Meditor SourceGen doesn't work for our needs right now, so let's build something on top of their library that allows us to do manual registration for now.

Framework/Foundation/Lifecycles/Mediator.cs

@@ -0,0 +1,71 @@
+using Mediator;
+using System.Diagnostics;
+
+namespace Toolkit.Framework.Foundation;
+
+public class Mediator : IMediator
+{
+    private readonly IServiceProvider factory;
+
+    public Mediator(IServiceProvider factory)
+    {
+        this.factory = factory;
+    }
+
+    public IAsyncEnumerable<TResponse> CreateStream<TResponse>(IStreamQuery<TResponse> query, CancellationToken cancellationToken = default)
+    {
+        throw new NotImplementedException();
+    }
+
+    public IAsyncEnumerable<TResponse> CreateStream<TResponse>(IStreamRequest<TResponse> request, CancellationToken cancellationToken = default)
+    {
+        throw new NotImplementedException();
+    }
+
+    public IAsyncEnumerable<TResponse> CreateStream<TResponse>(IStreamCommand<TResponse> command, CancellationToken cancellationToken = default)
+    {
+        throw new NotImplementedException();
+    }
+
+    public IAsyncEnumerable<object?> CreateStream(object request, CancellationToken cancellationToken = default)
+    {
+        throw new NotImplementedException();
+    }
+
+    public ValueTask Publish<TNotification>(TNotification notification, CancellationToken cancellationToken = default) where TNotification : INotification
+    {
+        throw new NotImplementedException();
+    }
+
+    public ValueTask Publish(object notification, CancellationToken cancellationToken = default)
+    {
+        throw new NotImplementedException();
+    }
+
+    public ValueTask<TResponse> Send<TResponse>(IRequest<TResponse> request, CancellationToken cancellationToken = default)
+    {
+        dynamic? handler = factory.GetService(typeof(RequestClassHandlerWrapper<,>).MakeGenericType(request.GetType(), typeof(TResponse)));
+        
+        if (handler is not null)
+        {
+            return handler.Handle((dynamic)request, cancellationToken);
+        }
+
+        return default;
+    }
+
+    public ValueTask<TResponse> Send<TResponse>(ICommand<TResponse> command, CancellationToken cancellationToken = default)
+    {
+        throw new NotImplementedException();
+    }
+
+    public ValueTask<TResponse> Send<TResponse>(IQuery<TResponse> query, CancellationToken cancellationToken = default)
+    {
+        throw new NotImplementedException();
+    }
+
+    public ValueTask<object?> Send(object message, CancellationToken cancellationToken = default)
+    {
+        throw new NotImplementedException();
+    }
+}

Framework/Foundation/Lifecycles/RequestClassHandlerWrapper.cs

@@ -0,0 +1,25 @@
+using Mediator;
+
+namespace Toolkit.Framework.Foundation;
+
+public class RequestClassHandlerWrapper<TRequest, TResponse> where TRequest : class, IRequest<TResponse>
+{
+    private readonly MessageHandlerDelegate<TRequest, TResponse> handler;
+
+    public RequestClassHandlerWrapper(IRequestHandler<TRequest, TResponse> concreteHandler,
+        IEnumerable<IPipelineBehavior<TRequest, TResponse>> pipelineBehaviours)
+    {
+        MessageHandlerDelegate<TRequest, TResponse> handler = concreteHandler.Handle;
+        foreach (var pipeline in pipelineBehaviours.Reverse())
+        {
+            MessageHandlerDelegate<TRequest, TResponse> handlerCopy = handler;
+            IPipelineBehavior<TRequest, TResponse> pipelineCopy = pipeline;
+
+            handler = (TRequest message, CancellationToken cancellationToken) => pipelineCopy.Handle(message, cancellationToken, handlerCopy);
+        }
+
+        this.handler = handler;
+    }
+
+    public ValueTask<TResponse> Handle(TRequest request, CancellationToken cancellationToken) => handler(request, cancellationToken);
+}