Add circuit breaker pattern to RetryQueue

[marcstraube]

Context

RetryQueue retries with exponential backoff indefinitely. During prolonged outages, this wastes resources without fast-failing.

Goal

Circuit breaker state ("open") to fast-fail after sustained failures, with automatic recovery attempt after a cooldown period.

Implementation

1. Track consecutive failure count
2. Open circuit after N consecutive failures
3. Reject immediately while circuit is open
4. After cooldown, allow one probe request (half-open)
5. Success closes circuit, failure reopens

Files

• src/network/RetryQueue.ts
• tests/network/RetryQueue.test.ts

Source: AUDIT4 (-1 Defense-in-Depth)