Fix: task system messages use broadcast_message (not broadcast_all)

broadcast_all bypasses agent filtering (system message @mention check),
so agents received ALL task lifecycle messages and processed them as
new requests, causing duplicate task creation.

src/tracker/api/tasks.py

@@ -142,9 +142,12 @@ async def _system_message(
         attachments=[],
         created_at=task_msg.created_at.isoformat() if task_msg.created_at else datetime.datetime.now(datetime.timezone.utc).isoformat(),
     )
-    await manager.broadcast_all(
-        {"type": WSEventType.MESSAGE_NEW, "data": task_msg_out.model_dump()},
-        exclude_slug="system",
+    # Broadcast task comment via broadcast_message (applies agent filtering: @mention check)
+    project_id = str(task.project_id)
+    await manager.broadcast_message(
+        project_id,
+        task_msg_out.model_dump(),
+        author_slug="system",
     )
 
     # Broadcast chat message

src/tracker/ws/handler.py

@@ -351,12 +351,15 @@ async def _handle_chat_send(session_id: str, data: dict):
 
 async def _handle_agent_stream(session_id: str, event_type: str, data: dict):
     """Relay agent streaming events to project subscribers."""
+    logger.info("STREAM event: %s data=%s", event_type, str(data)[:200])
     client = manager.sessions.get(session_id)
     if not client:
+        logger.warning("STREAM: no client for session %s", session_id[:8])
         return
 
     # Only agents can stream
     if client.member_type != MemberType.AGENT:
+        logger.warning("STREAM: non-agent %s tried to stream", client.member_slug)
         return
 
     # Determine project_id from chat_id or task_id in the data