Design a Highly Available Payment Processing System

Architect a **payment processing system** capable of handling secure credit card payments with ACID guarantees.

Include:
1. PCI-compliant service boundaries
2. Transaction orchestration (2PC/Saga)
3. Fraud detection pipeline
4. Idempotent payment retries
5. Audit logging architecture
6. Immutable ledger design (Append-only log)
7. Chargeback + refund workflow
8. Event-driven microservices approach
9. Tokenization vault service
10. High availability + disaster recovery model