#networking

"What happens between typing a URL and seeing the page?" I've shipped web apps for years, and in an interview I still fumbled it.

You tap your card, the machine freezes, you tap again. Were you charged twice? An HTTP payment endpoint faces the same question on every retry, and without an idempotency key it gets it wrong.

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.

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.