fix(dock): decouple DockLayout from window creation and remove redundant state

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

@@ -297,18 +297,17 @@ public sealed partial class DockLayout : Control
         return tabView;
     }
 
-    private object? _draggedItem;
     private DockPosition _currentDropPosition = DockPosition.None;
 
     private record DockDragPayload(object Item, DockPanelNode SourceNode);
 
+    public event EventHandler<TabTornOffEventArgs>? TabTornOff;
+
     private void TabView_TabDragStarting(Microsoft.UI.Xaml.Controls.TabView sender, Microsoft.UI.Xaml.Controls.TabViewTabDragStartingEventArgs args)
     {
-        _draggedItem = args.Item;
-
-        if (_draggedItem != null && sender.Tag is DockPanelNode sourceNode)
+        if (args.Item != null && sender.Tag is DockPanelNode sourceNode)
         {
-            var payload = new DockDragPayload(_draggedItem, sourceNode);
+            var payload = new DockDragPayload(args.Item, sourceNode);
             args.Data.Properties.Add(DRAG_PROPERTY_DOCK_TAB, payload); // Identify our drag
         }
     }
@@ -316,7 +315,7 @@ public sealed partial class DockLayout : Control
     private void TabView_DragOver(object sender, DragEventArgs e)
     {
         if (e.DataView.Properties.TryGetValue(DRAG_PROPERTY_DOCK_TAB, out var payloadObj) && 
-            payloadObj is DockDragPayload payload &&
+            payloadObj is DockDragPayload &&
             sender is FrameworkElement targetElement)
         {
             e.AcceptedOperation = global::Windows.ApplicationModel.DataTransfer.DataPackageOperation.Move;
@@ -349,7 +348,6 @@ public sealed partial class DockLayout : Control
     private void ClearDragOperationState()
     {
         ClearOverlayState();
-        _draggedItem = null;
     }
 
     private void UpdateDropOverlay(FrameworkElement targetElement, DockPosition position)
@@ -441,6 +439,9 @@ public sealed partial class DockLayout : Control
 
                     if (result.IsSuccess)
                     {
+                        // Raise event to let the host handle window creation
+                        TabTornOff?.Invoke(this, new TabTornOffEventArgs(args.Item, sourceNode));
+                        
                         DockMutationEngine.CleanupEmptyNodes(sourceNode);
                     }
                     else

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

@@ -10,8 +10,14 @@ public sealed class TabTornOffEventArgs : EventArgs
     /// </summary>
     public object TabContent { get; }
 
-    public TabTornOffEventArgs(object tabContent)
+    /// <summary>
+    /// Gets the source node the tab is being torn off from.
+    /// </summary>
+    public object SourceNode { get; }
+
+    public TabTornOffEventArgs(object tabContent, object sourceNode)
     {
         TabContent = tabContent;
+        SourceNode = sourceNode;
     }
 }

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

@@ -17,5 +17,13 @@ internal sealed partial class DockWindow : WindowEx
         rootGroup.AddChild(panel);
         
         PART_DockLayout.Root = rootGroup;
+        PART_DockLayout.TabTornOff += OnTabTornOff;
+    }
+
+    private void OnTabTornOff(object? sender, TabTornOffEventArgs e)
+    {
+        App.CreateAndShowDockWindow(e.TabContent);
     }
 }
+
+}

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

@@ -45,7 +45,11 @@ internal sealed partial class EngineEditorWindow : WindowEx
         {
             var result = TabTearOffService.TryTearOffTab(list, args.Item, sender);
             
-            if (!result.IsSuccess)
+            if (result.IsSuccess)
+            {
+                App.CreateAndShowDockWindow(args.Item);
+            }
+            else
             {
                 Logger.LogWarning($"Tab tear-off failed: {result.Message}");
             }

src/Editor/Ghost.Editor/View/Windows/TabTearOffService.cs

@@ -33,7 +33,8 @@ internal static class TabTearOffService
 
             try
             {
-                App.CreateAndShowDockWindow(tabItem);
+                // We no longer create the window here to decouple the service from the app shell.
+                // The caller is responsible for window creation (e.g. via an event handler).
                 return Result.Success();
             }
             catch (Exception ex)
@@ -49,10 +50,10 @@ internal static class TabTearOffService
                 catch (Exception rollbackEx)
                 {
                     Logger.LogError(rollbackEx);
-                    return Result.Failure($"Failed to create tear-off window and rollback failed: {ex.Message}. Rollback error: {rollbackEx.Message}");
+                    return Result.Failure($"Failed to tear off tab and rollback failed: {ex.Message}. Rollback error: {rollbackEx.Message}");
                 }
                 
-                return Result.Failure($"Failed to create tear-off window: {ex.Message}");
+                return Result.Failure($"Failed to tear off tab: {ex.Message}");
             }
         }
         catch (Exception ex)