//! Domain layer - Pure business logic with no external dependencies
//!
//! This module contains the core business domain for the StA relay control system.
//! It follows **Domain-Driven Design** principles with rich domain models and clear
//! ubiquitous language.
//!
//! # Architecture Principles
//!
//! - **No external dependencies**: Domain layer depends only on Rust standard library
//! - **Inward-pointing dependencies**: Infrastructure/Application depend on Domain, never reverse
//! - **Rich domain models**: Entities and value objects encapsulate business rules
//! - **Ubiquitous language**: Code reflects real-world relay control domain concepts
//!
//! # Planned Submodules
//!
//! - `relay`: Core relay domain (RelayId, RelayState, RelayLabel, Relay entity)
//!   - Value objects with validation (newtypes following TyDD principles)
//!   - Domain entities (Relay, RelayCollection)
//!   - Repository traits (RelayLabelRepository)
//!   - Controller traits (RelayController)
//!   - Domain errors (DomainError, ValidationError)
//!
//! # Type-Driven Development (TyDD)
//!
//! Domain types follow "make illegal states unrepresentable" principle:
//! - `RelayId`: Newtype wrapping u8, validated to 1..=8 range
//! - `RelayLabel`: String wrapper, validated max 50 chars
//! - `RelayState`: Enum (On, Off) - no invalid states possible
//!
//! See `specs/001-modbus-relay-control/types-design.md` for complete type design.
//!
//! # References
//!
//! - Architecture: `specs/constitution.md` - Hexagonal Architecture principles
//! - Type design: `specs/001-modbus-relay-control/types-design.md`
//! - Domain specification: `specs/001-modbus-relay-control/spec.md`

pub mod health;
pub mod modbus;
pub mod relay;