CQS with MediatR

IBrokeredRequest.cs

using System;
using System.Collections.Concurrent;
using System.Threading;
using System.Threading.Tasks;

using MediatR;

public interface INotificationWithIdentification : INotification
{
    Guid RequestID { get; set; }
}

public interface IBrokeredRequest<TResponse> : IRequest<TResponse>
    where TResponse : INotificationWithIdentification
{
    Guid RequestID { get; set; }
}

public interface IBrokeredRequestHandler<TBrokeredRequest, TResponse> : IRequestHandler<TBrokeredRequest, TResponse>
    where TBrokeredRequest : IBrokeredRequest<TResponse>
    where TResponse : INotificationWithIdentification
{

}

public abstract class BrokeredRequestHandler<TBrokeredRequest, TResponse> : IBrokeredRequestHandler<TBrokeredRequest, TResponse>, INotificationHandler<TResponse>
    where TBrokeredRequest : IBrokeredRequest<TResponse>
    where TResponse : INotificationWithIdentification
{
    protected static ConcurrentDictionary<Guid, TaskCompletionSource<TResponse>> Requests { get; private set; } = new ConcurrentDictionary<Guid, TaskCompletionSource<TResponse>>();

    public abstract Task Execute(TBrokeredRequest request, CancellationToken cancellationToken);

    Task<TResponse> IRequestHandler<TBrokeredRequest, TResponse>.Handle(TBrokeredRequest request, CancellationToken cancellationToken)
    {
        var tcs = new TaskCompletionSource<TResponse>(TaskCreationOptions.RunContinuationsAsynchronously);
        Requests.TryAdd(request.RequestID, tcs);

        Task.Run(async () =>
        {
            try
            {
                await Execute(request, cancellationToken).ConfigureAwait(false);
            }
            catch (Exception exc)
            {
                if (Requests.TryRemove(request.RequestID, out TaskCompletionSource<TResponse> removed))
                {
                    removed.SetException(exc);
                }
            }
        }, cancellationToken);

        return tcs.Task;
    }

    Task INotificationHandler<TResponse>.Handle(TResponse notification, CancellationToken cancellationToken)
    {
        if (Requests.TryRemove(notification.RequestID, out TaskCompletionSource<TResponse> tcs))
        {
            tcs.SetResult(notification);
        }

        return Task.CompletedTask;
    }
}