fix(dock): improve mutation engine safety and revert public surface expansion

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.

src/Editor/Ghost.Editor.Core/Controls/Internal/Docking/DockMutationEngine.cs

@@ -1,4 +1,3 @@
-using Ghost.Editor.Core.Controls.Internal.Docking;
 using Microsoft.UI.Xaml.Controls;
 
 namespace Ghost.Editor.Core.Controls.Internal.Docking;
@@ -6,7 +5,7 @@ namespace Ghost.Editor.Core.Controls.Internal.Docking;
 /// <summary>
 /// Provides methods for mutating the docking layout tree.
 /// </summary>
-public static class DockMutationEngine
+internal static class DockMutationEngine
 {
     /// <summary>
     /// Applies the tree mutation for a drop operation.
@@ -14,6 +13,14 @@ public static class DockMutationEngine
     /// <returns>True if the mutation was applied; otherwise, false.</returns>
     public static bool TryApplyDropMutation(DockGroupNode root, DockPanelNode targetNode, DockPanelNode sourceNode, object item, DockPosition position)
     {
+        if (position == DockPosition.None) return false;
+
+        // Validate ancestry
+        if (!IsDescendantOf(root, targetNode) || !IsDescendantOf(root, sourceNode))
+        {
+            return false;
+        }
+
         if (position == DockPosition.Center)
         {
             if (!sourceNode.Items.Remove(item)) return false;
@@ -139,4 +146,15 @@ public static class DockMutationEngine
             }
         }
     }
+
+    private static bool IsDescendantOf(DockGroupNode root, DockNode node)
+    {
+        var current = node.Parent;
+        while (current != null)
+        {
+            if (ReferenceEquals(current, root)) return true;
+            current = current.Parent;
+        }
+        return false;
+    }
 }