Foundational Messaging Module

ID: runtime.message-module
Name: Foundational messaging module
Maturity: GA
Summary: Bootstraps shared messaging services, registries, serializer, mediator, and scoped handler registrations.

What It Does

MessageModule creates or reuses IMessageRegistry and contract registry contexts, executes MessageModuleBuilder registration callbacks, registers core messaging services, and registers newly discovered handler types as scoped dependencies.

Public Surface

API	Role
`ILiteBusBuilder.AddMessaging(Action<MessageModuleBuilder>)`	Normal package-owned composition entry
`MessageModule(Action<MessageModuleBuilder>)`	Module entry
`MessageModuleBuilder.Register<T>()` / `Register(Type)`	Message and handler registration
`MessageModuleBuilder.RegisterFromAssembly(Assembly)`	Assembly scan registration
`MessageModuleBuilder.Contracts`	Durable contract registration
`MessageModuleBuilder.UseTimeProvider(TimeProvider)`	Optional custom clock

Packages

LiteBus.Messaging

Requires

runtime.message-registry
runtime.contract-registry
runtime.dispatch-scopes

Invariants

Message registry is shared per composition context.
Core services are registered during build.
New handlers are registered with scoped lifetime.
Composition fails when no IMessageDispatchScopeFactory is registered by a host adapter or explicit manual-host opt-in.

Non-Goals

Semantic command/query/event policy.

Observability

No dedicated runtime meter.

Test Coverage

Covered Use Cases

`QueryModulePrerequisiteGuardTests.AddQueryModule_WithoutMessageModule_ShouldFailModuleGraphValidation`

Test kind: Unit
Expected outcome: semantic module registration is blocked without message module foundation

`HandlerDependencyLifetimeTests.AddLiteBus_WhenMessageAndCommandModulesRegisterSameHandler_ShouldRegisterHandlerAsScoped`

Test kind: Unit
Expected outcome: shared handler registration remains scoped and stable

Untested Use Cases

Use case	Priority	Notes
Multiple message-module registration attempts in one graph	Medium	Blocked by duplicate module rules

Out-of-Scope Use Cases

Distributed mediator deployment behavior.

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