From a033721ac202471f161e316da69eae7e81bb7a98 Mon Sep 17 00:00:00 2001
From: Evan Mattson <35585003+moonbox3@users.noreply.github.com>
Date: Fri, 27 Feb 2026 03:28:14 +0900
Subject: [PATCH] Python: Fix response_format resolution in streaming finalizer
 (#4291)

* Python: Fix AgentResponse.value being None when streaming workflow (#3970)

The streaming path in BaseAgent.run() used the raw 'options' parameter
(passed by the caller) to bind response_format into the outer stream's
finalizer. When response_format was set in default_options rather than
runtime options, it was missing from the finalizer and value was None.

Fix: Use the merged chat_options from the run context (via ctx_holder),
matching the non-streaming path which already uses ctx['chat_options'].

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Address review feedback for #3970: safer ctx access, add test coverage

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 .../packages/core/agent_framework/_agents.py  |  9 ++--
 .../packages/core/tests/core/test_agents.py   | 52 +++++++++++++++++++
 2 files changed, 58 insertions(+), 3 deletions(-)

diff --git a/python/packages/core/agent_framework/_agents.py b/python/packages/core/agent_framework/_agents.py
index a3f4570b6e..580b6e2c6d 100644
--- a/python/packages/core/agent_framework/_agents.py
+++ b/python/packages/core/agent_framework/_agents.py
@@ -935,6 +935,11 @@ class RawAgent(BaseAgent, Generic[OptionsCoT]):  # type: ignore[misc]
                 session.service_session_id = conv_id
             return update
 
+        def _finalizer(updates: Sequence[AgentResponseUpdate]) -> AgentResponse[Any]:
+            ctx = ctx_holder["ctx"]
+            rf = ctx.get("chat_options", {}).get("response_format") if ctx else (options.get("response_format") if options else None)
+            return self._finalize_response_updates(updates, response_format=rf)
+
         return (
             ResponseStream
             .from_awaitable(_get_stream())
@@ -943,9 +948,7 @@ class RawAgent(BaseAgent, Generic[OptionsCoT]):  # type: ignore[misc]
                     map_chat_to_agent_update,
                     agent_name=self.name,
                 ),
-                finalizer=partial(
-                    self._finalize_response_updates, response_format=options.get("response_format") if options else None
-                ),
+                finalizer=_finalizer,
             )
             .with_transform_hook(_propagate_conversation_id)
             .with_result_hook(_post_hook)
diff --git a/python/packages/core/tests/core/test_agents.py b/python/packages/core/tests/core/test_agents.py
index 627987a1f2..b6f84dc970 100644
--- a/python/packages/core/tests/core/test_agents.py
+++ b/python/packages/core/tests/core/test_agents.py
@@ -97,6 +97,58 @@ async def test_chat_client_agent_run_streaming(client: SupportsChatGetResponse)
     assert result.text == "test streaming response another update"
 
 
+async def test_chat_client_agent_streaming_response_format_from_default_options(
+    client: SupportsChatGetResponse,
+) -> None:
+    """AgentResponse.value must be parsed when response_format is set in default_options and streaming."""
+    from pydantic import BaseModel
+
+    class Greeting(BaseModel):
+        greeting: str
+
+    json_text = '{"greeting": "Hello"}'
+    client.streaming_responses.append(  # type: ignore[attr-defined]
+        [ChatResponseUpdate(contents=[Content.from_text(json_text)], role="assistant", finish_reason="stop")]
+    )
+
+    agent = Agent(client=client, default_options={"response_format": Greeting})
+    stream = agent.run("Hello", stream=True)
+    async for _ in stream:
+        pass
+    result = await stream.get_final_response()
+
+    assert result.text == json_text
+    assert result.value is not None
+    assert isinstance(result.value, Greeting)
+    assert result.value.greeting == "Hello"
+
+
+async def test_chat_client_agent_streaming_response_format_from_run_options(
+    client: SupportsChatGetResponse,
+) -> None:
+    """AgentResponse.value must be parsed when response_format is passed via run() options kwarg."""
+    from pydantic import BaseModel
+
+    class Greeting(BaseModel):
+        greeting: str
+
+    json_text = '{"greeting": "Hi"}'
+    client.streaming_responses.append(  # type: ignore[attr-defined]
+        [ChatResponseUpdate(contents=[Content.from_text(json_text)], role="assistant", finish_reason="stop")]
+    )
+
+    agent = Agent(client=client)
+    stream = agent.run("Hello", stream=True, options={"response_format": Greeting})
+    async for _ in stream:
+        pass
+    result = await stream.get_final_response()
+
+    assert result.text == json_text
+    assert result.value is not None
+    assert isinstance(result.value, Greeting)
+    assert result.value.greeting == "Hi"
+
+
 async def test_chat_client_agent_create_session(client: SupportsChatGetResponse) -> None:
     agent = Agent(client=client)
     session = agent.create_session()