fix(security): revoke soundboard blob URLs on logout; cap the cache

Decrypted clip blob: URLs lived in an unbounded module Map for the page
lifetime and survived logout. Add clearSoundboardClipCache() (called from
both logout paths next to clearPlaintextCaches) and a 64-entry LRU that
revokes on evict. Unit-tested.

Fixes #57

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

src/client/initMatrix.ts

@@ -8,6 +8,7 @@ import { revokeOidcTokens } from './oidcLogout';
 import { pushSessionToSW } from '../sw-session';
 import { deleteSearchCacheDatabase } from '../app/utils/searchCache';
 import { clearPlaintextCaches } from '../app/state/plaintextCaches';
+import { clearSoundboardClipCache } from '../app/utils/soundboardClips';
 
 // Thrown when the local IndexedDB has a higher schema version than this SDK expects.
 // This happens after a downgrade (e.g. matrix-js-sdk was briefly upgraded and then reverted).
@@ -103,6 +104,9 @@ export const startClient = async (mx: MatrixClient) => {
 export const clearCacheAndReload = async (mx: MatrixClient) => {
   mx.stopClient();
   clearNavToActivePathStore(mx.getSafeUserId());
+  // [Gitea #57] Soundboard clip blob URLs hold decrypted media reachable for
+  // the whole page session — revoke them alongside the rest of the caches.
+  clearSoundboardClipCache();
   await mx.store.deleteAllData();
   window.location.reload();
 };
@@ -128,6 +132,9 @@ export const logoutClient = async (mx: MatrixClient) => {
   // scheduled messages, recent searches/forwards/gifs/stickers, nav paths) —
   // wipe them too.
   clearPlaintextCaches(mx.getUserId() ?? undefined);
+  // [Gitea #57] Same reasoning as clearPlaintextCaches: decrypted soundboard
+  // clip bytes stay reachable via live blob: URLs until the reload otherwise.
+  clearSoundboardClipCache();
   // Remove only the session credential keys, preserving user preferences and
   // unsent drafts (N98). The factory-reset path is clearLoginData() below.
   removeFallbackSession();