fix: filter out non-instantiable types during DI registration

Author: a.shafie

Changelog.md

@@ -2,10 +2,7 @@
 
 ## v2.2.1
 
-- **Fixed**: Support for record structs as message types (commands, queries, events). Previously record structs couldn't
-  be registered due to a type filtering condition that only allowed class types.
-- **Improved**: Message registration to handle all non-System types, allowing for greater flexibility in message
-  definitions.
+- **Fixed**: DI container registration now properly filters out interfaces and abstract classes during service registration. Previously, `RegisterFromAssembly()` would cause DI container errors when trying to register non-instantiable types. LiteBus message registry continues to accept all types to support polymorphic dispatch, but only concrete classes are registered with the DI container.
 
 ## v2.2.0
 

src/LiteBus.Messaging.Extensions.MicrosoftDependencyInjection/ModuleRegistry.cs

@@ -79,6 +79,14 @@ private void RegisterHandlersFromDescriptor(IMessageDescriptor descriptor)
         // Register each type once
         foreach (var handlerType in descriptorHandlerTypes)
         {
+            // Only register concrete classes with DI container - interfaces and abstract classes are kept in 
+            // LiteBus registry for polymorphic dispatch but cannot be instantiated by the DI container.
+            // Without this filter, DI would throw "Cannot instantiate implementation type" errors.
+            if (handlerType is { IsClass: true, IsAbstract: false })
+            {
+                _services.TryAddTransient(handlerType);
+            }
+
             _services.TryAddTransient(handlerType);
         }
     }