Single Broker Registration

ID: transport.single-broker-registration
Name: Single broker registration
Maturity: GA
Summary: Root composition and dependency-registry validation that allow one transport adapter in a host.

What It Does

Applications register their shared broker once through AddAmqpTransport, AddKafkaTransport, AddAwsSqsTransport, AddAzureServiceBusTransport, or AddInMemoryTransport. Inbox dispatch, outbox dispatch, and ingress modules depend on that root module through the validated module graph.

If advanced registry code adds a second broker module, the dependency registry rejects its duplicate singleton services with LiteBusConfigurationException. Transport modules do not scan registrations or store context markers during Build().

This rule keeps publisher and consumer runtime behavior aligned to one broker SDK graph and one breaker identity in a process.

Public Surface

API	Role
`ILiteBusBuilder.AddAmqpTransport(...)`	Registers the shared AMQP root transport
`ILiteBusBuilder.AddKafkaTransport(...)`	Registers the shared Kafka root transport
`ILiteBusBuilder.AddAwsSqsTransport(...)`	Registers the shared AWS SQS root transport
`ILiteBusBuilder.AddAzureServiceBusTransport(...)`	Registers the shared Azure Service Bus root transport
`ILiteBusBuilder.AddInMemoryTransport(...)`	Registers the shared in-memory root transport
`LiteBusConfigurationException`	Reports duplicate service or module composition

Packages

LiteBus.Transport.* (root registration extensions and adapters)
LiteBus.Runtime (module graph and dependency uniqueness validation)

Requires

runtime.module-configuration
transport.publish-consume-contracts

Invariants

Exactly one ITransportPublisher implementation per process.
A duplicate broker module fails composition through the standard duplicate-service validation.
Metric registration stays single-tagged because only one adapter survives compose.

Non-Goals

Dynamic multi-broker routing in one host.
Runtime broker hot swap without rebuild.
Meta registration API that pulls all broker adapters into one package graph.

Observability

No dedicated metrics for guard execution.
Indirect effect: only one broker tag value exists on shared transport metrics.

Test Coverage

Covered

Test method	Project
`Build_SecondTransportModule_ShouldThrow`	`LiteBus.Transport.UnitTests` (`Kafka/`)
`Build_SecondTransportModule_ShouldThrow`	`LiteBus.Transport.UnitTests` (`AwsSqs/`)
`Build_ShouldRejectDuplicateTransportRegistration`	`LiteBus.Transport.UnitTests` (`AzureServiceBus/`)
`InboxDispatchExtensions_ShouldRegisterTransportDispatcher`	`LiteBus.Durable.IntegrationTests` (`Registration/`)
`OutboxDispatchExtensions_ShouldRegisterTransportDispatcher`	`LiteBus.Durable.IntegrationTests` (`Registration/`)
`InboxIngressExtensions_ShouldRegisterIngressServices`	`LiteBus.Durable.IntegrationTests` (`Registration/`)

Untested

Duplicate registration path where an externally implemented transport module registers only part of the publisher and consumer service set.

Out-of-Scope

Multi-broker fan-out in one process.
Runtime adapter replacement.