feat(select): Ctrl+click picks one segment of a polyline

Ctrl+click on a polyline selects the segment under the cursor (again to
drop it); several segments can be picked. Only the picked segments are
highlighted, and MOVE, ROTATE, SCALE and MIRROR then change just their
vertices, so the neighbouring segments stretch to follow. Any other
selected objects are transformed whole as before.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/app/command_driver/transform.rs

@@ -24,6 +24,9 @@ impl OpenCADStudio {
         // component so each member keeps its own dimensions. Other
         // transforms retain their selected-object behavior.
         let pending = self.begin_undo(i, label, handles.len(), true);
+        let handles = self.tabs[i]
+            .scene
+            .transform_picked_segments(&handles, &transform);
         self.tabs[i].scene.transform_entities(&handles, &transform);
         self.apply_inferred_constraints(i, &handles);
         self.tabs[i].dirty = true;

src/app/update/viewport.rs

@@ -4014,6 +4014,39 @@ impl OpenCADStudio {
             }
         }
 
+        // Ctrl+click on a polyline picks the segment under the cursor; the
+        // edit commands then move just that part.
+        if self.ctrl_down && self.tabs[i].active_cmd.is_none() {
+            let (view_rot, eye) = {
+                let cam = self.tabs[i].scene.camera.borrow();
+                (cam.view_proj_rte(bounds), cam.eye())
+            };
+            let wires = self.tabs[i].scene.hit_test_wires();
+            let hit = scene::pick::hit_test::click_hit(
+                p,
+                &*wires,
+                view_rot,
+                eye,
+                bounds,
+                self.tabs[i].scene.document.header.lineweight_display,
+                crate::ui::overlay::pick_box_aperture_px(self.pick_box),
+                &self.tabs[i].scene.draw_depth_map(),
+            )
+            .and_then(Scene::handle_from_wire_name)
+            .filter(|handle| !self.tabs[i].scene.is_layer_locked(*handle));
+            drop(wires);
+            let point = self.tabs[i].last_cursor_world;
+            if hit.is_some_and(|handle| self.tabs[i].scene.toggle_sub_segment(handle, point)) {
+                self.tabs[i]
+                    .scene
+                    .selection
+                    .borrow_mut()
+                    .clear_left_selection_gesture();
+                self.refresh_properties();
+                return Task::none();
+            }
+        }
+
         // Ctrl+click on a composite solid picks the solid of it under the
         // cursor — the one the Properties palette and grips then edit.
         if self.ctrl_down