fix agent idle stream heartbeat visibility

SovereignAI-Starter/app/main.py

@@ -2385,9 +2385,9 @@ async def run_agent_stream(
                     message = await asyncio.wait_for(queue.get(), timeout=0.25)
                 except TimeoutError:
                     if perf_counter() - last_output_at >= AGENT_STREAM_HEARTBEAT_SECONDS:
-                        # Keep otherwise-idle SSE connections alive while the model
-                        # or a local tool is taking several minutes to finish.
-                        yield ": keep-alive\n\n"
+                        # Send a visible SSE event (not only a comment) so clients
+                        # can reset idle timers and tell the user the agent is alive.
+                        yield "event: heartbeat\ndata: {}\n\n"
                         last_output_at = perf_counter()
                     continue
                 yield f"event: progress\ndata: {json.dumps({'message': message}, ensure_ascii=False)}\n\n"