fix(security): widget consents and shared files cleared on logout; forged shares refused (#266, #267)

#266: remembered widget approvals (lotus.widgetConsent.*) survived logout,
so they applied silently to the next account on the device and listed the
previous account's rooms; clearPlaintextCaches now sweeps them. Space
structure, call membership and Lotus room-policy state join
PROTECTED_STATE_TYPES, so no widget can be granted them.

#267: any website could auto-submit a form to /share-target and land the
user in the share picker with attacker-chosen text and files. The worker
now refuses a share whose Origin is another site. (Sec-Fetch-Site, as the
issue suggested, never reaches a service worker: checked in Chromium.)
Origin null/absent, as the OS share sheet sends, stays accepted, and
/share now says the content came from another app or website. Both logout
paths await clearSharedPayload(); the server-forced one also clears the
soundboard clip cache, as #57 intended.

Fixes #266
Fixes #267

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 +26,10 @@ const api = {
       : Object.getOwnPropertyDescriptor(target, key),
 });
 
-const { clearPlaintextCaches, plaintextCachesWiped } = await import('./plaintextCaches');
+const { clearPlaintextCaches, plaintextCachesWiped, WIDGET_CONSENT_KEY_PREFIX } =
+  await import('./plaintextCaches');
+const { WIDGET_CONSENT_PREFIX, widgetConsentKey } =
+  await import('../features/room/widgets/widgetUtils');
 
 test('clearPlaintextCaches removes every plaintext/PII localStorage key', () => {
   store.clear();
@@ -104,3 +107,17 @@ test('clearPlaintextCaches clears the encrypted-search opt-in and flags the wipe
   assert.equal(store.has('mxjssdk_memory_filter_FILTER_SYNC_@me:server'), false);
   assert.equal(plaintextCachesWiped(), true, 'draft writes stop until the page reloads');
 });
+
+test('[#266] clearPlaintextCaches sweeps remembered widget approvals', () => {
+  assert.equal(WIDGET_CONSENT_KEY_PREFIX, WIDGET_CONSENT_PREFIX, 'prefix kept in sync');
+  store.clear();
+  const consent = widgetConsentKey('!room:server', 'widget-1');
+  store.set(consent, '{"url":"https://pad.example","allowed":[],"denied":[]}');
+  store.set('lotus.widgetConsentNotAKey', 'kept');
+  removed.length = 0;
+
+  clearPlaintextCaches('@me:server');
+
+  assert.ok(removed.includes(consent), 'consent cleared');
+  assert.ok(store.has('lotus.widgetConsentNotAKey'), 'unrelated key kept');
+});