How I Debugged LangChain #34974: A Case Study in ContextVar Thread Affinity
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How I Debugged LangChain #34974: A Case Study in ContextVar Thread Affinity TL;DR: A 10-line fix for a bug that broke Human-in-the-Loop for 5 months. Root cause: Python's ContextVar doesn't cross thread boundaries when an async def dispatches to a thread pool executor. The fix: copy_context() . Two days ago, I saw a GitHub Issue that had been open since February 2026. LangChain #34974: HumanInTheLoopMiddleware + ainvoke() → RuntimeError: Called get_config outside of a runnable context . 5…
1Key Takeaways
- How I Debugged LangChain #34974: A Case Study in ContextVar Thread Affinity TL;DR: A 10-line fix for a bug that broke Human-in-the-Loop for 5 months.
- Root cause: Python's ContextVar doesn't cross thread boundaries when an async def dispatches to a thread pool executor.
- Two days ago, I saw a GitHub Issue that had been open since February 2026.
- LangChain #34974: HumanInTheLoopMiddleware + ainvoke() → RuntimeError: Called get_config outside of a runnable context .
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3Why it matters
Coding AI shifts how fast software ships and how much human review each change needs. DEV — AI reports that how I Debugged LangChain #34974: A Case Study in ContextVar Thread Affinity TL;DR: A 10-line fix for a bug that broke Human-in-the-Loop for 5 months.
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