Wire heartbeat into NexusMind consciousness loop

The heartbeat module existed but was never called. Now write_heartbeat fires:
- On startup (cycle 0, status thinking)
- After every successful think cycle
- On graceful shutdown (status idle)

This gives the watchdog a signal that the mind is alive, not just running.

nexus/nexus_think.py

@@ -45,6 +45,7 @@ from nexus.perception_adapter import (
 )
 from nexus.experience_store import ExperienceStore
 from nexus.groq_worker import GroqWorker
+from nexus.heartbeat import write_heartbeat
 from nexus.trajectory_logger import TrajectoryLogger
 
 logging.basicConfig(
@@ -286,6 +287,13 @@ class NexusMind:
 
         self.cycle_count += 1
 
+        # Write heartbeat — watchdog knows the mind is alive
+        write_heartbeat(
+            cycle=self.cycle_count,
+            model=self.model,
+            status="thinking",
+        )
+
         # Periodically distill old memories
         if self.cycle_count % 50 == 0 and self.cycle_count > 0:
             await self._distill_memories()
@@ -383,6 +391,13 @@ class NexusMind:
             salience=1.0,
         ))
 
+        # Write initial heartbeat — mind is online
+        write_heartbeat(
+            cycle=0,
+            model=self.model,
+            status="thinking",
+        )
+
         while self.running:
             try:
                 await self.think_once()
@@ -423,6 +438,13 @@ class NexusMind:
         log.info("Nexus Mind shutting down...")
         self.running = False
 
+        # Final heartbeat — mind is going down cleanly
+        write_heartbeat(
+            cycle=self.cycle_count,
+            model=self.model,
+            status="idle",
+        )
+
         # Final stats
         stats = self.trajectory_logger.get_session_stats()
         log.info(f"Session stats: {json.dumps(stats, indent=2)}")

server.py

@@ -48,21 +48,24 @@ async def broadcast_handler(websocket: websockets.WebSocketServerProtocol):
                 pass
 
             # Broadcast to all OTHER clients
+            if not clients:
+                continue
+                
             disconnected = set()
-            # Create broadcast tasks paired with their target client
-            task_client_pairs = []
+            # Create broadcast tasks for efficiency
+            tasks = []
             for client in clients:
                 if client != websocket and client.open:
-                    task = asyncio.create_task(client.send(message))
-                    task_client_pairs.append((task, client))
-
-            if task_client_pairs:
-                tasks = [t for t, _ in task_client_pairs]
+                    tasks.append(asyncio.create_task(client.send(message)))
+            
+            if tasks:
                 results = await asyncio.gather(*tasks, return_exceptions=True)
-                for (task, client), result in zip(task_client_pairs, results):
+                for i, result in enumerate(results):
                     if isinstance(result, Exception):
-                        logger.error(f"Failed to send to a client {client.remote_address}: {result}")
-                        disconnected.add(client)
+                        # Find the client that failed
+                        target_client = [c for c in clients if c != websocket][i]
+                        logger.error(f"Failed to send to a client {target_client.remote_address}: {result}")
+                        disconnected.add(target_client)
             
             if disconnected:
                 clients.difference_update(disconnected)