Module Registration

ID: mediator.module-registration
Name: Module registration
Maturity: GA
Summary: Registers messaging, command, query, and event features with explicit dependencies and assembly scanning.

What It Does

Mediator composition is explicit:

Call AddMessaging once.
Call AddCommands, AddQueries, and/or AddEvents from the installed feature packages.

Semantic modules require MessageModule to exist. The complete graph validates that requirement after the callback, so declaration order does not affect the result. Registering MessageModule twice throws LiteBusConfigurationException because type-based module identity permits one instance of each module type.

Builders provide Register<T>(), Register(Type), and RegisterFromAssembly(Assembly). Semantic builders expose Contracts for stable durable contract registration.

Public Surface

services.AddLiteBus(bus =>
{
    bus.AddMessaging(message =>
    {
        message.RegisterFromAssembly(typeof(CreateOrderCommand).Assembly);
    });

    bus.AddCommands(commands =>
    {
        commands.RegisterFromAssembly(typeof(CreateOrderCommand).Assembly);
    });

    bus.AddQueries(queries =>
    {
        queries.RegisterFromAssembly(typeof(GetOrderByIdQuery).Assembly);
    });

    bus.AddEvents(events =>
    {
        events.RegisterFromAssembly(typeof(OrderPlacedEvent).Assembly);
    });
});

API	Role
`ILiteBusBuilder.AddMessaging(Action<MessageModuleBuilder>)`	Normal messaging composition extension
`ILiteBusBuilder.AddCommands(Action<CommandModuleBuilder>)`	Normal command composition extension
`ILiteBusBuilder.AddQueries(Action<QueryModuleBuilder>)`	Normal query composition extension
`ILiteBusBuilder.AddEvents(Action<EventModuleBuilder>)`	Normal event composition extension
`ILiteBusBuilder.Modules`	Advanced access to the underlying `IModuleRegistry` and `Add*Module` methods
`MessageModuleBuilder.RegisterFromAssembly(Assembly)`	Registers messages and handlers in one pass
`CommandModuleBuilder.RegisterFromAssembly(Assembly)`	Registers command constructs from assembly
`QueryModuleBuilder.RegisterFromAssembly(Assembly)`	Registers query constructs from assembly
`EventModuleBuilder.RegisterFromAssembly(Assembly)`	Registers event constructs from assembly

Packages

LiteBus.Messaging
LiteBus.Commands
LiteBus.Queries
LiteBus.Events

Requires

runtime.modules
runtime.message-module

Invariants

MessageModule must be present in the completed graph when semantic modules are used.
MessageModule can only be registered once.
Builder RegisterFromAssembly throws ArgumentNullException for null assembly arguments.
Semantic builder registration rejects unsupported construct types (LiteBusNotSupportedException for wrong shape).

Non-Goals

Implicit auto-registration of semantic modules.
Global assembly auto-scan without explicit module builder calls.
Multi-host module graph synchronization.

Observability

No dedicated compose-time metric or activity source is exposed for mediator module registration.

Operational alternatives:

Fail-fast exception handling at startup.
Dependency and duplicate-registration tests in LiteBus.Mediator.UnitTests.

Test Coverage

Covered

Test method	Project
`AddMessageModule_WhenCalledTwice_ShouldThrowLiteBusConfigurationException`	`LiteBus.Mediator.UnitTests`
`AddCommandModule_WithoutMessageModule_ShouldFailModuleGraphValidation`	`LiteBus.Mediator.UnitTests`
`AddQueryModule_WithoutMessageModule_ShouldFailModuleGraphValidation`	`LiteBus.Mediator.UnitTests`
`AddEventModule_WithoutMessageModule_ShouldFailModuleGraphValidation`	`LiteBus.Mediator.UnitTests`
`AddCommandModule_BeforeMessageModule_ShouldSucceed` and semantic equivalents	`LiteBus.Mediator.UnitTests`
`RegisterFromAssembly_WithNullAssembly_ThrowsArgumentNullException`	`LiteBus.Mediator.UnitTests`
`RegisterFromAssembly_DoesNotRegisterMarkerInterfaces`	`LiteBus.Mediator.UnitTests`

Untested

Very large assembly scans with high generic handler counts and cold start timing assertions.
Mixed registration from many assemblies with conflicting simple type names.

Out-of-Scope

Host-specific DI registration details outside AddLiteBus module composition.
Runtime hot-reload of module graph.