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/useLocalMessageSearch.ts

@@ -18,6 +18,12 @@ export type LocalSearchParams = {
   /** Optional date-range filter (ms). Applied to both memory and cached rows. */
   fromTs?: number;
   toTs?: number;
+  /**
+   * Set false to run the scan without writing it back to IndexedDB — used
+   * right after "Clear cached index" so the clear is not undone by the
+   * re-run of the active search (Gitea #184 O4).
+   */
+  persist?: boolean;
 };
 
 export type LocalSearchResult = {
@@ -149,6 +155,7 @@ export const useLocalMessageSearch = () => {
       senders,
       fromTs,
       toTs,
+      persist = true,
     }: LocalSearchParams): Promise<LocalSearchResult> => {
       const trimmedTerm = term.trim();
       const senderSet = senders && senders.length > 0 ? new Set(senders) : null;
@@ -302,7 +309,7 @@ export const useLocalMessageSearch = () => {
         // Fire-and-forget persist of freshly scanned rows + coverage.
         // saveRoomIndex swallows all errors internally, so a floating promise
         // here can never reject.
-        if (cacheEnabled && rowsToPersist.length > 0) {
+        if (cacheEnabled && persist && rowsToPersist.length > 0) {
           saveRoomIndex(roomId, rowsToPersist);
         }
       }