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Python: [Bug]: Harness Agent drops structured value on the streaming path with tool approval #7418
Description
Description
What happened?
ToolApprovalMiddleware._process_stream finalizes the outer stream with AgentResponse.from_updates without passing output_format_type:
return ResponseStream(_stream(), finalizer=AgentResponse.from_updates)
Because from_updates receives the text updates but no response_format, the final AgentResponse.value is None for streaming runs that combine tool approval with a structured-output schema.
The non-streaming path is unaffected because it returns the inner AgentResponse directly.
What did you expect to happen?
response.value should be parsed into the Pydantic model / schema supplied via response_format, matching the non-harness streaming path in _agents.py:1229.
Steps to reproduce the issue
- Create a
create_harness_agent(...)withstream=True. - Register a tool that requires approval.
- Pass
options={"response_format": SomePydanticModel}toagent.run. - Inspect
response.value— it isNone.
Same "per-run concept lost by a re-wrapping layer" family as #7402 and #7236.
Code Sample
from typing import Any
import asyncio
from pydantic import BaseModel
from agent_framework import (
AgentSession,
BaseChatClient,
ChatResponse,
Message,
create_harness_agent,
)
class Answer(BaseModel):
answer: str
class EchoTool:
@tool(approval_mode="always_require")
async def echo(self, text: str) -> str:
return text
class FakeStreamingClient(BaseChatClient):
async def _inner_get_response(self, *, messages, stream, options, **kwargs):
return ChatResponse(
messages=[Message("assistant", ['{"answer": "42"}'])]
)
async def main():
agent = create_harness_agent(
client=FakeStreamingClient(),
tools=[EchoTool().echo],
stream=True,
)
session = AgentSession()
response = await agent.run(
"Call echo and return an Answer.",
session=session,
options={"response_format": Answer},
)
print(type(response.value)) # Currently: NoneType
assert isinstance(response.value, Answer) # Fails today
asyncio.run(main())Error Messages / Stack Traces
Package Versions
agent-framework-core: 1.12.1
Python Version
No response
Additional Context
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github-actions commentedon Jul 30, 2026
👋 Hi lmx-2077 — thanks for the report!
Your issue describes a clear pattern where
ToolApprovalMiddleware._process_streamre-wraps the response stream viaResponseStream(_stream(), finalizer=AgentResponse.from_updates)without forwarding theoutput_format_typeparameter, which would causeresponse.valueto beNonefor structured-output streaming runs with tool approval. This appears consistent with the sibling issues you referenced (#7402, #7236). Unfortunately, were unable to verify against the current source code due to environment access issues, so it's possible this has already been addressed in a newer version; worth checking if you're on the latest release.If this still reproduces after trying the above, please reopen and we'll take another look. 🙏
lmx-2077 commentedon Jul 30, 2026
Confirmed this still reproduces on current main. The finalizer at python/packages/core/agent_framework/_harness/_tool_approval.py:500 still calls:
return ResponseStream(_stream(), finalizer=AgentResponse.from_updates)
without passing output_format_type. Because AgentResponse.value is a lazy property that only parses structured output when _response_format is set, streaming runs with tool approval currently return response.value = None.
This is a distinct finalizer omission from the sibling issues #7402 / #7236 (both are about the agent loop, not the harness middleware re-wrapping layer). I have a focused fix + regression test ready and will link a PR shortly. Could the likely-fixed label be removed?
Shivani767 commentedon Aug 20, 2026
Opened a fix in #7800.
ToolApprovalMiddleware._process_streamnow forwardsresponse_format(run options, then agentdefault_options) intoAgentResponse.from_updates, so streaming structured output is parsed the same way as the non-streaming path.Python: Preserve structured output on streaming harness tool-approval…