Manual Acknowledgement Model

ID: transport.manual-acknowledgement
Name: Manual acknowledgement model
Maturity: GA
Summary: Every inbound delivery exposes explicit accept, discard, and requeue operations mapped to broker-specific ack semantics.

What It Does

TransportMessage wraps broker acknowledgement as three user-facing methods. AcceptAsync signals successful processing. DiscardAsync rejects without requeue (delete, complete without retry, or dead-letter depending on broker). ReturnToQueueAsync rejects with requeue so the broker redelivers the message. Adapters supply AckAsync and NackAsync(requeue) delegates through TransportConsumerAckHandlers.

Each adapter maps these calls to its native API. The Architecture resilience matrix documents the minimum behavior per provider.

Provider	Accept	Requeue	Notes
AMQP	`basic.ack`	`basic.nack` requeue	Channel shutdown stops consumer
InMemory	Remove from channel	Re-enqueue	In-process only
Azure Service Bus	`CompleteMessage`	`AbandonMessage`	Exponential processor restart on errors
AWS SQS	`DeleteMessage`	`ChangeMessageVisibility` with backoff	Uses receive count when present
Kafka	Offset commit	Seek to failed offset	No queue-style lease; offset not advanced until accept

Public Surface

API	Role
`TransportMessage.AcceptAsync(CancellationToken)`	Acknowledge successful processing
`TransportMessage.DiscardAsync(CancellationToken)`	Reject without requeue
`TransportMessage.ReturnToQueueAsync(CancellationToken)`	Reject with requeue
`TransportMessage.Redelivered`	Broker redelivery hint
`TransportMessage.AckAsync` / `NackAsync`	Low-level delegates used by mappers
`TransportConsumerAckHandlers`	Factory for ack delegates on mapped messages

Packages

LiteBus.Transport.Abstractions
Broker adapters in LiteBus.Transport.*

Requires

transport.publish-consume-contracts

Invariants

Handlers that return without calling an ack method leave deliveries unacknowledged; broker behavior varies (peek-lock renewal, visibility timeout, or uncommitted Kafka offset).
Raw IMessageConsumer hosts have no LiteBus redelivery cap at the transport layer; poison handling requires DiscardAsync, broker DLQ policy, or inbox ingress.
Kafka commits offset only after AcceptAsync; ReturnToQueueAsync seeks back before the next read.

Non-Goals

Store-backed retry budgets, dead-letter tables, or idempotency enforcement (inbox processor and ingress own those).
Exactly-once delivery at the broker.
Automatic ack on successful handler return (explicit ack is required).

Observability

TransportMessage.Redelivered surfaces on Azure Service Bus when DeliveryCount > 1.
Process spans record destination, message id, and redelivery state when tracing is enabled.
No dedicated ack success/failure counters at the transport layer.

Test Coverage

Covered

Test method	Project
`PublishAsync_ThenConsume_AcknowledgesMessage`	`LiteBus.Transport.IntegrationTests` (`Amqp/`)
`ConsumeAsync_NackWithRequeue_RedeliversMessage`	`LiteBus.Transport.IntegrationTests` (`Amqp/`)
`ReturnToQueue_ShouldRedeliverMessage`	`LiteBus.Transport.UnitTests`
`ToTransportMessage_ShouldExposeCommitDelegate`	`LiteBus.Transport.UnitTests`
`ToTransportMessage_ReturnToQueueAsync_ShouldSeekToConsumedOffset`	`LiteBus.Transport.UnitTests`
`ToTransportMessage_DiscardAsync_ShouldNotSeek`	`LiteBus.Transport.UnitTests`
`ToTransportMessage_ShouldExposeAckDelegates`	`LiteBus.Transport.UnitTests`
`ComputeRequeueVisibilityTimeout_shouldHonorReceiveCount`	`LiteBus.Transport.UnitTests`
`RequeueEnabled_WithTransientStoreFailure_ShouldEventuallyAccept`	`LiteBus.Durable.IntegrationTests` (`Ingress/InMemory/`, `Ingress/Amqp/`, `Ingress/AwsSqs/`, `Ingress/AzureServiceBus/`)
`RequeueDisabled_WithPoisonMessage_ShouldDiscardWithoutStoreWrite`	`LiteBus.Durable.IntegrationTests` (`Ingress/InMemory/`)
`RequeueDisabled_WithPoisonMessage_ShouldDrainQueue`	`LiteBus.Durable.IntegrationTests` (`Ingress/AwsSqs/`)
`TransientAcceptFailure_ShouldRedeliverSameOffsetWithoutRestart`	`LiteBus.Durable.IntegrationTests` (`Ingress/Kafka/`)

Untested

Azure Service Bus DiscardAsync dead-letter path when DLQ is configured.
SQS ack failure after successful handler completion at raw consumer layer.
AMQP ack when channel closes mid-handler.

Out-of-Scope

Store-backed retry budgets, dead-letter tables, or idempotency enforcement.
Exactly-once delivery at the broker.
Automatic ack on successful handler return.

Deep Docs

Architecture.md (Transport resilience capability matrix, Poison message handling)
Kafka-Transport.md (offset and seek semantics)

On this page