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.test.ts

@@ -26,7 +26,7 @@ const api = {
       : Object.getOwnPropertyDescriptor(target, key),
 });
 
-const { clearPlaintextCaches } = await import('./plaintextCaches');
+const { clearPlaintextCaches, plaintextCachesWiped } = await import('./plaintextCaches');
 
 test('clearPlaintextCaches removes every plaintext/PII localStorage key', () => {
   store.clear();
@@ -94,3 +94,13 @@ test('clearPlaintextCaches removes the call-volume list and the settings-sync st
   assert.equal(store.has('settings-sync-meta:@me:server'), false);
   assert.equal(store.has('settings'), true, 'device preferences are kept');
 });
+
+test('clearPlaintextCaches clears the encrypted-search opt-in and flags the wipe (#296, #319)', () => {
+  store.clear();
+  store.set('searchCacheEnabled', 'true');
+  store.set('mxjssdk_memory_filter_FILTER_SYNC_@me:server', '0');
+  clearPlaintextCaches('@me:server');
+  assert.equal(store.has('searchCacheEnabled'), false);
+  assert.equal(store.has('mxjssdk_memory_filter_FILTER_SYNC_@me:server'), false);
+  assert.equal(plaintextCachesWiped(), true, 'draft writes stop until the page reloads');
+});