diff -r f3ab28ed22e5 -r ffa983c223c1 ui/cocoa/MainWindow.m
--- a/ui/cocoa/MainWindow.m	Mon Oct 13 21:31:58 2025 +0200
+++ b/ui/cocoa/MainWindow.m	Tue Oct 14 09:45:44 2025 +0200
@@ -129,7 +129,9 @@
             [vbox.trailingAnchor constraintEqualToAnchor:content.trailingAnchor],
             [vbox.bottomAnchor constraintEqualToAnchor:content.bottomAnchor],
         ]];
-        uic_object_push_container(obj, ui_create_container(obj, vbox));
+        UiContainerX *container = ui_create_container(obj, vbox);
+        vbox.container = container;
+        uic_object_push_container(obj, container);
     }
     _topOffset = top;
     
@@ -347,6 +349,7 @@
     
     // create a vertical stackview as default container
     BoxContainer *vbox = [[BoxContainer alloc] init:NSUserInterfaceLayoutOrientationVertical spacing:args->spacing];
+    vbox.container = ui_create_container(obj, vbox);
     //GridLayout *vbox = [[GridLayout alloc] init];
     vbox.translatesAutoresizingMaskIntoConstraints = false;
     [sidebar addSubview:vbox];
@@ -356,7 +359,7 @@
         [vbox.trailingAnchor constraintEqualToAnchor:sidebar.trailingAnchor],
         [vbox.bottomAnchor constraintEqualToAnchor:sidebar.bottomAnchor]
     ]];
-    uic_object_push_container(obj, ui_create_container(obj, vbox));
+    uic_object_push_container(obj, vbox.container);
     
     return NULL;
 }
@@ -365,6 +368,7 @@
     MainWindow *window = (__bridge MainWindow*)obj->wobj;
     BoxContainer *vbox = [[BoxContainer alloc] init:NSUserInterfaceLayoutOrientationVertical spacing:0];
     //GridLayout *vbox = [[GridLayout alloc] init];
+    vbox.container = ui_create_container(obj, vbox);
     vbox.translatesAutoresizingMaskIntoConstraints = false;
     [panel addSubview:vbox];
     [NSLayoutConstraint activateConstraints:@[
@@ -373,7 +377,7 @@
         [vbox.trailingAnchor constraintEqualToAnchor:panel.trailingAnchor],
         [vbox.bottomAnchor constraintEqualToAnchor:panel.bottomAnchor],
     ]];
-    uic_object_push_container(obj, ui_create_container(obj, vbox));
+    uic_object_push_container(obj, vbox.container);
     return (__bridge void*)vbox;
 }