Refactor MCPHandler to be a UINTERFACE

Plugins/BlueprintMCP/Source/BlueprintMCP/Private/BlueprintMCPServer.cpp

@@ -862,8 +862,9 @@ bool FBlueprintMCPServer::ProcessOneRequest()
 			GEditor->BeginTransaction(FText::FromString(FString::Printf(TEXT("BlueprintMCP: %s"), *Req->Endpoint)));
 		}
 
-		TStrongObjectPtr<UMCPHandler> Handler(NewObject<UMCPHandler>(GetTransientPackage(), *HandlerClass));
-		FString PopulateError = PopulateFromJson(Handler->GetClass(), Handler.Get(), Params.Get());
+		TStrongObjectPtr<UObject> HandlerObj(NewObject<UObject>(GetTransientPackage(), *HandlerClass));
+		IMCPHandler* Handler = Cast<IMCPHandler>(HandlerObj.Get());
+		FString PopulateError = PopulateFromJson(HandlerObj->GetClass(), HandlerObj.Get(), Params.Get());
 		if (PopulateError.IsEmpty())
 		{
 			Handler->Handle(Params.Get(), &*Result);
@@ -1057,11 +1058,13 @@ void FBlueprintMCPServer::RegisterHandlers()
 
 void FBlueprintMCPServer::BuildMCPHandlerRegistry()
 {
-	TArray<UClass*> HandlerClasses;
-	GetDerivedClasses(UMCPHandler::StaticClass(), HandlerClasses);
-
-	for (UClass* Class : HandlerClasses)
+	for (TObjectIterator<UClass> It; It; ++It)
 	{
+		UClass* Class = *It;
+		if (!Class->ImplementsInterface(UMCPHandler::StaticClass()))
+		{
+			continue;
+		}
 		if (Class->HasAnyClassFlags(CLASS_Abstract))
 		{
 			continue;

Plugins/BlueprintMCP/Source/BlueprintMCP/Public/BlueprintMCPHandlers_DiffBlueprints.h

@@ -5,7 +5,7 @@
 #include "BlueprintMCPHandlers_DiffBlueprints.generated.h"
 
 UCLASS(meta=(ToolName="diff_blueprints"))
-class UMCPHandler_DiffBlueprints : public UMCPHandler
+class UMCPHandler_DiffBlueprints : public UObject, public IMCPHandler
 {
 	GENERATED_BODY()
 

Plugins/BlueprintMCP/Source/BlueprintMCP/Public/BlueprintMCPHandlers_Interfaces.h

@@ -5,7 +5,7 @@
 #include "BlueprintMCPHandlers_Interfaces.generated.h"
 
 UCLASS(meta=(ToolName="list_interfaces"))
-class UMCPHandler_ListInterfaces : public UMCPHandler
+class UMCPHandler_ListInterfaces : public UObject, public IMCPHandler
 {
 	GENERATED_BODY()
 
@@ -23,7 +23,7 @@ public:
 };
 
 UCLASS(meta=(ToolName="add_interface"))
-class UMCPHandler_AddInterface : public UMCPHandler
+class UMCPHandler_AddInterface : public UObject, public IMCPHandler
 {
 	GENERATED_BODY()
 
@@ -44,7 +44,7 @@ public:
 };
 
 UCLASS(meta=(ToolName="remove_interface"))
-class UMCPHandler_RemoveInterface : public UMCPHandler
+class UMCPHandler_RemoveInterface : public UObject, public IMCPHandler
 {
 	GENERATED_BODY()
 

Plugins/BlueprintMCP/Source/BlueprintMCP/Public/BlueprintMCPHandlers_Mutation.h

@@ -23,7 +23,7 @@ struct FSetPinDefaultEntry
 };
 
 UCLASS(meta=(ToolName="set_pin_default"))
-class UMCPHandler_SetPinDefault : public UMCPHandler
+class UMCPHandler_SetPinDefault : public UObject, public IMCPHandler
 {
 	GENERATED_BODY()
 
@@ -55,7 +55,7 @@ struct FMoveNodeEntry
 };
 
 UCLASS(meta=(ToolName="move_node"))
-class UMCPHandler_MoveNode : public UMCPHandler
+class UMCPHandler_MoveNode : public UObject, public IMCPHandler
 {
 	GENERATED_BODY()
 
@@ -75,7 +75,7 @@ public:
 };
 
 UCLASS(meta=(ToolName="duplicate_nodes"))
-class UMCPHandler_DuplicateNodes : public UMCPHandler
+class UMCPHandler_DuplicateNodes : public UObject, public IMCPHandler
 {
 	GENERATED_BODY()
 
@@ -121,7 +121,7 @@ struct FSpawnNodeEntry
 };
 
 UCLASS(meta=(ToolName="spawn_node"))
-class UMCPHandler_SpawnNode : public UMCPHandler
+class UMCPHandler_SpawnNode : public UObject, public IMCPHandler
 {
 	GENERATED_BODY()
 
@@ -146,7 +146,7 @@ public:
 };
 
 UCLASS(meta=(ToolName="get_node_comment"))
-class UMCPHandler_GetNodeComment : public UMCPHandler
+class UMCPHandler_GetNodeComment : public UObject, public IMCPHandler
 {
 	GENERATED_BODY()
 
@@ -166,7 +166,7 @@ public:
 };
 
 UCLASS(meta=(ToolName="set_node_comment"))
-class UMCPHandler_SetNodeComment : public UMCPHandler
+class UMCPHandler_SetNodeComment : public UObject, public IMCPHandler
 {
 	GENERATED_BODY()
 
@@ -189,7 +189,7 @@ public:
 };
 
 UCLASS(meta=(ToolName="delete_node"))
-class UMCPHandler_DeleteNode : public UMCPHandler
+class UMCPHandler_DeleteNode : public UObject, public IMCPHandler
 {
 	GENERATED_BODY()
 
@@ -228,7 +228,7 @@ struct FConnectPinsEntry
 };
 
 UCLASS(meta=(ToolName="connect_pins"))
-class UMCPHandler_ConnectPins : public UMCPHandler
+class UMCPHandler_ConnectPins : public UObject, public IMCPHandler
 {
 	GENERATED_BODY()
 
@@ -266,7 +266,7 @@ struct FDisconnectPinEntry
 };
 
 UCLASS(meta=(ToolName="disconnect_pin"))
-class UMCPHandler_DisconnectPin : public UMCPHandler
+class UMCPHandler_DisconnectPin : public UObject, public IMCPHandler
 {
 	GENERATED_BODY()
 
@@ -287,7 +287,7 @@ public:
 };
 
 UCLASS(meta=(ToolName="replace_function_calls"))
-class UMCPHandler_ReplaceFunctionCalls : public UMCPHandler
+class UMCPHandler_ReplaceFunctionCalls : public UObject, public IMCPHandler
 {
 	GENERATED_BODY()
 
@@ -314,7 +314,7 @@ public:
 };
 
 UCLASS(meta=(ToolName="delete_asset"))
-class UMCPHandler_DeleteAsset : public UMCPHandler
+class UMCPHandler_DeleteAsset : public UObject, public IMCPHandler
 {
 	GENERATED_BODY()
 
@@ -335,7 +335,7 @@ public:
 };
 
 UCLASS(meta=(ToolName="refresh_all_nodes"))
-class UMCPHandler_RefreshAllNodes : public UMCPHandler
+class UMCPHandler_RefreshAllNodes : public UObject, public IMCPHandler
 {
 	GENERATED_BODY()
 
@@ -353,7 +353,7 @@ public:
 };
 
 UCLASS(meta=(ToolName="change_struct_node_type"))
-class UMCPHandler_ChangeStructNodeType : public UMCPHandler
+class UMCPHandler_ChangeStructNodeType : public UObject, public IMCPHandler
 {
 	GENERATED_BODY()
 
@@ -377,7 +377,7 @@ public:
 };
 
 UCLASS(meta=(ToolName="rename_asset"))
-class UMCPHandler_RenameAsset : public UMCPHandler
+class UMCPHandler_RenameAsset : public UObject, public IMCPHandler
 {
 	GENERATED_BODY()
 
@@ -397,7 +397,7 @@ public:
 };
 
 UCLASS(meta=(ToolName="set_blueprint_default"))
-class UMCPHandler_SetBlueprintDefault : public UMCPHandler
+class UMCPHandler_SetBlueprintDefault : public UObject, public IMCPHandler
 {
 	GENERATED_BODY()
 
@@ -421,7 +421,7 @@ public:
 };
 
 UCLASS(meta=(ToolName="search_node_types"))
-class UMCPHandler_SearchNodeTypes : public UMCPHandler
+class UMCPHandler_SearchNodeTypes : public UObject, public IMCPHandler
 {
 	GENERATED_BODY()
 

Plugins/BlueprintMCP/Source/BlueprintMCP/Public/BlueprintMCPServer.h

@@ -14,7 +14,7 @@ class UMaterial;
 class UMaterialInstanceConstant;
 class UMaterialFunction;
 class UMaterialExpression;
-class UMCPHandler;
+class IMCPHandler;
 
 // ----- Snapshot data structures -----
 

Plugins/BlueprintMCP/Source/BlueprintMCP/Public/MCPHandler.h

@@ -23,9 +23,9 @@ struct FMCPJsonArray
 	TArray<TSharedPtr<FJsonValue>> Array;
 };
 
-// Base class for self-registering MCP tool handlers.
+// Interface for self-registering MCP tool handlers.
 //
-// Subclasses declare their parameters as UPROPERTY fields, which are
+// Implementing classes declare their parameters as UPROPERTY fields, which are
 // automatically populated from the incoming JSON request and used to
 // generate the tool's JSON Schema for MCP tools/list.
 //
@@ -35,17 +35,20 @@ struct FMCPJsonArray
 // Property metadata:
 //   Optional      - marks a parameter as not required
 //
-UCLASS(Abstract)
-class BLUEPRINTMCP_API UMCPHandler : public UObject
+UINTERFACE(MinimalAPI, meta=(CannotImplementInterfaceInBlueprint))
+class UMCPHandler : public UInterface
+{
+	GENERATED_BODY()
+};
+
+class BLUEPRINTMCP_API IMCPHandler
 {
 	GENERATED_BODY()
 
 public:
 	// Human-readable tool description for MCP tools/list.
-	// Override in each subclass.
-	virtual FString GetDescription() const PURE_VIRTUAL(UMCPHandler::GetDescription, return FString(););
+	virtual FString GetDescription() const = 0;
 
 	// Called after parameter fields have been populated from JSON.
-	// Override in each subclass.
-	virtual void Handle(const FJsonObject* Json, FJsonObject* Result) PURE_VIRTUAL(UMCPHandler::Handle, );
+	virtual void Handle(const FJsonObject* Json, FJsonObject* Result) = 0;
 };