fix(ui): accept toolbar drops across panel labels and gaps (#454)

ROADMAP.md

@@ -287,6 +287,8 @@ PCB / Package, Render, Animation, Simulation, Manufacture/CAM, Drawings.
   record their coordinate frame; legacy wires migrate from known provenance without changing
   coordinates. Broken legacy links with missing provenance can require explicit refresh or relink.
   See [occurrence workflows](docs/occurrence-workflows.md).
+- Toolbar drops on panel labels, gaps and margins append commands with insertion feedback;
+  button drops keep insert-before ordering.
 - Parameters and Configurations have distinct actions in the SOLID toolbar's CONFIGURE panel.
   Parameters opens the user/model variable editor; Configurations opens the configuration table.
   Configure remains available in the panel dropdown.

crates/ui-egui/src/toolbar.rs

@@ -572,12 +572,6 @@ pub fn toolbar(app: &mut SolveApp, ui: &mut egui::Ui) {
             let free_x = bx + drawn as f32 * 40.0;
             let free = Rect::from_min_size(pos2(free_x, top + 2.0), vec2((px + width - 4.0 - free_x).max(8.0), 38.0));
             let fresp = ui.interact(free, ui.id().with(("panel_free", panel)), if collapsed { Sense::click() } else { Sense::hover() });
-            if fresp.dnd_hover_payload::<ToolbarDrag>().is_some() {
-                painter.line_segment([pos2(free.left(), free.top() + 2.0), pos2(free.left(), free.bottom() - 2.0)], Stroke::new(2.0, t.accent));
-            }
-            if let Some(d) = fresp.dnd_release_payload::<ToolbarDrag>() {
-                drop = Some((d.id, *panel, None));
-            }
             let mut opened = false;
             if collapsed {
                 // One button: the panel's first command's icon over a caret; it opens the
@@ -691,6 +685,20 @@ pub fn toolbar(app: &mut SolveApp, ui: &mut egui::Ui) {
             if lresp.clicked() {
                 ui.ctx().data_mut(|d| d.insert_temp(egui::Id::new("sc_panel_open"), popup_id));
             }
+            // Labels, gaps and margins append; actual buttons keep their insert-before target.
+            // Respect the current layer so a dropdown covering the panel is not a drop target.
+            let panel_rect = Rect::from_min_max(pos2(px, top + 2.0), pos2(px + width, r.bottom()));
+            let over_button = ui
+                .input(|input| input.pointer.hover_pos())
+                .is_some_and(|p| (0..drawn).any(|i| Rect::from_min_size(pos2(bx + i as f32 * 40.0, top + 2.0), vec2(38.0, 38.0)).contains(p)));
+            if !over_button && ui.rect_contains_pointer(panel_rect) && egui::DragAndDrop::payload::<ToolbarDrag>(ui.ctx()).is_some() {
+                painter.line_segment([pos2(px + width - 4.0, top + 4.0), pos2(px + width - 4.0, top + 38.0)], Stroke::new(2.0, t.accent));
+                if ui.input(|input| input.pointer.any_released())
+                    && let Some(d) = egui::DragAndDrop::take_payload::<ToolbarDrag>(ui.ctx())
+                {
+                    drop = Some((d.id, *panel, None));
+                }
+            }
             let open = ui.ctx().data(|d| d.get_temp::<egui::Id>(egui::Id::new("sc_panel_open"))) == Some(popup_id);
             if open {
                 let cmds = if collapsed { menu_commands(&cmds, &shown) } else { cmds.clone() };
@@ -1319,3 +1327,44 @@ mod dropdown_tests {
         assert!(menu.contains(*at), "the focused last row is out of view: {at:?} in {menu:?}");
     }
 }
+
+#[cfg(test)]
+mod panel_drop_tests {
+    use super::*;
+
+    #[test]
+    fn panel_label_gap_and_margins_append_while_buttons_insert_before() {
+        for target in ["label", "gap", "left margin", "right margin", "button"] {
+            let mut h = crate::scenario::Harness::new();
+            h.step(&json!({"click":{"handle":"panel:SOLID:CREATE"}})).unwrap();
+            let label = crate::scenario::handle_at("panel:SOLID:CREATE").unwrap();
+            let destination = match target {
+                "gap" => label - vec2(0.0, 10.0),
+                "left margin" => pos2(label.x - panel_width(4) / 2.0 + 1.0, label.y - 30.0),
+                "right margin" => pos2(label.x + panel_width(4) / 2.0 - 1.0, label.y - 30.0),
+                "button" => crate::scenario::handle_at("button:solid.extrude").unwrap(),
+                _ => label,
+            };
+            h.step(&json!({"drag":[{"handle":"dropdown:solid.cylinder"}, [destination.x,destination.y]],"steps":12})).unwrap();
+            h.step(&json!({"key":"Escape"})).unwrap();
+            let order = if target == "button" {
+                json!(["button:sketch.create", "button:solid.cylinder", "button:solid.extrude", "button:solid.revolve", "button:solid.sweep"])
+            } else {
+                json!(["button:sketch.create", "button:solid.extrude", "button:solid.revolve", "button:solid.sweep", "button:solid.cylinder"])
+            };
+            h.step(&json!({"expect":{"handle_order":order,"tool":null,"dialog":null,"errors":0}})).unwrap();
+            assert!(h.app.session.doc.features.is_empty(), "{target}: pinning must not run the command");
+            h.step(&json!({"restart":"close"})).unwrap();
+            h.step(&json!({"expect":{"handle_order":order}})).unwrap();
+        }
+    }
+
+    #[test]
+    fn panel_label_drop_moves_a_button_between_panels() {
+        let mut h = crate::scenario::Harness::new();
+        h.step(&json!({"drag":[{"handle":"button:solid.extrude"},{"handle":"panel:SOLID:MODIFY"}],"steps":12})).unwrap();
+        h.step(&json!({"expect":{"handle_order":["button:solid.fillet","button:solid.chamfer","button:solid.scale","button:solid.extrude"],"tool":null,"dialog":null,"errors":0}})).unwrap();
+        h.step(&json!({"restart":"close"})).unwrap();
+        h.step(&json!({"expect":{"handle_order":["button:solid.scale","button:solid.extrude"]}})).unwrap();
+    }
+}

crates/ui-egui/tests/scenarios/s50_toolbar_panel_drops.json

@@ -0,0 +1,21 @@
+[
+ {"note":"#333: dropping a dropdown command on a panel label appends it; moving between labels keeps the chosen order after restart."},
+ {"click":{"handle":"panel:SOLID:CREATE"}},
+ {"drag":[{"handle":"dropdown:solid.cylinder"},{"handle":"panel:SOLID:CREATE"}],"steps":12},
+ {"key":"Escape"},
+ {"expect":{"handle_order":["button:solid.sweep","button:solid.cylinder"],"dialog":null,"tool":null,"errors":0}},
+ {"click":{"handle":"panel:SOLID:CREATE"}},
+ {"drag":[{"handle":"dropdown:solid.torus"},{"handle":"panel:SOLID:MODIFY"}],"steps":12},
+ {"key":"Escape"},
+ {"expect":{"handle_order":["button:solid.scale","button:solid.torus"],"dialog":null,"tool":null,"errors":0}},
+ {"drag":[{"handle":"button:solid.torus"},{"handle":"panel:SOLID:CREATE"}],"steps":12},
+ {"expect":{"handle_order":["button:solid.cylinder","button:solid.torus"]}},
+ {"restart":"close"},
+ {"expect":{"handle_order":["button:solid.sweep","button:solid.cylinder","button:solid.torus"],"errors":0}},
+ {"call":"ui.resize","params":{"width":640,"height":720}},
+ {"click":{"handle":"panel:SOLID:CREATE"}},
+ {"drag":[{"handle":"dropdown:solid.box"},{"handle":"panel:SOLID:CREATE"}],"steps":12},
+ {"key":"Escape"},
+ {"call":"ui.resize","params":{"width":1600,"height":1000}},
+ {"expect":{"handle_order":["button:solid.torus","button:solid.box"],"tool":null,"dialog":null,"errors":0}}
+]

docs/book/src/guide/ui-tour.md

@@ -7,7 +7,9 @@
   undo history, selection and camera).
 - **Toolbar.** The workspace switcher (DESIGN) sits on the left. The tabs (SOLID, SURFACE,
   SHEET METAL, PLASTIC, UTILITIES, and SKETCH while you sketch) hold panels of commands. Click a
-  panel's name for all its commands.
+  panel's name for all its commands. Drag a command from the dropdown onto a panel's label
+  or empty space to append it; the insertion line shows its destination. Drop onto an existing
+  button to insert before it. Buttons can also move between panels, and the layout is saved.
 - **Browser** (left). The design as a tree: document settings and units, named views, the
   origin, bodies, sketches, construction planes, canvases, joints and components. The eye shows or
   hides an item, a component's radio button makes it the active component, and right-clicking any