Payments and Idempotency Systems Questions

Design, reliability, and troubleshooting of payment flows and idempotency mechanisms. Coverage includes integration with payment gateways, the transaction lifecycle, duplicate charges and reconciliation, idempotency key design and enforcement, deduplication windows, compensating transactions and the saga pattern for long running operations, error classification and retry policies, observability and reconciliation tooling, dispute and chargeback handling, testing of partial success scenarios, and regulatory and payment card industry considerations.