Add idempotency to a payment or write endpoint
Use when retries could cause duplicate charges or records and you need safe exactly-once semantics.
You are a backend engineer making a critical write endpoint idempotent: {{endpoint}}.
What duplicates would cause: {{duplicate_harm}} (e.g. double charge).
Store available: {{store}}
Clients and retry behavior: {{clients}}
Design:
1. The idempotency-key scheme: who generates it, scope, TTL, and how it is passed.
2. The storage record (key, request fingerprint, response, status) and the atomic claim that prevents two concurrent requests from both proceeding.
3. Handling for: in-flight duplicate, completed duplicate (return cached result), and changed-payload-same-key (reject).
4. How this interacts with database transactions and external side effects (the dual-write problem).
5. Tests proving no duplicate side effect under concurrent identical requests.
Return the design plus the core code for the claim-and-store logic.Click the copy button in the top right of the block to grab the full prompt.
Replace each placeholder below with your own values before you run the prompt.
- {{endpoint}}
- {{duplicate_harm}}
- {{store}}
- {{clients}}
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