Handle System.Object properties with runtime type dispatch

- Emit special serialization logic for properties declared as System.Object, using value.GetType() and writing type name metadata for correct polymorphic deserialization.
- Add IsObjectDeclaredType to PropInfo to support this logic.
- Update scan pass to use runtime type for object properties.
- Adjust IId reference test to ensure circular reference coverage.
- Default UseGeneratedCode to true in serializer options.

AyCode.Core.Serializers.SourceGenerator/AcBinarySourceGenerator.cs

@@ -248,6 +248,7 @@ public class AcBinarySourceGenerator : IIncrementalGenerator
                     typeNameForTypeof,
                     kind,
                     p.Type.NullableAnnotation == NullableAnnotation.Annotated || IsNullableVT(p.Type),
+                    p.Type.SpecialType == SpecialType.System_Object,
                     stringInternAttr, hasGenWriter, propTypeIsIId, writerClassName, propIdTypeName,
                     elemKind, elemHasGenWriter, elemIsIId, elemWriterClassName, elemIdTypeName, collKind, elemFullTypeName,
                     childTypeNameHash, childPropertyHashes,
@@ -536,6 +537,22 @@ public class AcBinarySourceGenerator : IIncrementalGenerator
                 // when the property type has a generated writer. Falls back to WriteObjectGenerated otherwise.
                 if (p.HasGeneratedWriter)
                     EmitDirectObjectWrite(sb, p, a, i);
+                else if (p.IsObjectDeclaredType)
+                {
+                    // System.Object property: runtime type unknown at compile time.
+                    // Write ObjectWithTypeName prefix so deserializer can resolve the concrete type.
+                    // Use value.GetType() for runtime type dispatch (not typeof(object)).
+                    sb.AppendLine($"{i}if ({a} == null) context.WriteByte(BinaryTypeCode.PropertySkip);");
+                    sb.AppendLine($"{i}else");
+                    sb.AppendLine($"{i}{{");
+                    sb.AppendLine($"{i}    if (!context.UseMetadata)");
+                    sb.AppendLine($"{i}    {{");
+                    sb.AppendLine($"{i}        context.WriteByte(BinaryTypeCode.ObjectWithTypeName);");
+                    sb.AppendLine($"{i}        context.WriteStringUtf8({a}.GetType().AssemblyQualifiedName!);");
+                    sb.AppendLine($"{i}    }}");
+                    sb.AppendLine($"{i}    AcBinarySerializer.WriteValueGenerated({a}, {a}.GetType(), context, depth);");
+                    sb.AppendLine($"{i}}}");
+                }
                 else if (p.IsNullable)
                 {
                     sb.AppendLine($"{i}if ({a} == null) context.WriteByte(BinaryTypeCode.PropertySkip);");
@@ -723,13 +740,17 @@ public class AcBinarySourceGenerator : IIncrementalGenerator
 
     /// <summary>
     /// Emits scan pass code for a Complex property without SGen writer (runtime fallback).
+    /// System.Object properties use value.GetType() for runtime type dispatch.
     /// </summary>
     private static void EmitScanComplexRuntime(StringBuilder sb, PropInfo p, string a, string i)
     {
         var childVar = $"sc_{p.Name}";
         sb.AppendLine($"{i}var {childVar} = {a};");
         sb.AppendLine($"{i}if ({childVar} != null)");
-        sb.AppendLine($"{i}    AcBinarySerializer.ScanValueGenerated({childVar}, typeof({p.TypeNameForTypeof}), context, depth + 1);");
+        if (p.IsObjectDeclaredType)
+            sb.AppendLine($"{i}    AcBinarySerializer.ScanValueGenerated({childVar}, {childVar}.GetType(), context, depth + 1);");
+        else
+            sb.AppendLine($"{i}    AcBinarySerializer.ScanValueGenerated({childVar}, typeof({p.TypeNameForTypeof}), context, depth + 1);");
     }
 
     /// <summary>
@@ -2046,6 +2067,8 @@ internal sealed class PropInfo
     /// </summary>
     public int InterningFlags { get; }
 
+    /// <summary>True when declared property type is System.Object. Runtime type dispatch needed.</summary>
+    public bool IsObjectDeclaredType { get; }
     /// <summary>True if the Complex property type has [AcBinarySerializable] → has a generated writer.</summary>
     public bool HasGeneratedWriter { get; }
     /// <summary>True if the Complex property type implements IId&lt;T&gt; → needs ref tracking in write pass.</summary>
@@ -2106,6 +2129,7 @@ internal sealed class PropInfo
     public bool ElementNeedsScan => ElementNeedsIdScan || ElementNeedsAllRefScan || ElementNeedsInternScan;
 
     public PropInfo(string n, string tn, string tnForTypeof, PropertyTypeKind tk, bool nullable,
+        bool isObjectDeclaredType = false,
         bool? stringInternAttr = null, bool hasGeneratedWriter = false, bool isIId = false, string? writerClassName = null, string? idTypeName = null,
         PropertyTypeKind elementKind = PropertyTypeKind.Unknown, bool elementHasGenWriter = false, bool elementIsIId = false,
         string? elementWriterClassName = null, string? elementIdTypeName = null, string? collectionKind = null, string? elementFullTypeName = null,
@@ -2120,6 +2144,7 @@ internal sealed class PropInfo
         TypeNameForTypeof = tnForTypeof;
         TypeKind = tk;
         IsNullable = nullable;
+        IsObjectDeclaredType = isObjectDeclaredType;
         HasGeneratedWriter = hasGeneratedWriter;
         IsIId = isIId;
         WriterClassName = writerClassName;

AyCode.Core.Tests/Serialization/AcBinarySerializerIIdReferenceTests.cs

@@ -114,9 +114,10 @@ public class AcBinarySerializerIIdReferenceTests
                 ]
             };
 
-            //order.Parent = order.Items[0];
+            if (mode != ReferenceHandlingMode.None) order.Parent = order.Items[1];
-            order.Parent = userPreferences;
+            else order.Parent = userPreferences;
-            order.Items[0].ParentOrder = order;
+
+            order.Items[1].ParentOrder = order;
 
             var options = new AcBinarySerializerOptions { ReferenceHandling = mode };
 

AyCode.Core/Serializers/Binaries/AcBinarySerializerOptions.cs

@@ -84,7 +84,7 @@ public sealed class AcBinarySerializerOptions : AcSerializerOptions
     /// </summary>
     public bool UseMetadata { get; set; } = false;
 
-    public bool UseGeneratedCode { get; set; } = false;
+    public bool UseGeneratedCode { get; set; } = true;
 
     /// <summary>
     /// Controls how string interning is applied during serialization.