[BUG] ValidationError After Direct Tool Calling with Agent Parameter

[cagataycali]

Checks

• I have updated to the lastest minor and patch version of Strands
• I have checked the documentation and this is not expected behavior
• I have searched ./issues and there are no duplicates of my issue

Strands Version

source

Python Version

3.13

Operating System

macOS

Installation Method

git clone

Steps to Reproduce

When we pass Agent instance to direct tool calls, tool executes successfully.

But after that

>>> from strands import Agent
>>> from strands_tools import slack
>>> agent = Agent(tools=[slack])
>>> agent.tool.slack(action="start_socket_mode", agent=agent)
As `installation_store` or `authorize` has been used, `token` (or SLACK_BOT_TOKEN env variable) will be ignored.
{'toolUseId': 'tooluse_slack_477600603', 'status': 'success', 'content': [{'text': '✅ Socket Mode connection established and ready to receive real-time events'}]}
>>> agent("list your tools")
Traceback (most recent call last):
  File "<python-input-4>", line 1, in <module>
    agent("list your tools")
    ~~~~~^^^^^^^^^^^^^^^^^^^
  File "/Users/cagatay/report-agent/.venv/lib/python3.13/site-packages/strands/agent/agent.py", line 377, in __call__
    return future.result()
           ~~~~~~~~~~~~~^^
  File "/opt/homebrew/Cellar/python@3.13/3.13.5/Frameworks/Python.framework/Versions/3.13/lib/python3.13/concurrent/futures/_base.py", line 456, in result
    return self.__get_result()
           ~~~~~~~~~~~~~~~~~^^
  File "/opt/homebrew/Cellar/python@3.13/3.13.5/Frameworks/Python.framework/Versions/3.13/lib/python3.13/concurrent/futures/_base.py", line 401, in __get_result
    raise self._exception
  File "/opt/homebrew/Cellar/python@3.13/3.13.5/Frameworks/Python.framework/Versions/3.13/lib/python3.13/concurrent/futures/thread.py", line 59, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/Users/cagatay/report-agent/.venv/lib/python3.13/site-packages/opentelemetry/instrumentation/threading/__init__.py", line 171, in wrapped_func
    return original_func(*func_args, **func_kwargs)
  File "/Users/cagatay/report-agent/.venv/lib/python3.13/site-packages/strands/agent/agent.py", line 373, in execute
    return asyncio.run(self.invoke_async(prompt, **kwargs))
           ~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/python@3.13/3.13.5/Frameworks/Python.framework/Versions/3.13/lib/python3.13/asyncio/runners.py", line 195, in run
    return runner.run(main)
           ~~~~~~~~~~^^^^^^
  File "/opt/homebrew/Cellar/python@3.13/3.13.5/Frameworks/Python.framework/Versions/3.13/lib/python3.13/asyncio/runners.py", line 118, in run
    return self._loop.run_until_complete(task)
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/opt/homebrew/Cellar/python@3.13/3.13.5/Frameworks/Python.framework/Versions/3.13/lib/python3.13/asyncio/base_events.py", line 725, in run_until_complete
    return future.result()
           ~~~~~~~~~~~~~^^
  File "/Users/cagatay/report-agent/.venv/lib/python3.13/site-packages/strands/agent/agent.py", line 398, in invoke_async
    async for event in events:
        _ = event
  File "/Users/cagatay/report-agent/.venv/lib/python3.13/site-packages/strands/agent/agent.py", line 508, in stream_async
    async for event in events:
    ...<2 lines>...
            yield event["callback"]
  File "/Users/cagatay/report-agent/.venv/lib/python3.13/site-packages/strands/agent/agent.py", line 544, in _run_loop
    async for event in events:
    ...<13 lines>...
        yield event
  File "/Users/cagatay/report-agent/.venv/lib/python3.13/site-packages/strands/agent/agent.py", line 583, in _execute_event_loop_cycle
    async for event in events:
        yield event
  File "/Users/cagatay/report-agent/.venv/lib/python3.13/site-packages/strands/event_loop/event_loop.py", line 187, in event_loop_cycle
    raise e
  File "/Users/cagatay/report-agent/.venv/lib/python3.13/site-packages/strands/event_loop/event_loop.py", line 132, in event_loop_cycle
    async for event in stream_messages(agent.model, agent.system_prompt, agent.messages, tool_specs):
    ...<6 lines>...
            }
  File "/Users/cagatay/report-agent/.venv/lib/python3.13/site-packages/strands/event_loop/streaming.py", line 318, in stream_messages
    async for event in process_stream(chunks):
        yield event
  File "/Users/cagatay/report-agent/.venv/lib/python3.13/site-packages/strands/event_loop/streaming.py", line 273, in process_stream
    async for chunk in chunks:
    ...<16 lines>...
            handle_redact_content(chunk["redactContent"], state)
  File "/Users/cagatay/report-agent/.venv/lib/python3.13/site-packages/strands/models/bedrock.py", line 350, in stream
    await task
  File "/opt/homebrew/Cellar/python@3.13/3.13.5/Frameworks/Python.framework/Versions/3.13/lib/python3.13/asyncio/threads.py", line 25, in to_thread
    return await loop.run_in_executor(None, func_call)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/python@3.13/3.13.5/Frameworks/Python.framework/Versions/3.13/lib/python3.13/concurrent/futures/thread.py", line 59, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/Users/cagatay/report-agent/.venv/lib/python3.13/site-packages/opentelemetry/instrumentation/threading/__init__.py", line 171, in wrapped_func
    return original_func(*func_args, **func_kwargs)
  File "/Users/cagatay/report-agent/.venv/lib/python3.13/site-packages/strands/models/bedrock.py", line 384, in _stream
    response = self.client.converse_stream(**request)
  File "/Users/cagatay/report-agent/.venv/lib/python3.13/site-packages/botocore/client.py", line 601, in _api_call
    return self._make_api_call(operation_name, kwargs)
           ~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/cagatay/report-agent/.venv/lib/python3.13/site-packages/botocore/context.py", line 123, in wrapper
    return func(*args, **kwargs)
  File "/Users/cagatay/report-agent/.venv/lib/python3.13/site-packages/botocore/client.py", line 1031, in _make_api_call
    request_dict = self._convert_to_request_dict(
        api_params=api_params,
    ...<3 lines>...
        headers=additional_headers,
    )
  File "/Users/cagatay/report-agent/.venv/lib/python3.13/site-packages/botocore/client.py", line 1098, in _convert_to_request_dict
    request_dict = self._serializer.serialize_to_request(
        api_params, operation_model
    )
  File "/Users/cagatay/report-agent/.venv/lib/python3.13/site-packages/botocore/validate.py", line 381, in serialize_to_request
    raise ParamValidationError(report=report.generate_report())
botocore.exceptions.ParamValidationError: Parameter validation failed:
Invalid type for document parameter agent, value: <strands.agent.agent.Agent object at 0x1041d9a90>, type: <class 'strands.agent.agent.Agent'>, valid types: <class 'str'>, <class 'int'>, <class 'bool'>, <class 'float'>, <class 'list'>, <class 'dict'>
>>> 

>>> agent.messages
[{'role': 'user', 'content': [{'text': 'agent.tool.slack direct tool call.\nInput parameters: {"action": "start_socket_mode", "agent": "<<non-serializable: Agent>>"}\n'}]}, {'role': 'assistant', 'content': [{'toolUse': {'toolUseId': 'tooluse_slack_477600603', 'name': 'slack', 'input': {'action': 'start_socket_mode', 'agent': <strands.agent.agent.Agent object at 0x1041d9a90>}}}]}, {'role': 'user', 'content': [{'toolResult': {'toolUseId': 'tooluse_slack_477600603', 'status': 'success', 'content': [{'text': '✅ Socket Mode connection established and ready to receive real-time events'}]}}]}, {'role': 'assistant', 'content': [{'text': 'agent.tool.slack was called.'}]}, {'role': 'user', 'content': [{'text': 'list your tools'}]}]

From agent.messages we can see that toolUse block have Agent object reference which breaks JSON parsing.

Expected Behavior

Replace / remove non-serializable parameter of agent from toolUse block and continue inference.

Actual Behavior

Crash because of reference.

Additional Context

No response

Possible Solution

No response

Related Issues

No response

[cagataycali]

We had a discussion in our standup today, couple action items:

1. Making the agent injection for direct tool calls:

agent.tool.slack(..., agent=agent) # parent agent will be auto-injected

1.1. Allowing anyone to override the injected parent agent

Anyone can override parent agent passed as direct tool calls.

2. Making agent str serializable and de-serializable so we can keep the agent instance in string form.

For this PR, these action items are not blocker.

[JackYPCOnline]

After discussion: Resolution for now is striping out the paramter that is not in tool spec.

[zastrowm]

Pending action items:

• Auto-inject agent into tool-calls (restoring pre-release behavior)
• But still allow callers to override it