fix(docking): prevent layout tree loss and enforce cross-layout ownership

src/Editor/Ghost.Editor/View/Controls/Docking/DockContainer.cs

@@ -47,6 +47,9 @@ public abstract class DockContainer : DockModule
     {
         ValidateChild(module);
 
+        if (module.Owner == null && module.Root != null && module.Root != this.Root)
+            throw new InvalidOperationException("Cannot insert a module that is the root of another layout. Detach it first.");
+
         if (index < 0 || index > _children.Count)
             throw new ArgumentOutOfRangeException(nameof(index));
 
@@ -94,6 +97,9 @@ public abstract class DockContainer : DockModule
         ArgumentNullException.ThrowIfNull(oldChild);
         ValidateChild(newChild);
 
+        if (newChild.Owner == null && newChild.Root != null && newChild.Root != this.Root)
+            throw new InvalidOperationException("Cannot insert a module that is the root of another layout. Detach it first.");
+
         if (oldChild == newChild) return;
 
         int index = _children.IndexOf(oldChild);

src/Editor/Ghost.Editor/View/Controls/Docking/DockingLayout.cs

@@ -104,12 +104,23 @@ public class DockingLayout : Control
                 {
                     // Root is not a container, or contains no groups. Wrap it.
                     var newGroup = new DockGroup();
+                    newGroup.AddChild(document);
+                    
                     if (RootModule is DockDocument existingDoc)
                     {
-                        RootModule = null; // Detach first
+                        RootModule = null;
                         newGroup.AddChild(existingDoc);
-                    }
                         RootModule = newGroup;
+                    }
+                    else
+                    {
+                        var oldRoot = RootModule;
+                        RootModule = null;
+                        var panel = new DockPanel();
+                        panel.AddChild(oldRoot);
+                        panel.AddChild(newGroup);
+                        RootModule = panel;
+                    }
                     targetGroup = newGroup;
                 }
             }