The Stripe webhook race condition that silently charged users twice (and the Node.js fix)

Indie Hackers researchers identified a race condition in Stripe webhook handling where automatic retries caused duplicate payment charges. The root cause is that most handlers lack idempotency guards, so concurrent retry deliveries insert duplicate payment records. KeelStack's fix wraps each webhook in an atomic idempotency guard keyed on the Stripe event ID, short-circuiting duplicate processing before any database mutation occurs.