# CLAUDE.md — httpx

## Commands

```bash
go build ./...                          # compile
go test ./...                           # all tests
go test -race ./...                     # tests with race detector
go test -v -run TestName ./package/     # single test
go vet ./...                            # static analysis
```

## Architecture

- **Module**: `git.codelab.vc/pkg/httpx`, Go 1.24, zero external dependencies
- **Core pattern**: middleware is `func(http.RoundTripper) http.RoundTripper`
- **Chain assembly order** (client.go): Logging → User MW → Retry → CB → Balancer → Transport
  - Retry wraps CB+Balancer so each attempt can hit a different endpoint
- **Circuit breaker** is per-host (`sync.Map` of host → Breaker)
- **Sentinel errors**: canonical values live in sub-packages, root package re-exports as aliases
- **balancer.Transport** returns `(Middleware, *Closer)` — Closer must be tracked for health checker shutdown
- **Client.Close()** stops the health checker goroutine

## Conventions

- Functional options for all configuration
- Test helpers: `mockTransport(fn)` wrapping `middleware.RoundTripperFunc`
- No external test frameworks — stdlib only
- Thread safety required (`sync.Mutex`/`atomic`)
- `internal/clock` for deterministic time testing