Currency Rate Caching

Cache currency exchange rates used during checkout.

● ACTIVE CONTRACT

Requirements

  • ✓Reuse RedisStore
  • ✓Use retry/backoff logic
  • ✓Preserve checkout compatibility
  • ✓Handle cache failures gracefully

Architecture Rules

  • ADR-008
    Use the shared cache abstraction.
  • ADR-012
    Do not instantiate Redis clients inside services.

Required Dependencies

  • pkg/cache/redis_store
  • pkg/network/backoff

Forbidden Patterns

  • new Redis(
  • createClient(
  • new RedisClient(
  • new IORedis(

Expected Interfaces

getRate(from: string, to: string): Promise<ExchangeRate>
Existing checkout consumers must remain compatible.

Edge Cases

  • •Cache unavailable
  • •External API timeout
  • •Rate provider failure
  • •Invalid currency
  • •Cache expiration

Architecture Diagram

PaymentProcessor
↓
CurrencyService
↓
RedisStore
↓
Shared Cache
CurrencyService
↓
withBackoff()
↓
External Rate Provider
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