feat(area): add object and aggregate modes

Mesh-backed measurements need cached surface metrics. Keep shared loop collection available in web builds.

src/app/command_driver.rs

@@ -1789,6 +1789,14 @@ impl OpenCADStudio {
                 self.restore_pre_cmd_tangent();
                 self.command_line.push_output(&msg);
             }
+            CmdResult::ReportMeasurement(msg) => {
+                self.tabs[i].snap_result = None;
+                self.tabs[i].scene.clear_preview_wire();
+                self.command_line.push_output(&msg);
+                if let Some(prompt) = self.tabs[i].active_cmd.as_ref().map(|c| c.prompt()) {
+                    self.command_line.push_info(&prompt);
+                }
+            }
             CmdResult::AlignSelected {
                 handles,
                 src1,

src/app/update/viewport.rs

@@ -2710,11 +2710,20 @@ impl OpenCADStudio {
                         .map(|c| c.inject_before_entity_pick())
                         .unwrap_or(false);
                     if inject_first {
+                        let surface_area = self.tabs[i]
+                            .scene
+                            .meshes
+                            .get(&handle)
+                            .or_else(|| self.tabs[i].scene.block_meshes.get(&handle))
+                            .map(|mesh| mesh.metrics.surface_area);
                         if let Some(entity) =
                             self.tabs[i].scene.document.get_entity(handle).cloned()
                         {
                             if let Some(cmd) = self.tabs[i].active_cmd.as_mut() {
                                 cmd.inject_picked_entity(entity);
+                                if let Some(area) = surface_area {
+                                    cmd.inject_picked_surface_area(area);
+                                }
                             }
                         }
                     }