fix(middleware): prevent title middleware from streaming tokens (#3566)

backend/packages/harness/deerflow/agents/middlewares/title_middleware.py

@@ -7,6 +7,7 @@ from typing import TYPE_CHECKING, Any, NotRequired, override
 from langchain.agents import AgentState
 from langchain.agents.middleware import AgentMiddleware
 from langgraph.config import get_config
+from langgraph.constants import TAG_NOSTREAM
 from langgraph.runtime import Runtime
 
 from deerflow.agents.middlewares.dynamic_context_middleware import is_dynamic_context_reminder
@@ -140,7 +141,11 @@ class TitleMiddleware(AgentMiddleware[TitleMiddlewareState]):
             parent = {}
         config = {**parent}
         config["run_name"] = "title_agent"
-        config["tags"] = [*(config.get("tags") or []), "middleware:title"]
+        config["tags"] = [
+            *(config.get("tags") or []),
+            "middleware:title",
+            TAG_NOSTREAM,
+        ]
         return config
 
     def _generate_title_result(self, state: TitleMiddlewareState) -> dict | None:

backend/tests/test_title_middleware_core_logic.py

@@ -5,6 +5,7 @@ from types import SimpleNamespace
 from unittest.mock import AsyncMock, MagicMock
 
 from langchain_core.messages import AIMessage, HumanMessage
+from langgraph.constants import TAG_NOSTREAM
 
 from deerflow.agents.middlewares import title_middleware as title_middleware_module
 from deerflow.agents.middlewares.dynamic_context_middleware import _DYNAMIC_CONTEXT_REMINDER_KEY
@@ -113,9 +114,22 @@ class TestTitleMiddlewareCoreLogic:
         model.ainvoke.assert_awaited_once()
         assert model.ainvoke.await_args.kwargs["config"] == {
             "run_name": "title_agent",
-            "tags": ["middleware:title"],
+            "tags": ["middleware:title", TAG_NOSTREAM],
         }
 
+    def test_title_model_config_preserves_parent_tags_and_adds_nostream(self, monkeypatch):
+        middleware = TitleMiddleware()
+        monkeypatch.setattr(
+            title_middleware_module,
+            "get_config",
+            MagicMock(return_value={"tags": ["parent"]}),
+        )
+
+        config = middleware._get_runnable_config()
+
+        assert config["run_name"] == "title_agent"
+        assert config["tags"] == ["parent", "middleware:title", TAG_NOSTREAM]
+
     def test_generate_title_uses_explicit_app_config_without_global_config(self, monkeypatch):
         title_config = TitleConfig(enabled=True, model_name="title-model", max_chars=20)
         app_config = SimpleNamespace(title=title_config)