Instruction file imported from U2UTraining/gamestore-sdlc-starter (.github/instructions/application.instructions.md). Copyright stays with the author.

Application layer

This project orchestrates. It does not decide — business rules belong in the Domain (ADR-0003).

Binding decisions: ADR-0004, ADR-0005.

Use cases

One per file, named for the action: Checkout.cs, AddItemToBasket.cs.

Each file holds, in this order:

public interface IThingUseCase : IUseCase
{
  Task<Result> DoThing(SomeId id, CancellationToken cancellationToken);
}

internal sealed class ThingUseCase(IDependency dep, IUnitOfWork unitOfWork) : IThingUseCase
{
  ...
}

• Interface public, implementation internal sealed.
• Dependencies through the primary constructor.
• CancellationToken is the last parameter, always, and is passed on.
• Register it in DependencyInjection.AddApplication. Forgetting this fails at startup.

The shape of the body is: load aggregates through repositories, call domain methods, commit once through IUnitOfWork, then publish events. If you find yourself writing an if about a business rule, it belongs on the entity instead.

Domain events

Publish after CommitAsync, never before. Nothing may observe an event for a transaction that did not commit.

Handlers implement IDomainEventHandler<TEvent>, live in EventHandlers/, and are registered in Infrastructure/DependencyInjection.cs — not here. Several handlers may subscribe to one event; they run sequentially in registration order, in-process, inside the request.

There is no retry and no outbox. A handler that throws leaves the committed change in place and its consequence undone. If that is unacceptable for what you are adding, say so rather than building a private retry.

Repository interfaces

Declared here, implemented in Infrastructure. They return domain aggregates, never DTOs, and never IQueryable.

Boundaries

No EF Core, no DbContext, no ASP.NET types in this project. If you need something from the outside world, declare an interface in Abstractions/ and let Infrastructure implement it.