implement webhook handler that guarantees idempotency on retries + returns correct error responses. idempotency key in header, store in redis with TTL. dedupe before processing. distinguish between 4xx (dont retry) vs 5xx (retry). got follow ups on: what if redis is down? what if the same event arrives via 2 different webhooks? what about partial-success?

stripe webhook idempotency onsite

implement webhook handler that guarantees idempotency on retries + returns correct error responses.