docking: Floating::stack is public, and four-way handles take the pointer only

Floating::stack builds a window from groups stacked top to bottom, so an
app's own stacked layouts migrate without building the split chain. The
four-way handle no longer takes keyboard focus: it has no label or key
action, and the two dividers it joins take arrow keys.

crates/ui/src/docking/floating_tests.rs

@@ -38,7 +38,7 @@ fn workspace() -> Layout<u32> {
             second: Box::new(tabs(&[0], 0)),
         }),
         floating: vec![
-            Floating::stack(vec![Group::new(vec![5], 0), Group::new(vec![6, 7], 1)], [300.0, 80.0, 240.0, 300.0]),
+            Floating::stack(vec![Group::new(vec![5], 0), Group::new(vec![6, 7], 1)], [300.0, 80.0, 240.0, 300.0]).unwrap(),
             Floating::single(vec![8], 0, [560.0, 300.0, 200.0, 200.0]),
         ],
     }
@@ -678,7 +678,7 @@ fn undock_panel_group_floats_one_group_of_a_floating_window() {
     use egui_kittest::{Harness, kittest::Queryable};
     let stacked = || Layout {
         root: Some(tabs(&[1], 0)),
-        floating: vec![Floating::stack(vec![Group::new(vec![5], 0), Group::new(vec![6, 7], 0)], [300.0, 80.0, 300.0, 400.0])],
+        floating: vec![Floating::stack(vec![Group::new(vec![5], 0), Group::new(vec![6, 7], 0)], [300.0, 80.0, 300.0, 400.0]).unwrap()],
     };
     type State = (Content, Layout<u32>, Vec<Action<u32>>);
     let mut h = Harness::builder().with_size(vec2(800.0, 600.0)).build_ui_state(

crates/ui/src/docking/group_tests.rs

@@ -551,7 +551,7 @@ fn drag_bar_menu_has_the_group_items_and_opens_from_the_keyboard() {
 
 #[test]
 fn a_group_dragged_out_of_a_floating_stack_tears_out_alone() {
-    let stack = Floating::stack(vec![Group::new(vec![5], 0), Group::new(vec![6, 7], 1)], [80.0, 70.0, 300.0, 400.0]);
+    let stack = Floating::stack(vec![Group::new(vec![5], 0), Group::new(vec![6, 7], 1)], [80.0, 70.0, 300.0, 400.0]).unwrap();
     let layout = Layout { root: Some(tabs(&[1], 0)), floating: vec![stack] };
     let mut d = Driver::new(layout);
     let from = d.rect("drag-bar", 6).center();

crates/ui/src/docking/iconic_tests.rs

@@ -283,7 +283,7 @@ fn hit_rects_cover_every_gesture_source() {
         first: Box::new(Node::Tabs { panels: vec![0], active: 0 }),
         second: Box::new(stack),
     };
-    let window = Floating::stack(vec![Group::new(vec![12], 0), Group::new(vec![13], 0)], [500.0, 60.0, 220.0, 300.0]);
+    let window = Floating::stack(vec![Group::new(vec![12], 0), Group::new(vec![13], 0)], [500.0, 60.0, 220.0, 300.0]).unwrap();
     let layout = Layout {
         root: Some(Node::Split { axis: SplitAxis::Horizontal, size: SplitSize::FixedFirst(200.0), first: Box::new(dock), second: Box::new(frames) }),
         floating: vec![window],

crates/ui/src/docking/model.rs

@@ -87,10 +87,10 @@ impl<P> Floating<P> {
         tree_panels(&self.root).into_iter()
     }
 
-    /// Groups stacked top to bottom, as a v1 layout stored them.
-    #[cfg(test)]
-    pub(crate) fn stack(groups: Vec<Group<P>>, rect: [f32; 4]) -> Self {
-        Self::new(super::dock_model::stack_tree(groups).expect("a group"), rect)
+    /// Groups stacked top to bottom, as a v1 layout stored them: each group over a vertical
+    /// split of the ones below it, sized by their heights. `None` without groups.
+    pub fn stack(groups: Vec<Group<P>>, rect: [f32; 4]) -> Option<Self> {
+        super::dock_model::stack_tree(groups).map(|root| Self::new(root, rect))
     }
 
     /// The window's groups, first to last.

crates/ui/src/docking/model_tests.rs

@@ -23,7 +23,7 @@ pub(super) fn docked() -> Layout<u32> {
         Node::Dock { side: Side::End, columns: vec![Column::new(vec![g(&[2, 3], 1), g(&[4], 0)], 180.0), Column::new(vec![g(&[5], 0)], 120.0)] };
     Layout {
         root: Some(hsplit(SplitSize::FixedSecond(300.0), middle, dock)),
-        floating: vec![Floating::stack(vec![g(&[6, 7], 1), g(&[8], 0)], [100.0, 100.0, 300.0, 400.0])],
+        floating: vec![Floating::stack(vec![g(&[6, 7], 1), g(&[8], 0)], [100.0, 100.0, 300.0, 400.0]).unwrap()],
     }
 }
 
@@ -213,7 +213,7 @@ fn restore_into_a_column_group_seam_and_new_column_round_trips() {
     let start = Node::Dock { side: Side::Start, columns: vec![Column::new(vec![g(&[10], 0)], 200.0)] };
     let original = Layout {
         root: Some(hsplit(SplitSize::FixedFirst(200.0), start, hsplit(SplitSize::FixedSecond(300.0), tabs(&[1], 0), end))),
-        floating: vec![Floating::stack(vec![g(&[6], 0), Group { height: Some(90.0), ..g(&[7], 0) }], [10.0, 10.0, 200.0, 300.0])],
+        floating: vec![Floating::stack(vec![g(&[6], 0), Group { height: Some(90.0), ..g(&[7], 0) }], [10.0, 10.0, 200.0, 300.0]).unwrap()],
     };
     original.validate().unwrap();
     // 4: the seam between [2, 3] and [9]; 9: below [4]; 5: a new column after A; 10: alone in
@@ -415,7 +415,7 @@ mod serde_tests {
         let plain = Floating::single(vec![4u32, 5], 1, rect);
         assert_eq!(serde_json::to_value(&plain).unwrap(), json!({"panels": [4, 5], "active": 1, "rect": rect}));
         let minimized = Floating { minimized: true, ..Floating::single(vec![4u32], 0, rect) };
-        let stacked = Floating::stack(vec![g(&[4], 0), g(&[5], 0)], rect);
+        let stacked = Floating::stack(vec![g(&[4], 0), g(&[5], 0)], rect).unwrap();
         let native = Floating { native: Some(rect), ..Floating::single(vec![4u32], 0, rect) };
         for window in [minimized, stacked, native] {
             let value = serde_json::to_value(&window).unwrap();

crates/ui/src/docking/render/mod.rs

@@ -295,7 +295,8 @@ impl<P: Clone + Eq + Hash + Debug + Send + Sync + 'static> Renderer<'_, P> {
                 None => self.id.with(("intersection", outer, inner_layout)),
                 Some((panel, _)) => self.id.with(("window-intersection", panel, outer, inner_layout)),
             };
-            let response = ui.interact(hit, id, Sense::drag());
+            // Pointer only: each of the two dividers it joins already takes keyboard focus.
+            let response = ui.interact(hit, id, Sense::DRAG);
             self.register_interaction(ui.ctx(), id);
             if response.hovered() || response.dragged() {
                 ui.ctx().set_cursor_icon(CursorIcon::Move);

docs/ui-docking.md

@@ -39,8 +39,9 @@ their sides.
 
 A `Floating` window holds a tree like the docked layout's (`root`: splits, tab groups and
 accordions, no docks), a rect, an optional native-window rect and `minimized`.
-`Floating::single` makes a window with one group and `Floating::new` one with a tree; `panels()`
-and `contains()` read it. Saved layouts keep loading: a window stored as one group (v1) or as a
+`Floating::single` makes a window with one group, `Floating::new` one with a tree, and
+`Floating::stack` one with groups stacked top to bottom (a vertical split sized by the groups'
+heights, as an app's own stacked layouts migrate); `panels()` and `contains()` read it. Saved layouts keep loading: a window stored as one group (v1) or as a
 stack of groups loads as that group or as a vertical split of the stacked groups, sized by their
 heights.