Post · Sep 11, 2026
A plain payment endpoint looks correct until you trace what a double-click, a timed-out request, or a redelivered webhook actually does to it. Each one turns one payment into two. Idempotency keys are the fix, at two layers most write-ups skip.
Snippet · Sep 1, 2026
A generic `retry(task, options)` that re-runs a failing async task with exponential backoff and full jitter, an optional `shouldRetry` predicate, and a cap on any single delay.
Cheatsheet · Sep 1, 2026
A client that retries a POST after a timeout can create the resource twice or charge a card twice. An idempotency key lets the server spot the retry and replay the first response instead of doing the work again.