store: redis, in-progress ttl: 2 s
attempt 1 (process dies after the write) -> HTTP 500  replayed=-    retry-after=-    {"timestamp":"2026-11-08T18:16:50.214Z","status":500,"error":"Internal Server Error","path":"/payments"}
payments in the table: 1
attempt 2, immediately             -> HTTP 409  replayed=-    retry-after=1    {"title":"A request is outstanding for this Idempotency-Key","status":409}
payments in the table: 1
attempt 3, after the lock expired  -> HTTP 201  replayed=-    retry-after=-    {"id":2,"customer":"cus_42","amount":1999,"currency":"INR"}
payments in the table: 2