Migrate sharedGroupNames from model attribute to Redux selector

ts/util/sharedGroupNames.dom.ts

@@ -0,0 +1,87 @@
+// Copyright 2026 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { useState } from 'react';
+import { useStore } from 'react-redux';
+import type { StateType } from '../state/reducer.preload.js';
+import type { ConversationType } from '../state/ducks/conversations.preload.js';
+import {
+  getConversationLookup,
+  getAllComposableConversations,
+} from '../state/selectors/conversations.dom.js';
+
+const EMPTY_ARRAY: ReadonlyArray<string> = [];
+
+function getServiceIdForConversation(
+  state: StateType,
+  conversationId: string
+): string | null {
+  const conversation = getConversationLookup(state)[conversationId];
+  if (!conversation || conversation.type !== 'direct') {
+    return null;
+  }
+  return conversation.serviceId ?? null;
+}
+
+function findSharedGroups(
+  allConversations: ReadonlyArray<ConversationType>,
+  serviceId: string
+): ReadonlyArray<ConversationType> {
+  return allConversations.filter(
+    conv =>
+      conv.type === 'group' && conv.memberships?.some(m => m.aci === serviceId)
+  );
+}
+
+/**
+ * Returns shared group names sorted by recency.
+ */
+export function getSharedGroupNames(
+  state: StateType,
+  conversationId: string
+): ReadonlyArray<string> {
+  const serviceId = getServiceIdForConversation(state, conversationId);
+  if (!serviceId) {
+    return EMPTY_ARRAY;
+  }
+
+  const groups = findSharedGroups(
+    getAllComposableConversations(state),
+    serviceId
+  );
+  if (groups.length === 0) {
+    return EMPTY_ARRAY;
+  }
+
+  return [...groups]
+    .sort((a, b) => (b.timestamp ?? 0) - (a.timestamp ?? 0))
+    .map(g => g.title ?? '');
+}
+
+/**
+ * Type for the selector function. Exported so smart components can pass
+ * the selector down to presentational components that need shared group
+ * names but don't have direct Redux access.
+ */
+export type GetSharedGroupNamesType = typeof getSharedGroupNames;
+
+/**
+ * React hook that fetches shared group names ONCE on mount.
+ * Does not subscribe to Redux - value is stale after mount.
+ * Use for performance when live updates aren't needed.
+ *
+ * @param conversationId - The conversation to get shared groups for
+ * @param getSharedGroupNamesFn - Passed from smart components via props;
+ *   allows presentational components to use this selector without Redux access
+ */
+export function useSharedGroupNamesOnMount(
+  conversationId: string,
+  getSharedGroupNamesFn?: GetSharedGroupNamesType
+): ReadonlyArray<string> {
+  const store = useStore<StateType>();
+  const [names] = useState(() => {
+    const selector = getSharedGroupNamesFn ?? getSharedGroupNames;
+    return selector(store.getState(), conversationId);
+  });
+  return names;
+}