fix(security): logout's search-index wipe coordinates across tabs

deleteSearchCacheDatabase() resolved after a 3 s "blocked" timeout while
another tab still held the DB, so decrypted rows could survive logout.
It now broadcasts lotus-logout first; every tab closes its handle and
refuses to reopen, then the delete proceeds. A boot with no session
re-runs the wipe once in case a race was still lost. Unit-tested.

Fixes #45

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/client/initMatrix.ts

@@ -6,7 +6,7 @@ import { getFallbackSession, removeFallbackSession, Session } from '../app/state
 import { LotusOidcTokenRefresher } from './oidcTokenRefresher';
 import { revokeOidcTokens } from './oidcLogout';
 import { pushSessionToSW } from '../sw-session';
-import { deleteSearchCacheDatabase } from '../app/utils/searchCache';
+import { deleteSearchCacheDatabase, shouldRunBootCleanup } from '../app/utils/searchCache';
 import { clearPlaintextCaches } from '../app/state/plaintextCaches';
 import { clearSoundboardClipCache } from '../app/utils/soundboardClips';
 
@@ -141,6 +141,21 @@ export const logoutClient = async (mx: MatrixClient) => {
   window.location.reload();
 };
 
+// Gitea #45 — deleteSearchCacheDatabase()'s onblocked handling is a bounded
+// best-effort wait; if another tab held `lotus-search-cache` open through it
+// (the pre-broadcast case, or a browser without BroadcastChannel), the delete
+// stayed queued and plaintext survived on disk despite logout "succeeding".
+// Complete it on the next boot with no session, once per boot — call this
+// wherever the app decides there is no session to hydrate (e.g. alongside the
+// existing getFallbackSession() checks in src/index.tsx).
+let bootCleanupRan = false;
+export const cleanupSearchCacheIfSignedOut = async (): Promise<void> => {
+  const hasSession = !!getFallbackSession();
+  if (!shouldRunBootCleanup(hasSession, bootCleanupRan)) return;
+  bootCleanupRan = true;
+  await deleteSearchCacheDatabase();
+};
+
 export const clearLoginData = async () => {
   const dbs = await window.indexedDB.databases();