fix(agent): expose stable web stream message ids

app/application/messaging/webagentstream.py

@@ -290,7 +290,13 @@ def _build_web_agent_event_generator(
         disconnected = False
         terminal_sent = False
         try:
-            yield {"type": "start", "session_id": session_id}
+            yield {
+                "type": "start",
+                "session_id": session_id,
+                # 让前端把本地占位助手段绑定到服务端展示段，后续 steering
+                # 应用事件即可按稳定 ID 定位真实消息边界。
+                "assistant_message_id": assistant_message_ref["message"].get("id"),
+            }
             while not runtime_stop_state.is_system_stopped:
                 if await is_disconnected():
                     disconnected = True

tests/test_web_agent_stream.py

@@ -1480,6 +1480,7 @@ def test_web_agent_stream_queues_mid_run_input_into_the_same_assistant_stream():
 
     assert '"status": "queued"' in second_body
     assert '"status": "applied"' in first_body
+    assert '"assistant_message_id":' in first_body
     assert first_body.count('data: {"type": "start"') == 1
     assert first_body.count('data: {"type": "done"') == 1
     assert len(instances) == 1