fix(security): composer drafts no longer survive logout or cross accounts

draft-msg-<roomId> was unscoped and deliberately skipped on logout, then
hydrated into whoever logged in next. Wipe drafts in clearPlaintextCaches,
and only hydrate a draft whose stored userId matches the current user.
Drafts written before this change carry no userId and are dropped on
first load (a one-time loss of unsent drafts, accepted for the leak fix).

Fixes #41

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

src/app/state/plaintextCaches.ts

@@ -5,6 +5,31 @@ import { clearRecentForwardTargets } from './recentForwardTargets';
 import { clearRecentGifs } from './recentGifs';
 import { clearRecentStickers } from './recentStickers';
 import { clearNavToActivePathStore } from './navToActivePath';
+import { DRAFT_MSG_KEY_PREFIX } from '../utils/draft';
+
+/**
+ * [Gitea #41] Wipe every persisted composer draft (`draft-msg-<roomId>`). Drafts
+ * hold decrypted, unsent message text with no user scoping, so leaving them in
+ * place across logout lets the next account on this device see (and send) the
+ * previous user's draft the moment they open the same room.
+ */
+const clearMsgDrafts = (): void => {
+  let keys: string[];
+  try {
+    keys = Object.keys(localStorage);
+  } catch {
+    return;
+  }
+  keys.forEach((key) => {
+    if (key.startsWith(DRAFT_MSG_KEY_PREFIX)) {
+      try {
+        localStorage.removeItem(key);
+      } catch {
+        // Best-effort — a single unreadable/blocked key must not abort the sweep.
+      }
+    }
+  });
+};
 
 /**
  * Single auditable place that wipes the `localStorage` caches holding decrypted
@@ -18,6 +43,10 @@ import { clearNavToActivePathStore } from './navToActivePath';
  * - `cinny_recent_forward_targets_v1` — recent forward contact/room graph (PII)
  * - `cinny_recent_gifs_v1` / `cinny_recent_stickers_v1` — media the user sent
  * - `navToActivePath<userId>` — per-space last-visited room paths (needs userId)
+ * - `draft-msg-*` — unsent composer drafts (decrypted message text, unscoped by
+ *   user — see [Gitea #41]; previously deliberately preserved across logout
+ *   (N98), which let the next account on this device see/send a prior user's
+ *   draft, so this is no longer a "by design" exemption)
  *
  * NOT swept here (by design):
  * - session credential keys → `removeFallbackSession()`
@@ -25,9 +54,8 @@ import { clearNavToActivePathStore } from './navToActivePath';
  *   bookmarks, user notes, status presets — themselves plaintext) → wiped by
  *   `mx.clearStores()` on both logout paths
  * - the opt-in encrypted-search index (IndexedDB) → `deleteSearchCacheDatabase()`
- * - unsent composer drafts (`draft-msg-*`) and the presence status message
- *   (`lotus-status-msg-*`) are deliberately preserved across a normal logout
- *   (N98); clearing them is a separate product decision
+ * - the presence status message (`lotus-status-msg-*`) is deliberately
+ *   preserved across a normal logout; clearing it is a separate product decision
  * - low-sensitivity UI/metadata residue (`io.lotus.mute_timers`, collapsed
  *   nav/space categories, `cinny_oidc_dynamic_clients`) is treated as
  *   preferences, not swept here
@@ -39,5 +67,6 @@ export const clearPlaintextCaches = (userId?: string): void => {
   clearRecentForwardTargets();
   clearRecentGifs();
   clearRecentStickers();
+  clearMsgDrafts();
   if (userId) clearNavToActivePathStore(userId);
 };