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feat(langchain): prevent dangling tool calls in HITL middleware #33489

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feat(langchain): prevent dangling tool calls in HITL middleware #33489

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  • Description: Adds before_agent hook to HITL middleware that will append ToolMessages for any dangling ToolCall from an AIMessage. This can happen when a new message comes in on a previously interrupted thread.

@github-actions github-actions bot added feature langchain Related to the package `langchain` v1 Issue specific to LangChain 1.0 labels Oct 15, 2025
sydney-runkle
sydney-runkle reviewed Oct 15, 2025
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libs/langchain_v1/langchain/agents/middleware/human_in_the_loop.py

patched_messages = []
# Iterate over the messages and add any dangling tool calls
for i, msg in enumerate(messages):
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do we want to only check the last AIMessage? I have a helper for finding the last AI message + any tool messages after the fact

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feature langchain Related to the package `langchain` v1 Issue specific to LangChain 1.0

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@nhuang-lc @sydney-runkle