State Reducer · Tool Skill Scope: a single decision — for each state key, declare a reducer or guarantee single-writer. Out of scope: checkpointers, HITL, supervisor vs. swarm — see for those. --- 1. 何时激活 (Activation Rules) Activate when any trigger fires: - The task involves a LangGraph , / schema, or typing. - The graph has ≥1 of: parallel branches via static fan-out, API, multiple agents writing shared state, or a supervisor pattern where workers return concurrently. - The run raises — message looks like - The user pastes a state schema and asks "why does this crash on parallel?" or "do I…