fix(security): persistent search index forgets redacted and left-room text

Nothing ever removed an indexed row: redacted messages stayed searchable
with full plaintext and rendered as normal results. Now: a client-level
RoomEvent.Redaction listener deletes the row, leave/ban clears the room
(clearRoom finally has a caller), m.replace edits upsert the original
row instead of indexing the "* fallback" separately, and cached rows
whose local event is redacted render through the existing
redacted_because placeholder. Unit-tested.

Fixes #14

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

src/app/utils/searchCacheInvalidation.ts

@@ -0,0 +1,43 @@
+import { useEffect } from 'react';
+import { useAtomValue } from 'jotai';
+import { MatrixEvent, Room, RoomEvent } from 'matrix-js-sdk';
+import { useMatrixClient } from '../hooks/useMatrixClient';
+import { searchCacheEnabledAtom } from '../state/searchCacheEnabled';
+import { clearRoom, deleteRow } from './searchCache';
+
+/**
+ * Gitea #14 — the persistent search cache (`searchCache.ts`) had no
+ * invalidation path other than logout or the manual "Clear cached index"
+ * button, so redacted messages and rooms the user left kept their decrypted
+ * plaintext searchable on disk indefinitely.
+ *
+ * While the cache is enabled, listen client-wide for redactions (delete the
+ * redacted row) and for leaving/being banned from a room (wipe the room's
+ * cached rows via the existing `clearRoom`).
+ */
+export const useSearchCacheInvalidation = (): void => {
+  const mx = useMatrixClient();
+  const cacheEnabled = useAtomValue(searchCacheEnabledAtom);
+
+  useEffect(() => {
+    if (!cacheEnabled) return undefined;
+
+    const onRedaction = (event: MatrixEvent, room: Room) => {
+      const redactedEventId = event.getAssociatedId();
+      if (redactedEventId) deleteRow(room.roomId, redactedEventId);
+    };
+
+    const onMyMembership = (room: Room, membership: string) => {
+      if (membership === 'leave' || membership === 'ban') {
+        clearRoom(room.roomId);
+      }
+    };
+
+    mx.on(RoomEvent.Redaction, onRedaction);
+    mx.on(RoomEvent.MyMembership, onMyMembership);
+    return () => {
+      mx.off(RoomEvent.Redaction, onRedaction);
+      mx.off(RoomEvent.MyMembership, onMyMembership);
+    };
+  }, [mx, cacheEnabled]);
+};