diff --git a/AyCode.Core/Serializers/IdentityMap.cs b/AyCode.Core/Serializers/IdentityMap.cs
index 8d251a4..68256cf 100644
--- a/AyCode.Core/Serializers/IdentityMap.cs
+++ b/AyCode.Core/Serializers/IdentityMap.cs
@@ -46,8 +46,9 @@ public interface IIdentityMap
 /// <typeparam name="TId">The ID type (int, long, Guid, string)</typeparam>
 public sealed class IdentityMap<TId> : IIdentityMap where TId : notnull
 {
-    private bool _useSmallInt = false;
+    private const bool _useSmallInt = true;
 
+    // Small int optimization (TId = int only, 0-4095), 512 bytes (fits in L1 cache!)
     private const int SmallBitmapSize = 64;
     private const int SmallSize = 4096;
 
@@ -55,10 +56,6 @@ public sealed class IdentityMap<TId> : IIdentityMap where TId : notnull
     //private const int SmallBitmapSize = 1024;
     //private const int SmallSize = SmallBitmapSize * 64;
 
-    // Small int optimization (TId = int only, 0-4095)
-    //private const int SmallSize = 4096;
-    //private const int SmallBitmapSize = SmallSize / 64;  // 64 ulongs = 512 bytes (fits in L1 cache!)
-
     // Slot for hash table entries (generation needed for hash table validity)
     private struct HashSlot
     {
@@ -90,8 +87,7 @@ public sealed class IdentityMap<TId> : IIdentityMap where TId : notnull
     public IdentityMap()
     {
     }
-
-
+    
     /// <summary>
     /// Tries to add a key to tracking (serialization).
     /// Returns true if first occurrence (key was added).
@@ -311,16 +307,16 @@ public sealed class IdentityMap<TId> : IIdentityMap where TId : notnull
         // NOTE: SmallInt path DISABLED for deserializer.
         // The 512KB _smallValues sparse array causes cache misses.
         // Hash table has better cache locality.
-        
-        // // Small int fast path
-        // if (_useSmallInt && IsInt32)
-        // {
-        //     var intKey = Unsafe.As<TId, int>(ref key);
-        //     if ((uint)intKey < SmallSize)
-        //     {
-        //         return TryGetOrAddSmallInt(intKey, out existing);
-        //     }
-        // }
+
+        //// Small int fast path
+        //if (_useSmallInt && IsInt32)
+        //{
+        //    var intKey = Unsafe.As<TId, int>(ref key);
+        //    if ((uint)intKey < SmallSize)
+        //    {
+        //        return TryGetOrAddSmallInt(intKey, out existing);
+        //    }
+        //}
 
         // Hash table path
         if (!TryAddHash(key, out var slotIndex))
@@ -335,19 +331,13 @@ public sealed class IdentityMap<TId> : IIdentityMap where TId : notnull
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     private bool TryGetOrAddSmallInt(int key, out object? existing)
     {
-        // Lazy init bitmap
+        // Lazy init bitmap only - NOT _smallValues!
+        // This method is for tracking (key seen?), not value storage.
         if (_smallBitmap == null)
         {
             _smallBitmap = ArrayPool<ulong>.Shared.Rent(SmallBitmapSize);
             Array.Clear(_smallBitmap, 0, SmallBitmapSize);
         }
-        
-        // Lazy init values array (only when needed for deserialization)
-        if (_smallValues == null)
-        {
-            _smallValues = ArrayPool<object?>.Shared.Rent(SmallSize);
-            Array.Clear(_smallValues, 0, SmallSize);
-        }
 
         var wordIdx = key >> 6;
         var bit = 1UL << (key & 63);
@@ -355,14 +345,13 @@ public sealed class IdentityMap<TId> : IIdentityMap where TId : notnull
         ref var word = ref _smallBitmap[wordIdx];
         if ((word & bit) != 0)
         {
-            // Bitmap says seen - value is valid
-            existing = _smallValues![key];
+            // Bitmap says seen - return stored value if any
+            existing = _smallValues?[key];
             return false;  // Already seen
         }
 
-        // First occurrence - mark as seen
+        // First occurrence - mark as seen (don't touch _smallValues!)
         word |= bit;
-        _smallValues![key] = null;
         existing = null;
         return true;
     }
@@ -378,16 +367,16 @@ public sealed class IdentityMap<TId> : IIdentityMap where TId : notnull
         // The 512KB _smallValues sparse array causes cache misses.
         // Hash table has better cache locality (only stores actual entries).
         // Bitmap is only useful for tracking (serializer) - not for value storage.
-        
-        // // Small int fast path
-        // if (_useSmallInt && IsInt32)
-        // {
-        //     var intKey = Unsafe.As<TId, int>(ref key);
-        //     if ((uint)intKey < SmallSize)
-        //     {
-        //         return TryGetOrAddSmallIntValue(intKey, newValue);
-        //     }
-        // }
+
+        //// Small int fast path
+        //if (_useSmallInt && IsInt32)
+        //{
+        //    var intKey = Unsafe.As<TId, int>(ref key);
+        //    if ((uint)intKey < SmallSize)
+        //    {
+        //        return TryGetOrAddSmallIntValue(intKey, newValue);
+        //    }
+        //}
 
         // Hash table path
         if (!TryAddHash(key, out var slotIndex))
@@ -441,28 +430,24 @@ public sealed class IdentityMap<TId> : IIdentityMap where TId : notnull
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public bool TryGetValue(TId key, out object? value)
     {
-        // NOTE: SmallInt path DISABLED for deserializer value lookup.
-        // The 512KB _smallValues sparse array causes cache misses.
-        // Hash table has better cache locality.
-        
-        // // Small int fast path - bitmap check first (cache-friendly, 512 bytes)
-        // if (_useSmallInt && IsInt32)
-        // {
-        //     var intKey = Unsafe.As<TId, int>(ref key);
-        //     if ((uint)intKey < SmallSize && _smallBitmap != null)
-        //     {
-        //         var wordIdx = intKey >> 6;
-        //         var bit = 1UL << (intKey & 63);
-        //         if ((_smallBitmap[wordIdx] & bit) != 0)
-        //         {
-        //             // Bitmap says seen - value is valid
-        //             value = _smallValues![intKey];
-        //             return true;
-        //         }
-        //         value = null;
-        //         return false;
-        //     }
-        // }
+        //// Small int fast path - bitmap check first (cache-friendly, 512 bytes)
+        //if (_useSmallInt && IsInt32)
+        //{
+        //    var intKey = Unsafe.As<TId, int>(ref key);
+        //    if ((uint)intKey < SmallSize && _smallBitmap != null)
+        //    {
+        //        var wordIdx = intKey >> 6;
+        //        var bit = 1UL << (intKey & 63);
+        //        if ((_smallBitmap[wordIdx] & bit) != 0)
+        //        {
+        //            // Bitmap says seen - return value if exists
+        //            value = _smallValues?[intKey];
+        //            return value != null;
+        //        }
+        //        value = null;
+        //        return false;
+        //    }
+        //}
 
         // Hash table path
         if (_buckets == null)