- Deduplicate sentinel errors: httpx.ErrNoHealthy, ErrCircuitOpen, and
ErrRetryExhausted are now aliases to the canonical sub-package values
so errors.Is works across package boundaries
- Retry transport returns ErrRetryExhausted only when all attempts are
actually exhausted, not on early policy exit
- Balancer: pre-parse endpoint URLs at construction, replace req.Clone
with cheap shallow struct copy to avoid per-request allocations
- Circuit breaker: Load before LoadOrStore to avoid allocating a Breaker
on every request for known hosts
- Health checker: drain response body before close for connection reuse,
probe endpoints concurrently, run initial probe synchronously in Start
- Client: add Close() to shut down health checker goroutine, propagate
URL resolution errors instead of silently discarding them
- MockClock: fix lock ordering in Reset (clock.mu before t.mu), fix
timer slice compaction to avoid backing-array aliasing, extract
fireExpired to deduplicate Advance/Set
Implements balancer middleware with URL rewriting per-request:
- RoundRobin, Failover, and WeightedRandom endpoint selection strategies
- Background HealthChecker with configurable probe interval and path
- Thread-safe health state tracking with sync.RWMutex
