fix(dock): restore core docking behavior and fix build breaks

src/Editor/Ghost.Editor/View/Controls/DockLayout.cs

@@ -297,6 +297,128 @@ public sealed partial class DockLayout : Control
         return tabView;
     }
 
+    private object? _draggedItem;
+    private DockPanelNode? _sourceNode;
+    private DockPosition _currentDropPosition = DockPosition.None;
+
+    private void TabView_TabDragStarting(Microsoft.UI.Xaml.Controls.TabView sender, Microsoft.UI.Xaml.Controls.TabViewTabDragStartingEventArgs args)
+    {
+        _draggedItem = args.Item;
+        _sourceNode = sender.Tag as DockPanelNode;
+        args.Data.Properties.Add(DRAG_PROPERTY_DOCK_TAB, _draggedItem); // Identify our drag
+    }
+
+    private void TabView_DragOver(object sender, DragEventArgs e)
+    {
+        if (e.DataView.Properties.ContainsKey(DRAG_PROPERTY_DOCK_TAB) && sender is FrameworkElement targetElement)
+        {
+            e.AcceptedOperation = global::Windows.ApplicationModel.DataTransfer.DataPackageOperation.Move;
+
+            var position = e.GetPosition(targetElement);
+            var newPosition = DockMath.CalculateDockPosition(targetElement.ActualWidth, targetElement.ActualHeight, position.X, position.Y, DROP_EDGE_THRESHOLD);
+
+            if (newPosition != _currentDropPosition)
+            {
+                _currentDropPosition = newPosition;
+                UpdateDropOverlay(targetElement, _currentDropPosition);
+            }
+        }
+    }
+
+    private void TabView_DragLeave(object sender, DragEventArgs e)
+    {
+        ClearOverlayState();
+    }
+
+    private void ClearOverlayState()
+    {
+        if (_dropTargetOverlay != null)
+        {
+            _dropTargetOverlay.Visibility = Visibility.Collapsed;
+        }
+        _currentDropPosition = DockPosition.None;
+    }
+
+    private void ClearDragOperationState()
+    {
+        ClearOverlayState();
+        _draggedItem = null;
+        _sourceNode = null;
+    }
+
+    private void UpdateDropOverlay(FrameworkElement targetElement, DockPosition position)
+    {
+        if (_dropTargetOverlay == null) return;
+        if (position == DockPosition.None)
+        {
+            _dropTargetOverlay.Visibility = Visibility.Collapsed;
+            return;
+        }
+
+        var transform = targetElement.TransformToVisual(this);
+        var bounds = transform.TransformBounds(new global::Windows.Foundation.Rect(0, 0, targetElement.ActualWidth, targetElement.ActualHeight));
+
+        _dropTargetOverlay.Visibility = Visibility.Visible;
+        _dropTargetOverlay.Width = double.NaN;
+        _dropTargetOverlay.Height = double.NaN;
+
+        switch (position)
+        {
+            case DockPosition.Center:
+                _dropTargetOverlay.Margin = new Thickness(bounds.Left, bounds.Top, ActualWidth - bounds.Right, ActualHeight - bounds.Bottom);
+                break;
+            case DockPosition.Left:
+                _dropTargetOverlay.Margin = new Thickness(bounds.Left, bounds.Top, ActualWidth - (bounds.Left + bounds.Width / 2), ActualHeight - bounds.Bottom);
+                break;
+            case DockPosition.Right:
+                _dropTargetOverlay.Margin = new Thickness(bounds.Left + bounds.Width / 2, bounds.Top, ActualWidth - bounds.Right, ActualHeight - bounds.Bottom);
+                break;
+            case DockPosition.Top:
+                _dropTargetOverlay.Margin = new Thickness(bounds.Left, bounds.Top, ActualWidth - bounds.Right, ActualHeight - (bounds.Top + bounds.Height / 2));
+                break;
+            case DockPosition.Bottom:
+                _dropTargetOverlay.Margin = new Thickness(bounds.Left, bounds.Top + bounds.Height / 2, ActualWidth - bounds.Right, ActualHeight - bounds.Bottom);
+                break;
+        }
+    }
+
+    private void TabView_Drop(object sender, DragEventArgs e)
+    {
+        if (_dropTargetOverlay != null) _dropTargetOverlay.Visibility = Visibility.Collapsed;
+
+        if (_draggedItem == null || _sourceNode == null || !(sender is FrameworkElement targetElement) || !(targetElement.Tag is DockPanelNode targetNode))
+        {
+            ClearDragOperationState();
+            return;
+        }
+
+        if (_currentDropPosition == DockPosition.None)
+        {
+            ClearDragOperationState();
+            return;
+        }
+
+        if (_sourceNode == targetNode && _currentDropPosition == DockPosition.Center)
+        {
+            ClearDragOperationState();
+            return; // Reordering within same tab is handled natively by TabView
+        }
+
+        if (Root == null)
+        {
+            ClearDragOperationState();
+            return;
+        }
+
+        // 1. Execute mutation
+        if (DockMutationEngine.TryApplyDropMutation(Root, targetNode, _sourceNode, _draggedItem, _currentDropPosition))
+        {
+            DockMutationEngine.CleanupEmptyNodes(_sourceNode);
+        }
+
+        ClearDragOperationState();
+    }
+
     private void TabView_TabDroppedOutside(Microsoft.UI.Xaml.Controls.TabView sender, Microsoft.UI.Xaml.Controls.TabViewTabDroppedOutsideEventArgs args)
     {
         if (_sourceNode != null && _draggedItem != null)

src/Editor/Ghost.Editor/View/Windows/EngineEditorWindow.xaml.cs

@@ -41,9 +41,9 @@ internal sealed partial class EngineEditorWindow : WindowEx
     private void OnTabDroppedOutside(Microsoft.UI.Xaml.Controls.TabView sender, Microsoft.UI.Xaml.Controls.TabViewTabDroppedOutsideEventArgs args)
     {
         // For static tabs in EngineEditorWindow, we remove the item from TabItems
-        if (sender.TabItems.Contains(args.Item))
+        if (sender.TabItems is System.Collections.IList list && list.Contains(args.Item))
         {
-            var result = TabTearOffService.TryTearOffTab((System.Collections.IList)sender.TabItems, args.Item, sender);
+            var result = TabTearOffService.TryTearOffTab(list, args.Item, sender);
             
             if (!result.IsSuccess)
             {