some changes

Femto.Common/Integration/IEventHandler.cs

@@ -0,0 +1,24 @@
+namespace Femto.Common.Integration;
+
+public interface IEventHandler
+{
+    Task Handle(IEvent evt, CancellationToken cancellationToken = default);
+}
+
+public abstract class EventHandler<T> : IEventHandler
+    where T : IEvent
+{
+    protected abstract Task Handle(T evt, CancellationToken cancellationToken);
+
+    public async Task Handle(IEvent evt, CancellationToken cancellationToken = default)
+    {
+        if (evt is not T typedEvt)
+        {
+            throw new InvalidOperationException(
+                $"Event {evt.GetType()} is not of type {typeof(T)}"
+            );
+        }
+
+        await Handle(typedEvt, cancellationToken);
+    }
+}