Topic
Guarding handlers against duplicate delivery by recording and checking event IDs before performing side effects.
The Spring Boot dedupe most payment handlers ship relies on a unique-key exception. A dev.to walkthrough shows the insert that would raise it never runs, and gives the native ON CONFLICT statement that does claim the event.
Reality
GoVueKit's Go handler records the event id, answers Stripe in a millisecond, and does the billing work in a background loop. The design closes a race that a SELECT-then-INSERT check leaves open, and it costs one table.
Reality
Gate of AI's Node tutorial validates the webhook, writes the row, enqueues the job and answers 202 before a single token is generated. The parts worth keeping are the unique idempotency key and the Zod parse on the reply.
Reality
Shadow mode hands a candidate email agent the same live inbound events as production and no way to act on them. The work that makes it trustworthy sits in idempotent ingest and in the columns that grade the proposal.
Reality
A dev.to tutorial builds an Express receiver with SHA-256 idempotency keys, four attempts and a dead_letters table. The dedupe holds up, right until you run two copies of it.
Reality
A Node and Postgres webhook guide gets the storage choice right and the ordering wrong: SELECT then INSERT leaves a race that answers a concurrent duplicate with a 500.
Reality
A reviewer of a dozen Next.js Stripe integrations says almost none guard against duplicate or out-of-order deliveries. The failure mode is a second welcome email and no error anywhere.
Reality