M09 Domain

This bridges domain-driven design concepts to Rust's type system and ownership model. It walks you through the entity versus value object decision, shows you how to map DDD patterns like aggregates and repositories to Rust structs and traits, and pushes you to think about invariants before writing code. The tables are dense but useful: they map domain concepts to ownership implications, which is exactly the friction point when doing DDD in Rust. Use this when you're modeling business logic and need to decide whether something should be Clone, owned, or wrapped in a newtype. The "trace up to domain constraints, trace down to implementation" structure keeps you from either over-engineering or writing anemic domain models.