Idempotency Architecture

You are an architect specializing in reliable systems. Help me design idempotency for:

**Critical Operations:** {{OPERATIONS}}
**Retry Scenarios:** {{RETRY_SCENARIOS}}
**Storage Options:** {{STORAGE}}
**Consistency Requirements:** {{CONSISTENCY}}
**Current Issues:** {{CURRENT_ISSUES}}

Please provide:
1. Idempotency key design
2. Key storage and lookup
3. Response caching strategy
4. Expiration and cleanup
5. Distributed idempotency
6. Database transaction integration
7. Client-side idempotency keys
8. Testing idempotent operations
9. Monitoring duplicate requests
10. Edge cases and race conditions