Merged tasks are endlessly re-rendering (vibe-kanban) (#938)

* ## ✅ Fix Complete

**Problem:** Merged tasks caused endless WebSocket reconnections because `useJsonPatchWsStream` incorrectly treated `{finished: true}` messages as signals to reconnect.

**Solution:** Modified [useJsonPatchWsStream.ts](file:///private/var/folders/m1/9q_ct1913z10v6wbnv54j25r0000gn/T/vibe-kanban/worktrees/0f2d-merged-tasks-are/frontend/src/hooks/useJsonPatchWsStream.ts) to treat "finished" as terminal:

1. Added `finishedRef` to track when stream completes
2. On `{finished: true}`: set flag, close cleanly (code 1000), **no reconnect**
3. On socket close: skip reconnection if finished flag is set or clean close
4. Reset flag on cleanup and new connections

**Result:**
- Merged tasks connect once, receive final state, and stop cleanly
- Active tasks still reconnect on network errors
- Aligned behavior with existing `streamJsonPatchEntries` utility
- All type checks pass ✅

* Cleanup script changes for task attempt 0f2d0086-1de2-4517-a023-1ee8cf133181

frontend/src/hooks/useJsonPatchWsStream.ts

@@ -40,6 +40,7 @@ export const useJsonPatchWsStream = <T>(
   const retryTimerRef = useRef<number | null>(null);
   const retryAttemptsRef = useRef<number>(0);
   const [retryNonce, setRetryNonce] = useState(0);
+  const finishedRef = useRef<boolean>(false);
 
   function scheduleReconnect() {
     if (retryTimerRef.current) return; // already scheduled
@@ -64,6 +65,7 @@ export const useJsonPatchWsStream = <T>(
         retryTimerRef.current = null;
       }
       retryAttemptsRef.current = 0;
+      finishedRef.current = false;
       setData(undefined);
       setIsConnected(false);
       setError(null);
@@ -85,6 +87,9 @@ export const useJsonPatchWsStream = <T>(
 
     // Create WebSocket if it doesn't exist
     if (!wsRef.current) {
+      // Reset finished flag for new connection
+      finishedRef.current = false;
+
       // Convert HTTP endpoint to WebSocket endpoint
       const wsEndpoint = endpoint.replace(/^http/, 'ws');
       const ws = new WebSocket(wsEndpoint);
@@ -124,13 +129,12 @@ export const useJsonPatchWsStream = <T>(
           }
 
           // Handle finished messages ({finished: true})
+          // Treat finished as terminal - do NOT reconnect
           if ('finished' in msg) {
-            ws.close();
+            finishedRef.current = true;
+            ws.close(1000, 'finished');
             wsRef.current = null;
             setIsConnected(false);
-            // Treat finished as terminal and schedule reconnect; servers may rotate
-            retryAttemptsRef.current += 1;
-            scheduleReconnect();
           }
         } catch (err) {
           console.error('Failed to process WebSocket message:', err);
@@ -142,9 +146,16 @@ export const useJsonPatchWsStream = <T>(
         setError('Connection failed');
       };
 
-      ws.onclose = () => {
+      ws.onclose = (evt) => {
         setIsConnected(false);
         wsRef.current = null;
+
+        // Do not reconnect if we received a finished message or clean close
+        if (finishedRef.current || (evt?.code === 1000 && evt?.wasClean)) {
+          return;
+        }
+
+        // Otherwise, reconnect on unexpected/error closures
         retryAttemptsRef.current += 1;
         scheduleReconnect();
       };
@@ -170,6 +181,7 @@ export const useJsonPatchWsStream = <T>(
         window.clearTimeout(retryTimerRef.current);
         retryTimerRef.current = null;
       }
+      finishedRef.current = false;
       dataRef.current = undefined;
       setData(undefined);
     };