fix(core): Fix AgentCancel propagation for LangChain and smolagents#897
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fix(core): Fix AgentCancel propagation for LangChain and smolagents#897
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Some frameworks (e.g., smolagents) catch callback exceptions and re-raise them wrapped in their own error types using `raise ... from e`. This caused AgentCancel to be wrapped in AgentRunError instead of propagating directly. Add _unwrap_agent_cancel() helper that traverses Python's exception chain (__cause__ and __context__) to find any wrapped AgentCancel, allowing it to propagate correctly to the caller.
LangChain's BaseCallbackHandler defaults to raise_error=False, which catches exceptions in callbacks, logs a warning, and continues execution. This silently broke the circuit-breaker pattern for callback exceptions. Set raise_error=True on our callback handler to ensure exceptions (including AgentCancel subclasses) propagate correctly to run_async.
peteski22
added
callbacks
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daavoo
approved these changes
Jan 19, 2026
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Summary
_unwrap_agent_cancel()helper to traverse exception chains and find wrappedAgentCancelinstances. This fixes smolagents (which usesraise ... from e) and acts as a defensive catch-all for any future frameworks that follow the same pattern.raise_error=Trueon LangChain callback handler to propagate exceptions instead of swallowing them. LangChain defaults to logging warnings and continuing execution, which silently broke the circuit-breaker pattern for callback exceptions.Fixes integration test failures on main for
test_agent_cancel_not_wrapped[LANGCHAIN]andtest_agent_cancel_not_wrapped[SMOLAGENTS].Tests can be checked using:
uv run pytest tests/integration/frameworks/test_error_handling.py::test_agent_cancel_not_wrapped -k "LANGCHAIN or SMOLAGENTS" -v