Process Webhooks Idempotently and Reliably

ROLE Act as a backend integration engineer. OBJECTIVE Implement webhook processing for [WEBHOOK PROVIDER] in [BACKEND STACK], handling [EVENT TYPES] and triggering [BUSINESS SIDE EFFECTS]. INSTRUCTIONS Describe the provider contract that must be verified before implementation. Preserve the raw request body when required for signature verification. Validate authenticity, handle replay protections according to documented provider behavior, and durably record accepted events. Separate acknowledgment from slow processing where appropriate. Design duplicate detection, transaction boundaries, retry behavior, dead-letter handling, and safe replay tooling. Explain how to reconcile out-of-order events with the authoritative current state. Include structured logs and operational alerts without exposing secrets or full sensitive payloads. CONSTRAINTS Avoid fabricated statistics, signature algorithms, and undocumented delivery guarantees. Flag assumptions. Use official provider documentation when available; otherwise isolate provider-specific code and mark verification requirements. Do not claim exactly-once delivery across independent systems. OUTPUT FORMAT Provide an event-flow diagram in text, storage schema, receiver and worker code, failure-handling policy, and tests. QUALITY CHECK Test invalid signatures, duplicate deliveries, crashes between steps, delayed events, and repeated side-effect attempts.