Preserve DateTime.Kind in ContinuationToken serialization

Author: pwelter34

src/Arbiter.Services/ContinuationToken.cs

@@ -204,7 +204,7 @@ public static (T1, T2) Parse<T1, T2>(string token)
     }
 
     /// <summary>
-    /// Parses a continuation token and extracts three values.
+    /// Parsing a continuation token and extracts three values.
     /// </summary>
     /// <typeparam name="T1">The type of the first value.</typeparam>
     /// <typeparam name="T2">The type of the second value.</typeparam>
@@ -235,7 +235,7 @@ private static int EstimateSize<T>(T value)
         {
             bool => 2,
             byte => 2,
-            DateTime => 9,
+            DateTime => 10,
             DateTimeOffset => 11,
             decimal => 17,
             double => 9,
@@ -396,16 +396,23 @@ private static int WriteDateTime(Span<byte> buffer, DateTime value)
         buffer[0] = (byte)TypeMarker.DateTime;
 
         BinaryPrimitives.WriteInt64LittleEndian(buffer[1..], value.Ticks);
+        
+        // Store DateTime.Kind to preserve it during round-trip
+        // 0 = Unspecified, 1 = Utc, 2 = Local
+        buffer[9] = (byte)value.Kind;
 
-        return 9;
+        return 10;
     }
 
     private static DateTime ReadDateTime(ReadOnlySpan<byte> buffer, ref int position)
     {
         var ticks = BinaryPrimitives.ReadInt64LittleEndian(buffer[position..]);
         position += 8;
+        
+        // Read DateTime.Kind to restore the original kind
+        var kind = (DateTimeKind)buffer[position++];
 
-        return new DateTime(ticks);
+        return new DateTime(ticks, kind);
     }
 
     private static int WriteDateTimeOffset(Span<byte> buffer, DateTimeOffset value)

test/Arbiter.Services.Tests/ContinuationTokenTests.cs

@@ -202,10 +202,37 @@ public void RoundTrip_WithDateTime_PreservesValue()
         }
     }
 
+    [Test]
+    public void RoundTrip_WithDateTime_PreservesKind()
+    {
+        // Arrange
+        var testValues = new[]
+        {
+            new DateTime(2024, 1, 15, 10, 30, 45, DateTimeKind.Utc),
+            new DateTime(2024, 1, 15, 10, 30, 45, DateTimeKind.Local),
+            new DateTime(2024, 1, 15, 10, 30, 45, DateTimeKind.Unspecified),
+            DateTime.UtcNow,
+            DateTime.Now,
+            DateTime.MinValue,
+            DateTime.MaxValue
+        };
+
+        foreach (var value in testValues)
+        {
+            // Act
+            var token = ContinuationToken.Create(value);
+            var result = ContinuationToken.Parse<DateTime>(token);
+
+            // Assert
+            result.Should().Be(value);
+            result.Kind.Should().Be(value.Kind, $"DateTime.Kind should be preserved for value {value}");
+        }
+    }
+
     [Test]
     public void RoundTrip_WithDateTimeOffset_PreservesValue()
     {
-        // Arrange - Test values with UTC offset (zero) which round-trip correctly
+        // Arrange
         var testValues = new[]
         {
             DateTimeOffset.MinValue,