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,

crates/oa-desktop/src/behavior/state_view.rs

@@ -141,12 +141,16 @@ pub fn view<'a>(app: &'a App, machine: Id, mut out: Column<'a, Message>) -> Elem
             label: format!("{} · {}", p.named(element), p.elements[&element].kind()),
         })
         .collect::<Vec<_>>();
+    // Keep the optional picker in its own stable slot. Inserting it as a
+    // sibling before the canvas would replace the positional Iced focus tree.
+    let missing_spacing = if missing.is_empty() { 0.0_f32 } else { 8.0 };
+    let mut missing_controls = Column::new();
     if !missing.is_empty() {
         let position = Position {
             x: (48. - state.pan.x) / state.zoom,
             y: (90. - state.pan.y) / state.zoom,
         };
-        out = out.push(
+        missing_controls = missing_controls.push(
             pick_list(missing, None::<Choice>, move |c| {
                 event(Event::Place {
                     context,
@@ -173,13 +177,20 @@ pub fn view<'a>(app: &'a App, machine: Id, mut out: Column<'a, Message>) -> Elem
     .width(Fill)
     .height(Fill)
     .into();
-    out = out.push(crate::diagram::focus::wrap(
-        canvas.map(event),
-        context,
-        crate::app::diagram_removal::focus_enabled(app),
-        app.busy,
-        Message::DiagramTraverse,
-    ));
+    out = out.push(
+        column![
+            missing_controls,
+            crate::diagram::focus::wrap(
+                canvas.map(event),
+                context,
+                crate::app::diagram_removal::focus_enabled(app),
+                app.busy,
+                Message::DiagramTraverse,
+            )
+        ]
+        .spacing(missing_spacing)
+        .height(Fill),
+    );
     let base: Element<'_, Message> = container(out.spacing(8))
         .padding(14)
         .width(Fill)