Keep state canvas focus tree stable when placement controls change

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)