Mediator pattern (MediatR) — как работает, плюсы и минусы?

public sealed record GetOrderQuery(Guid Id) : IRequest<OrderDto?>;

public sealed class GetOrderHandler(ShopDbContext db) : IRequestHandler<GetOrderQuery, OrderDto?>
{
    public Task<OrderDto?> Handle(GetOrderQuery q, CancellationToken ct) =>
        db.Orders.Where(o => o.Id == q.Id).Select(o => new OrderDto(o.Id, o.Status, o.Total)).FirstOrDefaultAsync(ct);
}

builder.Services.AddMediatR(cfg =>
{
    cfg.RegisterServicesFromAssemblyContaining<GetOrderHandler>();
    cfg.AddOpenBehavior(typeof(LoggingBehavior<,>));
    cfg.AddOpenBehavior(typeof(ValidationBehavior<,>));
    cfg.AddOpenBehavior(typeof(TransactionBehavior<,>));
});

app.MapGet("/orders/{id:guid}", async (Guid id, ISender sender, CancellationToken ct) =>
    await sender.Send(new GetOrderQuery(id), ct) is { } dto ? Results.Ok(dto) : Results.NotFound());

public sealed class ValidationBehavior<TRequest, TResponse>(IEnumerable<IValidator<TRequest>> validators)
    : IPipelineBehavior<TRequest, TResponse> where TRequest : notnull
{
    public async Task<TResponse> Handle(TRequest request, RequestHandlerDelegate<TResponse> next, CancellationToken ct)
    {
        if (!validators.Any()) return await next();

        var context = new ValidationContext<TRequest>(request);
        var failures = (await Task.WhenAll(validators.Select(v => v.ValidateAsync(context, ct))))
            .SelectMany(r => r.Errors).Where(e => e is not null).ToList();

        if (failures.Count != 0) throw new ValidationException(failures);
        return await next();
    }
}

public sealed class LoggingBehavior<TRequest, TResponse>(ILogger<LoggingBehavior<TRequest, TResponse>> log)
    : IPipelineBehavior<TRequest, TResponse> where TRequest : notnull
{
    public async Task<TResponse> Handle(TRequest request, RequestHandlerDelegate<TResponse> next, CancellationToken ct)
    {
        var name = typeof(TRequest).Name;
        var sw = Stopwatch.StartNew();
        try { return await next(); }
        finally { log.LogInformation("{Request} выполнен за {Ms} мс", name, sw.ElapsedMilliseconds); }
    }
}

public sealed record OrderPlaced(Guid OrderId, Guid CustomerId) : INotification;

public sealed class SendConfirmationEmail(IEmailSender email) : INotificationHandler<OrderPlaced>
{
    public Task Handle(OrderPlaced n, CancellationToken ct) => email.SendOrderConfirmationAsync(n.OrderId, ct);
}
public sealed class UpdateCustomerStats(ShopDbContext db) : INotificationHandler<OrderPlaced> { /* ... */ }

await publisher.Publish(new OrderPlaced(order.Id, order.CustomerId), ct);