feat(desktop): wipe local crypto + caches on sign-out

apps/desktop/src/context/AuthContext.tsx

@@ -20,6 +20,7 @@ import {
 import { useTranslation } from 'react-i18next';
 
 import { ensureInstallId } from '../lib/installId';
+import { wipeLocalState } from '../lib/memoryWipe';
 import { setSecretStoreUser } from '../lib/secretStore';
 import { supabase } from '../lib/supabase';
 import { cachedUserKey, ensureLegacyMigrated } from '../lib/userIdentity';
@@ -235,11 +236,13 @@ export function AuthProvider({ children }: { children: ReactNode }) {
   }, [session, profile, refreshProfile]);
 
   const signOut = useCallback(async () => {
+    const uid = session?.user.id ?? null;
     await updateOwnProfile(supabase, { presenceState: 'offline' }).catch((err: unknown) => {
       console.warn('offline update before sign-out failed', err);
     });
     await supabaseSignOut(supabase);
-  }, []);
+    await wipeLocalState(uid);
+  }, [session]);
 
   const value = useMemo<AuthContextValue>(
     () => ({

apps/desktop/src/lib/memoryWipe.ts

@@ -0,0 +1,54 @@
+import { clearConvKeyCache } from '@chat-app/shared/chat';
+
+import { devLocalSecretStore } from './secretStore';
+
+// Aggressively scrub local crypto + chat caches on sign-out (and on
+// app-close if the user opted in). Preserves things that aren't sensitive
+// and would be annoying to lose (theme, locale, install-id).
+//
+// We can't enumerate IndexedDB names without async + the indexedDB API,
+// so we list the ones we know about explicitly. Adding a new local store
+// later? Append to LOCAL_DBS.
+
+const LOCAL_DBS = ['soundboard', 'message-cache', 'chatapp-attachments'];
+const PRESERVE_LOCAL_STORAGE = new Set([
+  'chatapp.theme',
+  'chatapp.locale',
+  'chatapp.installId',
+  'i18nextLng',
+]);
+
+export async function wipeLocalState(userId: string | null): Promise<void> {
+  // 1. Per-conversation key cache (in-memory).
+  try { clearConvKeyCache(); } catch { /* never throws but be defensive */ }
+
+  // 2. Stronghold / secret-store: drop the user-priv blob for this user.
+  if (userId) {
+    try { await devLocalSecretStore.removeSecret('chatapp.userpriv.' + userId); }
+    catch (err) { console.warn('[wipe] userpriv remove failed', err); }
+  }
+
+  // 3. localStorage — preserve only the explicit whitelist.
+  try {
+    const keysToDrop: string[] = [];
+    for (let i = 0; i < window.localStorage.length; i++) {
+      const k = window.localStorage.key(i);
+      if (k && !PRESERVE_LOCAL_STORAGE.has(k)) keysToDrop.push(k);
+    }
+    for (const k of keysToDrop) window.localStorage.removeItem(k);
+  } catch (err) { console.warn('[wipe] localStorage clear failed', err); }
+
+  // 4. sessionStorage — always full.
+  try { window.sessionStorage.clear(); } catch { /* ignored */ }
+
+  // 5. IndexedDB — delete known databases. Resolves even when blocked so
+  // we don't hang sign-out forever.
+  await Promise.allSettled(LOCAL_DBS.map((name) => new Promise<void>((resolve) => {
+    try {
+      const req = window.indexedDB.deleteDatabase(name);
+      req.onsuccess = () => resolve();
+      req.onerror = () => resolve();
+      req.onblocked = () => resolve();
+    } catch { resolve(); }
+  })));
+}