fix: use AIMessage content for summarization response parsing

Agent-Logs-Url: https://github.com/bytedance/deer-flow/sessions/0b34cccd-f69a-4f68-bfa6-9a41256b63b5

Co-authored-by: WillemJiang <219644+WillemJiang@users.noreply.github.com>

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

@@ -201,7 +201,7 @@ class DeerFlowSummarizationMiddleware(SummarizationMiddleware):
                     "callbacks": [],
                 },
             )
-            return response.text.strip()
+            return self._extract_summary_text(response)
         except Exception as e:
             return f"Error generating summary: {e!s}"
 
@@ -230,10 +230,16 @@ class DeerFlowSummarizationMiddleware(SummarizationMiddleware):
                     "callbacks": [],
                 },
             )
-            return response.text.strip()
+            return self._extract_summary_text(response)
         except Exception as e:
             return f"Error generating summary: {e!s}"
 
+    def _extract_summary_text(self, response: Any) -> str:
+        summary_text = getattr(response, "content", None)
+        if summary_text is None:
+            summary_text = getattr(response, "text", "")
+        return summary_text.strip() if isinstance(summary_text, str) else str(summary_text).strip()
+
     @override
     def _build_new_messages(self, summary: str) -> list[HumanMessage]:
         """Override the base implementation to let the human message with the special name 'summary'.

backend/tests/test_summarization_middleware.py

@@ -50,7 +50,7 @@ def _middleware(
     preserve_recent_skill_tokens_per_skill: int = 0,
 ) -> DeerFlowSummarizationMiddleware:
     model = MagicMock()
-    model.invoke.return_value = SimpleNamespace(text="compressed summary")
+    model.invoke.return_value = AIMessage(content="compressed summary")
     return DeerFlowSummarizationMiddleware(
         model=model,
         trigger=trigger,
@@ -672,7 +672,7 @@ async def test_acreate_summary_suppresses_callbacks() -> None:
     """_acreate_summary must pass callbacks=[] to prevent the internal LLM call
     from producing visible streaming events in the frontend (issue #2804)."""
     middleware = _middleware()
-    middleware.model.ainvoke = mock.AsyncMock(return_value=SimpleNamespace(text="async summary"))
+    middleware.model.ainvoke = mock.AsyncMock(return_value=AIMessage(content="async summary"))
 
     await middleware._acreate_summary(_messages())