fix(langgraph): validate node outputs against State schema before checkpointing#6512
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Sidharth Rajmohan (dumko2001) wants to merge 1 commit into
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This prevents invalid state (e.g. None in a list field) from being saved to the checkpoint, which causes permanent corruption. Validation is now performed in CompiledStateGraph.attach_node for LastValue channels.
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Description:
This PR adds output validation to
StateGraphnodes to prevent invalid state from corrupting checkpoints.Previously,
StateGraphvalidated inputs but allowed nodes to return data that violated theStateschema (e.g., returningNonefor aList[str]field). This invalid data would be saved to the checkpoint, causing aValidationErroronly when attempting to load the thread later, effectively rendering the thread permanently inaccessible.This change injects a validation step in
CompiledStateGraph.attach_node. If a PydanticBaseModelis used as the state schema, node updates are validated usingTypeAdapterbefore being applied. This ensures the run fails fast with aValidationErrorrather than persisting corrupt data.Issue: Fixes #6491
Dependencies: None
Twitter handle: SidharthRajmoh2