Architect Circuit Breaker Pattern for External Vercel API Service Resilience

[temma02]

Description

Implement a circuit breaker around the Vercel API client to prevent cascading failures during Vercel outages, failing fast when the API is unhealthy and recovering automatically when it stabilizes.

Requirements and Context

• Reliability: Circuit breaker must have closed, open, and half-open states
• Testing: Test all circuit breaker state transitions
• Documentation: Document the circuit breaker configuration

Suggested Execution

Branch: feat/issue-052-vercel-circuit-breaker

Implement Changes

• Implement a circuit breaker wrapper around apps/backend/src/services/vercel.service.ts
• Open the circuit after a configurable failure threshold and fail fast
• Transition to half-open after a cooldown and test recovery with a probe request
• Emit metrics/logs on circuit state transitions

Test and Commit

• Test closed→open, open→half-open, and half-open→closed transitions
• Test fail-fast behavior when the circuit is open
• Document circuit breaker thresholds and cooldown values

Example Commit Message

feat(vercel): add circuit breaker for external API resilience

- Implement circuit breaker with closed/open/half-open states
- Fail fast when Vercel API is unhealthy
- Emit logs on circuit state transitions

Guidelines

• Make thresholds and cooldown configurable via environment variables
• Ensure the circuit breaker is thread-safe under concurrency
• Log state transitions with correlation IDs

[Grace-CODE-D]

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