fix(search): "Clear cached index" was undone immediately by the active search re-persisting its in-memory rows (#184 O4)

Clearing bumps cacheVersion so the search re-runs, and the re-run wrote
the scanned rows straight back to IndexedDB, so the index was never empty
while the button was visible. Skip persistence for that one re-run.
Verified: IDB stores go to 0/0 after Clear; logout still deletes the DB.

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

src/app/features/message-search/MessageSearch.tsx

@@ -246,8 +246,15 @@ export function MessageSearch({
   const [cacheVersion, setCacheVersion] = useState(0);
   const handleCacheLoaded = useCallback(() => setCacheVersion((v) => v + 1), []);
   // Explicit wipe of the persistent on-disk index, then re-run the merge.
+  // After a clear, the active search re-runs (cacheVersion) and would persist
+  // the in-memory rows straight back — skip that one write so "Clear cached
+  // index" actually leaves the disk empty until the next new search.
+  const skipPersistOnceRef = useRef(false);
   const handleClearSearchCache = useCallback(() => {
-    clearSearchCache().then(() => setCacheVersion((v) => v + 1));
+    clearSearchCache().then(() => {
+      skipPersistOnceRef.current = true;
+      setCacheVersion((v) => v + 1);
+    });
   }, []);
 
   // The rooms actually in scope for this search (mirrors server-side logic)
@@ -277,12 +284,15 @@ export function MessageSearch({
       return undefined;
     }
     let cancelled = false;
+    const persist = !skipPersistOnceRef.current;
+    skipPersistOnceRef.current = false;
     searchLocalMessages({
       term: msgSearchParams.term ?? '',
       roomIds: localSearchRooms,
       senders: msgSearchParams.senders,
       fromTs: msgSearchParams.fromTs,
       toTs: msgSearchParams.toTs,
+      persist,
     }).then((result) => {
       if (!cancelled) setLocalResult(result);
     });