Fix #2091 copy a named layer even when a mask is selected

edit.copy {"layer": id} copied the selected mask instead of the layer:
the mask branch only checked for `layers`, but `layer` is an explicit
target too.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/edit.rs

@@ -313,8 +313,9 @@ fn copy(s: &mut Session, p: &Value) -> Result<Value> {
     if p.get("layers").is_none() && !super::effect::selected_effects(s).is_empty() {
         return s.execute("effect.copy", json!({}));
     }
-    // Masks selected → copy them (not their layer), for Paste onto other layers (#2091).
-    if p.get("layers").is_none() {
+    // Masks selected → copy them (not their layer), for Paste onto other layers (#2091), unless
+    // a layer is named explicitly.
+    if p.get("layers").is_none() && p.get("layer").is_none_or(Value::is_null) {
         let masks = super::prop_groups::copy_masks(s);
         if !masks.is_empty() {
             clear_clipboards(s);

crates/engine/src/tests/menu_cmds.rs

@@ -1993,3 +1993,16 @@ fn paste_masks_skips_locked_layers() {
     assert!(s.execute("edit.paste", json!({})).is_err());
     assert_eq!(layer(&s, b).masks().unwrap().groups().count(), 0);
 }
+
+#[test]
+fn copy_with_an_explicit_layer_ignores_the_selected_mask() {
+    let mut s = comp();
+    let a = solid(&mut s, "#ff0000");
+    s.execute("layer.select", json!({"layers": [a]})).unwrap();
+    s.execute("layer.addMask", json!({})).unwrap();
+    let mask = layer(&s, a).masks().unwrap().groups().next().unwrap().uid;
+    s.execute("prop.select", json!({"layer": a, "prop": mask})).unwrap();
+    s.execute("edit.copy", json!({"layer": a})).unwrap();
+    assert_eq!(s.state.clipboard.len(), 1, "the named layer is copied");
+    assert!(s.state.mask_clipboard.is_empty());
+}