diff --git a/Libraries/Esiur/Data/TruTypeDef.cs b/Libraries/Esiur/Data/TruTypeDef.cs
index 404854d..681c9ee 100644
--- a/Libraries/Esiur/Data/TruTypeDef.cs
+++ b/Libraries/Esiur/Data/TruTypeDef.cs
@@ -89,48 +89,20 @@ namespace Esiur.Data
             if (TypeDef is RemoteTypeDef remoteTypeDef)
             {
                 if (connection.RemoteDomain == remoteTypeDef.Domain)
-                {
                     // this is local in respect to the connection, send the remote typdef id.
-                    if (Nullable)
-                        rt.AddUInt8(0x80 | (byte)TruIdentifier.LocalType8);
-                    else
-                        rt.AddUInt8((byte)TruIdentifier.LocalType8);
-
-                    rt.AddUInt8((byte)remoteTypeDef.Id);
-                }
+                    WriteTypeReference(rt, isLocal: true, Nullable, remoteTypeDef.Id);
                 else
-                {
                     // this is remote in respect to the connection and the local typedef id is used.
-                    if (Nullable)
-                        rt.AddUInt8(0x80 | (byte)TruIdentifier.RemoteType8);
-                    else
-                        rt.AddUInt8((byte)TruIdentifier.RemoteType8);
-
-                    rt.AddUInt8((byte)remoteTypeDef.LocalTypeDefId);
-                }
+                    WriteTypeReference(rt, isLocal: false, Nullable, remoteTypeDef.LocalTypeDefId);
             }
             else if (TypeDef is LocalTypeDef localTypeDef)
             {
                 if (connection == null)
-                {
                     // if there is no connection, we assume it's local.
-                    if (Nullable)
-                        rt.AddUInt8(0x80 | (byte)TruIdentifier.LocalType8);
-                    else
-                        rt.AddUInt8((byte)TruIdentifier.LocalType8);
-
-                    rt.AddUInt8((byte)localTypeDef.Id);
-                }
+                    WriteTypeReference(rt, isLocal: true, Nullable, localTypeDef.Id);
                 else
-                {
                     // this is remote, unless the connection is to self @TODO: solve for this state.
-                    if (Nullable)
-                        rt.AddUInt8(0x80 | (byte)TruIdentifier.RemoteType8);
-                    else
-                        rt.AddUInt8((byte)TruIdentifier.RemoteType8);
-
-                    rt.AddUInt8((byte)localTypeDef.Id);
-                }
+                    WriteTypeReference(rt, isLocal: false, Nullable, localTypeDef.Id);
             }
             else
                 throw new NotImplementedException();
@@ -138,6 +110,45 @@ namespace Esiur.Data
             return rt.ToArray();
         }
 
+        // Picks the narrowest Local/RemoteType{8,16,32,64} identifier that fits `id`,
+        // matching the widths Tru.Parse already knows how to read.
+        // Internal (rather than private) so it can be unit-tested directly without
+        // needing a real LocalTypeDef/Warehouse registration for every width tier.
+        internal static void WriteTypeReference(BinaryList rt, bool isLocal, bool nullable, ulong id)
+        {
+            TruIdentifier identifier;
+
+            if (id <= byte.MaxValue)
+                identifier = isLocal ? TruIdentifier.LocalType8 : TruIdentifier.RemoteType8;
+            else if (id <= ushort.MaxValue)
+                identifier = isLocal ? TruIdentifier.LocalType16 : TruIdentifier.RemoteType16;
+            else if (id <= uint.MaxValue)
+                identifier = isLocal ? TruIdentifier.LocalType32 : TruIdentifier.RemoteType32;
+            else
+                identifier = isLocal ? TruIdentifier.LocalType64 : TruIdentifier.RemoteType64;
+
+            rt.AddUInt8((byte)((nullable ? 0x80 : 0) | (byte)identifier));
+
+            switch (identifier)
+            {
+                case TruIdentifier.LocalType8:
+                case TruIdentifier.RemoteType8:
+                    rt.AddUInt8((byte)id);
+                    break;
+                case TruIdentifier.LocalType16:
+                case TruIdentifier.RemoteType16:
+                    rt.AddUInt16((ushort)id);
+                    break;
+                case TruIdentifier.LocalType32:
+                case TruIdentifier.RemoteType32:
+                    rt.AddUInt32((uint)id);
+                    break;
+                default:
+                    rt.AddUInt64(id);
+                    break;
+            }
+        }
+
         public override Tru ToNullable()
         {
             throw new NotImplementedException();
diff --git a/Libraries/Esiur/Data/Types/TypeDefInfo.cs b/Libraries/Esiur/Data/Types/TypeDefInfo.cs
index 5d6ffe5..111209d 100644
--- a/Libraries/Esiur/Data/Types/TypeDefInfo.cs
+++ b/Libraries/Esiur/Data/Types/TypeDefInfo.cs
@@ -64,6 +64,7 @@ public class TypeDefInfo : IndexedStructure
             Version = definition.Version,
             Id = definition.Id,
             Name = definition.Name,
+            Namespace = (definition as LocalTypeDef)?.DefinedType?.Namespace,
             Kind = definition.Kind,
             Parent = definition.ParentTypeId,
             Usage = definition.Usage,
diff --git a/Tests/Unit/TypeDefInfoSerializationTests.cs b/Tests/Unit/TypeDefInfoSerializationTests.cs
index 7e6f472..a510f27 100644
--- a/Tests/Unit/TypeDefInfoSerializationTests.cs
+++ b/Tests/Unit/TypeDefInfoSerializationTests.cs
@@ -127,4 +127,70 @@ public class TypeDefInfoSerializationTests
         Assert.Equal(TruIdentifier.String, Assert.Single(parsed.Events!).ArgumentType.Identifier);
         Assert.Equal(100, Convert.ToInt32(Assert.Single(parsed.Constants!).Value));
     }
+
+    [Theory]
+    [InlineData(0ul, TruIdentifier.LocalType8, 1)]
+    [InlineData(255ul, TruIdentifier.LocalType8, 1)]
+    [InlineData(256ul, TruIdentifier.LocalType16, 2)]
+    [InlineData(65535ul, TruIdentifier.LocalType16, 2)]
+    [InlineData(65536ul, TruIdentifier.LocalType32, 4)]
+    [InlineData(4294967295ul, TruIdentifier.LocalType32, 4)]
+    [InlineData(4294967296ul, TruIdentifier.LocalType64, 8)]
+    public void WriteTypeReference_SelectsNarrowestSufficientWidth(ulong id, TruIdentifier expectedIdentifier, int expectedIdBytes)
+    {
+        var rt = new BinaryList();
+        TruTypeDef.WriteTypeReference(rt, isLocal: true, nullable: false, id);
+        var bytes = rt.ToArray();
+
+        Assert.Equal(1 + expectedIdBytes, bytes.Length);
+        Assert.Equal((byte)expectedIdentifier, bytes[0]);
+
+        ulong roundTripped = expectedIdBytes switch
+        {
+            1 => bytes[1],
+            2 => bytes.GetUInt16(1, Endian.Little),
+            4 => bytes.GetUInt32(1, Endian.Little),
+            _ => bytes.GetUInt64(1, Endian.Little),
+        };
+        Assert.Equal(id, roundTripped);
+    }
+
+    [Fact]
+    public void WriteTypeReference_NullableAndRemote_SetHeaderBitsCorrectly()
+    {
+        var rt = new BinaryList();
+        TruTypeDef.WriteTypeReference(rt, isLocal: false, nullable: true, 42ul);
+        var bytes = rt.ToArray();
+
+        Assert.Equal((byte)(0x80 | (byte)TruIdentifier.RemoteType8), bytes[0]);
+        Assert.Equal(42, bytes[1]);
+    }
+
+    [Fact]
+    public void TypeDefInfo_FromTypeDef_PopulatesNamespaceFromDefinedType()
+    {
+        var typeDef = new LocalTypeDef(typeof(TruTypeDefTestRecord), Warehouse.Default);
+        var info = TypeDefInfo.FromTypeDef(typeDef);
+
+        Assert.Equal(typeof(TruTypeDefTestRecord).Namespace, info.Namespace);
+        Assert.False(string.IsNullOrEmpty(info.Namespace));
+    }
+
+    [Fact]
+    public void TruTypeDef_Compose_LocalTypeDefWithoutConnection_RoundTrips()
+    {
+        var typeDef = new LocalTypeDef(typeof(TruTypeDefTestRecord), Warehouse.Default);
+        var tru = new TruTypeDef(false, typeDef);
+
+        var bytes = tru.Compose(null);
+        var result = Tru.Parse(bytes, 0, Warehouse.Default);
+
+        Assert.Equal((uint)bytes.Length, result.Size);
+        var parsed = Assert.IsType<TruTypeDef>(result.Value);
+        Assert.Equal(typeDef.Id, parsed.TypeDef!.Id);
+    }
+}
+
+public sealed class TruTypeDefTestRecord : IRecord
+{
 }