ios-networkinglisted

# iOS Networking Skill ## Core Rules 1. **Always use async/await** (NOT completion handlers) for new networking code. Completion handlers are legacy — Swift Concurrency is the standard since iOS 15. 2. **Build a generic APIClient** with an Endpoint protocol for type-safe requests. Never scatter raw URLSession calls throughout the codebase. 3. **Use actor-based TokenManager** for thread-safe OAuth2 token refresh with deduplication. Never allow multiple simultaneous refresh requests. 4. **Handle ALL HTTP status codes properly**: - 401 → refresh token, retry original request - 429 → respect Retry-After header, exponential backoff - 5xx → retry with exponential backoff + jitter - 4xx (other) → client error, do not retry 5. **Use URLProtocol mocking for tests** (NOT mocking URLSession itself). URLProtocol intercepts at the transport layer and tests real serialization paths. 6. **Reuse URLSession instances** — creating a session per request prevents HTTP/2 connection multiplexing and wastes memory. 7. **Use URLCache** with `.useProtocolCachePolicy` as the default cache policy. Configure cache size explicitly for production apps. 8. **NWPathMonitor for connectivity awareness**, NOT pre-flight checks. Never gate a request on reachability — just make the request and handle the error. 9. **Codable with `.convertFromSnakeCase`** and custom date strategies. Avoid manual CodingKeys when snake_case conversion handles it. 10. **Keep ATS enabled.** Use domain-specific exception