fix issues

docs/02_components/15_sse_event_streamer/sse_event_streamer_spec.md

@@ -28,9 +28,19 @@ class ISSEEventStreamer(ABC):
     def send_refinement(self, flight_id: str, frame_id: int, updated_result: FrameResult) -> bool:
         pass
     
+    @abstractmethod
+    def send_heartbeat(self, flight_id: str) -> bool:
+        """Sends heartbeat/keepalive to all clients subscribed to flight."""
+        pass
+    
     @abstractmethod
     def close_stream(self, flight_id: str, client_id: str) -> bool:
         pass
+    
+    @abstractmethod
+    def get_active_connections(self, flight_id: str) -> int:
+        """Returns count of active SSE connections for a flight."""
+        pass
 ```
 
 ## Component Description
@@ -170,12 +180,50 @@ StreamConnection:
 
 ---
 
+### `send_heartbeat(flight_id: str) -> bool`
+
+**Description**: Sends heartbeat/keepalive ping to all clients subscribed to a flight. Keeps connections alive and helps detect stale connections.
+
+**Called By**:
+- Background heartbeat task (every 30 seconds)
+- F02 Flight Processor (periodically during processing)
+
+**Event Format**:
+```
+:heartbeat
+```
+
+**Behavior**:
+- Sends SSE comment (`:heartbeat`) which doesn't trigger event handlers
+- Keeps TCP connection alive
+- Client can use to detect connection health
+
+**Test Cases**:
+1. Send heartbeat → all clients receive ping
+2. Client timeout → connection marked stale
+
+---
+
 ### `close_stream(flight_id: str, client_id: str) -> bool`
 
 **Description**: Closes SSE connection.
 
 **Called By**: F01 REST API (on client disconnect)
 
+---
+
+### `get_active_connections(flight_id: str) -> int`
+
+**Description**: Returns count of active SSE connections for a flight.
+
+**Called By**:
+- F02 Flight Processor (monitoring)
+- Admin tools
+
+**Test Cases**:
+1. No connections → returns 0
+2. 5 clients connected → returns 5
+
 ## Integration Tests
 
 ### Test 1: Real-Time Streaming