Langgraph Human In The Loop

LangGraph's human-in-the-loop patterns are essential for building AI agents that need approval gates, error recovery, or validation loops. This skill covers the core mechanics: interrupt() to pause execution, Command(resume=value) to continue with human input, and the critical requirement for checkpointers and thread IDs. The examples walk through approval workflows, input validation loops, and multi-branch interrupts. The 4-tier error handling strategy alone makes this worth having. One gotcha to remember: when graphs resume, nodes restart from the beginning, so interrupt() calls need to come first to avoid re-running setup code.