refactor: move registry_pubsub cleanup into worker function

Instead of tracking pubsub externally with nonlocal, let the worker
function own and clean up its own resource in a local finally block.
This is cleaner and makes the code easier to understand for type checkers.

autogpt_platform/backend/backend/api/ws_api.py

@@ -79,39 +79,36 @@ async def event_broadcaster(manager: ConnectionManager):
                     payload=notification.payload,
                 )
 
-        # Track registry pubsub for cleanup
-        from redis.asyncio.client import PubSub
-
-        registry_pubsub: PubSub | None = None
-
         async def registry_refresh_worker():
             """Listen for LLM registry refresh notifications and broadcast to all clients."""
-            nonlocal registry_pubsub
             from backend.data.llm_registry import REGISTRY_REFRESH_CHANNEL
             from backend.data.redis_client import connect_async
 
             redis = await connect_async()
-            registry_pubsub = redis.pubsub()
-            await registry_pubsub.subscribe(REGISTRY_REFRESH_CHANNEL)
-            logger.info(
-                "Subscribed to LLM registry refresh notifications for WebSocket broadcast"
-            )
+            pubsub = redis.pubsub()
+            try:
+                await pubsub.subscribe(REGISTRY_REFRESH_CHANNEL)
+                logger.info(
+                    "Subscribed to LLM registry refresh notifications for WebSocket broadcast"
+                )
 
-            async for message in registry_pubsub.listen():
-                if (
-                    message["type"] == "message"
-                    and message["channel"] == REGISTRY_REFRESH_CHANNEL
-                ):
-                    logger.info(
-                        "Broadcasting LLM registry refresh to all WebSocket clients"
-                    )
-                    await manager.broadcast_to_all(
-                        method=WSMethod.NOTIFICATION,
-                        data={
-                            "type": "LLM_REGISTRY_REFRESH",
-                            "event": "registry_updated",
-                        },
-                    )
+                async for message in pubsub.listen():
+                    if (
+                        message["type"] == "message"
+                        and message["channel"] == REGISTRY_REFRESH_CHANNEL
+                    ):
+                        logger.info(
+                            "Broadcasting LLM registry refresh to all WebSocket clients"
+                        )
+                        await manager.broadcast_to_all(
+                            method=WSMethod.NOTIFICATION,
+                            data={
+                                "type": "LLM_REGISTRY_REFRESH",
+                                "event": "registry_updated",
+                            },
+                        )
+            finally:
+                await pubsub.close()
 
         await asyncio.gather(
             execution_worker(),
@@ -122,8 +119,6 @@ async def event_broadcaster(manager: ConnectionManager):
         # Ensure PubSub connections are closed on any exit to prevent leaks
         await execution_bus.close()
         await notification_bus.close()
-        if registry_pubsub is not None:  # type: ignore[reportPossiblyUnboundVariable]
-            await registry_pubsub.close()  # type: ignore[reportUnboundVariable]
 
 
 async def authenticate_websocket(websocket: WebSocket) -> str: