LangChain LangGraph Human-in-the-Loop (Python) Overview A team adds to require a human approval before the email goes out. First integration test crashes at the interrupt boundary with: The culprit is two nodes upstream: a node stashed into state. Every node-level unit test passed because node completion does not serialize state — only the checkpointer does, and only at supersteps that include an interrupt. The failure is invisible until interrupt time (P17). A week later the resume path ships. The human reviews the draft, clicks "approve with edits," and the backend runs: The prior 47 messag…