m12-lifecycle

Design resource creation, cleanup, and scope using RAII, lazy initialization, and pooling patterns. Layer 2: Design Choices When should this resource be created, used, and cleaned up? Before implementing lifecycle: Before designing lifecycle: What's the resource cost? What's the scope? What about errors? To domain constraints (Layer 3): To implementation (Layer 1): - Covers five lifecycle patterns: RAII with Drop trait, lazy initialization via OnceLock/LazyLock, connection pooling with r2d2/deadpool, guard-based scoped access, and transaction scope boundaries - Includes decision framework for resource cost, scope determination, and error handling during cleanup - Provides pattern templates for RAII guards and lazy singletons, plus common errors and anti-patterns to avoid - Traces connections to ownership models (Layer 1) and domain constraints (Layer 3) for integrated design - What's the resource's scope? - Who owns the cleanup responsibility? - What happens on error?