fix(dock): centralize transactional tear-off logic and fix build break

src/Editor/Ghost.Editor/App.xaml.cs

@@ -53,6 +53,50 @@ public partial class App : Application
         }
     }
 
+    /// <summary>
+    /// Attempts to tear off a tab into a new window.
+    /// </summary>
+    /// <param name="sourceItems">The collection to remove the item from.</param>
+    /// <param name="tabItem">The item to tear off.</param>
+    /// <param name="onSuccess">Optional callback after successful tear-off.</param>
+    /// <returns>A result indicating success or failure.</returns>
+    internal static Result TryTearOffTab(System.Collections.IList sourceItems, object tabItem, Action? onSuccess = null)
+    {
+        int originalIndex = sourceItems.IndexOf(tabItem);
+        if (originalIndex == -1)
+        {
+            return Result.Failure("Item not found in source collection.");
+        }
+
+        object? originalSelection = null;
+        // Try to capture selection if the source is a DockPanelNode or similar
+        // For now, we'll just handle the collection mutation.
+
+        try
+        {
+            sourceItems.Remove(tabItem);
+
+            try
+            {
+                CreateAndShowDockWindow(tabItem);
+                onSuccess?.Invoke();
+                return Result.Success();
+            }
+            catch (Exception ex)
+            {
+                // Rollback
+                sourceItems.Insert(originalIndex, tabItem);
+                Logger.LogError(ex);
+                return Result.Failure($"Failed to create tear-off window: {ex.Message}");
+            }
+        }
+        catch (Exception ex)
+        {
+            Logger.LogError(ex);
+            return Result.Failure($"Failed to remove item from source: {ex.Message}");
+        }
+    }
+
     /// <summary>
     /// Creates, registers, and shows a new DockWindow for a torn-off tab.
     /// </summary>