Keep state canvas focus tree stable when placement controls change

crates/oa-desktop/src/app/diagram_removal_tests.rs

@@ -1046,6 +1046,16 @@ async fn mounted_state_delete_uses_state_placement_and_preserves_architecture_pl
     assert_eq!(app.selected, state);
     assert_eq!(app.behavior.diagram.placement, Some(node));
     let before = app.document.snapshot();
+    assert!(crate::behavior::state_edit::unplaced(app.project(), diagram).is_empty());
+    let owner = app.state_context().unwrap();
+    let focused = |mounted: &mut Mounted, app: &App| {
+        mounted.geometry(app).focused.iter().any(|(id, _, focused)| {
+            *focused
+                && id.as_ref()
+                    == Some(&iced::advanced::widget::Id::from("diagram-keyboard-owner"))
+        })
+    };
+    assert!(focused(&mut mounted, &app));
     let messages = delete(&mut mounted, &mut app, false).await;
     assert!(messages.iter().any(|message| matches!(
         message,
@@ -1053,13 +1063,35 @@ async fn mounted_state_delete_uses_state_placement_and_preserves_architecture_pl
     )));
     assert!(!app.project().contains(node));
     assert!(app.project().contains(architecture_node) && app.project().contains(state));
+    assert_eq!(
+        crate::behavior::state_edit::unplaced(app.project(), diagram),
+        vec![state]
+    );
+    mounted.settle(&mut app).await;
+    let hidden = app.state_context().unwrap();
+    assert_eq!(
+        (hidden.document, hidden.diagram, hidden.epoch),
+        (owner.document, owner.diagram, owner.epoch),
+        "hiding one placement does not change the logical canvas owner"
+    );
+    assert!(
+        focused(&mut mounted, &app),
+        "showing the unplaced-element picker must retain the actual canvas focus tree"
+    );
     consistent(&app);
     let directory = tempfile::tempdir().unwrap();
     let path = directory.path().join(&app.document.bundle().entry);
     save_with_busy_view(&mut mounted, &mut app, &path).await;
+    assert!(focused(&mut mounted, &app), "Save retains the same owner");
     let task = app.update(Message::Undo);
     mounted.perform(&mut app, task).await;
     assert_eq!(app.document.bundle(), &before.bundle);
+    assert!(crate::behavior::state_edit::unplaced(app.project(), diagram).is_empty());
+    mounted.settle(&mut app).await;
+    assert!(
+        focused(&mut mounted, &app),
+        "Undo removes the picker without replacing the actual canvas focus tree"
+    );
     delete(&mut mounted, &mut app, true).await;
     assert_eq!(
         app.delete_target.as_ref().unwrap().snapshot.request.object,