContacts,
         composeGroups: [],
@@ -280,11 +280,11 @@ describe('LeftPaneComposeHelper', () => {
       const composeContacts = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
       const composeGroups = [
         getDefaultGroupListItem(),
         getDefaultGroupListItem(),
-      ];
+      ] as const;
       const helper = new LeftPaneComposeHelper({
         composeContacts,
         composeGroups,
@@ -329,7 +329,7 @@ describe('LeftPaneComposeHelper', () => {
       const composeContacts = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
       const helper = new LeftPaneComposeHelper({
         composeContacts,
         composeGroups: [],
@@ -407,7 +407,7 @@ describe('LeftPaneComposeHelper', () => {
       const composeContacts = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
       const helper = new LeftPaneComposeHelper({
         composeContacts,
         composeGroups: [],
diff --git a/ts/test-node/components/leftPane/LeftPaneInboxHelper_test.dom.tsx b/ts/test-node/components/leftPane/LeftPaneInboxHelper_test.dom.tsx
index 2396e8fea5..77eceac1cb 100644
--- a/ts/test-node/components/leftPane/LeftPaneInboxHelper_test.dom.tsx
+++ b/ts/test-node/components/leftPane/LeftPaneInboxHelper_test.dom.tsx
@@ -125,7 +125,7 @@ describe('LeftPaneInboxHelper', () => {
     });
 
     it('returns undefined if the selected conversation is not pinned or non-pinned', () => {
-      const archivedConversations = [getDefaultConversation()];
+      const archivedConversations = [getDefaultConversation()] as const;
       const helper = new LeftPaneInboxHelper({
         ...defaultProps,
         conversations: [getDefaultConversation(), getDefaultConversation()],
@@ -142,7 +142,7 @@ describe('LeftPaneInboxHelper', () => {
       const pinnedConversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
       const helper = new LeftPaneInboxHelper({
         ...defaultProps,
         pinnedConversations,
@@ -162,7 +162,7 @@ describe('LeftPaneInboxHelper', () => {
       const conversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
       const helper = new LeftPaneInboxHelper({
         ...defaultProps,
         conversations,
@@ -176,7 +176,7 @@ describe('LeftPaneInboxHelper', () => {
       const pinnedConversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
       const helper = new LeftPaneInboxHelper({
         ...defaultProps,
         conversations: [getDefaultConversation()],
@@ -197,7 +197,7 @@ describe('LeftPaneInboxHelper', () => {
       const conversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
       const helper = new LeftPaneInboxHelper({
         ...defaultProps,
         conversations,
@@ -234,7 +234,7 @@ describe('LeftPaneInboxHelper', () => {
       const pinnedConversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
 
       const helper = new LeftPaneInboxHelper({
         ...defaultProps,
@@ -260,7 +260,7 @@ describe('LeftPaneInboxHelper', () => {
       const pinnedConversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
 
       const helper = new LeftPaneInboxHelper({
         ...defaultProps,
@@ -291,7 +291,7 @@ describe('LeftPaneInboxHelper', () => {
       const conversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
 
       const helper = new LeftPaneInboxHelper({
         ...defaultProps,
@@ -313,7 +313,7 @@ describe('LeftPaneInboxHelper', () => {
       const conversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
 
       const helper = new LeftPaneInboxHelper({
         ...defaultProps,
@@ -341,11 +341,11 @@ describe('LeftPaneInboxHelper', () => {
         getDefaultConversation(),
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
       const pinnedConversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
 
       const helper = new LeftPaneInboxHelper({
         ...defaultProps,
@@ -389,11 +389,11 @@ describe('LeftPaneInboxHelper', () => {
         getDefaultConversation(),
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
       const pinnedConversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
 
       const helper = new LeftPaneInboxHelper({
         ...defaultProps,
@@ -444,11 +444,11 @@ describe('LeftPaneInboxHelper', () => {
         getDefaultConversation(),
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
       const pinnedConversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
 
       const helper = new LeftPaneInboxHelper({
         ...defaultProps,
@@ -482,7 +482,7 @@ describe('LeftPaneInboxHelper', () => {
       const pinnedConversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
 
       const helper = new LeftPaneInboxHelper({
         ...defaultProps,
@@ -509,7 +509,7 @@ describe('LeftPaneInboxHelper', () => {
       const conversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
 
       const helper = new LeftPaneInboxHelper({
         ...defaultProps,
@@ -536,11 +536,11 @@ describe('LeftPaneInboxHelper', () => {
       const conversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
       const pinnedConversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
 
       const helper = new LeftPaneInboxHelper({
         ...defaultProps,
@@ -581,8 +581,8 @@ describe('LeftPaneInboxHelper', () => {
       const pinnedConversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
-      const conversations = [getDefaultConversation()];
+      ] as const;
+      const conversations = [getDefaultConversation()] as const;
       const helper = new LeftPaneInboxHelper({
         ...defaultProps,
         conversations,
diff --git a/ts/test-node/components/leftPane/LeftPaneSearchHelper_test.dom.ts b/ts/test-node/components/leftPane/LeftPaneSearchHelper_test.dom.ts
index fe45057c87..70ab1bc13a 100644
--- a/ts/test-node/components/leftPane/LeftPaneSearchHelper_test.dom.ts
+++ b/ts/test-node/components/leftPane/LeftPaneSearchHelper_test.dom.ts
@@ -174,18 +174,18 @@ describe('LeftPaneSearchHelper', () => {
       const conversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
-      const contacts = [getDefaultConversation()];
-      const messages = [fakeMessage(), fakeMessage()];
+      ] as const;
+      const contacts = [getDefaultConversation()] as const;
+      const messages = [fakeMessage(), fakeMessage()] as const;
 
       const helper = new LeftPaneSearchHelper({
         ...baseSearchHelperArgs,
         conversationResults: {
           isLoading: false,
-          results: conversations,
+          results: [...conversations],
         },
-        contactResults: { isLoading: false, results: contacts },
-        messageResults: { isLoading: false, results: messages },
+        contactResults: { isLoading: false, results: [...contacts] },
+        messageResults: { isLoading: false, results: [...messages] },
       });
 
       assert.deepEqual(
@@ -217,13 +217,13 @@ describe('LeftPaneSearchHelper', () => {
     });
 
     it('omits conversations when there are no conversation results', () => {
-      const contacts = [getDefaultConversation()];
-      const messages = [fakeMessage(), fakeMessage()];
+      const contacts = [getDefaultConversation()] as const;
+      const messages = [fakeMessage(), fakeMessage()] as const;
 
       const helper = new LeftPaneSearchHelper({
         ...baseSearchHelperArgs,
-        contactResults: { isLoading: false, results: contacts },
-        messageResults: { isLoading: false, results: messages },
+        contactResults: { isLoading: false, results: [...contacts] },
+        messageResults: { isLoading: false, results: [...messages] },
       });
 
       assert.deepEqual(_testHeaderText(helper.getRow(0)), 'icu:contactsHeader');
@@ -246,16 +246,16 @@ describe('LeftPaneSearchHelper', () => {
       const conversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
-      const messages = [fakeMessage(), fakeMessage()];
+      ] as const;
+      const messages = [fakeMessage(), fakeMessage()] as const;
 
       const helper = new LeftPaneSearchHelper({
         ...baseSearchHelperArgs,
         conversationResults: {
           isLoading: false,
-          results: conversations,
+          results: [...conversations],
         },
-        messageResults: { isLoading: false, results: messages },
+        messageResults: { isLoading: false, results: [...messages] },
       });
 
       assert.deepEqual(
@@ -330,16 +330,19 @@ describe('LeftPaneSearchHelper', () => {
   });
 
   it('omits messages when there are no message results', () => {
-    const conversations = [getDefaultConversation(), getDefaultConversation()];
-    const contacts = [getDefaultConversation()];
+    const conversations = [
+      getDefaultConversation(),
+      getDefaultConversation(),
+    ] as const;
+    const contacts = [getDefaultConversation()] as const;
 
     const helper = new LeftPaneSearchHelper({
       ...baseSearchHelperArgs,
       conversationResults: {
         isLoading: false,
-        results: conversations,
+        results: [...conversations],
       },
-      contactResults: { isLoading: false, results: contacts },
+      contactResults: { isLoading: false, results: [...contacts] },
     });
 
     assert.deepEqual(
@@ -605,14 +608,14 @@ describe('LeftPaneSearchHelper', () => {
       const conversations = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
 
       const helper = new LeftPaneSearchHelper({
         ...baseSearchHelperArgs,
         filterByUnread: true,
         conversationResults: {
           isLoading: false,
-          results: conversations,
+          results: [...conversations],
         },
         contactResults: { isLoading: false, results: [] },
         messageResults: { isLoading: false, results: [] },
diff --git a/ts/test-node/components/leftPane/LeftPaneSetGroupMetadataHelper_test.dom.ts b/ts/test-node/components/leftPane/LeftPaneSetGroupMetadataHelper_test.dom.ts
index a773dd0bcf..1c70f75b23 100644
--- a/ts/test-node/components/leftPane/LeftPaneSetGroupMetadataHelper_test.dom.ts
+++ b/ts/test-node/components/leftPane/LeftPaneSetGroupMetadataHelper_test.dom.ts
@@ -89,7 +89,7 @@ describe('LeftPaneSetGroupMetadataHelper', () => {
       const selectedContacts = [
         getDefaultConversation(),
         getDefaultConversation(),
-      ];
+      ] as const;
       const helper = new LeftPaneSetGroupMetadataHelper({
         ...getComposeState(),
         selectedContacts,
diff --git a/ts/test-node/components/leftPane/getConversationInDirection_test.dom.ts b/ts/test-node/components/leftPane/getConversationInDirection_test.dom.ts
index c7b2ed0516..c46a665f08 100644
--- a/ts/test-node/components/leftPane/getConversationInDirection_test.dom.ts
+++ b/ts/test-node/components/leftPane/getConversationInDirection_test.dom.ts
@@ -17,7 +17,7 @@ describe('getConversationInDirection', () => {
     fakeConversation(true),
     fakeConversation(true),
     fakeConversation(),
-  ];
+  ] as const;
 
   describe('searching for any conversation', () => {
     const up: ToFindType = {
@@ -107,7 +107,7 @@ describe('getConversationInDirection', () => {
       fakeConversation(),
       fakeConversation(),
       fakeConversation(),
-    ];
+    ] as const;
 
     it('returns undefined if there are no conversations', () => {
       assert.isUndefined(getConversationInDirection([], up, undefined));
diff --git a/ts/test-node/components/media-gallery/groupMediaItemsByDate.std.ts b/ts/test-node/components/media-gallery/groupMediaItemsByDate.std.ts
index a2b5de8d2e..3a0b1841ea 100644
--- a/ts/test-node/components/media-gallery/groupMediaItemsByDate.std.ts
+++ b/ts/test-node/components/media-gallery/groupMediaItemsByDate.std.ts
@@ -70,37 +70,37 @@ describe('groupMediaItemsByDate', () => {
 
     const actual = groupMediaItemsByDate(referenceTime, input);
 
-    assert.strictEqual(actual[0].type, 'today');
+    assert.strictEqual(actual[0]?.type, 'today');
     assert.strictEqual(actual[0].mediaItems.length, 2, 'today');
-    assert.strictEqual(actual[0].mediaItems[0].message.id, 'today-1');
-    assert.strictEqual(actual[0].mediaItems[1].message.id, 'today-2');
+    assert.strictEqual(actual[0].mediaItems[0]?.message.id, 'today-1');
+    assert.strictEqual(actual[0].mediaItems[1]?.message.id, 'today-2');
 
-    assert.strictEqual(actual[1].type, 'yesterday');
-    assert.strictEqual(actual[1].mediaItems.length, 2, 'yesterday');
-    assert.strictEqual(actual[1].mediaItems[0].message.id, 'yesterday-1');
-    assert.strictEqual(actual[1].mediaItems[1].message.id, 'yesterday-2');
+    assert.strictEqual(actual[1]?.type, 'yesterday');
+    assert.strictEqual(actual[1]?.mediaItems.length, 2, 'yesterday');
+    assert.strictEqual(actual[1].mediaItems[0]?.message.id, 'yesterday-1');
+    assert.strictEqual(actual[1].mediaItems[1]?.message.id, 'yesterday-2');
 
-    assert.strictEqual(actual[2].type, 'thisWeek');
-    assert.strictEqual(actual[2].mediaItems.length, 4, 'thisWeek');
-    assert.strictEqual(actual[2].mediaItems[0].message.id, 'thisWeek-1');
-    assert.strictEqual(actual[2].mediaItems[1].message.id, 'thisWeek-2');
-    assert.strictEqual(actual[2].mediaItems[2].message.id, 'thisWeek-3');
-    assert.strictEqual(actual[2].mediaItems[3].message.id, 'thisWeek-4');
+    assert.strictEqual(actual[2]?.type, 'thisWeek');
+    assert.strictEqual(actual[2]?.mediaItems.length, 4, 'thisWeek');
+    assert.strictEqual(actual[2].mediaItems[0]?.message.id, 'thisWeek-1');
+    assert.strictEqual(actual[2].mediaItems[1]?.message.id, 'thisWeek-2');
+    assert.strictEqual(actual[2].mediaItems[2]?.message.id, 'thisWeek-3');
+    assert.strictEqual(actual[2].mediaItems[3]?.message.id, 'thisWeek-4');
 
-    assert.strictEqual(actual[3].type, 'thisMonth');
+    assert.strictEqual(actual[3]?.type, 'thisMonth');
     assert.strictEqual(actual[3].mediaItems.length, 2, 'thisMonth');
-    assert.strictEqual(actual[3].mediaItems[0].message.id, 'thisMonth-1');
-    assert.strictEqual(actual[3].mediaItems[1].message.id, 'thisMonth-2');
+    assert.strictEqual(actual[3].mediaItems[0]?.message.id, 'thisMonth-1');
+    assert.strictEqual(actual[3].mediaItems[1]?.message.id, 'thisMonth-2');
 
-    assert.strictEqual(actual[4].type, 'yearMonth');
+    assert.strictEqual(actual[4]?.type, 'yearMonth');
     assert.strictEqual(actual[4].mediaItems.length, 2, 'mar2024');
-    assert.strictEqual(actual[4].mediaItems[0].message.id, 'mar2024-1');
-    assert.strictEqual(actual[4].mediaItems[1].message.id, 'mar2024-2');
+    assert.strictEqual(actual[4].mediaItems[0]?.message.id, 'mar2024-1');
+    assert.strictEqual(actual[4].mediaItems[1]?.message.id, 'mar2024-2');
 
-    assert.strictEqual(actual[5].type, 'yearMonth');
+    assert.strictEqual(actual[5]?.type, 'yearMonth');
     assert.strictEqual(actual[5].mediaItems.length, 2, 'feb2011');
-    assert.strictEqual(actual[5].mediaItems[0].message.id, 'feb2011-1');
-    assert.strictEqual(actual[5].mediaItems[1].message.id, 'feb2011-2');
+    assert.strictEqual(actual[5].mediaItems[0]?.message.id, 'feb2011-1');
+    assert.strictEqual(actual[5].mediaItems[1]?.message.id, 'feb2011-2');
 
     assert.strictEqual(actual.length, 6, 'total sections');
   });
diff --git a/ts/test-node/jobs/JobQueue_test.node.ts b/ts/test-node/jobs/JobQueue_test.node.ts
index e31dca5317..ab179e9792 100644
--- a/ts/test-node/jobs/JobQueue_test.node.ts
+++ b/ts/test-node/jobs/JobQueue_test.node.ts
@@ -246,8 +246,8 @@ describe('JobQueue', () => {
 
       const queueTypes = groupBy(store.storedJobs, 'queueType');
       assert.hasAllKeys(queueTypes, ['test 1', 'test 2']);
-      assert.lengthOf(queueTypes['test 1'], 3);
-      assert.lengthOf(queueTypes['test 2'], 2);
+      assert.lengthOf(queueTypes['test 1'] ?? [], 3);
+      assert.lengthOf(queueTypes['test 2'] ?? [], 2);
     });
 
     it('can override the insertion logic, skipping storage persistence', async () => {
diff --git a/ts/test-node/messages/MessageSendState_test.std.ts b/ts/test-node/messages/MessageSendState_test.std.ts
index 6454d75fd4..94f1cd2150 100644
--- a/ts/test-node/messages/MessageSendState_test.std.ts
+++ b/ts/test-node/messages/MessageSendState_test.std.ts
@@ -47,7 +47,7 @@ describe('message send state utilities', () => {
 
     it('orders the statuses', () => {
       times(100, () => {
-        const [a, b] = sampleSize(expectedOrder, 2);
+        const [a, b] = sampleSize(expectedOrder, 2) as [SendStatus, SendStatus];
         const isABigger = expectedOrder.indexOf(a) > expectedOrder.indexOf(b);
         const expected = isABigger ? a : b;
 
diff --git a/ts/test-node/reactions/util_test.std.ts b/ts/test-node/reactions/util_test.std.ts
index 233e225259..96ff5f48ac 100644
--- a/ts/test-node/reactions/util_test.std.ts
+++ b/ts/test-node/reactions/util_test.std.ts
@@ -44,7 +44,7 @@ describe('reaction utilities', () => {
         { ...rxn('💬'), fromId: uuid() },
         { ...rxn('🥀', { isPending: true }), timestamp: 1 },
         { ...rxn('🌹', { isPending: true }), timestamp: 2 },
-      ];
+      ] as const;
       const reaction = rxn('😀');
       const newReactions = addOutgoingReaction(oldReactions, reaction);
       assert.deepStrictEqual(newReactions, [oldReactions[1], reaction]);
diff --git a/ts/test-node/sql/migration_1000_test.node.ts b/ts/test-node/sql/migration_1000_test.node.ts
index 9d4fffbb9d..a741c3386b 100644
--- a/ts/test-node/sql/migration_1000_test.node.ts
+++ b/ts/test-node/sql/migration_1000_test.node.ts
@@ -134,12 +134,12 @@ describe('SQL/updateToSchemaVersion1000', () => {
 
     assert.strictEqual(messages.length, 2);
 
-    assert.strictEqual(messages[0].message.readStatus, ReadStatus.Read);
+    assert.strictEqual(messages[0]?.message.readStatus, ReadStatus.Read);
     assert.strictEqual(messages[0].message.seenStatus, SeenStatus.Unseen);
     assert.strictEqual(messages[0].readStatus, ReadStatus.Read);
     assert.strictEqual(messages[0].seenStatus, SeenStatus.Unseen);
 
-    assert.strictEqual(messages[1].message.readStatus, ReadStatus.Read);
+    assert.strictEqual(messages[1]?.message.readStatus, ReadStatus.Read);
     assert.strictEqual(messages[1].message.seenStatus, SeenStatus.Unseen);
     assert.strictEqual(messages[1].readStatus, ReadStatus.Read);
     assert.strictEqual(messages[1].seenStatus, SeenStatus.Unseen);
@@ -174,12 +174,12 @@ describe('SQL/updateToSchemaVersion1000', () => {
 
     assert.strictEqual(messages.length, 2);
 
-    assert.strictEqual(messages[0].message.readStatus, ReadStatus.Read);
+    assert.strictEqual(messages[0]?.message.readStatus, ReadStatus.Read);
     assert.strictEqual(messages[0].message.seenStatus, SeenStatus.Seen);
     assert.strictEqual(messages[0].readStatus, ReadStatus.Read);
     assert.strictEqual(messages[0].seenStatus, SeenStatus.Seen);
 
-    assert.strictEqual(messages[1].message.readStatus, ReadStatus.Read);
+    assert.strictEqual(messages[1]?.message.readStatus, ReadStatus.Read);
     assert.strictEqual(messages[1].message.seenStatus, SeenStatus.Seen);
     assert.strictEqual(messages[1].readStatus, ReadStatus.Read);
     assert.strictEqual(messages[1].seenStatus, SeenStatus.Seen);
diff --git a/ts/test-node/sql/migration_1040_test.node.ts b/ts/test-node/sql/migration_1040_test.node.ts
index a18f67f87d..3250a43578 100644
--- a/ts/test-node/sql/migration_1040_test.node.ts
+++ b/ts/test-node/sql/migration_1040_test.node.ts
@@ -201,7 +201,7 @@ describe('SQL/updateToSchemaVersion1040', () => {
 
       const attachments = getAttachmentDownloadJobs(db);
       assert.strictEqual(attachments.length, 1);
-      assert.strictEqual(attachments[0].attempts, 0);
+      assert.strictEqual(attachments[0]?.attempts, 0);
     });
 
     it('uses indices searching for next job', () => {
diff --git a/ts/test-node/sql/migration_1060_test.node.ts b/ts/test-node/sql/migration_1060_test.node.ts
index b588ebb8d7..36e509794f 100644
--- a/ts/test-node/sql/migration_1060_test.node.ts
+++ b/ts/test-node/sql/migration_1060_test.node.ts
@@ -204,7 +204,7 @@ describe('SQL/updateToSchemaVersion1060', () => {
   describe('Sync Tasks', () => {
     it('creates tasks in bulk, and fetches all', () => {
       const now = Date.now();
-      const expected: Array<SyncTaskType> = [
+      const expected = [
         {
           id: generateGuid(),
           attempts: 1,
@@ -241,7 +241,7 @@ describe('SQL/updateToSchemaVersion1060', () => {
           sentAt: 3,
           type: 'delete-conversation',
         },
-      ];
+      ] as const satisfies Array<SyncTaskType>;
 
       saveSyncTasks(db, expected);
 
diff --git a/ts/test-node/sql/migration_1200_test.node.ts b/ts/test-node/sql/migration_1200_test.node.ts
index acaec9c4f6..f5dbac0819 100644
--- a/ts/test-node/sql/migration_1200_test.node.ts
+++ b/ts/test-node/sql/migration_1200_test.node.ts
@@ -172,7 +172,7 @@ describe('SQL/updateToSchemaVersion1200', () => {
     const [query, params] = template;
     const result = db.prepare(query).all(params);
     assert.strictEqual(result.length, 1);
-    assert.deepStrictEqual(result[0].messageId, 'message12');
+    assert.deepStrictEqual(result[0]?.messageId, 'message12');
     const details = explain(db, template);
     assert.equal(
       details,
diff --git a/ts/test-node/sql/migration_89_test.preload.ts b/ts/test-node/sql/migration_89_test.preload.ts
index 5ad2e29e29..2abb347b48 100644
--- a/ts/test-node/sql/migration_89_test.preload.ts
+++ b/ts/test-node/sql/migration_89_test.preload.ts
@@ -194,8 +194,8 @@ describe('SQL/updateToSchemaVersion89', () => {
     const callHistory = getAllCallHistory();
 
     assert.strictEqual(callHistory.length, 2);
-    assert.strictEqual(callHistory[0].callId, callId1);
-    assert.strictEqual(callHistory[1].callId, getCallIdFromEra(eraId2));
+    assert.strictEqual(callHistory[0]?.callId, callId1);
+    assert.strictEqual(callHistory[1]?.callId, getCallIdFromEra(eraId2));
   });
 
   it('migrates older messages without a callId', () => {
@@ -215,7 +215,7 @@ describe('SQL/updateToSchemaVersion89', () => {
     const callHistory = getAllCallHistory();
 
     assert.strictEqual(callHistory.length, 1);
-    assert.isTrue(isValidUuid(callHistory[0].callId));
+    assert.isTrue(isValidUuid(callHistory[0]?.callId));
   });
 
   it('migrates older messages without a callMode', () => {
@@ -245,8 +245,8 @@ describe('SQL/updateToSchemaVersion89', () => {
     const callHistory = getAllCallHistory();
 
     assert.strictEqual(callHistory.length, 2);
-    assert.strictEqual(callHistory[0].mode, CallMode.Direct);
-    assert.strictEqual(callHistory[1].mode, CallMode.Group);
+    assert.strictEqual(callHistory[0]?.mode, CallMode.Direct);
+    assert.strictEqual(callHistory[1]?.mode, CallMode.Group);
   });
 
   it('handles unique constraint violations', () => {
@@ -298,8 +298,8 @@ describe('SQL/updateToSchemaVersion89', () => {
 
     const callHistory = getAllCallHistory();
     assert.strictEqual(callHistory.length, 2);
-    assert.strictEqual(callHistory[0].peerId, conversation1.serviceId);
-    assert.strictEqual(callHistory[1].peerId, conversation2.groupId);
+    assert.strictEqual(callHistory[0]?.peerId, conversation1.serviceId);
+    assert.strictEqual(callHistory[1]?.peerId, conversation2.groupId);
   });
 
   it('migrates older unregistered conversations with no serviceId', () => {
@@ -318,7 +318,7 @@ describe('SQL/updateToSchemaVersion89', () => {
 
     const callHistory = getAllCallHistory();
     assert.strictEqual(callHistory.length, 1);
-    assert.strictEqual(callHistory[0].peerId, conversation.id);
+    assert.strictEqual(callHistory[0]?.peerId, conversation.id);
   });
 
   it('migrates call-history messages with no timestamp', () => {
@@ -374,14 +374,14 @@ describe('SQL/updateToSchemaVersion89', () => {
 
     const callHistory = getAllCallHistory();
     assert.strictEqual(callHistory.length, 8);
-    assert.strictEqual(callHistory[0].timestamp, 0);
-    assert.strictEqual(callHistory[1].timestamp, 0);
-    assert.strictEqual(callHistory[2].timestamp, 1);
-    assert.strictEqual(callHistory[3].timestamp, 1);
-    assert.strictEqual(callHistory[4].timestamp, 2);
-    assert.strictEqual(callHistory[5].timestamp, 2);
-    assert.strictEqual(callHistory[6].timestamp, 3);
-    assert.strictEqual(callHistory[7].timestamp, 3);
+    assert.strictEqual(callHistory[0]?.timestamp, 0);
+    assert.strictEqual(callHistory[1]?.timestamp, 0);
+    assert.strictEqual(callHistory[2]?.timestamp, 1);
+    assert.strictEqual(callHistory[3]?.timestamp, 1);
+    assert.strictEqual(callHistory[4]?.timestamp, 2);
+    assert.strictEqual(callHistory[5]?.timestamp, 2);
+    assert.strictEqual(callHistory[6]?.timestamp, 3);
+    assert.strictEqual(callHistory[7]?.timestamp, 3);
   });
 
   describe('clients with schema version 87', () => {
@@ -482,8 +482,8 @@ describe('SQL/updateToSchemaVersion89', () => {
 
       const callHistory = getAllCallHistory();
       assert.strictEqual(callHistory.length, 2);
-      assert.strictEqual(callHistory[0].peerId, conversation1.serviceId);
-      assert.strictEqual(callHistory[1].peerId, conversation2.groupId);
+      assert.strictEqual(callHistory[0]?.peerId, conversation1.serviceId);
+      assert.strictEqual(callHistory[1]?.peerId, conversation2.groupId);
     });
 
     it('migrates duplicate call history where the first was already migrated', () => {
@@ -522,12 +522,12 @@ describe('SQL/updateToSchemaVersion89', () => {
       const callHistory = getAllCallHistory();
 
       assert.strictEqual(callHistory.length, 1);
-      assert.strictEqual(callHistory[0].status, DirectCallStatus.Declined);
+      assert.strictEqual(callHistory[0]?.status, DirectCallStatus.Declined);
 
       const messages = getMessages();
       assert.strictEqual(messages.length, 1);
-      assert.strictEqual(messages[0].type, 'call-history');
-      assert.strictEqual(messages[0].callId, '123');
+      assert.strictEqual(messages[0]?.type, 'call-history');
+      assert.strictEqual(messages[0]?.callId, '123');
       assert.notProperty(messages[0], 'callHistoryDetails');
     });
   });
diff --git a/ts/test-node/sql/migrations_test.node.ts b/ts/test-node/sql/migrations_test.node.ts
index eb306dae6d..3dd606ad23 100644
--- a/ts/test-node/sql/migrations_test.node.ts
+++ b/ts/test-node/sql/migrations_test.node.ts
@@ -3371,35 +3371,22 @@ describe('SQL migrations test', () => {
       return json;
     }
 
-    function addMessages(
-      messages: Array<{
-        mentions?: Array<AciString>;
-        boldRanges?: Array<Array<number>>;
-      }>
-    ) {
-      const formattedMessages = messages.map(composeMessage);
+    function addMessage(message: {
+      mentions?: Array<AciString>;
+      boldRanges?: Array<Array<number>>;
+    }) {
+      const formattedMessage = composeMessage(message);
 
       db.exec(
         `
         INSERT INTO messages
           (id, json)
         VALUES
-          ${formattedMessages
-            .map(message => `('${message.id}', '${objectToJSON(message)}')`)
-            .join(', ')};
+          ('${formattedMessage.id}', '${objectToJSON(formattedMessage)}')
         `
       );
 
-      assert.equal(
-        db
-          .prepare('SELECT COUNT(*) FROM messages;', {
-            pluck: true,
-          })
-          .get(),
-        messages.length
-      );
-
-      return { formattedMessages };
+      return formattedMessage;
     }
 
     function getMentions() {
@@ -3408,17 +3395,24 @@ describe('SQL migrations test', () => {
         .all();
     }
 
+    const userIds = [
+      generateAci(),
+      generateAci(),
+      generateAci(),
+      generateAci(),
+      generateAci(),
+    ] as const;
+
     it('Creates and populates the mentions table with existing mentions', () => {
       updateToVersion(db, schemaVersion - 1);
 
-      const userIds = new Array(5).fill(undefined).map(() => generateAci());
-      const { formattedMessages } = addMessages([
-        { mentions: [userIds[0]] },
-        { mentions: [userIds[1]], boldRanges: [[1, 1]] },
-        { mentions: [userIds[1], userIds[2]] },
-        {},
-        { boldRanges: [[1, 4]] },
-      ]);
+      const formattedMessages = [
+        addMessage({ mentions: [userIds[0]] }),
+        addMessage({ mentions: [userIds[1]], boldRanges: [[1, 1]] }),
+        addMessage({ mentions: [userIds[1], userIds[2]] }),
+        addMessage({}),
+        addMessage({ boldRanges: [[1, 4]] }),
+      ] as const;
 
       // now create mentions table
       updateToVersion(db, schemaVersion);
@@ -3467,14 +3461,13 @@ describe('SQL migrations test', () => {
         0
       );
 
-      const userIds = new Array(5).fill(undefined).map(() => generateAci());
-      const { formattedMessages } = addMessages([
-        { mentions: [userIds[0]] },
-        { mentions: [userIds[1]], boldRanges: [[1, 1]] },
-        { mentions: [userIds[1], userIds[2]] },
-        {},
-        { boldRanges: [[1, 4]] },
-      ]);
+      const formattedMessages = [
+        addMessage({ mentions: [userIds[0]] }),
+        addMessage({ mentions: [userIds[1]], boldRanges: [[1, 1]] }),
+        addMessage({ mentions: [userIds[1], userIds[2]] }),
+        addMessage({}),
+        addMessage({ boldRanges: [[1, 4]] }),
+      ] as const;
 
       // the 4 mentions should be included, with multiple rows for multiple mentions in a
       // message
@@ -3519,11 +3512,13 @@ describe('SQL migrations test', () => {
         0
       );
 
-      const userIds = new Array(5).fill(undefined).map(() => generateAci());
-      const { formattedMessages } = addMessages([
-        { mentions: [userIds[0]] },
-        { mentions: [userIds[1], userIds[2]], boldRanges: [[1, 1]] },
-      ]);
+      const formattedMessages = [
+        addMessage({ mentions: [userIds[0]] }),
+        addMessage({
+          mentions: [userIds[1], userIds[2]],
+          boldRanges: [[1, 1]],
+        }),
+      ] as const;
 
       assert.equal(getMentions().length, 3);
 
@@ -3553,8 +3548,9 @@ describe('SQL migrations test', () => {
         0
       );
 
-      const userIds = new Array(5).fill(undefined).map(() => generateAci());
-      const { formattedMessages } = addMessages([{ mentions: [userIds[0]] }]);
+      const formattedMessages = [
+        addMessage({ mentions: [userIds[0]] }),
+      ] as const;
 
       assert.equal(getMentions().length, 1);
 
diff --git a/ts/test-node/state/selectors/conversations_test.preload.ts b/ts/test-node/state/selectors/conversations_test.preload.ts
index 95ac938d70..e20b1e9007 100644
--- a/ts/test-node/state/selectors/conversations_test.preload.ts
+++ b/ts/test-node/state/selectors/conversations_test.preload.ts
@@ -1269,11 +1269,11 @@ describe('both/state/selectors/conversations-extra', () => {
           stableSelectedConversationIdInChatFolder: null,
         });
 
-      assert.strictEqual(conversations[0].name, 'First!');
-      assert.strictEqual(conversations[1].name, 'Á');
-      assert.strictEqual(conversations[2].name, 'B');
-      assert.strictEqual(conversations[3].name, 'C');
-      assert.strictEqual(conversations[4].name, 'No timestamp');
+      assert.strictEqual(conversations[0]?.name, 'First!');
+      assert.strictEqual(conversations[1]?.name, 'Á');
+      assert.strictEqual(conversations[2]?.name, 'B');
+      assert.strictEqual(conversations[3]?.name, 'C');
+      assert.strictEqual(conversations[4]?.name, 'No timestamp');
       assert.strictEqual(conversations.length, 5);
 
       assert.strictEqual(archivedConversations.length, 0);
@@ -1364,9 +1364,9 @@ describe('both/state/selectors/conversations-extra', () => {
             stableSelectedConversationIdInChatFolder: null,
           });
 
-        assert.strictEqual(pinnedConversations[0].name, 'Pin One');
-        assert.strictEqual(pinnedConversations[1].name, 'Pin Two');
-        assert.strictEqual(pinnedConversations[2].name, 'Pin Three');
+        assert.strictEqual(pinnedConversations[0]?.name, 'Pin One');
+        assert.strictEqual(pinnedConversations[1]?.name, 'Pin Two');
+        assert.strictEqual(pinnedConversations[2]?.name, 'Pin Three');
 
         assert.strictEqual(archivedConversations.length, 0);
 
@@ -1495,12 +1495,12 @@ describe('both/state/selectors/conversations-extra', () => {
             stableSelectedConversationIdInChatFolder: null,
           });
 
-        assert.strictEqual(pinnedConversations[0].name, 'Pin One');
-        assert.strictEqual(pinnedConversations[1].name, 'Pin Two');
-        assert.strictEqual(pinnedConversations[2].name, 'Pin Three');
+        assert.strictEqual(pinnedConversations[0]?.name, 'Pin One');
+        assert.strictEqual(pinnedConversations[1]?.name, 'Pin Two');
+        assert.strictEqual(pinnedConversations[2]?.name, 'Pin Three');
         assert.strictEqual(pinnedConversations.length, 3);
 
-        assert.strictEqual(archivedConversations[0].name, 'Pin Four');
+        assert.strictEqual(archivedConversations[0]?.name, 'Pin Four');
         assert.strictEqual(archivedConversations.length, 1);
 
         assert.strictEqual(conversations.length, 0);
@@ -1685,7 +1685,7 @@ describe('both/state/selectors/conversations-extra', () => {
           role: 0,
           joinedAtVersion: 0,
         },
-      ];
+      ] as const;
       const group: ConversationType = {
         ...makeGroup('group'),
         membersV2,
diff --git a/ts/test-node/state/selectors/search_test.preload.ts b/ts/test-node/state/selectors/search_test.preload.ts
index efcd23133b..4d0d783a08 100644
--- a/ts/test-node/state/selectors/search_test.preload.ts
+++ b/ts/test-node/state/selectors/search_test.preload.ts
@@ -457,10 +457,10 @@ describe('both/state/selectors/search', () => {
     });
 
     it('adds isSelected flag to conversations when filterByUnread is true', () => {
-      const conversations: Array<ConversationType> = [
+      const conversations = [
         getDefaultConversation({ id: '1' }),
         getDefaultConversation({ id: 'selected-id' }),
-      ];
+      ] as const;
 
       const state: StateType = {
         ...getEmptyRootState(),
diff --git a/ts/test-node/types/BodyRange_test.std.ts b/ts/test-node/types/BodyRange_test.std.ts
index 979fae9e91..4fd8c48f48 100644
--- a/ts/test-node/types/BodyRange_test.std.ts
+++ b/ts/test-node/types/BodyRange_test.std.ts
@@ -860,7 +860,7 @@ describe('BodyRanges', () => {
           replacementText: 'Eve',
           conversationID: 'x',
         },
-      ];
+      ] as const;
       const { cleanedSnippet, bodyRanges: processedBodyRanges } =
         processBodyRangesForSearchResult({
           snippet:
diff --git a/ts/test-node/types/EmbeddedContact_test.std.ts b/ts/test-node/types/EmbeddedContact_test.std.ts
index 3835b86158..8da9eb22a2 100644
--- a/ts/test-node/types/EmbeddedContact_test.std.ts
+++ b/ts/test-node/types/EmbeddedContact_test.std.ts
@@ -271,7 +271,7 @@ describe('Contact', () => {
             ],
           },
         ],
-      };
+      } as const;
       const result = await upgradeVersion(
         message.contact[0],
         defaultContext,
@@ -301,7 +301,7 @@ describe('Contact', () => {
             ],
           },
         ],
-      };
+      } as const;
       const expected = {
         name: {
           nickname: 'Someone Somewhere',
@@ -348,7 +348,7 @@ describe('Contact', () => {
             } as unknown as Avatar,
           },
         ],
-      };
+      } as const;
       const expected = {
         name: {
           nickname: 'Someone Somewhere',
@@ -411,7 +411,7 @@ describe('Contact', () => {
             } as unknown as Avatar,
           },
         ],
-      };
+      } as const;
       const expected = {
         name: {
           nickname: 'Someone Somewhere',
@@ -474,11 +474,11 @@ describe('Contact', () => {
               {
                 type: 0,
                 value: 'someone@somewhere.com',
-              },
+              } as unknown as Email,
             ],
           },
         ],
-      };
+      } as const;
       const expected = {
         name: {
           nickname: 'Someone Somewhere',
@@ -524,7 +524,7 @@ describe('Contact', () => {
             ],
           },
         ],
-      };
+      } as const;
       const expected = {
         name: {
           nickname: 'Someone Somewhere',
@@ -572,7 +572,7 @@ describe('Contact', () => {
             ],
           },
         ],
-      };
+      } as const;
       const expected = {
         name: {
           nickname: 'Someone Somewhere',
@@ -605,7 +605,7 @@ describe('Contact', () => {
             ],
           },
         ],
-      };
+      } as const;
       const result = await upgradeVersion(
         message.contact[0],
         defaultContext,
diff --git a/ts/test-node/types/NotificationProfile_test.node.ts b/ts/test-node/types/NotificationProfile_test.node.ts
index 5990735df4..13ab3d5770 100644
--- a/ts/test-node/types/NotificationProfile_test.node.ts
+++ b/ts/test-node/types/NotificationProfile_test.node.ts
@@ -1036,9 +1036,9 @@ describe('NotificationProfile', () => {
       const starting = [middle, old, newest];
       const actual = sortProfiles(starting);
 
-      assert.strictEqual(actual[0].name, 'newest');
-      assert.strictEqual(actual[1].name, 'middle');
-      assert.strictEqual(actual[2].name, 'old');
+      assert.strictEqual(actual[0]?.name, 'newest');
+      assert.strictEqual(actual[1]?.name, 'middle');
+      assert.strictEqual(actual[2]?.name, 'old');
     });
   });
 
diff --git a/ts/test-node/updater/differential_test.node.ts b/ts/test-node/updater/differential_test.node.ts
index 9ff53b1933..99e24a50ac 100644
--- a/ts/test-node/updater/differential_test.node.ts
+++ b/ts/test-node/updater/differential_test.node.ts
@@ -97,7 +97,9 @@ describe('updater/differential', () => {
 
         const fullFile = await fs.readFile(path.join(FIXTURES, file));
 
-        const rangeHeader = req.headers.range?.match(/^bytes=([\d,\s-]+)$/);
+        const rangeHeader = req.headers.range?.match(/^bytes=([\d,\s-]+)$/) as
+          | (RegExpMatchArray & { 1: string })
+          | null;
         if (!rangeHeader) {
           res.writeHead(200);
           res.end(fullFile);
@@ -105,10 +107,12 @@ describe('updater/differential', () => {
         }
 
         const ranges = rangeHeader[1].split(/\s*,\s*/g).map(value => {
-          const range = value.match(/^(\d+)-(\d+)$/);
+          const range = value.match(/^(\d+)-(\d+)$/) as
+            | (RegExpMatchArray & { 1: string; 2: string })
+            | null;
           strictAssert(range, `Invalid header: ${rangeHeader}`);
 
-          return [parseInt(range[1], 10), parseInt(range[2], 10)];
+          return [parseInt(range[1], 10), parseInt(range[2], 10)] as const;
         });
 
         if (ranges.length === 1) {
@@ -120,7 +124,9 @@ describe('updater/differential', () => {
             return;
           }
 
-          const [from, to] = ranges[0];
+          const range = ranges[0];
+          strictAssert(range, 'Missing range');
+          const [from, to] = range;
           res.end(fullFile.slice(from, to + 1));
           return;
         }
diff --git a/ts/test-node/updater/signature_test.main.ts b/ts/test-node/updater/signature_test.main.ts
index 0a1d4dbbf2..26b1e04740 100644
--- a/ts/test-node/updater/signature_test.main.ts
+++ b/ts/test-node/updater/signature_test.main.ts
@@ -154,7 +154,8 @@ describe('updater/signatures', () => {
         version,
         privateKeyPath
       );
-      signature[4] += 3;
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      signature[4]! += 3;
 
       const verified = await verifySignature(
         updatePath,
diff --git a/ts/test-node/util/getFontNameByTextScript_test.dom.ts b/ts/test-node/util/getFontNameByTextScript_test.dom.ts
index a7792a6419..6893bad60e 100644
--- a/ts/test-node/util/getFontNameByTextScript_test.dom.ts
+++ b/ts/test-node/util/getFontNameByTextScript_test.dom.ts
@@ -64,10 +64,12 @@ describe('getFontNameByTextScript', () => {
     const text = 'abc';
 
     assert.throws(() => {
+      // @ts-expect-error invalid text style
       getFontNameByTextScript(text, -1);
     });
 
     assert.throws(() => {
+      // @ts-expect-error invalid text style
       getFontNameByTextScript(text, 99);
     });
   });
diff --git a/ts/test-node/util/iterables_test.std.ts b/ts/test-node/util/iterables_test.std.ts
index 90beb6c89d..5bc8777c77 100644
--- a/ts/test-node/util/iterables_test.std.ts
+++ b/ts/test-node/util/iterables_test.std.ts
@@ -334,8 +334,8 @@ describe('iterable utilities', () => {
     it('returns a map of groups', () => {
       assert.deepEqual(
         groupBy(
-          ['apple', 'aardvark', 'orange', 'orange', 'zebra'],
-          str => str[0]
+          ['apple', 'aardvark', 'orange', 'orange', 'zebra'] as const,
+          str => str[0] ?? ''
         ),
         {
           a: ['apple', 'aardvark'],
diff --git a/ts/test-node/util/logPadding_test.node.ts b/ts/test-node/util/logPadding_test.node.ts
index 1c071e2bac..df710152c6 100644
--- a/ts/test-node/util/logPadding_test.node.ts
+++ b/ts/test-node/util/logPadding_test.node.ts
@@ -35,12 +35,13 @@ const BUCKET_SIZES = [
   40453710, 42476396, 44600216, 46830227, 49171738, 51630325, 54211841,
   56922433, 59768555, 62756983, 65894832, 69189573, 72649052, 76281505,
   80095580, 84100359, 88305377, 92720646, 97356678, 102224512, 107335738,
-];
+] as const;
 
 describe('logPadSize', () => {
   it('properly calculates first bucket', () => {
-    for (let size = 0, max = BUCKET_SIZES[0]; size < max; size += 1) {
-      assert.strictEqual(BUCKET_SIZES[0], logPadSize(size));
+    const max = BUCKET_SIZES[0];
+    for (let size = 0; size < max; size += 1) {
+      assert.strictEqual(max, logPadSize(size));
     }
   });
 
@@ -48,29 +49,27 @@ describe('logPadSize', () => {
     let count = 0;
 
     const failures = new Array<string>();
-    for (let i = 0, max = BUCKET_SIZES.length - 1; i < max; i += 1) {
+    for (const [i, bucketSize] of BUCKET_SIZES.slice(0, -1).entries()) {
       // Exact
-      if (BUCKET_SIZES[i] !== logPadSize(BUCKET_SIZES[i])) {
+      if (bucketSize !== logPadSize(bucketSize)) {
         count += 1;
-        failures.push(
-          `${BUCKET_SIZES[i]} does not equal ${logPadSize(BUCKET_SIZES[i])}`
-        );
+        failures.push(`${bucketSize} does not equal ${logPadSize(bucketSize)}`);
       }
 
       // Just under
-      if (BUCKET_SIZES[i] !== logPadSize(BUCKET_SIZES[i] - 1)) {
+      if (bucketSize !== logPadSize(bucketSize - 1)) {
         count += 1;
         failures.push(
-          `${BUCKET_SIZES[i]} does not equal ${logPadSize(BUCKET_SIZES[i] - 1)}`
+          `${bucketSize} does not equal ${logPadSize(bucketSize - 1)}`
         );
       }
 
       // Just over
-      if (BUCKET_SIZES[i + 1] !== logPadSize(BUCKET_SIZES[i] + 1)) {
+      if (BUCKET_SIZES[i + 1] !== logPadSize(bucketSize + 1)) {
         count += 1;
         failures.push(
           `${BUCKET_SIZES[i + 1]} does not equal ` +
-            `${logPadSize(BUCKET_SIZES[i] + 1)}`
+            `${logPadSize(bucketSize + 1)}`
         );
       }
     }
diff --git a/ts/test-node/util/queueAttachmentDownloads_test.preload.ts b/ts/test-node/util/queueAttachmentDownloads_test.preload.ts
index 595ba6f8d1..9d425d2597 100644
--- a/ts/test-node/util/queueAttachmentDownloads_test.preload.ts
+++ b/ts/test-node/util/queueAttachmentDownloads_test.preload.ts
@@ -1,9 +1,11 @@
 // Copyright 2025 Signal Messenger, LLC
 // SPDX-License-Identifier: AGPL-3.0-only
 
-/* eslint-disable @typescript-eslint/no-non-null-assertion */
 import { assert } from 'chai';
-import type { MessageAttributesType } from '../../model-types.d.ts';
+import type {
+  EditHistoryType,
+  MessageAttributesType,
+} from '../../model-types.d.ts';
 import type { AttachmentType } from '../../types/Attachment.std.js';
 import { IMAGE_JPEG, LONG_MESSAGE } from '../../types/MIME.std.js';
 import { generateMessageId } from '../../util/generateMessageId.node.js';
@@ -84,80 +86,78 @@ describe('ensureBodyAttachmentsAreSeparated', () => {
     assert.deepEqual(result.bodyAttachment, msg.bodyAttachment);
   });
   it('separates first body attachment out for all editHistory', () => {
+    const normalAttachment = composeAttachment({
+      clientUuid: 'normal attachment',
+      contentType: IMAGE_JPEG,
+    });
+
+    const longMessageAttachment1 = composeAttachment({
+      clientUuid: 'long message attachment 1',
+      contentType: LONG_MESSAGE,
+    });
+
+    const longMessageAttachment2 = composeAttachment({
+      clientUuid: 'long message attachment 2',
+      contentType: LONG_MESSAGE,
+    });
+
+    const editAttachment1 = composeAttachment({
+      clientUuid: 'edit attachment 1',
+      contentType: IMAGE_JPEG,
+    });
+
+    const editAttachment2 = composeAttachment({
+      clientUuid: 'edit attachment 2',
+      contentType: IMAGE_JPEG,
+    });
+
+    const bodyAttachment = composeAttachment({
+      clientUuid: 'long message attachment already as bodyattachment',
+      contentType: LONG_MESSAGE,
+    });
+
+    const edit1: EditHistoryType = {
+      timestamp: Date.now(),
+      received_at: Date.now(),
+      attachments: [
+        editAttachment1,
+        longMessageAttachment1,
+        longMessageAttachment2,
+      ],
+    };
+
+    const edit2: EditHistoryType = {
+      timestamp: Date.now(),
+      received_at: Date.now(),
+      bodyAttachment,
+      attachments: [editAttachment1, editAttachment2],
+    };
+
     const msg = composeMessage({
       attachments: [
-        composeAttachment({
-          clientUuid: 'normal attachment',
-          contentType: IMAGE_JPEG,
-        }),
-        composeAttachment({
-          clientUuid: 'long message attachment 1',
-          contentType: LONG_MESSAGE,
-        }),
-        composeAttachment({
-          clientUuid: 'long message attachment 2',
-          contentType: LONG_MESSAGE,
-        }),
-      ],
-      editHistory: [
-        {
-          timestamp: Date.now(),
-          received_at: Date.now(),
-          attachments: [
-            composeAttachment({
-              clientUuid: 'edit attachment',
-              contentType: IMAGE_JPEG,
-            }),
-            composeAttachment({
-              clientUuid: 'long message attachment 1',
-              contentType: LONG_MESSAGE,
-            }),
-            composeAttachment({
-              clientUuid: 'long message attachment 2',
-              contentType: LONG_MESSAGE,
-            }),
-          ],
-        },
-        {
-          timestamp: Date.now(),
-          received_at: Date.now(),
-          bodyAttachment: composeAttachment({
-            clientUuid: 'long message attachment already as bodyattachment',
-            contentType: LONG_MESSAGE,
-          }),
-          attachments: [
-            composeAttachment({
-              clientUuid: 'edit attachment 1',
-              contentType: IMAGE_JPEG,
-            }),
-            composeAttachment({
-              clientUuid: 'edit attachment 2',
-              contentType: IMAGE_JPEG,
-            }),
-          ],
-        },
+        normalAttachment,
+        longMessageAttachment1,
+        longMessageAttachment2,
       ],
+      editHistory: [edit1, edit2],
     });
     const result = ensureBodyAttachmentsAreSeparated(msg, {
       logId: 'test',
       logger,
     });
 
-    assert.deepEqual(result.attachments, [msg.attachments?.[0]]);
-    assert.deepEqual(result.bodyAttachment, msg.attachments?.[1]);
+    assert.deepEqual(result.attachments, [normalAttachment]);
+    assert.deepEqual(result.bodyAttachment, longMessageAttachment1);
     assert.deepEqual(result.editHistory, [
       {
-        ...msg.editHistory![0],
-        attachments: [msg.editHistory![0].attachments![0]],
-        bodyAttachment: msg.editHistory![0].attachments![1],
+        ...edit1,
+        attachments: [editAttachment1],
+        bodyAttachment: longMessageAttachment1,
       },
       {
-        ...msg.editHistory![1],
-        attachments: [
-          msg.editHistory![1].attachments![0],
-          msg.editHistory![1].attachments![1],
-        ],
-        bodyAttachment: msg.editHistory![1].bodyAttachment,
+        ...edit2,
+        attachments: [editAttachment1, editAttachment2],
+        bodyAttachment,
       },
     ]);
   });
diff --git a/ts/textsecure/Errors.std.ts b/ts/textsecure/Errors.std.ts
index 64c052eae2..e7480a5719 100644
--- a/ts/textsecure/Errors.std.ts
+++ b/ts/textsecure/Errors.std.ts
@@ -46,7 +46,7 @@ export class OutgoingIdentityKeyError extends ReplayableError {
 
   // Note: Data to resend message is no longer captured
   constructor(incomingIdentifier: string, cause?: LibSignalErrorBase) {
-    const identifier = incomingIdentifier.split('.')[0];
+    const [identifier] = incomingIdentifier.split('.');
 
     super({
       name: 'OutgoingIdentityKeyError',
@@ -70,7 +70,7 @@ export class OutgoingMessageError extends ReplayableError {
     _t: unknown,
     httpError?: HTTPError
   ) {
-    const identifier = incomingIdentifier.split('.')[0];
+    const [identifier] = incomingIdentifier.split('.', 1);
 
     super({
       name: 'OutgoingMessageError',
@@ -101,7 +101,8 @@ export class SendMessageNetworkError extends ReplayableError {
       message: httpError.message,
     });
 
-    [this.identifier] = identifier.split('.');
+    const [id] = identifier.split('.', 1);
+    this.identifier = id;
     this.httpError = httpError;
 
     appendStack(this, httpError);
@@ -137,7 +138,8 @@ export class SendMessageChallengeError extends ReplayableError {
       cause: httpError,
     });
 
-    [this.identifier] = identifier.split('.');
+    const [id] = identifier.split('.', 1);
+    this.identifier = id;
     this.httpError = httpError;
 
     this.data = httpError.response as SendMessageChallengeData;
diff --git a/ts/textsecure/EventTarget.std.ts b/ts/textsecure/EventTarget.std.ts
index b8d5d18a61..05acf3dee4 100644
--- a/ts/textsecure/EventTarget.std.ts
+++ b/ts/textsecure/EventTarget.std.ts
@@ -73,8 +73,8 @@ export default class EventTarget {
           return;
         }
       }
+      this.listeners[eventName] = listeners;
     }
-    this.listeners[eventName] = listeners;
   }
 
   extend(source: any): any {
diff --git a/ts/textsecure/Helpers.std.ts b/ts/textsecure/Helpers.std.ts
index 914c4c875b..f981a52ac7 100644
--- a/ts/textsecure/Helpers.std.ts
+++ b/ts/textsecure/Helpers.std.ts
@@ -69,7 +69,8 @@ const utils = {
     number[0] === '+' && /^[0-9]+$/.test(number.substring(1)),
   // eslint-disable-next-line @typescript-eslint/explicit-module-boundary-types
   jsonThing: (thing: unknown) => JSON.stringify(ensureStringed(thing)),
-  unencodeNumber: (number: string): Array<string> => number.split('.'),
+  unencodeNumber: (number: string): [string, ...Array<string>] =>
+    number.split('.'),
 };
 
 export default utils;
diff --git a/ts/textsecure/MessageReceiver.preload.ts b/ts/textsecure/MessageReceiver.preload.ts
index 2435d6b8e2..3a935ec37a 100644
--- a/ts/textsecure/MessageReceiver.preload.ts
+++ b/ts/textsecure/MessageReceiver.preload.ts
@@ -848,10 +848,9 @@ export default class MessageReceiver
     }
 
     for await (const batch of this.#getAllFromCache()) {
-      const max = batch.length;
-      for (let i = 0; i < max; i += 1) {
+      for (const item of batch) {
         // eslint-disable-next-line no-await-in-loop
-        await this.#queueCached(batch[i]);
+        await this.#queueCached(item);
       }
     }
     log.info('queueAllCached - finished');
diff --git a/ts/textsecure/Provisioner.preload.ts b/ts/textsecure/Provisioner.preload.ts
index 587abb92c3..e614a6715e 100644
--- a/ts/textsecure/Provisioner.preload.ts
+++ b/ts/textsecure/Provisioner.preload.ts
@@ -99,7 +99,12 @@ const MAX_ROTATIONS = 6;
 
 const TIMEOUT_ERROR = new PTimeoutError();
 
-const QR_CODE_TIMEOUTS = [10 * SECOND, 20 * SECOND, 30 * SECOND, 60 * SECOND];
+const QR_CODE_TIMEOUTS = [
+  10 * SECOND,
+  20 * SECOND,
+  30 * SECOND,
+  60 * SECOND,
+] as const;
 
 export class Provisioner {
   readonly #subscribers = new Set<SubscriberType>();
@@ -242,7 +247,8 @@ export class Provisioner {
       let delay: number;
 
       try {
-        const sleepMs = QR_CODE_TIMEOUTS[this.#attemptCount];
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        const sleepMs = QR_CODE_TIMEOUTS[this.#attemptCount]!;
 
         // eslint-disable-next-line no-await-in-loop
         await this.#connect(signal, sleepMs);
diff --git a/ts/textsecure/SendMessage.preload.ts b/ts/textsecure/SendMessage.preload.ts
index b8871c21e8..fd68d379c5 100644
--- a/ts/textsecure/SendMessage.preload.ts
+++ b/ts/textsecure/SendMessage.preload.ts
@@ -778,7 +778,8 @@ export class MessageSender {
   static getRandomPadding(): Uint8Array {
     // Generate a random int from 1 and 512
     const buffer = getRandomBytes(2);
-    const paddingLength = (new Uint16Array(buffer)[0] & 0x1ff) + 1;
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const paddingLength = (new Uint16Array(buffer)[0]! & 0x1ff) + 1;
 
     // Generate a random padding buffer of the chosen size
     return getRandomBytes(paddingLength);
@@ -2174,7 +2175,8 @@ export class MessageSender {
         `syncViewOnceOpen: ${viewOnceOpens.length} opens provided. Can only handle one.`
       );
     }
-    const { senderAci, timestamp } = viewOnceOpens[0];
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const { senderAci, timestamp } = viewOnceOpens[0]!;
 
     if (!senderAci) {
       throw new Error('syncViewOnceOpen: Missing senderAci');
diff --git a/ts/textsecure/WebAPI.preload.ts b/ts/textsecure/WebAPI.preload.ts
index 90557a3116..9917b170e3 100644
--- a/ts/textsecure/WebAPI.preload.ts
+++ b/ts/textsecure/WebAPI.preload.ts
@@ -379,7 +379,7 @@ async function getFetchOptions<Type extends ResponseType, OutputShape>(
     };
   }
   const agentEntry = agents[cacheKey];
-  const agent = agentEntry?.agent ?? null;
+  const agent = agentEntry?.agent ?? undefined;
 
   const fetchOptions: FetchOptionsType = {
     method: options.type,
@@ -729,12 +729,11 @@ function makeHTTPError(
 export function makeKeysLowercase<V>(
   headers: Record<string, V>
 ): Record<string, V> {
-  const keys = Object.keys(headers);
   const lowerCase: Record<string, V> = Object.create(null);
 
-  keys.forEach(key => {
-    lowerCase[key.toLowerCase()] = headers[key];
-  });
+  for (const [key, value] of Object.entries(headers)) {
+    lowerCase[key.toLowerCase()] = value;
+  }
 
   return lowerCase;
 }
@@ -3877,7 +3876,9 @@ export async function putStickers(
   });
   await Promise.all(
     stickers.map(async (sticker: ServerV2AttachmentType, index: number) => {
-      const stickerParams = makePutParams(sticker, encryptedStickers[index]);
+      const encryptedSticker = encryptedStickers[index];
+      strictAssert(encryptedSticker, 'Missing encryptedSticker');
+      const stickerParams = makePutParams(sticker, encryptedSticker);
       await queue.add(async () =>
         _outerAjax(`${cdnUrlObject['0']}/`, {
           ...stickerParams,
@@ -4044,7 +4045,8 @@ async function _getAttachment({
 
       const match = PARSE_RANGE_HEADER.exec(range);
       strictAssert(match != null, 'Attachment Content-Range is invalid');
-      const maybeSize = safeParseNumber(match[1]);
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      const maybeSize = safeParseNumber(match[1]!);
       strictAssert(
         maybeSize != null,
         'Attachment Content-Range[1] is not a number'
@@ -4193,7 +4195,8 @@ export async function putEncryptedAttachment(
     if (range != null) {
       const match = range.match(/^bytes=0-(\d+)$/);
       strictAssert(match != null, `Invalid range header: ${range}`);
-      start = parseInt(match[1], 10);
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      start = parseInt(match[1]!, 10);
     } else {
       log.warn(`${logId}: No range header`);
     }
@@ -4753,9 +4756,12 @@ export async function getGroupLog(
     const range = response.headers.get('Content-Range');
     const match = PARSE_GROUP_LOG_RANGE_HEADER.exec(range || '');
 
-    const start = match ? parseInt(match[1], 10) : undefined;
-    const end = match ? parseInt(match[2], 10) : undefined;
-    const currentRevision = match ? parseInt(match[3], 10) : undefined;
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const start = match ? parseInt(match[1]!, 10) : undefined;
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const end = match ? parseInt(match[2]!, 10) : undefined;
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const currentRevision = match ? parseInt(match[3]!, 10) : undefined;
 
     if (
       match &&
diff --git a/ts/types/AttachmentSize.std.ts b/ts/types/AttachmentSize.std.ts
index d1ab1ee80e..6b61cb1df2 100644
--- a/ts/types/AttachmentSize.std.ts
+++ b/ts/types/AttachmentSize.std.ts
@@ -75,6 +75,7 @@ export function getRenderDetailsForLimit(limitKb: number): {
 
   return {
     limit: Math.trunc(limit),
-    units: units[u],
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    units: units[u]!,
   };
 }
diff --git a/ts/types/BodyRange.std.ts b/ts/types/BodyRange.std.ts
index 6db4b95725..be4562c997 100644
--- a/ts/types/BodyRange.std.ts
+++ b/ts/types/BodyRange.std.ts
@@ -510,6 +510,9 @@ export function processBodyRangesForSearchResult({
 
   // To format the matches identified by FTS, we create synthetic BodyRanges to mix in
   // with all the other formatting embedded in this message.
+  type HighlightMatch = RegExpExecArray & {
+    indices: Record<0 | 1, [number, number]>;
+  };
   const highlightMatches = snippet.matchAll(
     new RegExp(
       `${SNIPPET_LEFT_PLACEHOLDER}(.*?)${SNIPPET_RIGHT_PLACEHOLDER}`,
@@ -520,9 +523,7 @@ export function processBodyRangesForSearchResult({
   let placeholderCharsSkipped = 0;
   for (const highlightMatch of highlightMatches) {
     // TS < 5 does not have types for RegExpIndicesArray
-    const { indices } = highlightMatch as RegExpMatchArray & {
-      indices: Array<Array<number>>;
-    };
+    const { indices } = highlightMatch as HighlightMatch;
     const [wholeMatchStartIdx] = indices[0];
     const [matchedWordStartIdx, matchedWordEndIdx] = indices[1];
     adjustedBodyRanges.push({
diff --git a/ts/types/Colors.std.ts b/ts/types/Colors.std.ts
index e01e5532ca..9422540f4c 100644
--- a/ts/types/Colors.std.ts
+++ b/ts/types/Colors.std.ts
@@ -75,7 +75,7 @@ export const ContactNameColors = [
   '190',
   '310',
   '110',
-];
+] as const;
 
 export type ContactNameColorType = (typeof ContactNameColors)[number];
 
@@ -112,5 +112,6 @@ export type CustomColorsItemType = {
 };
 
 export function getAvatarColor(color?: AvatarColorType): AvatarColorType {
-  return color || AvatarColors[0];
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  return color || AvatarColors[0]!;
 }
diff --git a/ts/types/Megaphone.std.ts b/ts/types/Megaphone.std.ts
index 8b7faba5a8..d623c3bb57 100644
--- a/ts/types/Megaphone.std.ts
+++ b/ts/types/Megaphone.std.ts
@@ -143,5 +143,6 @@ export function getMegaphoneLastSnoozeDurationMs(
   const { snoozeDurationDays } = getMegaphoneSnoozeConfig(megaphone);
   const lastSnoozeCount = Math.max(megaphone.snoozeCount - 1, 0);
   const snoozeIndex = Math.min(lastSnoozeCount, snoozeDurationDays.length - 1);
-  return snoozeDurationDays[snoozeIndex] * DAY;
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  return snoozeDurationDays[snoozeIndex]! * DAY;
 }
diff --git a/ts/types/Message2.preload.ts b/ts/types/Message2.preload.ts
index 65a4f862b8..7106d3c68b 100644
--- a/ts/types/Message2.preload.ts
+++ b/ts/types/Message2.preload.ts
@@ -66,6 +66,7 @@ import {
 } from '../util/migrations.preload.js';
 import type { getExistingAttachmentDataForReuse } from '../util/attachments/deduplicateAttachment.preload.js';
 import type { getPlaintextHashForInMemoryAttachment } from '../AttachmentCrypto.node.js';
+import { strictAssert } from '../util/assert.std.js';
 
 const { isFunction, isObject, identity } = lodash;
 
@@ -746,6 +747,7 @@ export const upgradeSchema = async (
 
     const currentVersion = versions[index];
     try {
+      strictAssert(currentVersion, 'Missing currentVersion');
       // We really do want this intra-loop await because this is a chained async action,
       //   each step dependent on the previous
       // eslint-disable-next-line no-await-in-loop
diff --git a/ts/types/QualifiedAddress.std.ts b/ts/types/QualifiedAddress.std.ts
index 5b9e1bff6f..56cf57f58a 100644
--- a/ts/types/QualifiedAddress.std.ts
+++ b/ts/types/QualifiedAddress.std.ts
@@ -8,6 +8,11 @@ import { isServiceIdString } from './ServiceId.std.js';
 import type { AddressStringType } from './Address.std.js';
 import { Address } from './Address.std.js';
 
+type QualifiedAddressMatch = RegExpMatchArray & {
+  1: string;
+  2: string;
+  3: string;
+};
 const QUALIFIED_ADDRESS_REGEXP =
   /^((?:PNI:)?[:0-9a-f-]+):((?:PNI:)?[:0-9a-f-]+).(\d+)$/i;
 
@@ -41,7 +46,8 @@ export class QualifiedAddress {
   public static parse(value: string): QualifiedAddress {
     const match = value.match(QUALIFIED_ADDRESS_REGEXP);
     strictAssert(match != null, `Invalid QualifiedAddress: ${value}`);
-    const [whole, ourServiceId, serviceId, deviceId] = match;
+    const [whole, ourServiceId, serviceId, deviceId] =
+      match as QualifiedAddressMatch;
     strictAssert(whole === value, 'Integrity check');
     strictAssert(
       isServiceIdString(ourServiceId),
diff --git a/ts/types/Stickers.preload.ts b/ts/types/Stickers.preload.ts
index c80dd3910d..74f077949a 100644
--- a/ts/types/Stickers.preload.ts
+++ b/ts/types/Stickers.preload.ts
@@ -322,9 +322,8 @@ export function downloadQueuedPacks(): void {
   log.info('downloadQueuedPacks');
   strictAssert(packsToDownload, 'Stickers not initialized');
 
-  const ids = Object.keys(packsToDownload);
-  for (const id of ids) {
-    const { key, status } = packsToDownload[id];
+  for (const [id, packToDownload] of Object.entries(packsToDownload)) {
+    const { key, status } = packToDownload;
 
     // The queuing is done inside this function, no need to await here
     drop(
@@ -345,8 +344,7 @@ function capturePacksToDownload(
   const toDownload: DownloadMap = Object.create(null);
 
   // First, ensure that blessed packs are in good shape
-  const blessedIds = Object.keys(BLESSED_PACKS);
-  blessedIds.forEach(id => {
+  for (const [id, blessedPack] of Object.entries(BLESSED_PACKS)) {
     const existing = existingPackLookup[id];
     if (
       !existing ||
@@ -354,29 +352,26 @@ function capturePacksToDownload(
     ) {
       toDownload[id] = {
         id,
-        ...BLESSED_PACKS[id],
+        ...blessedPack,
       };
     }
-  });
+  }
 
   // Then, find error cases in packs we already know about
-  const existingIds = Object.keys(existingPackLookup);
-  existingIds.forEach(id => {
+  for (const [id, existing] of Object.entries(existingPackLookup)) {
     if (toDownload[id]) {
-      return;
+      continue;
     }
 
-    const existing = existingPackLookup[id];
-
     // These packs should never end up in the database, but if they do we'll delete them
     if (existing.status === 'ephemeral') {
       void deletePack(id);
-      return;
+      continue;
     }
 
     // We don't automatically download these; not until a user action kicks it off
     if (existing.status === 'known') {
-      return;
+      continue;
     }
 
     if (doesPackNeedDownload(existing)) {
@@ -388,7 +383,7 @@ function capturePacksToDownload(
         status,
       };
     }
-  });
+  }
 
   return toDownload;
 }
diff --git a/ts/updater/common.main.ts b/ts/updater/common.main.ts
index 366d77b302..fe6fbd1e13 100644
--- a/ts/updater/common.main.ts
+++ b/ts/updater/common.main.ts
@@ -1065,7 +1065,8 @@ export function getUpdateFileName(
     const candidates = files.filter(fileFilter);
 
     if (candidates.length === 1) {
-      path = candidates[0].url;
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      path = candidates[0]!.url;
     }
   }
 
diff --git a/ts/updater/curve.node.ts b/ts/updater/curve.node.ts
index 1e7fb94569..9af06952a3 100644
--- a/ts/updater/curve.node.ts
+++ b/ts/updater/curve.node.ts
@@ -3,7 +3,12 @@
 
 import { PrivateKey, PublicKey } from '@signalapp/libsignal-client';
 
-export function keyPair(): Record<string, Uint8Array> {
+type KeyPair = Readonly<{
+  publicKey: Uint8Array;
+  privateKey: Uint8Array;
+}>;
+
+export function keyPair(): KeyPair {
   const privKey = PrivateKey.generate();
   const pubKey = privKey.getPublicKey();
 
diff --git a/ts/updater/differential.node.ts b/ts/updater/differential.node.ts
index 474bda1ce4..2cfdad5be1 100644
--- a/ts/updater/differential.node.ts
+++ b/ts/updater/differential.node.ts
@@ -111,11 +111,13 @@ export async function parseBlockMap(data: Buffer): Promise<BlockMapType> {
   );
 
   const [file] = json.files;
+  strictAssert(file, 'Missing file');
   let { offset } = file;
 
   const blocks = new Array<BlockMapBlockType>();
   for (const [i, checksum] of file.checksums.entries()) {
-    const size = file.sizes[i];
+    // TypeScript gets confused about this type for some reason.
+    const size: number | undefined = file.sizes[i];
     strictAssert(size !== undefined, `missing block size: ${i}`);
 
     blocks.push({
@@ -407,7 +409,8 @@ export async function downloadRanges(
     // When the result is single range we might non-multipart response
     if (ranges.length === 1 && !match) {
       await saveDiffStream({
-        diff: ranges[0],
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        diff: ranges[0]!,
         stream,
         abortSignal,
         output,
@@ -466,7 +469,9 @@ async function takeDiffFromPart(
   const contentRange = headers['content-range'];
   strictAssert(contentRange, 'Missing Content-Range header for the part');
 
-  const match = contentRange.join(', ').match(/^bytes\s+(\d+-\d+)/);
+  const match = contentRange.join(', ').match(/^bytes\s+(\d+-\d+)/) as
+    | (RegExpMatchArray & { 1: string })
+    | null;
   strictAssert(
     match,
     `Invalid Content-Range header for the part: "${contentRange}"`
diff --git a/ts/updater/generateSignature.main.ts b/ts/updater/generateSignature.main.ts
index 09486294d8..b59bd78e42 100644
--- a/ts/updater/generateSignature.main.ts
+++ b/ts/updater/generateSignature.main.ts
@@ -78,10 +78,8 @@ async function findUpdatePaths(): Promise<Array<string>> {
   const releaseDir = resolve('release');
   const files: Array<string> = await readdir(releaseDir);
 
-  const max = files.length;
   const results = new Array<string>();
-  for (let i = 0; i < max; i += 1) {
-    const file = files[i];
+  for (const file of files) {
     const fullPath = join(releaseDir, file);
 
     if (IS_EXE.test(file) || IS_ZIP.test(file)) {
diff --git a/ts/util/Attachment.std.ts b/ts/util/Attachment.std.ts
index c9b10bdf6c..751207b855 100644
--- a/ts/util/Attachment.std.ts
+++ b/ts/util/Attachment.std.ts
@@ -354,7 +354,7 @@ export function isGIF(attachments?: ReadonlyArray<AttachmentType>): boolean {
   const flag = SignalService.AttachmentPointer.Flags.GIF;
   const hasFlag =
     // eslint-disable-next-line no-bitwise
-    !isUndefined(attachment.flags) && (attachment.flags & flag) === flag;
+    !isUndefined(attachment?.flags) && (attachment.flags & flag) === flag;
 
   return hasFlag && isVideoAttachment(attachment);
 }
@@ -499,7 +499,8 @@ export function getGridDimensions(
   }
 
   if (attachments.length === 1) {
-    return getImageDimensionsForTimeline(attachments[0]);
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    return getImageDimensionsForTimeline(attachments[0]!);
   }
 
   if (attachments.length === 2) {
diff --git a/ts/util/BackOff.std.ts b/ts/util/BackOff.std.ts
index 81bca6f58c..b378c1b09b 100644
--- a/ts/util/BackOff.std.ts
+++ b/ts/util/BackOff.std.ts
@@ -46,7 +46,8 @@ export class BackOff {
   ) {}
 
   public get(): number {
-    let result = this.timeouts[this.#count];
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    let result = this.timeouts[this.#count]!;
     const { jitter = 0, random = DEFAULT_RANDOM } = this.options;
 
     // Do not apply jitter larger than the timeout value. It is supposed to be
diff --git a/ts/util/DelimitedStream.node.ts b/ts/util/DelimitedStream.node.ts
index f262f05063..6a52f312a4 100644
--- a/ts/util/DelimitedStream.node.ts
+++ b/ts/util/DelimitedStream.node.ts
@@ -40,7 +40,8 @@ export class DelimitedStream extends Transform {
     let offset = 0;
     while (offset < chunk.length) {
       if (this.#state.kind === 'prefix') {
-        const b = chunk[offset];
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        const b = chunk[offset]!;
         offset += 1;
 
         // See: https://protobuf.dev/programming-guides/encoding/
diff --git a/ts/util/arePinnedConversationsEqual.node.ts b/ts/util/arePinnedConversationsEqual.node.ts
index a3bacbb302..b100bb8418 100644
--- a/ts/util/arePinnedConversationsEqual.node.ts
+++ b/ts/util/arePinnedConversationsEqual.node.ts
@@ -17,7 +17,7 @@ export function arePinnedConversationsEqual(
   }
   return localValue.every(
     (localPinnedConversation: PinnedConversation, index: number) => {
-      const remotePinnedConversation = remoteValue[index].identifier;
+      const remotePinnedConversation = remoteValue[index]?.identifier;
       if (!remotePinnedConversation) {
         return false;
       }
diff --git a/ts/util/benchmark/stats.std.ts b/ts/util/benchmark/stats.std.ts
index 8209903183..89f53dc983 100644
--- a/ts/util/benchmark/stats.std.ts
+++ b/ts/util/benchmark/stats.std.ts
@@ -33,7 +33,8 @@ export function stats(
   const result: StatsType = { mean, stddev };
 
   for (const p of percentiles) {
-    result[`p${p}`] = sorted[Math.floor((sorted.length * p) / 100)];
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    result[`p${p}`] = sorted[Math.floor((sorted.length * p) / 100)]!;
   }
 
   return result;
@@ -146,7 +147,8 @@ export function regress(samples: ReadonlyArray<Sample>): Regression {
     yIntercept,
     slope,
     confidence:
-      STUDENT_T[Math.min(samples.length, STUDENT_T.length - 1)] * stdError,
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      STUDENT_T[Math.min(samples.length, STUDENT_T.length - 1)]! * stdError,
     outliers,
     severeOutliers,
   };
diff --git a/ts/util/cleanup.preload.ts b/ts/util/cleanup.preload.ts
index f0d6c31606..ea59379dfb 100644
--- a/ts/util/cleanup.preload.ts
+++ b/ts/util/cleanup.preload.ts
@@ -212,8 +212,10 @@ async function cleanupStoryReplies(
   }
 
   return cleanupStoryReplies(story, {
-    messageId: lastMessageId,
-    receivedAt: lastReceivedAt,
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    messageId: lastMessageId!,
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    receivedAt: lastReceivedAt!,
   });
 }
 
diff --git a/ts/util/computeBlurHashUrl.std.ts b/ts/util/computeBlurHashUrl.std.ts
index 3dec5daa96..d676a2e366 100644
--- a/ts/util/computeBlurHashUrl.std.ts
+++ b/ts/util/computeBlurHashUrl.std.ts
@@ -112,9 +112,12 @@ export function computeBlurHashUrl(
     i += 4, j += 3
   ) {
     // BMP uses BGR ordering
-    bitmap[j + 2] = rgba[i];
-    bitmap[j + 1] = rgba[i + 1];
-    bitmap[j] = rgba[i + 2];
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    bitmap[j + 2]! = rgba[i]!;
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    bitmap[j + 1]! = rgba[i + 1]!;
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    bitmap[j]! = rgba[i + 2]!;
   }
 
   return `data:image/bmp;base64,${Bytes.toBase64(bitmap)}`;
diff --git a/ts/util/createHTTPSAgent.node.ts b/ts/util/createHTTPSAgent.node.ts
index a71f87e700..624a27ca94 100644
--- a/ts/util/createHTTPSAgent.node.ts
+++ b/ts/util/createHTTPSAgent.node.ts
@@ -137,6 +137,7 @@ export async function happyEyeballs({
   const results = await Promise.allSettled(
     interleaved.map(async (addr, index) => {
       const abortController = abortControllers[index];
+      strictAssert(abortController, 'Missing abortController');
       if (index !== 0) {
         await sleep(index * DELAY_MS, abortController.signal);
       }
@@ -185,17 +186,22 @@ export async function happyEyeballs({
       'Fulfilled promise was not fulfilled'
     );
     const { socket, index } = fulfilled.value;
+    const address = interleaved[index];
+    strictAssert(address, 'Missing address');
 
     return {
       socket,
-      address: interleaved[index],
+      address,
       v4Attempts,
       v6Attempts,
     };
   }
 
+  const firstResult = results[0];
+  strictAssert(firstResult, 'Missing firstResult');
+
   strictAssert(
-    results[0].status === 'rejected',
+    firstResult.status === 'rejected',
     'No fulfilled promises, but no rejected either'
   );
 
@@ -203,7 +209,7 @@ export async function happyEyeballs({
   for (const controller of abortControllers) {
     controller.abort();
   }
-  throw results[0].reason;
+  throw firstResult.reason;
 }
 
 export type ConnectOptionsType = Readonly<{
diff --git a/ts/util/createIdenticon.preload.tsx b/ts/util/createIdenticon.preload.tsx
index 0ca3eb3fe4..2ccc8e5f87 100644
--- a/ts/util/createIdenticon.preload.tsx
+++ b/ts/util/createIdenticon.preload.tsx
@@ -14,6 +14,7 @@ import {
 } from '../components/IdenticonSVG.dom.js';
 import { missingCaseError } from './missingCaseError.std.js';
 import { writeNewPlaintextTempData } from './migrations.preload.js';
+import { strictAssert } from './assert.std.js';
 
 const TARGET_MIME = 'image/png';
 
@@ -35,6 +36,7 @@ export function createIdenticon(
   { saveToDisk }: { saveToDisk?: boolean } = {}
 ): Promise<{ url: string; path?: string }> {
   const [defaultColorValue] = Array.from(AvatarColorMap.values());
+  strictAssert(defaultColorValue, 'Missing defaultColorValue');
   const avatarColor = AvatarColorMap.get(color);
   let html: string;
 
diff --git a/ts/util/createProxyAgent.node.ts b/ts/util/createProxyAgent.node.ts
index e1c65aeefd..8696c955d7 100644
--- a/ts/util/createProxyAgent.node.ts
+++ b/ts/util/createProxyAgent.node.ts
@@ -47,7 +47,8 @@ export async function createProxyAgent(proxyUrl: string): Promise<ProxyAgent> {
     // SOCKS 4/5 resolve target host before sending it to the proxy.
     if (host !== proxyHost) {
       const idx = Math.floor(Math.random() * addresses.length);
-      return addresses[idx];
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      return addresses[idx]!;
     }
 
     const start = Date.now();
diff --git a/ts/util/createSupportUrl.std.ts b/ts/util/createSupportUrl.std.ts
index cda22fa65e..5cba2cb68c 100644
--- a/ts/util/createSupportUrl.std.ts
+++ b/ts/util/createSupportUrl.std.ts
@@ -51,11 +51,11 @@ export function createSupportUrl({
 
   url.searchParams.set('desktop', '');
 
-  for (const key of Object.keys(query)) {
+  for (const [key, value] of Object.entries(query)) {
     if (key === 'desktop') {
       continue;
     }
-    url.searchParams.set(key, query[key]);
+    url.searchParams.set(key, value);
   }
 
   // Support page requires `?desktop&...` not `?desktop=&...`
diff --git a/ts/util/deleteStoryForEveryone.preload.ts b/ts/util/deleteStoryForEveryone.preload.ts
index 96c3047da5..5515ca9a0d 100644
--- a/ts/util/deleteStoryForEveryone.preload.ts
+++ b/ts/util/deleteStoryForEveryone.preload.ts
@@ -141,7 +141,8 @@ export async function deleteStoryForEveryone(
       let recipient = newStoryRecipients.get(destinationServiceId);
       if (!recipient) {
         const isAllowedToReply =
-          sendStateByConversationId[conversationId].isAllowedToReplyToStory;
+          // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+          sendStateByConversationId[conversationId]!.isAllowedToReplyToStory;
         recipient = {
           distributionListIds: new Set(),
           isAllowedToReply: isAllowedToReply !== false,
diff --git a/ts/util/deliveryReceipt.preload.ts b/ts/util/deliveryReceipt.preload.ts
index daf584147b..0a4ff18889 100644
--- a/ts/util/deliveryReceipt.preload.ts
+++ b/ts/util/deliveryReceipt.preload.ts
@@ -29,12 +29,12 @@ export const deliveryReceiptBatcher = createBatcher<Receipt>({
   processBatch: async deliveryReceipts => {
     const groups = groupBy(deliveryReceipts, 'conversationId');
     await Promise.all(
-      Object.keys(groups).map(async conversationId => {
+      Object.entries(groups).map(async ([conversationId, receipts]) => {
         await conversationJobQueue.add({
           type: conversationQueueJobEnum.enum.Receipts,
           conversationId,
           receiptsType: ReceiptType.Delivery,
-          receipts: groups[conversationId],
+          receipts,
         });
       })
     );
diff --git a/ts/util/desktopCapturer.preload.ts b/ts/util/desktopCapturer.preload.ts
index 672734d209..00ac26395e 100644
--- a/ts/util/desktopCapturer.preload.ts
+++ b/ts/util/desktopCapturer.preload.ts
@@ -338,11 +338,11 @@ export class DesktopCapturer {
       return i18n('icu:calling__SelectPresentingSourcesModal--entireScreen');
     }
 
+    type Match = RegExpMatchArray & { 1: string };
     const match = name.match(/^Screen (\d+)$/);
     if (match) {
-      return i18n('icu:calling__SelectPresentingSourcesModal--screen', {
-        id: match[1],
-      });
+      const [, id] = match as Match;
+      return i18n('icu:calling__SelectPresentingSourcesModal--screen', { id });
     }
 
     return name;
diff --git a/ts/util/downloadOnboardingStory.preload.ts b/ts/util/downloadOnboardingStory.preload.ts
index cda0e3b3bf..11f838bbcd 100644
--- a/ts/util/downloadOnboardingStory.preload.ts
+++ b/ts/util/downloadOnboardingStory.preload.ts
@@ -56,9 +56,9 @@ export async function downloadOnboardingStory(): Promise<void> {
   log.info('got manifest version:', manifest.version);
 
   const imageFilenames =
-    userLocale in manifest.languages
-      ? manifest.languages[userLocale]
-      : manifest.languages.en;
+    manifest.languages[userLocale] ??
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    manifest.languages.en!;
 
   const imageBuffers = await downloadOnboardingStories(
     manifest.version,
diff --git a/ts/util/editHelpers.std.ts b/ts/util/editHelpers.std.ts
index 693de9540e..42515e6384 100644
--- a/ts/util/editHelpers.std.ts
+++ b/ts/util/editHelpers.std.ts
@@ -41,11 +41,13 @@ export function getTargetOfThisEditTimestamp({
 
   // We want the second-to-last item, because we may have partially sent targetTimestamp
   if (length > 1) {
-    return mostRecent[length - 2].timestamp;
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    return mostRecent[length - 2]!.timestamp;
   }
   // If there's only one item, we'll use it
   if (length > 0) {
-    return mostRecent[length - 1].timestamp;
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    return mostRecent[length - 1]!.timestamp;
   }
 
   // This is a good failover in case we ever stop duplicating data in editHistory
diff --git a/ts/util/expirationTimer.std.ts b/ts/util/expirationTimer.std.ts
index c5f05d6f03..2767901f79 100644
--- a/ts/util/expirationTimer.std.ts
+++ b/ts/util/expirationTimer.std.ts
@@ -49,7 +49,7 @@ export function format(
   // but humanizeDuration uses an underscore
   const locale: string = i18n.getLocale().replace(/-/g, '_');
 
-  const localeWithoutRegion: string = locale.split('_', 1)[0];
+  const [localeWithoutRegion] = locale.split('_', 1);
   const fallbacks: Array<string> = [];
   if (localeWithoutRegion !== locale) {
     fallbacks.push(localeWithoutRegion);
diff --git a/ts/util/exponentialBackoff.std.ts b/ts/util/exponentialBackoff.std.ts
index 8615f7c297..d15d746260 100644
--- a/ts/util/exponentialBackoff.std.ts
+++ b/ts/util/exponentialBackoff.std.ts
@@ -38,7 +38,8 @@ export function exponentialBackoffSleepTime(
   );
 
   if (attempt - 1 < numHardcodedBackoffs) {
-    return options.firstBackoffs[attempt - 1];
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    return options.firstBackoffs[attempt - 1]!;
   }
 
   const lastHardcodedBackoff = options.firstBackoffs.at(-1);
diff --git a/ts/util/filterAndSortConversations.std.ts b/ts/util/filterAndSortConversations.std.ts
index 5b321aa636..1991a14cf3 100644
--- a/ts/util/filterAndSortConversations.std.ts
+++ b/ts/util/filterAndSortConversations.std.ts
@@ -120,13 +120,14 @@ function searchConversations(
   searchTerm: string,
   regionCode: string | undefined
 ): ReadonlyArray<Pick<Fuse.FuseResult<ConversationType>, 'item' | 'score'>> {
+  type CommandMatch = RegExpMatchArray & { 1: string; 2: string | undefined };
   const maybeCommand = searchTerm.match(/^!([^\s:]+)(?::(.*))?$/);
   if (maybeCommand) {
-    const [, commandName, query] = maybeCommand;
+    const [, commandName, query] = maybeCommand as CommandMatch;
 
     const command = COMMANDS.get(commandName);
     if (command) {
-      return command(conversations, query).map(item => ({ item }));
+      return command(conversations, query ?? '').map(item => ({ item }));
     }
   }
 
diff --git a/ts/util/findAndDeleteOnboardingStoryIfExists.preload.ts b/ts/util/findAndDeleteOnboardingStoryIfExists.preload.ts
index 47956ab686..00c847e975 100644
--- a/ts/util/findAndDeleteOnboardingStoryIfExists.preload.ts
+++ b/ts/util/findAndDeleteOnboardingStoryIfExists.preload.ts
@@ -21,7 +21,8 @@ export async function findAndDeleteOnboardingStoryIfExists(): Promise<void> {
   }
 
   const hasExpired = await (async () => {
-    const [storyId] = existingOnboardingStoryMessageIds;
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const storyId = existingOnboardingStoryMessageIds[0]!;
     try {
       const message = await getMessageById(storyId);
       if (!message) {
diff --git a/ts/util/generateDonationReceipt.dom.ts b/ts/util/generateDonationReceipt.dom.ts
index ab54f4c9c2..74d04da347 100644
--- a/ts/util/generateDonationReceipt.dom.ts
+++ b/ts/util/generateDonationReceipt.dom.ts
@@ -396,7 +396,7 @@ export async function generateDonationReceiptBlob(
 
   // Extract the base64 encoded data from the data URL
   // Data URL format: "data:image/png;base64,iVBORw0KGgoAAAANS..."
-  const base64Data = dataURL.split(',')[1];
+  const [base64Data] = dataURL.split(',');
 
   // Decode the base64 string to binary data
   const binaryString = atob(base64Data);
diff --git a/ts/util/generateMessageId.node.ts b/ts/util/generateMessageId.node.ts
index a4fcc90090..9f0a0422aa 100644
--- a/ts/util/generateMessageId.node.ts
+++ b/ts/util/generateMessageId.node.ts
@@ -14,7 +14,7 @@ export type GeneratedMessageIdType = Readonly<{
 export function generateMessageId(counter: number): GeneratedMessageIdType {
   const uuid = getRandomBytes(16);
 
-  /* eslint-disable no-bitwise */
+  /* eslint-disable no-bitwise, @typescript-eslint/no-non-null-assertion */
 
   // We compose uuid out of 48 bits (6 bytes of) timestamp-like counter:
   // `incrementMessageCounter`. Note big-endian encoding (which ensures proper
@@ -29,16 +29,16 @@ export function generateMessageId(counter: number): GeneratedMessageIdType {
   uuid[5] = (counter / 0x00000000001) & 0xff;
 
   // Mask out 4 bits of version number
-  uuid[6] &= 0x0f;
+  uuid[6]! &= 0x0f;
   // And set the version to 7
-  uuid[6] |= 0x70;
+  uuid[6]! |= 0x70;
 
   // Mask out 2 bits of variant
-  uuid[8] &= 0x3f;
+  uuid[8]! &= 0x3f;
   // And set it to "2"
-  uuid[8] |= 0x80;
+  uuid[8]! |= 0x80;
 
-  /* eslint-enable no-bitwise */
+  /* eslint-enable no-bitwise, @typescript-eslint/no-non-null-assertion */
 
   return {
     id: stringify(uuid),
diff --git a/ts/util/getColorForCallLink.std.ts b/ts/util/getColorForCallLink.std.ts
index 611541a1e7..c991cc7b90 100644
--- a/ts/util/getColorForCallLink.std.ts
+++ b/ts/util/getColorForCallLink.std.ts
@@ -12,8 +12,11 @@ export function getColorForCallLink(
 ): AxoTokens.Avatar.ColorName {
   const rootKeyStart = rootKey.slice(0, 2);
 
-  const upper = (BASE_16_CONSONANT_ALPHABET.indexOf(rootKeyStart[0]) || 0) * 16;
-  const lower = BASE_16_CONSONANT_ALPHABET.indexOf(rootKeyStart[1]) || 0;
+  const upper =
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    (BASE_16_CONSONANT_ALPHABET.indexOf(rootKeyStart[0]!) || 0) * 16;
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  const lower = BASE_16_CONSONANT_ALPHABET.indexOf(rootKeyStart[1]!) || 0;
   const firstByte = upper + lower;
 
   return AxoTokens.Avatar.getColorNameByHash(firstByte);
diff --git a/ts/util/getCountryData.dom.ts b/ts/util/getCountryData.dom.ts
index 8b6096c5af..d6e92c3ebd 100644
--- a/ts/util/getCountryData.dom.ts
+++ b/ts/util/getCountryData.dom.ts
@@ -65,7 +65,8 @@ function getCountryCodeForRegion(region: string): string {
 function computeCountryDataForLocale(
   locale: string
 ): ReadonlyArray<CountryDataType> {
-  const map = window.SignalContext.getCountryDisplayNames()[locale];
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  const map = window.SignalContext.getCountryDisplayNames()[locale]!;
 
   const list = Object.entries(map).map(([region, displayName]) => {
     return {
diff --git a/ts/util/getFontNameByTextScript.std.ts b/ts/util/getFontNameByTextScript.std.ts
index 2d91735e81..19842c6c78 100644
--- a/ts/util/getFontNameByTextScript.std.ts
+++ b/ts/util/getFontNameByTextScript.std.ts
@@ -1,82 +1,85 @@
 // Copyright 2022 Signal Messenger, LLC
 // SPDX-License-Identifier: AGPL-3.0-only
 
+import { TextAttachmentStyleType } from '../types/Attachment.std.js';
 import type { LocalizerType } from '../types/Util.std.js';
 import { strictAssert } from './assert.std.js';
 
+const TextStyle = TextAttachmentStyleType;
+
 const FONT_MAP = {
-  base: [
-    'sans-serif',
-    'sans-serif',
-    'sans-serif',
-    'serif',
-    'serif',
-    'sans-serif',
-  ],
-  latin: [
-    'Inter',
-    'Inter',
-    'Inter',
-    '"EB Garamond"',
-    'Parisienne',
-    '"Barlow Condensed"',
-  ],
-  cyrillic: [
-    'Inter',
-    'Inter',
-    'Inter',
-    '"EB Garamond"',
-    '"American Typewriter Semibold", "Cambria Bold"',
-    '"SF Pro Light (System Light)", "Calibri Light"',
-  ],
-  devanagari: [
-    '"Kohinoor Devanagari Regular", "Utsaah Regular"',
-    '"Kohinoor Devanagari Regular", "Utsaah Regular"',
-    '"Kohinoor Devanagari Semibold", "Utsaah Bold"',
-    '"Devanagari Sangam MN Regular", "Kokila Regular"',
-    '"Devanagari Sangam MN Bold", "Kokila Bold"',
-    '"Kohinoor Devanagari Light", "Utsaah Regular"',
-  ],
-  arabic: [
-    '"SF Arabic Regular", "Segoe UI Arabic Regular"',
-    '"SF Arabic Regular", "Segoe UI Arabic Regular"',
-    '"SF Arabic Bold", "Segoe UI Arabic Bold"',
-    '"Geeza Pro Regular", "Sakkal Majalla Regular"',
-    '"Geeza Pro Bold", "Sakkal Majalla Bold"',
-    '"SF Arabic Black", "Segoe UI Arabic Bold"',
-  ],
-  japanese: [
-    '"Hiragino Sans W3"',
-    '"Hiragino Sans W3"',
-    '"Hiragino Sans W7"',
-    '"Hiragino Mincho Pro W3"',
-    '"Hiragino Mincho Pro W6"',
-    '"Hiragino Maru Gothic Pro N"',
-  ],
-  zhhk: [
-    '"PingFang HK Regular", "MingLiU Regular"',
-    '"PingFang HK Regular", "MingLiU Regular"',
-    '"PingFang HK Semibold", "MingLiU Regular"',
-    '"PingFang HK Ultralight", "MingLiU Regular"',
-    '"PingFang HK Thin", "MingLiU Regular"',
-    '"PingFang HK Light", "MingLiU Regular"',
-  ],
-  zhtc: [
-    '"PingFang TC Regular", "JhengHei TC Regular"',
-    '"PingFang TC Regular", "JhengHei TC Regular"',
-    '"PingFang TC Semibold", "JhengHei TC Bold"',
-    '"PingFang TC Ultralight", "JhengHei TC Light"',
-    '"PingFang TC Thin", "JhengHei TC Regular"',
-    '"PingFang TC Light", "JhengHei TC Bold"',
-  ],
-  zhsc: [
-    '"PingFang SC Regular", SimHei',
-    '"PingFang SC Regular", SimHei',
-    '"PingFang SC Semibold", SimHei',
-    '"PingFang SC Ultralight", SimHei',
-    '"PingFang SC Thin", SimHei',
-    '"PingFang SC Light", SimHei',
-  ],
+  base: {
+    [TextStyle.DEFAULT]: 'sans-serif',
+    [TextStyle.REGULAR]: 'sans-serif',
+    [TextStyle.BOLD]: 'sans-serif',
+    [TextStyle.SERIF]: 'serif',
+    [TextStyle.SCRIPT]: 'serif',
+    [TextStyle.CONDENSED]: 'sans-serif',
+  },
+  latin: {
+    [TextStyle.DEFAULT]: 'Inter',
+    [TextStyle.REGULAR]: 'Inter',
+    [TextStyle.BOLD]: 'Inter',
+    [TextStyle.SERIF]: '"EB Garamond"',
+    [TextStyle.SCRIPT]: 'Parisienne',
+    [TextStyle.CONDENSED]: '"Barlow Condensed"',
+  },
+  cyrillic: {
+    [TextStyle.DEFAULT]: 'Inter',
+    [TextStyle.REGULAR]: 'Inter',
+    [TextStyle.BOLD]: 'Inter',
+    [TextStyle.SERIF]: '"EB Garamond"',
+    [TextStyle.SCRIPT]: '"American Typewriter Semibold", "Cambria Bold"',
+    [TextStyle.CONDENSED]: '"SF Pro Light (System Light)", "Calibri Light"',
+  },
+  devanagari: {
+    [TextStyle.DEFAULT]: '"Kohinoor Devanagari Regular", "Utsaah Regular"',
+    [TextStyle.REGULAR]: '"Kohinoor Devanagari Regular", "Utsaah Regular"',
+    [TextStyle.BOLD]: '"Kohinoor Devanagari Semibold", "Utsaah Bold"',
+    [TextStyle.SERIF]: '"Devanagari Sangam MN Regular", "Kokila Regular"',
+    [TextStyle.SCRIPT]: '"Devanagari Sangam MN Bold", "Kokila Bold"',
+    [TextStyle.CONDENSED]: '"Kohinoor Devanagari Light", "Utsaah Regular"',
+  },
+  arabic: {
+    [TextStyle.DEFAULT]: '"SF Arabic Regular", "Segoe UI Arabic Regular"',
+    [TextStyle.REGULAR]: '"SF Arabic Regular", "Segoe UI Arabic Regular"',
+    [TextStyle.BOLD]: '"SF Arabic Bold", "Segoe UI Arabic Bold"',
+    [TextStyle.SERIF]: '"Geeza Pro Regular", "Sakkal Majalla Regular"',
+    [TextStyle.SCRIPT]: '"Geeza Pro Bold", "Sakkal Majalla Bold"',
+    [TextStyle.CONDENSED]: '"SF Arabic Black", "Segoe UI Arabic Bold"',
+  },
+  japanese: {
+    [TextStyle.DEFAULT]: '"Hiragino Sans W3"',
+    [TextStyle.REGULAR]: '"Hiragino Sans W3"',
+    [TextStyle.BOLD]: '"Hiragino Sans W7"',
+    [TextStyle.SERIF]: '"Hiragino Mincho Pro W3"',
+    [TextStyle.SCRIPT]: '"Hiragino Mincho Pro W6"',
+    [TextStyle.CONDENSED]: '"Hiragino Maru Gothic Pro N"',
+  },
+  zhhk: {
+    [TextStyle.DEFAULT]: '"PingFang HK Regular", "MingLiU Regular"',
+    [TextStyle.REGULAR]: '"PingFang HK Regular", "MingLiU Regular"',
+    [TextStyle.BOLD]: '"PingFang HK Semibold", "MingLiU Regular"',
+    [TextStyle.SERIF]: '"PingFang HK Ultralight", "MingLiU Regular"',
+    [TextStyle.SCRIPT]: '"PingFang HK Thin", "MingLiU Regular"',
+    [TextStyle.CONDENSED]: '"PingFang HK Light", "MingLiU Regular"',
+  },
+  zhtc: {
+    [TextStyle.DEFAULT]: '"PingFang TC Regular", "JhengHei TC Regular"',
+    [TextStyle.REGULAR]: '"PingFang TC Regular", "JhengHei TC Regular"',
+    [TextStyle.BOLD]: '"PingFang TC Semibold", "JhengHei TC Bold"',
+    [TextStyle.SERIF]: '"PingFang TC Ultralight", "JhengHei TC Light"',
+    [TextStyle.SCRIPT]: '"PingFang TC Thin", "JhengHei TC Regular"',
+    [TextStyle.CONDENSED]: '"PingFang TC Light", "JhengHei TC Bold"',
+  },
+  zhsc: {
+    [TextStyle.DEFAULT]: '"PingFang SC Regular", SimHei',
+    [TextStyle.REGULAR]: '"PingFang SC Regular", SimHei',
+    [TextStyle.BOLD]: '"PingFang SC Semibold", SimHei',
+    [TextStyle.SERIF]: '"PingFang SC Ultralight", SimHei',
+    [TextStyle.SCRIPT]: '"PingFang SC Thin", SimHei',
+    [TextStyle.CONDENSED]: '"PingFang SC Light", SimHei',
+  },
 };
 
 const rxArabic = /\p{Script=Arab}/u;
@@ -114,46 +117,46 @@ export const fontSniffer = {
 
 export function getFontNameByTextScript(
   text: string,
-  textStyleIndex: number,
+  textStyleType: TextAttachmentStyleType,
   i18n?: LocalizerType
 ): string {
   strictAssert(
-    textStyleIndex >= 0 && textStyleIndex <= 5,
-    'text style is not between 0-5'
+    TextAttachmentStyleType[textStyleType],
+    `Invalid textStyleType: ${textStyleType}`
   );
 
-  const fonts: Array<string> = [FONT_MAP.base[textStyleIndex]];
+  const fonts: Array<string> = [FONT_MAP.base[textStyleType]];
 
   if (fontSniffer.hasArabic(text)) {
-    fonts.push(FONT_MAP.arabic[textStyleIndex]);
+    fonts.push(FONT_MAP.arabic[textStyleType]);
   }
 
   if (fontSniffer.hasCJK(text)) {
     const locale = i18n?.getLocale();
 
     if (locale === 'zh-TW') {
-      fonts.push(FONT_MAP.zhtc[textStyleIndex]);
+      fonts.push(FONT_MAP.zhtc[textStyleType]);
     } else if (locale === 'zh-HK') {
-      fonts.push(FONT_MAP.zhhk[textStyleIndex]);
+      fonts.push(FONT_MAP.zhhk[textStyleType]);
     } else {
-      fonts.push(FONT_MAP.zhsc[textStyleIndex]);
+      fonts.push(FONT_MAP.zhsc[textStyleType]);
     }
   }
 
   if (fontSniffer.hasCyrillic(text)) {
-    fonts.push(FONT_MAP.cyrillic[textStyleIndex]);
+    fonts.push(FONT_MAP.cyrillic[textStyleType]);
   }
 
   if (fontSniffer.hasDevanagari(text)) {
-    fonts.push(FONT_MAP.devanagari[textStyleIndex]);
+    fonts.push(FONT_MAP.devanagari[textStyleType]);
   }
 
   if (fontSniffer.hasJapanese(text)) {
-    fonts.push(FONT_MAP.japanese[textStyleIndex]);
+    fonts.push(FONT_MAP.japanese[textStyleType]);
   }
 
   if (fontSniffer.hasLatin(text)) {
-    fonts.push(FONT_MAP.latin[textStyleIndex]);
+    fonts.push(FONT_MAP.latin[textStyleType]);
   }
 
   return fonts.reverse().join(', ');
diff --git a/ts/util/getHSL.std.ts b/ts/util/getHSL.std.ts
index 92bffd8bfa..8a6ab41857 100644
--- a/ts/util/getHSL.std.ts
+++ b/ts/util/getHSL.std.ts
@@ -1,16 +1,22 @@
 // Copyright 2021 Signal Messenger, LLC
 // SPDX-License-Identifier: AGPL-3.0-only
 
-const LIGHTNESS_TABLE: Record<number, number> = {
+const LIGHTNESS_TABLE = {
   0: 45,
   60: 30,
   180: 30,
   240: 50,
   300: 40,
   360: 45,
-};
+} as const satisfies Record<number, number>;
 
-function getLightnessFromHue(hue: number, min: number, max: number) {
+type LightnessKey = keyof typeof LIGHTNESS_TABLE;
+
+function getLightnessFromHue(
+  hue: number,
+  min: LightnessKey,
+  max: LightnessKey
+) {
   const percentage = ((hue - min) * 100) / (max - min);
   const minValue = LIGHTNESS_TABLE[min];
   const maxValue = LIGHTNESS_TABLE[max];
diff --git a/ts/util/getInitials.std.ts b/ts/util/getInitials.std.ts
index 4e7233b171..3d63774963 100644
--- a/ts/util/getInitials.std.ts
+++ b/ts/util/getInitials.std.ts
@@ -27,5 +27,6 @@ export function getInitials(name?: string): string | undefined {
 
   return partsLen === 1
     ? parts[0].charAt(0)
-    : parts[0].charAt(0) + parts[partsLen - 1].charAt(0);
+    : // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      parts[0].charAt(0) + parts[partsLen - 1]!.charAt(0);
 }
diff --git a/ts/util/getNotificationDataForMessage.preload.ts b/ts/util/getNotificationDataForMessage.preload.ts
index c1e068bbd4..a0867869e0 100644
--- a/ts/util/getNotificationDataForMessage.preload.ts
+++ b/ts/util/getNotificationDataForMessage.preload.ts
@@ -318,7 +318,8 @@ export function getNotificationDataForMessage(
         }
       } else {
         const joinedContact = window.ConversationController.getOrCreate(
-          groupUpdate.joined[0],
+          // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+          groupUpdate.joined[0]!,
           'private'
         );
         if (isMe(joinedContact.attributes)) {
@@ -326,7 +327,8 @@ export function getNotificationDataForMessage(
         } else {
           messages.push(
             i18n('icu:joinedTheGroup', {
-              name: joinedContacts[0].getTitle(),
+              // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+              name: joinedContacts[0]!.getTitle(),
             })
           );
         }
@@ -476,7 +478,8 @@ export function getNotificationDataForMessage(
   const { contact: contacts } = attributes;
   if (contacts && contacts.length) {
     return {
-      text: EmbeddedContact.getName(contacts[0]) || i18n('icu:unknownContact'),
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      text: EmbeddedContact.getName(contacts[0]!) || i18n('icu:unknownContact'),
       emoji: '👤',
     };
   }
diff --git a/ts/util/getQuoteBodyText.std.ts b/ts/util/getQuoteBodyText.std.ts
index fea5307ee3..865ff023ee 100644
--- a/ts/util/getQuoteBodyText.std.ts
+++ b/ts/util/getQuoteBodyText.std.ts
@@ -29,7 +29,8 @@ export function getQuoteBodyText({
   const { body, contact: embeddedContact, poll } = messageAttributes;
   const embeddedContactName =
     embeddedContact && embeddedContact.length > 0
-      ? EmbeddedContact.getName(embeddedContact[0])
+      ? // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        EmbeddedContact.getName(embeddedContact[0]!)
       : '';
 
   const pollText = poll
diff --git a/ts/util/graphemeAndLinkAwareSlice.std.ts b/ts/util/graphemeAndLinkAwareSlice.std.ts
index 389f1e7075..0797e0eea9 100644
--- a/ts/util/graphemeAndLinkAwareSlice.std.ts
+++ b/ts/util/graphemeAndLinkAwareSlice.std.ts
@@ -61,7 +61,8 @@ const expandToIncludeEntireLink = (
     return truncated;
   }
 
-  return original.slice(0, truncatedLink[0].lastIndex);
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  return original.slice(0, truncatedLink[0]!.lastIndex);
 };
 
 type LinkRange = {
diff --git a/ts/util/groupAndOrderReactions.dom.ts b/ts/util/groupAndOrderReactions.dom.ts
index 4cb947da9f..e2a80f5d2f 100644
--- a/ts/util/groupAndOrderReactions.dom.ts
+++ b/ts/util/groupAndOrderReactions.dom.ts
@@ -81,7 +81,8 @@ export function useGroupedAndOrderedReactions(
 
     return orderBy(
       groupedReactions,
-      ['length', ([{ timestamp }]) => timestamp],
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      ['length', ([first]) => first!.timestamp],
       ['desc', 'desc']
     );
   }, [reactions, groupByKey, emojiLocalization]);
diff --git a/ts/util/groupSendEndorsements.preload.ts b/ts/util/groupSendEndorsements.preload.ts
index 60a75d37ec..e66c7405ab 100644
--- a/ts/util/groupSendEndorsements.preload.ts
+++ b/ts/util/groupSendEndorsements.preload.ts
@@ -279,6 +279,7 @@ export class GroupSendEndorsementState {
     // Fast path sending to one person
     if (serviceIds.size === 1) {
       const [serviceId] = serviceIds;
+      strictAssert(serviceId, 'Missing serviceId');
       log.info(`${logId}: using single member endorsement (${serviceId})`);
       return this.#getMemberEndorsement(serviceId);
     }
diff --git a/ts/util/handleRetry.preload.ts b/ts/util/handleRetry.preload.ts
index bc1b07b341..5786be7a63 100644
--- a/ts/util/handleRetry.preload.ts
+++ b/ts/util/handleRetry.preload.ts
@@ -458,7 +458,8 @@ async function getRetryConversation({
     return window.ConversationController.get(requestGroupId);
   }
 
-  const [messageId] = messageIds;
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  const messageId = messageIds[0]!;
   const message = await DataReader.getMessageById(messageId);
   if (!message) {
     log.warn(
diff --git a/ts/util/lint/license_comments.node.ts b/ts/util/lint/license_comments.node.ts
index 61c139faf0..7a1e6c14d0 100644
--- a/ts/util/lint/license_comments.node.ts
+++ b/ts/util/lint/license_comments.node.ts
@@ -162,6 +162,7 @@ async function getCommitFileWasAdded(
 
   const commitYear = new Date(dateString).getFullYear();
   assert(!Number.isNaN(commitYear), `Could not read commit year for ${file}`);
+  assert(commitHash, 'Missing commitHash');
   return { commitYear, commitHash };
 }
 
@@ -196,7 +197,10 @@ async function main() {
 
     const warnings = [];
 
-    if (!/Copyright \d{4} Signal Messenger, LLC/.test(firstLine)) {
+    if (
+      firstLine == null ||
+      !/Copyright \d{4} Signal Messenger, LLC/.test(firstLine)
+    ) {
       const commit = await getCommitFileWasAdded(file);
       warnings.push(
         chalk.red('Missing/Incorrect copyright line'),
diff --git a/ts/util/objectMap.std.ts b/ts/util/objectMap.std.ts
index 390e6ddf8d..79bec8f6dc 100644
--- a/ts/util/objectMap.std.ts
+++ b/ts/util/objectMap.std.ts
@@ -5,6 +5,5 @@ export function objectMap<T, R>(
   obj: Record<string, T>,
   f: (key: keyof typeof obj, value: (typeof obj)[keyof typeof obj]) => R
 ): Array<R> {
-  const keys: Array<keyof typeof obj> = Object.keys(obj);
-  return keys.map(key => f(key, obj[key]));
+  return Object.entries(obj).map(([key, value]) => f(key, value));
 }
diff --git a/ts/util/scaleImageToLevel.preload.ts b/ts/util/scaleImageToLevel.preload.ts
index 9a10037dad..3f5fc302f5 100644
--- a/ts/util/scaleImageToLevel.preload.ts
+++ b/ts/util/scaleImageToLevel.preload.ts
@@ -156,8 +156,7 @@ export async function scaleImageToLevel({
     };
   }
 
-  for (let i = 0; i < SCALABLE_DIMENSIONS.length; i += 1) {
-    const scalableDimensions = SCALABLE_DIMENSIONS[i];
+  for (const scalableDimensions of SCALABLE_DIMENSIONS) {
     if (maxDimensions < scalableDimensions) {
       continue;
     }
diff --git a/ts/util/search.std.ts b/ts/util/search.std.ts
index 8cc43de179..26d45161b4 100644
--- a/ts/util/search.std.ts
+++ b/ts/util/search.std.ts
@@ -53,8 +53,10 @@ export function generateSnippetAroundMention({
   // Gradually narrow the substring, word by word, until a snippet of appropriate length
   // is found
   while (leftWordIdx <= rightWordIdx) {
-    const leftWord = words[leftWordIdx];
-    const rightWord = words[rightWordIdx];
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const leftWord = words[leftWordIdx]!;
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const rightWord = words[rightWordIdx]!;
 
     snippetStartIdx = Math.min(leftWord.index, mentionStart);
     snippetEndIdx = Math.max(
diff --git a/ts/util/sendStoryMessage.preload.ts b/ts/util/sendStoryMessage.preload.ts
index bb9b17fbfc..4e23396257 100644
--- a/ts/util/sendStoryMessage.preload.ts
+++ b/ts/util/sendStoryMessage.preload.ts
@@ -141,7 +141,8 @@ export async function sendStoryMessage(
 
   const linkPreview = attachment?.textAttachment?.preview;
   const sanitizedLinkPreview = linkPreview
-    ? sanitizeLinkPreview((await loadPreviewData([linkPreview]))[0])
+    ? // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      sanitizeLinkPreview((await loadPreviewData([linkPreview]))[0]!)
     : undefined;
   // If a text attachment has a link preview we remove it from the
   // textAttachment data structure and instead process the preview and add
diff --git a/ts/util/sendToGroup.preload.ts b/ts/util/sendToGroup.preload.ts
index 91b067de57..8c0a6fd235 100644
--- a/ts/util/sendToGroup.preload.ts
+++ b/ts/util/sendToGroup.preload.ts
@@ -1262,8 +1262,8 @@ function getXorOfAccessKeys(
     }
 
     for (let i = 0; i < ACCESS_KEY_LENGTH; i += 1) {
-      // eslint-disable-next-line no-bitwise
-      result[i] ^= accessKeyBuffer[i];
+      // eslint-disable-next-line no-bitwise, @typescript-eslint/no-non-null-assertion
+      result[i]! ^= accessKeyBuffer[i]!;
     }
   });
 
diff --git a/ts/util/sniffImageMimeType.std.ts b/ts/util/sniffImageMimeType.std.ts
index dba89c5669..74626651f9 100644
--- a/ts/util/sniffImageMimeType.std.ts
+++ b/ts/util/sniffImageMimeType.std.ts
@@ -17,8 +17,7 @@ import {
  * [0]: https://mimesniff.spec.whatwg.org/#matching-an-image-type-pattern
  */
 export function sniffImageMimeType(bytes: Uint8Array): undefined | MIMEType {
-  for (let i = 0; i < TYPES.length; i += 1) {
-    const type = TYPES[i];
+  for (const type of TYPES) {
     if (matchesType(bytes, type)) {
       return type.mimeType;
     }
@@ -85,8 +84,8 @@ function matchesType(input: Uint8Array, type: Type): boolean {
   for (let p = 0; p < type.bytePattern.length; p += 1) {
     const mask = type.patternMask ? type.patternMask[p] : 0xff;
     // We need to use a bitwise operator here, per the spec.
-    // eslint-disable-next-line no-bitwise
-    const maskedData = input[p] & mask;
+    // eslint-disable-next-line no-bitwise, @typescript-eslint/no-non-null-assertion
+    const maskedData = input[p]! & mask!;
     if (maskedData !== type.bytePattern[p]) {
       return false;
     }
diff --git a/ts/util/syncTasks.preload.ts b/ts/util/syncTasks.preload.ts
index 42231c6fdb..80312e6453 100644
--- a/ts/util/syncTasks.preload.ts
+++ b/ts/util/syncTasks.preload.ts
@@ -78,8 +78,7 @@ export async function queueSyncTasks(
 ): Promise<void> {
   const logId = 'queueSyncTasks';
 
-  for (let i = 0, max = tasks.length; i < max; i += 1) {
-    const task = tasks[i];
+  for (const task of tasks) {
     const { id, envelopeId, type, sentAt, data } = task;
     const innerLogId = `${logId}(${toLogId(task)})`;
 
diff --git a/ts/util/userLanguages.std.ts b/ts/util/userLanguages.std.ts
index 0929090b58..603d258524 100644
--- a/ts/util/userLanguages.std.ts
+++ b/ts/util/userLanguages.std.ts
@@ -21,7 +21,8 @@ export function formatAcceptLanguageHeader(
 
   const length = Math.min(languages.length, MAX_LANGUAGES_TO_FORMAT);
   for (let i = 0; i < length; i += 1) {
-    const language = languages[i];
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const language = languages[i]!;
 
     // ["If no 'q' parameter is present, the default weight is 1."][1]
     //
diff --git a/ts/util/whitespaceStringUtil.std.ts b/ts/util/whitespaceStringUtil.std.ts
deleted file mode 100644
index 19e0037f06..0000000000
--- a/ts/util/whitespaceStringUtil.std.ts
+++ /dev/null
@@ -1,47 +0,0 @@
-// Copyright 2022 Signal Messenger, LLC
-// SPDX-License-Identifier: AGPL-3.0-only
-
-const WHITESPACE = new Set([
-  ' ',
-  '\u200E', // left-to-right mark
-  '\u200F', // right-to-left mark
-  '\u2007', // figure space
-  '\u200B', // zero-width space
-  '\u2800', // braille blank
-]);
-
-export function trim(str: string): string {
-  let start = 0;
-  let end = str.length - 1;
-
-  for (start; start < str.length; start += 1) {
-    const char = str[start];
-    if (!WHITESPACE.has(char)) {
-      break;
-    }
-  }
-
-  for (end; end > 0; end -= 1) {
-    const char = str[end];
-    if (!WHITESPACE.has(char)) {
-      break;
-    }
-  }
-
-  if (start > 0 || end < str.length - 1) {
-    return str.substring(start, end + 1);
-  }
-
-  return str;
-}
-
-export function isWhitespace(str: string): boolean {
-  for (let i = 0; i < str.length; i += 1) {
-    const char = str[i];
-    if (!WHITESPACE.has(char)) {
-      return false;
-    }
-  }
-
-  return true;
-}
diff --git a/ts/window.d.ts b/ts/window.d.ts
index 1c1d00b0fc..ecfa09a8e8 100644
--- a/ts/window.d.ts
+++ b/ts/window.d.ts
@@ -243,6 +243,36 @@ declare global {
   interface SharedArrayBuffer {
     __arrayBuffer: never;
   }
+
+  interface StringSplitSplitter<T> {
+    [Symbol.split](string: string, limit?: number): T;
+  }
+
+  interface String {
+    split(splitter: string | RegExp): [string, ...Array<string>];
+    split(splitter: string | RegExp, limit: 0): [];
+    split(splitter: string | RegExp, limit: 1): [string];
+    split(splitter: string | RegExp, limit: 2): [string, string?];
+    split(splitter: string | RegExp, limit: 3): [string, string?, string?];
+    split(
+      splitter: string | RegExp,
+      limit: 4
+    ): [string, string?, string?, string?];
+    split(
+      splitter: string | RegExp,
+      limit: 5
+    ): [string, string?, string?, string?, string?];
+    split(splitter: string | RegExp, limit: number): [string, ...Array<string>];
+    split(
+      splitter: string | RegExp,
+      limit?: number
+    ): [string, ...Array<string>];
+    split<T>(splitter: StringSplitSplitter<T>, limit?: number): T;
+    split(
+      splitter: string | RegExp | StringSplitSplitter<Array<string>>,
+      limit?: number
+    ): [string, ...Array<string>];
+  }
 }
 
 export type WhisperType = {
diff --git a/ts/windows/main/preload_test.preload.ts b/ts/windows/main/preload_test.preload.ts
index a1dcee6d9a..7b4f70b17d 100644
--- a/ts/windows/main/preload_test.preload.ts
+++ b/ts/windows/main/preload_test.preload.ts
@@ -160,15 +160,15 @@ window.testUtilities = {
       cwd: __dirname,
     });
 
-    for (let i = 0; i < files.length; i += 1) {
+    for (const [i, file] of files.entries()) {
       if (i % workerCount === worker) {
         try {
           // eslint-disable-next-line import/no-dynamic-require, global-require
-          require(files[i]);
+          require(file);
         } catch (error) {
           window.testUtilities.onTestEvent({
             type: 'fail',
-            title: ['Failed to load test:', files[i]],
+            title: ['Failed to load test:', file],
             error: error.stack || String(error),
           });
         }
diff --git a/ts/windows/main/start.preload.ts b/ts/windows/main/start.preload.ts
index 48bd31393e..e0774e3bcc 100644
--- a/ts/windows/main/start.preload.ts
+++ b/ts/windows/main/start.preload.ts
@@ -132,7 +132,7 @@ if (
         backgroundColor: '#3b82f6',
       });
       const dataURL = canvas.toDataURL({ format: 'png' });
-      const base64Data = dataURL.split(',')[1];
+      const [base64Data] = dataURL.split(',');
       const data = Uint8Array.from(atob(base64Data), c => c.charCodeAt(0));
 
       await conversation.enqueueMessageForSend(
diff --git a/tsconfig.json b/tsconfig.json
index 58be676e65..f6415c410f 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -208,7 +208,7 @@
     /* Enable error reporting for fallthrough cases in switch statements. */
     "noFallthroughCasesInSwitch": true,
     /* Add 'undefined' to a type when accessed using an index. */
-    "noUncheckedIndexedAccess": false, // TODO: Major migration needed
+    "noUncheckedIndexedAccess": true,
     /* Ensure overriding members in derived classes are marked with an override modifier. */
     "noImplicitOverride": true,
     /* Enforces using indexed accessors for keys declared using an indexed type. */
@@ -232,6 +232,7 @@
    * ts-node
    */
   "ts-node": {
+    "transpileOnly": true,
     // Override TypeScript options for `ts-node` only
     "compilerOptions": {
       // Necessary for `ts-node` to work with CommonJS modules until we migrate to package.json#type: "module"