Nan Gao bbb3deb231
fix(subagents): classify LLM error fallbacks as failed (#4042)
* fix(subagents): classify LLM error fallbacks as failed (#4041)

* fix(subagents): address #4042 review on LLM error fallback

- clarify _extract_llm_error_fallback docstring: tail-only scan is safe
  because subagents append their own terminal message, so the last
  AIMessage is never a stale parent-history marker (cross-ref worker.py)
- compute final_result and pop stop_reason only on the COMPLETED branch
  so the guard stop-reason pop no longer fires on the discarded FAILED path
- note the error_detail/"LLM request failed" fallbacks are defensive;
  the middleware always populates a non-empty content
- add regression test locking the stale parent-history marker invariant

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Co-authored-by: Willem Jiang <willem.jiang@gmail.com>
2026-07-11 09:25:15 +08:00
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