fix(langgraph): yield task_result events with errors in single debug stream mode#6984
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Br1an (Br1an67) wants to merge 1 commit intolangchain-ai:mainfrom
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fix(langgraph): yield task_result events with errors in single debug stream mode#6984Br1an (Br1an67) wants to merge 1 commit intolangchain-ai:mainfrom
Br1an (Br1an67) wants to merge 1 commit intolangchain-ai:mainfrom
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…stream mode In the runner fast path (single task, no waiter), yield control back to the caller before raising the exception. This allows the main loop to drain the stream queue and emit the task_result event containing the error before the exception propagates. The concurrent path already yields before _panic_or_proceed, which is why stream_mode=["debug", "messages"] worked correctly. Fixes langchain-ai#5764
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Description: When using
stream_mode="debug"(single mode),task_resultevents containing errors were not yielded before the exception was raised. This happened because the runner's fast path (single task, no waiter/timeout) raised the exception immediately after committing the error writes without yielding control back to the caller to drain the stream queue.The fix adds a
yieldin the fast path error handling of bothtick()andatick(), matching the behavior of the concurrent path which already yields before_panic_or_proceed. This allows the main loop to call_output()and emit thetask_resultevent before the exception propagates.With
stream_mode=["debug", "messages"]the issue didn't occur becauseget_waiteris not None when "messages" is in stream_modes, bypassing the fast path.Fixes #5764
Dependencies: None