fix(layers): push undo for transparency edits

LayerTransparencyEdit applied without begin/commit_layer_undo, so the edit was permanent while every sibling arm is undoable. Mirrors the color arm inside the non-empty guard. Test: layer_transparency_edit_pushes_undo asserts the entry plus undo-restores (RED first). Full suite: 1991 passed / 0 failed / 25 ignored.

src/app/update/command.rs

@@ -4656,6 +4656,37 @@ mod layer_name_target_tests {
             .collect();
         assert_eq!(before, after, "unknown name must change nothing");
     }
+
+    #[test]
+    fn layer_transparency_edit_pushes_undo() {
+        // #43: every sibling layer arm pushes an undo entry; transparency must too.
+        let mut app = OpenCADStudio::new_for_test();
+        app.automation_op(r#"{"op":"new"}"#);
+        let i = app.active_tab;
+        app.finish_pending_history(i);
+        let before = app.tabs[i].history.undo_stack.len();
+        let _ = app.update(Message::LayerTransparencyEdit("0".to_string(), "50".to_string()));
+        assert_eq!(
+            app.tabs[i].history.undo_stack.len(),
+            before + 1,
+            "transparency edit must push an undo entry like its siblings"
+        );
+        let panel = app.tabs[i]
+            .layers
+            .layers
+            .iter()
+            .find(|l| l.name == "0")
+            .expect("layer 0 in panel");
+        assert_eq!(panel.transparency, 50);
+        app.undo_active_tab();
+        let panel = app.tabs[i]
+            .layers
+            .layers
+            .iter()
+            .find(|l| l.name == "0")
+            .expect("layer 0 in panel");
+        assert_eq!(panel.transparency, 0, "undo must restore transparency");
+    }
 }
 
 #[cfg(test)]

src/app/update/mod.rs

@@ -3717,23 +3717,25 @@ impl OpenCADStudio {
                 // Apply the edited transparency to every selected layer (#236).
                 if let Some(v) = val {
                     let targets = self.layer_row_action_targets(i, idx);
-                    for name in &targets {
-                        if let Some(layer) = self.tabs[i].scene.document.layers.get_mut(name) {
-                            layer.transparency =
-                                codec::types::Transparency::from_percent(v as f64 / 100.0);
-                        }
-                        if let Some(pl) = self.tabs[i]
-                            .layers
-                            .layers
-                            .iter_mut()
-                            .find(|l| &l.name == name)
-                        {
-                            pl.transparency = v;
-                        }
-                    }
                     if !targets.is_empty() {
+                        let undo = self.begin_layer_undo(i, "LAYER TRANSPARENCY", &targets);
+                        for name in &targets {
+                            if let Some(layer) = self.tabs[i].scene.document.layers.get_mut(name) {
+                                layer.transparency =
+                                    codec::types::Transparency::from_percent(v as f64 / 100.0);
+                            }
+                            if let Some(pl) = self.tabs[i]
+                                .layers
+                                .layers
+                                .iter_mut()
+                                .find(|l| &l.name == name)
+                            {
+                                pl.transparency = v;
+                            }
+                        }
                         self.tabs[i].scene.invalidate_layer_dependencies(&targets);
                         self.tabs[i].dirty = true;
+                        self.commit_layer_undo(i, undo);
                     }
                 }
                 Task::none()