diff --git a/src/Editor/Ghost.Editor.Core/Controls/Internal/Docking/DockMath.cs b/src/Editor/Ghost.Editor.Core/Controls/Internal/Docking/DockMath.cs
index 6d87c55..ad49763 100644
--- a/src/Editor/Ghost.Editor.Core/Controls/Internal/Docking/DockMath.cs
+++ b/src/Editor/Ghost.Editor.Core/Controls/Internal/Docking/DockMath.cs
@@ -3,7 +3,7 @@ namespace Ghost.Editor.Core.Controls.Internal.Docking;
 /// <summary>
 /// Defines the possible dock positions for a drop operation.
 /// </summary>
-public enum DockPosition
+internal enum DockPosition
 {
     Center,
     Top,
@@ -16,7 +16,7 @@ public enum DockPosition
 /// <summary>
 /// Helper class for docking-related calculations.
 /// </summary>
-public static class DockMath
+internal static class DockMath
 {
     /// <summary>
     /// Calculates the dock position based on the relative position within a target element.
@@ -24,6 +24,12 @@ public static class DockMath
     /// </summary>
     public static DockPosition CalculateDockPosition(double width, double height, double x, double y, double threshold)
     {
+        // Guard against invalid inputs
+        if (width <= 0 || height <= 0) return DockPosition.None;
+        
+        // Clamp threshold to valid range [0, 0.5]
+        threshold = Math.Max(0, Math.Min(0.5, threshold));
+
         if (x < width * threshold) return DockPosition.Left;
         if (x > width * (1 - threshold)) return DockPosition.Right;
         if (y < height * threshold) return DockPosition.Top;
diff --git a/src/Editor/Ghost.Editor/View/Controls/DockLayout.cs b/src/Editor/Ghost.Editor/View/Controls/DockLayout.cs
index 94572db..99934da 100644
--- a/src/Editor/Ghost.Editor/View/Controls/DockLayout.cs
+++ b/src/Editor/Ghost.Editor/View/Controls/DockLayout.cs
@@ -324,16 +324,21 @@ public sealed partial class DockLayout : Control
 
     private void TabView_DragLeave(object sender, DragEventArgs e)
     {
-        ClearDragState();
+        ClearOverlayState();
     }
 
-    private void ClearDragState()
+    private void ClearOverlayState()
     {
         if (_dropTargetOverlay != null)
         {
             _dropTargetOverlay.Visibility = Visibility.Collapsed;
         }
         _currentDropPosition = DockPosition.None;
+    }
+
+    private void ClearDragOperationState()
+    {
+        ClearOverlayState();
         _draggedItem = null;
         _sourceNode = null;
     }
@@ -374,10 +379,9 @@ public sealed partial class DockLayout : Control
         }
     }
 
-    // Add a dummy TabView_Drop method so it compiles, we will implement it in Task 6
     private void TabView_Drop(object sender, DragEventArgs e)
     {
-        ClearDragState();
+        ClearDragOperationState();
     }
 
     protected override void OnApplyTemplate()
diff --git a/src/Test/Ghost.UnitTest/DockLayoutTest.cs b/src/Test/Ghost.UnitTest/DockLayoutTest.cs
index ab39bc3..f8f249c 100644
--- a/src/Test/Ghost.UnitTest/DockLayoutTest.cs
+++ b/src/Test/Ghost.UnitTest/DockLayoutTest.cs
@@ -59,4 +59,48 @@ public class DockLayoutTest
         var pos = DockMath.CalculateDockPosition(100, 100, 90, 90, THRESHOLD);
         Assert.AreEqual(DockPosition.Right, pos);
     }
+
+    [TestMethod]
+    public void TestCalculateDockPosition_Boundary_Left()
+    {
+        // x = 25 is exactly on the threshold. Current logic: x < 25 is Left, so 25 is Center.
+        var pos = DockMath.CalculateDockPosition(100, 100, 25, 50, THRESHOLD);
+        Assert.AreEqual(DockPosition.Center, pos);
+
+        pos = DockMath.CalculateDockPosition(100, 100, 24.9, 50, THRESHOLD);
+        Assert.AreEqual(DockPosition.Left, pos);
+    }
+
+    [TestMethod]
+    public void TestCalculateDockPosition_Boundary_Right()
+    {
+        // x = 75 is exactly on the threshold (100 * (1 - 0.25)). Current logic: x > 75 is Right, so 75 is Center.
+        var pos = DockMath.CalculateDockPosition(100, 100, 75, 50, THRESHOLD);
+        Assert.AreEqual(DockPosition.Center, pos);
+
+        pos = DockMath.CalculateDockPosition(100, 100, 75.1, 50, THRESHOLD);
+        Assert.AreEqual(DockPosition.Right, pos);
+    }
+
+    [TestMethod]
+    public void TestCalculateDockPosition_InvalidSize()
+    {
+        var pos = DockMath.CalculateDockPosition(0, 100, 50, 50, THRESHOLD);
+        Assert.AreEqual(DockPosition.None, pos);
+
+        pos = DockMath.CalculateDockPosition(100, -10, 50, 50, THRESHOLD);
+        Assert.AreEqual(DockPosition.None, pos);
+    }
+
+    [TestMethod]
+    public void TestCalculateDockPosition_ThresholdClamping()
+    {
+        // Threshold > 0.5 should be clamped to 0.5
+        var pos = DockMath.CalculateDockPosition(100, 100, 40, 50, 0.8);
+        Assert.AreEqual(DockPosition.Left, pos);
+
+        // Threshold < 0 should be clamped to 0
+        pos = DockMath.CalculateDockPosition(100, 100, 0.1, 50, -0.1);
+        Assert.AreEqual(DockPosition.Center, pos);
+    }
 }