feat(desktop): expose reactions reveal-gate flag (ready)

apps/desktop/src/lib/useMessageReactions.ts

@@ -19,6 +19,10 @@ export interface UseMessageReactionsResult {
   byMessage: Map<string, AggregatedReaction[]>;
   toggle: (messageId: string, emoji: string) => Promise<void>;
   voteExclusive: (messageId: string, emoji: string, exclusiveEmojis: string[]) => Promise<void>;
+  // True once the reactions for the current message-id set have been fetched
+  // (or there are no messages). Drives MessageList's deferred reveal so the
+  // chat opens already showing reaction chips — no post-paint height jump.
+  ready: boolean;
 }
 
 // Batch-fetches reactions for the given message ids + subscribes to the
@@ -29,10 +33,12 @@ export function useMessageReactions(
 ): UseMessageReactionsResult {
   const idsKey = useMemo(() => messageIds.join(','), [messageIds]);
   const [rows, setRows] = useState<MessageReaction[]>([]);
+  const [readyKey, setReadyKey] = useState<string | null>(null);
 
   const refresh = useCallback(async () => {
     if (messageIds.length === 0) {
       setRows([]);
+      setReadyKey(idsKey);
       return;
     }
     try {
@@ -40,6 +46,8 @@ export function useMessageReactions(
       setRows(data);
     } catch (err: unknown) {
       console.error('listReactionsForMessages failed', err);
+    } finally {
+      setReadyKey(idsKey);
     }
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [idsKey]);
@@ -129,5 +137,7 @@ export function useMessageReactions(
     [byMessage, myId, refresh],
   );
 
-  return { byMessage, toggle, voteExclusive };
+  const ready = readyKey === idsKey;
+
+  return { byMessage, toggle, voteExclusive, ready };
 }