Update local backups availability during rollout

Co-authored-by: trevor-signal <131492920+trevor-signal@users.noreply.github.com>

ts/util/isLocalBackupsEnabled.preload.ts

@@ -0,0 +1,44 @@
+// Copyright 2025 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import type { ReadonlyObjectDeep } from 'type-fest/source/readonly-deep.js';
+import { isEnabled, type ConfigMapType } from '../RemoteConfig.dom.js';
+import {
+  isFeaturedEnabledNoRedux,
+  isFeaturedEnabledSelector,
+} from './isFeatureEnabled.dom.js';
+import { itemStorage } from '../textsecure/Storage.preload.js';
+import { isNightly } from './version.std.js';
+import { isTestOrMockEnvironment } from '../environment.std.js';
+
+const IOS_USER_AGENT = 'OWI';
+
+export function isLocalBackupsEnabled(reduxArgs?: {
+  currentVersion: string;
+  remoteConfig: ReadonlyObjectDeep<ConfigMapType> | undefined;
+}): boolean {
+  // This is a temporary guard until iOS supports importing local backups
+  // Android no longer sends its OWA agent string, so we have to rely on iOS
+  if (
+    itemStorage.get('userAgent') === IOS_USER_AGENT &&
+    !isNightly(window.getVersion()) &&
+    !isTestOrMockEnvironment() &&
+    !isEnabled('desktop.internalUser', reduxArgs?.remoteConfig)
+  ) {
+    return false;
+  }
+
+  if (reduxArgs) {
+    return isFeaturedEnabledSelector({
+      currentVersion: reduxArgs.currentVersion,
+      remoteConfig: reduxArgs.remoteConfig,
+      betaKey: 'desktop.localBackups.beta',
+      prodKey: 'desktop.localBackups.prod',
+    });
+  }
+
+  return isFeaturedEnabledNoRedux({
+    betaKey: 'desktop.localBackups.beta',
+    prodKey: 'desktop.localBackups.prod',
+  });
+}