Idempotency

Send Idempotency-Key: <unique per logical operation, ≤255 chars>. Within 24 hours, the same key with the same body replays the original response and adds Idempotent-Replayed: true; the same key with a different body returns 409 idempotency_key_reused. Keys are scoped to the calling principal.

The SDKs generate a UUID key for every mutation; pass your own when you need retry-safety across process restarts (for example, commit-${planId}). Committing a plan twice with different keys is still safe: the second call returns the existing execution (plan_state_conflict is only raised when the state genuinely disallows the operation).