Web service architecture with async handlers, type-safe extractors, and middleware composition.

• Enforces async-first design to prevent blocking request handlers; use spawn_blocking for CPU-intensive work
• Manages shared application state via Arc<T> and Arc<RwLock<T>> to ensure thread safety across concurrent requests
• Provides extractor pattern for request parsing and validation (e.g., State(db), Json(payload)) with unified error responses via IntoResponse
• Supports tower-based middleware layers for cross-cutting concerns like authentication, logging, and rate limiting
• Covers framework patterns for axum, actix-web, warp, and rocket with guidance on state lifecycle and request resource ownership