Add add_mass_config_trait tool + PyPI auto-publish (v1.2.1)

New MCP tool: add_mass_config_trait
- Safely appends a single trait to a MassEntityConfigAsset
- Never replaces existing traits (prevents replicator data loss)
- Duplicate detection (returns error if trait class already exists)
- Supports property initialization via JSON dict
- C++ bridge: EpicUnrealMCPDataAssetCommands.cpp
- Python wrapper: data_assets.py
- Go CLI: data_assets.go

CI/CD: Added PyPI publishing to release workflow
- Builds sdist + wheel via python -m build
- Publishes via twine using PYPI_TOKEN secret
- Version auto-synced from git tag
- Triggers on v* tag push alongside npm publish

Version bumped to 1.2.1 (pyproject.toml + package.json)

Author: aadeshrao123

.github/workflows/release.yml

@@ -120,3 +120,33 @@ jobs:
         env:
           NODE_AUTH_TOKEN: ${{ secrets.NPM_TOKEN }}
         run: npm publish --access public
+
+  publish-pypi:
+    needs: release
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+
+      - name: Install build tools
+        run: pip install build twine
+
+      - name: Update version from tag
+        run: |
+          VERSION="${GITHUB_REF_NAME#v}"
+          sed -i "s/^version = .*/version = \"$VERSION\"/" pyproject.toml
+
+      - name: Build package
+        run: python -m build
+
+      - name: Publish to PyPI
+        env:
+          TWINE_USERNAME: __token__
+          TWINE_PASSWORD: ${{ secrets.PYPI_TOKEN }}
+        run: twine upload dist/*

Source/UnrealMCPBridge/Private/Commands/EpicUnrealMCPDataAssetCommands.cpp

@@ -58,6 +58,10 @@ TSharedPtr<FJsonObject> FEpicUnrealMCPDataAssetCommands::HandleCommand(
 	{
 		return HandleGetMassConfigTraits(Params);
 	}
+	if (CommandType == TEXT("add_mass_config_trait"))
+	{
+		return HandleAddMassConfigTrait(Params);
+	}
 
 	return FEpicUnrealMCPCommonUtils::CreateErrorResponse(
 		FString::Printf(TEXT("Unknown data asset command: %s"), *CommandType));
@@ -1047,3 +1051,156 @@ TSharedPtr<FJsonObject> FEpicUnrealMCPDataAssetCommands::HandleGetMassConfigTrai
 	Result->SetArrayField(TEXT("traits"), TraitsArray);
 	return Result;
 }
+
+// ============================================================================
+// add_mass_config_trait — Add a SINGLE trait to a Mass Entity Config without
+// replacing existing traits. Safe for configs with complex replicator settings.
+// ============================================================================
+
+TSharedPtr<FJsonObject> FEpicUnrealMCPDataAssetCommands::HandleAddMassConfigTrait(
+	const TSharedPtr<FJsonObject>& Params)
+{
+	FString AssetPath;
+	if (!Params->TryGetStringField(TEXT("asset_path"), AssetPath))
+	{
+		return FEpicUnrealMCPCommonUtils::CreateErrorResponse(TEXT("Missing 'asset_path'"));
+	}
+
+	FString TraitClassName;
+	if (!Params->TryGetStringField(TEXT("trait_class"), TraitClassName))
+	{
+		return FEpicUnrealMCPCommonUtils::CreateErrorResponse(TEXT("Missing 'trait_class' (e.g. '/Script/Jiggify.MassBuildingHealthTrait')"));
+	}
+
+	UObject* Asset = StaticLoadObject(UObject::StaticClass(), nullptr, *AssetPath);
+	if (!Asset)
+	{
+		return FEpicUnrealMCPCommonUtils::CreateErrorResponse(
+			FString::Printf(TEXT("Asset not found: %s"), *AssetPath));
+	}
+
+	// Resolve trait class
+	UClass* TraitClass = StaticLoadClass(UObject::StaticClass(), nullptr, *TraitClassName);
+	if (!TraitClass)
+	{
+		return FEpicUnrealMCPCommonUtils::CreateErrorResponse(
+			FString::Printf(TEXT("Trait class not found: %s"), *TraitClassName));
+	}
+
+	// Find Config struct property
+	FStructProperty* ConfigProp = nullptr;
+	for (TFieldIterator<FStructProperty> It(Asset->GetClass()); It; ++It)
+	{
+		if (It->GetName() == TEXT("Config"))
+		{
+			ConfigProp = *It;
+			break;
+		}
+	}
+
+	if (!ConfigProp)
+	{
+		return FEpicUnrealMCPCommonUtils::CreateErrorResponse(TEXT("Asset has no 'Config' struct property"));
+	}
+
+	void* ConfigPtr = ConfigProp->ContainerPtrToValuePtr<void>(Asset);
+
+	// Find Traits array
+	FArrayProperty* TraitsArrayProp = nullptr;
+	for (TFieldIterator<FArrayProperty> It(ConfigProp->Struct); It; ++It)
+	{
+		if (It->GetName() == TEXT("Traits"))
+		{
+			TraitsArrayProp = *It;
+			break;
+		}
+	}
+
+	if (!TraitsArrayProp)
+	{
+		return FEpicUnrealMCPCommonUtils::CreateErrorResponse(TEXT("Config has no 'Traits' array"));
+	}
+
+	FObjectProperty* InnerObjProp = CastField<FObjectProperty>(TraitsArrayProp->Inner);
+	if (!InnerObjProp)
+	{
+		return FEpicUnrealMCPCommonUtils::CreateErrorResponse(TEXT("Traits array inner type is not an object"));
+	}
+
+	// Check if trait already exists
+	FScriptArrayHelper ArrayHelper(TraitsArrayProp, TraitsArrayProp->ContainerPtrToValuePtr<void>(ConfigPtr));
+	for (int32 i = 0; i < ArrayHelper.Num(); ++i)
+	{
+		UObject* Existing = InnerObjProp->GetObjectPropertyValue(ArrayHelper.GetRawPtr(i));
+		if (Existing && Existing->GetClass() == TraitClass)
+		{
+			return FEpicUnrealMCPCommonUtils::CreateErrorResponse(
+				FString::Printf(TEXT("Trait '%s' already exists at index %d"), *TraitClass->GetName(), i));
+		}
+	}
+
+	// Create new trait instance
+	UObject* NewTrait = NewObject<UObject>(Asset, TraitClass);
+	if (!NewTrait)
+	{
+		return FEpicUnrealMCPCommonUtils::CreateErrorResponse(TEXT("Failed to create trait instance"));
+	}
+
+	// Set properties if provided
+	const TSharedPtr<FJsonObject>* PropertiesObj = nullptr;
+	if (Params->TryGetObjectField(TEXT("properties"), PropertiesObj) && PropertiesObj)
+	{
+		for (auto& Pair : (*PropertiesObj)->Values)
+		{
+			FProperty* Prop = NewTrait->GetClass()->FindPropertyByName(*Pair.Key);
+			if (Prop)
+			{
+				void* ValuePtr = Prop->ContainerPtrToValuePtr<void>(NewTrait);
+				FString ValueStr;
+				if (Pair.Value->TryGetString(ValueStr))
+				{
+					Prop->ImportText_Direct(*ValueStr, ValuePtr, nullptr, PPF_None);
+				}
+				else if (Pair.Value->Type == EJson::Number)
+				{
+					// Handle numeric values
+					double NumVal = Pair.Value->AsNumber();
+					if (FFloatProperty* FloatProp = CastField<FFloatProperty>(Prop))
+					{
+						FloatProp->SetPropertyValue(ValuePtr, static_cast<float>(NumVal));
+					}
+					else if (FDoubleProperty* DoubleProp = CastField<FDoubleProperty>(Prop))
+					{
+						DoubleProp->SetPropertyValue(ValuePtr, NumVal);
+					}
+					else if (FIntProperty* IntProp = CastField<FIntProperty>(Prop))
+					{
+						IntProp->SetPropertyValue(ValuePtr, static_cast<int32>(NumVal));
+					}
+				}
+				else if (Pair.Value->Type == EJson::Boolean)
+				{
+					if (FBoolProperty* BoolProp = CastField<FBoolProperty>(Prop))
+					{
+						BoolProp->SetPropertyValue(ValuePtr, Pair.Value->AsBool());
+					}
+				}
+			}
+		}
+	}
+
+	// Add to array
+	int32 NewIndex = ArrayHelper.AddValue();
+	InnerObjProp->SetObjectPropertyValue(ArrayHelper.GetRawPtr(NewIndex), NewTrait);
+
+	// Mark dirty
+	Asset->MarkPackageDirty();
+
+	TSharedPtr<FJsonObject> Result = MakeShared<FJsonObject>();
+	Result->SetBoolField(TEXT("success"), true);
+	Result->SetStringField(TEXT("asset_path"), AssetPath);
+	Result->SetStringField(TEXT("trait_class"), TraitClass->GetName());
+	Result->SetNumberField(TEXT("trait_index"), NewIndex);
+	Result->SetNumberField(TEXT("total_traits"), ArrayHelper.Num());
+	return Result;
+}

Source/UnrealMCPBridge/Private/EpicUnrealMCPBridge.cpp

@@ -672,7 +672,8 @@ FString UEpicUnrealMCPBridge::ExecuteCommand(
 				CommandType == TEXT("list_data_assets") ||
 				CommandType == TEXT("get_property_valid_types") ||
 				CommandType == TEXT("search_class_paths") ||
-				CommandType == TEXT("get_mass_config_traits"))
+				CommandType == TEXT("get_mass_config_traits") ||
+				CommandType == TEXT("add_mass_config_trait"))
 			{
 				ResultJson = DataAssetCommands->HandleCommand(CommandType, Params);
 			}

Source/UnrealMCPBridge/Public/Commands/EpicUnrealMCPDataAssetCommands.h

@@ -27,6 +27,7 @@ class UNREALMCPBRIDGE_API FEpicUnrealMCPDataAssetCommands
 	TSharedPtr<FJsonObject> HandleGetPropertyValidTypes(const TSharedPtr<FJsonObject>& Params);
 	TSharedPtr<FJsonObject> HandleSearchClassPaths(const TSharedPtr<FJsonObject>& Params);
 	TSharedPtr<FJsonObject> HandleGetMassConfigTraits(const TSharedPtr<FJsonObject>& Params);
+	TSharedPtr<FJsonObject> HandleAddMassConfigTrait(const TSharedPtr<FJsonObject>& Params);
 
 	// Limited to UDataAsset subclasses. For any class use PU::ResolveAnyClass.
 	static UClass* ResolveDataAssetClass(const FString& ClassName);

cli/cmd/data_assets.go

@@ -101,6 +101,18 @@ ue-cli get_data_asset_properties --asset-path /Game/Data/DA_MyRecipe --filter "P
 			{Name: "asset_path", Type: "string", Required: true, Help: "Content path to the Mass Entity config asset"},
 		},
 	},
+	{
+		Name:  "add_mass_config_trait",
+		Group: "dataassets",
+		Short: "Add a single trait to a Mass Entity config",
+		Long:  "Safely appends a single trait to a MassEntityConfigAsset without replacing existing traits. Returns error if the trait already exists. Use for adding health, combat, or any trait to building configs without risking replicator or other complex trait data.",
+		Example: `ue-cli add_mass_config_trait --asset-path /Game/Mass/DA_MinerConfig --trait-class /Script/Jiggify.MassBuildingHealthTrait --properties '{"MaxHealth":100}'`,
+		Params: []ParamSpec{
+			{Name: "asset_path", Type: "string", Required: true, Help: "Content path to the Mass Entity config asset"},
+			{Name: "trait_class", Type: "string", Required: true, Help: "Full class path (e.g. /Script/Jiggify.MassBuildingHealthTrait)"},
+			{Name: "properties", Type: "json", Help: "JSON object of property values to set on the new trait"},
+		},
+	},
 	{
 		Name:  "list_data_assets",
 		Group: "dataassets",

cli/npm/package.json

@@ -1,6 +1,6 @@
 {
   "name": "unrealcli",
-  "version": "1.0.0",
+  "version": "1.2.1",
   "description": "CLI for controlling Unreal Engine 5 Editor — create materials, blueprints, spawn actors, modify assets. No Python, no MCP, no dependencies.",
   "keywords": [
     "unreal",

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "unrealmcp"
-version = "1.1.0"
+version = "1.2.1"
 description = "MCP (Model Context Protocol) bridge for Unreal Engine 5 — lets AI assistants control the UE5 editor"
 readme = "README.md"
 license = "MIT"

unrealmcp/tools/data_assets.py

@@ -202,6 +202,33 @@ def get_mass_config_traits(asset_path: str) -> str:
     })
 
 
+@mcp.tool()
+def add_mass_config_trait(
+    asset_path: str,
+    trait_class: str,
+    properties: dict | None = None,
+) -> str:
+    """Add a SINGLE trait to a Mass Entity Config without replacing existing traits.
+
+    Safe for configs with complex replicator settings — only appends, never replaces.
+    Returns error if the trait already exists on the config.
+
+    Args:
+        asset_path: Path to MassEntityConfigAsset (e.g. "/Game/.../DA_MinerMassEntityConfig_Mk1")
+        trait_class: Full class path (e.g. "/Script/Jiggify.MassBuildingHealthTrait")
+        properties: Optional dict of property values to set on the new trait.
+            Supports floats, ints, bools, strings.
+            Example: {"MaxHealth": 150, "Resistance_Fire": 0.2}
+    """
+    params = {
+        "asset_path": asset_path,
+        "trait_class": trait_class,
+    }
+    if properties is not None:
+        params["properties"] = properties
+    return _call("add_mass_config_trait", params)
+
+
 @mcp.tool()
 def list_data_assets(
     path: str = "/Game",