Fix: Prevent infinite loop when serializing assets with reflection types

Unity-MCP-Plugin/Assets/root/Editor/Scripts/API/Tool/GameObject.AddComponent.cs

@@ -60,6 +60,12 @@ GameObjectRef gameObjectRef
 
                 var newComponent = go.AddComponent(type);
 
+                if (newComponent == null)
+                {
+                    stringBuilder.AppendLine($"[Warning] Component '{componentName}' already exists on GameObject or cannot be added.");
+                    continue;
+                }
+
                 stringBuilder.AppendLine($"[Success] Added component '{componentName}'. Component instanceID='{newComponent.GetInstanceID()}'.");
             }
 

Unity-MCP-Plugin/Assets/root/Runtime/ReflectionConverters/Base/ReflectionTypeFilter.cs

@@ -0,0 +1,41 @@
+/*
+┌──────────────────────────────────────────────────────────────────┐
+│  Author: Ivan Murzak (https://github.com/IvanMurzak)             │
+│  Repository: GitHub (https://github.com/IvanMurzak/Unity-MCP)    │
+│  Copyright (c) 2025 Ivan Murzak                                  │
+│  Licensed under the Apache License, Version 2.0.                 │
+│  See the LICENSE file in the project root for more information.  │
+└──────────────────────────────────────────────────────────────────┘
+*/
+#pragma warning disable CS8632 // The annotation for nullable reference types should only be used in code within a '#nullable' annotations context.
+using System;
+
+namespace com.IvanMurzak.Unity.MCP.Common.Reflection.Convertor
+{
+    /// <summary>
+    /// Utility class for filtering reflection types that cause circular references during serialization.
+    /// </summary>
+    public static class ReflectionTypeFilter
+    {
+        /// <summary>
+        /// Determines if a type is a System.Reflection type that should be excluded from serialization.
+        /// Reflection types form circular references (RuntimeType -> RuntimeModule -> RuntimeAssembly -> RuntimeModule)
+        /// and cannot be meaningfully serialized to JSON or reconstructed during deserialization.
+        /// </summary>
+        /// <param name="type">The type to check.</param>
+        /// <returns>True if the type should be excluded from serialization; otherwise, false.</returns>
+        public static bool IsReflectionType(Type type)
+        {
+            if (type == null) return false;
+
+            var fullName = type.FullName;
+            if (string.IsNullOrEmpty(fullName)) return false;
+
+            // Catch System.Reflection.* namespace types
+            // Note: System.RuntimeType and System.Type are in System namespace, not System.Reflection
+            return fullName.StartsWith("System.Reflection.") ||
+                   fullName == "System.RuntimeType" ||
+                   fullName == "System.Type";
+        }
+    }
+}

Unity-MCP-Plugin/Assets/root/Runtime/ReflectionConverters/Base/UnityArrayReflectionConvertor.cs

@@ -24,6 +24,15 @@ public partial class UnityArrayReflectionConvertor : ArrayReflectionConvertor
         public override IEnumerable<FieldInfo>? GetSerializableFields(Reflector reflector, Type objType, BindingFlags flags, ILogger? logger = null)
             => objType.GetFields(flags)
                 .Where(field => field.GetCustomAttribute<ObsoleteAttribute>() == null)
-                .Where(field => field.IsPublic || field.IsPrivate && field.GetCustomAttribute<SerializeField>() != null);
+                .Where(field => field.IsPublic || field.IsPrivate && field.GetCustomAttribute<SerializeField>() != null)
+                .Where(field => !ReflectionTypeFilter.IsReflectionType(field.FieldType));
+
+        public override IEnumerable<PropertyInfo>? GetSerializableProperties(Reflector reflector, Type objType, BindingFlags flags, ILogger? logger = null)
+        {
+            var baseProperties = base.GetSerializableProperties(reflector, objType, flags, logger);
+            if (baseProperties == null) return null;
+
+            return baseProperties.Where(prop => !ReflectionTypeFilter.IsReflectionType(prop.PropertyType));
+        }
     }
 }

Unity-MCP-Plugin/Assets/root/Runtime/ReflectionConverters/Base/UnityGenericReflectionConvertor.cs

@@ -24,6 +24,15 @@ public partial class UnityGenericReflectionConvertor<T> : GenericReflectionConve
         public override IEnumerable<FieldInfo>? GetSerializableFields(Reflector reflector, Type objType, BindingFlags flags, ILogger? logger = null)
             => objType.GetFields(flags)
                 .Where(field => field.GetCustomAttribute<ObsoleteAttribute>() == null)
-                .Where(field => field.IsPublic || field.IsPrivate && field.GetCustomAttribute<SerializeField>() != null);
+                .Where(field => field.IsPublic || field.IsPrivate && field.GetCustomAttribute<SerializeField>() != null)
+                .Where(field => !ReflectionTypeFilter.IsReflectionType(field.FieldType));
+
+        public override IEnumerable<PropertyInfo>? GetSerializableProperties(Reflector reflector, Type objType, BindingFlags flags, ILogger? logger = null)
+        {
+            var baseProperties = base.GetSerializableProperties(reflector, objType, flags, logger);
+            if (baseProperties == null) return null;
+
+            return baseProperties.Where(prop => !ReflectionTypeFilter.IsReflectionType(prop.PropertyType));
+        }
     }
 }