Designing Idempotent Decision Endpoints That Survive Real Retries

Designing idempotent decision endpoints is crucial in distributed systems to prevent double-charging, duplication, or conflicting outcomes. This is achieved by using an idempotency key that identifies the logical business request, not a network attempt. Implement a unique constraint, transaction, or compare-and-set operation to ensure only one execution owns the request. Document key expiry and handle duplicate attempts according to the API contract. Idempotency is a durable business contract, not an in-memory cache.