Make a write endpoint or operation safe to retry by adding idempotency keys — so a duplicate request (from a client retry, double-click, or network timeout) produces one effect, not two. Use when the user says "add idempotency", "make this endpoint idempotent", "prevent duplicate charges", "add an idempotency key", "deduplicate requests", "handle double submits", or "this can be called twice and double-writes".
