fix(logout): no draft or search opt-in left behind after logout (#319, #296)

- #319: logout wiped the drafts, then reloaded, and the reload's pagehide
  made RoomInput flush the open composer's (decrypted) draft straight back
  to localStorage. clearPlaintextCaches now sets a module flag and
  persistDraft stops writing once it's set (resets with the new page).
- #296: the device-wide encrypted-search opt-in (searchCacheEnabled)
  survived logout, so the next account started indexing decrypted text
  without opting in. It's now cleared, along with the SDK's per-user
  filter key.

Verified headless with a throwaway account (search opt-in on, "SECRET
half-typed reply" in the composer, Settings → Log out): before, the draft
and searchCacheEnabled=true remained; now neither does. Unit test added.

Fixes #319
Fixes #296

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5

src/app/state/plaintextCaches.ts

@@ -112,7 +112,34 @@ const clearCallVolumesAndSyncMeta = (userId?: string): void => {
   });
 };
 
+// [Gitea #319] Set once a logout has wiped the caches. Logout then reloads the
+// page, and the reload's `pagehide` made RoomInput flush the open composer's
+// draft straight back to localStorage; draft writes check this and stop.
+// Module state, so it resets with the new page.
+let wiped = false;
+export const plaintextCachesWiped = (): boolean => wiped;
+
+/**
+ * [Gitea #296] Device-wide flags/keys that carry the previous account's choice
+ * or id: the encrypted-search opt-in (the next account would otherwise start
+ * indexing decrypted text without opting in) and the SDK's per-user filter key.
+ */
+const clearAccountScopedFlags = (userId?: string): void => {
+  const keys = [
+    'searchCacheEnabled',
+    ...(userId ? [`mxjssdk_memory_filter_FILTER_SYNC_${userId}`] : []),
+  ];
+  keys.forEach((key) => {
+    try {
+      localStorage.removeItem(key);
+    } catch {
+      // best-effort
+    }
+  });
+};
+
 export const clearPlaintextCaches = (userId?: string): void => {
+  wiped = true;
   clearTranslationCache();
   clearScheduledMessages();
   clearRecentSearches();
@@ -124,5 +151,6 @@ export const clearPlaintextCaches = (userId?: string): void => {
   clearCallSession();
   clearStatusMessage();
   clearCallVolumesAndSyncMeta(userId);
+  clearAccountScopedFlags(userId);
   if (userId) clearNavToActivePathStore(userId);
 };