feat(props): uniform-scale checkbox for block references

A selected INSERT's Geometry section gains a "Uniform scale" box
(#427): while the three factors are equal it is checked and the panel
shows a single Scale row that writes all three axes; unchecking
expands the familiar Scale X/Y/Z rows without touching the values
(remembered per entity), and re-checking collapses Y/Z onto X as an
undoable CHPROP step.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/app/mod.rs

@@ -250,6 +250,10 @@ pub(super) struct OpenCADStudio {
     video_thumbs: std::collections::HashMap<String, iced::widget::image::Handle>,
     /// True while the boot-time playlist fetch is still in flight.
     videos_loading: bool,
+    /// Block references whose properties panel shows per-axis Scale X/Y/Z even
+    /// though the three factors are currently equal — the user unchecked the
+    /// "Uniform scale" box for them (#427). Keyed by entity handle.
+    props_asym_scale: std::collections::HashSet<u64>,
     /// Which Start-page section is shown when the page is too narrow for all
     /// three side by side and falls back to a tab bar.
     start_section: StartSection,
@@ -2201,6 +2205,7 @@ impl OpenCADStudio {
             videos: Vec::new(),
             video_thumbs: std::collections::HashMap::new(),
             videos_loading: false,
+            props_asym_scale: std::collections::HashSet::new(),
             start_section: StartSection::default(),
             props_expanded: false,
             history_content: iced::widget::text_editor::Content::new(),

src/app/properties.rs

@@ -139,6 +139,51 @@ impl OpenCADStudio {
                         }
                     }
 
+                    // Uniform-scale checkbox for block references (#427):
+                    // while the three scale factors are equal (and the user
+                    // hasn't opted into per-axis editing) the panel shows one
+                    // Scale row plus a checked "Uniform scale" box; unchecking
+                    // expands the familiar Scale X/Y/Z rows.
+                    if let acadrust::EntityType::Insert(ins) = entity {
+                        let eq = (ins.x_scale() - ins.y_scale()).abs() < 1e-12
+                            && (ins.x_scale() - ins.z_scale()).abs() < 1e-12;
+                        let uniform =
+                            eq && !self.props_asym_scale.contains(&handle.value());
+                        for section in sections.iter_mut() {
+                            let Some(xi) =
+                                section.props.iter().position(|p| p.field == "x_scale")
+                            else {
+                                continue;
+                            };
+                            let toggle = crate::scene::model::object::Property {
+                                label: "Uniform scale".into(),
+                                field: "ins_uniform",
+                                value: crate::scene::model::object::PropValue::BoolToggle {
+                                    field: "ins_uniform",
+                                    value: uniform,
+                                },
+                            };
+                            if uniform {
+                                section
+                                    .props
+                                    .retain(|p| p.field != "y_scale" && p.field != "z_scale");
+                                let xi = section
+                                    .props
+                                    .iter()
+                                    .position(|p| p.field == "x_scale")
+                                    .unwrap_or(xi.min(section.props.len()));
+                                section.props[xi] = crate::entities::common::edit_prop(
+                                    "Scale",
+                                    "u_scale",
+                                    ins.x_scale(),
+                                );
+                                section.props.insert(xi, toggle);
+                            } else {
+                                section.props.insert(xi, toggle);
+                            }
+                        }
+                    }
+
                     // In named plot-style mode (PSTYLEMODE=1) the Plot style row
                     // picks a named style from the drawing's plot style table. In
                     // the color-dependent mode it stays read-only (the object's

src/app/update/mod.rs

@@ -2622,6 +2622,32 @@ impl OpenCADStudio {
                                     crate::scene::view::dispatch::toggle_invisible(entity);
                                 }
                             }
+                            // Uniform-scale checkbox on a block reference
+                            // (#427): checking collapses Y/Z onto X; unchecking
+                            // only switches the panel to per-axis rows.
+                            "ins_uniform" => {
+                                let scales = match self.tabs[i].scene.document.get_entity(handle) {
+                                    Some(acadrust::EntityType::Insert(ins)) => {
+                                        Some((ins.x_scale(), ins.y_scale(), ins.z_scale()))
+                                    }
+                                    _ => None,
+                                };
+                                let Some((sx, sy, sz)) = scales else { continue };
+                                let eq = (sx - sy).abs() < 1e-12 && (sx - sz).abs() < 1e-12;
+                                let checked =
+                                    eq && !self.props_asym_scale.contains(&handle.value());
+                                if checked {
+                                    self.props_asym_scale.insert(handle.value());
+                                } else {
+                                    self.props_asym_scale.remove(&handle.value());
+                                    if let Some(acadrust::EntityType::Insert(ins)) =
+                                        self.tabs[i].scene.document.get_entity_mut(handle)
+                                    {
+                                        ins.set_y_scale(sx);
+                                        ins.set_z_scale(sx);
+                                    }
+                                }
+                            }
                             _ => {
                                 if let Some(entity) =
                                     self.tabs[i].scene.document.get_entity_mut(handle)

src/entities/insert.rs

@@ -94,6 +94,12 @@ fn apply_geom_prop(ins: &mut Insert, field: &str, value: &str) {
                 acadrust::Entity::translate(att, delta);
             }
         }
+        // Single Scale row shown while "Uniform scale" is checked (#427).
+        "u_scale" => {
+            ins.set_x_scale(v);
+            ins.set_y_scale(v);
+            ins.set_z_scale(v);
+        }
         "x_scale" => ins.set_x_scale(v),
         "y_scale" => ins.set_y_scale(v),
         "z_scale" => ins.set_z_scale(v),