feat(blocks): wire Stretch actions and independent reference evaluation

Author a native Stretch action from a Linear, Polar or XY parameter, a two-corner stretch frame, an object selection and a marker. Preview and retain its frame in BEDIT, with selectable and movable action markers.

Freeze line and planar lightweight-polyline vertex bindings, preserve curved-segment height, move wholly selected objects, and evaluate independent saved INSERTs from their definition. Retain native DWG/DXF data, copied-reference isolation and undo/redo.

Validate with synthetic frame, topology, parameter, history, Test Block, drawing-reference, COPY and roundtrip regressions: 340 block tests pass (6 existing opt-in ignored), plus 41 dock and 27 viewport tests. Other entity types, Polar Stretch, custom multipliers and chaining remain unsupported.

src/app/dock/tests.rs

@@ -1244,6 +1244,27 @@ fn block_actions_palette_controls_require_compatible_parameters_and_start_comman
     });
 }
 
+#[test]
+fn block_actions_stretch_palette_requires_distance_parameter() {
+    with_stack(|| {
+        let mut app = authoring_app();
+        let _ = app.dispatch_command("BAUTHORPALETTE");
+        app.authoring_palette_tab = crate::ui::window::authoring_palettes::Tab::Actions;
+        let point = authoring_control(&app, "authoring-tool-stretch-action");
+        authoring_click(&mut app, point);
+        assert!(app.tabs[app.active_tab].active_cmd.is_none());
+        let _ = app.run_command_line("BPARAMETER LINEAR 0,0 10,0 5,2");
+        let point = authoring_control(&app, "authoring-tool-stretch-action");
+        authoring_click(&mut app, point);
+        assert!(app.tabs[app.active_tab]
+            .active_cmd
+            .as_ref()
+            .unwrap()
+            .prompt()
+            .contains("Stretch"));
+    });
+}
+
 #[test]
 fn block_actions_rotate_flip_palette_requires_matching_parameters() {
     with_stack(|| {

src/app/dock/view.rs

@@ -415,6 +415,7 @@ impl OpenCADStudio {
                     self.action_error(Some(crate::scene::block_actions::Kind::Scale)),
                     self.action_error(Some(crate::scene::block_actions::Kind::Rotate)),
                     self.action_error(Some(crate::scene::block_actions::Kind::Flip)),
+                    self.action_error(Some(crate::scene::block_actions::Kind::Stretch)),
                 )
             }
             crate::ui::dock::PanelId::BlockPalette => {