implement-domain-types

Guide for implementing domain types (value objects and entities) with invariants in this Rust project. Covers the "always valid" pattern with private fields and validated constructors, custom Deserialize implementations to prevent bypass, and expressive error types with actionable help text. Use when creating or modifying domain value objects, entities, or types with business rules. Triggers on "domain type", "value object", "entity", "invariant", "validated constructor", "domain entity", "DDD practices", "domain model", or "implement domain".