Restore the clipboard when a command fails and is rolled back (#1167)

Fixes #1100

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/lib.rs

@@ -966,6 +966,8 @@ impl Session {
             ds.end_preview();
         }
         let before = self.ds().ok().map(|d| (d.doc.clone(), d.selection.clone(), d.page, d.uid));
+        // Cut and copy write the clipboard before a later check can refuse the command.
+        let clipboard_before = self.clipboard.clone();
         let result = guard::run(id, || (spec.run)(self, params))
             .and_then(|v| self.check_instance_structure(id, &before).map(|()| v))
             .and_then(|v| self.check_preview(id, &before).map(|()| v))
@@ -998,6 +1000,7 @@ impl Session {
                     ds.selection = sel;
                     ds.page = page;
                 }
+                self.clipboard = clipboard_before;
             }
         }
         result

crates/engine/src/version_preview_tests.rs

@@ -97,3 +97,22 @@ fn preview_keeps_the_unsaved_state_and_saving_saves_the_document() {
     assert_eq!(count(&s), three);
     let _ = std::fs::remove_dir_all(&dir);
 }
+
+#[test]
+fn a_refused_cut_leaves_the_clipboard_as_it_was() {
+    let mut s = Session::new();
+    let a = rect(&mut s, 0.0);
+    s.execute("file.saveVersion", &json!({"name": "One"})).unwrap();
+    let b = rect(&mut s, 20.0);
+    s.execute("edit.copy", &json!({"ids": [b]})).unwrap();
+    let roots = |s: &Session| s.clipboard.nodes.iter().map(|(r, _)| *r).collect::<Vec<_>>();
+    assert_eq!(roots(&s), vec![b]);
+    let source = s.clipboard.source.clone().unwrap();
+    let depth = s.undo_depth();
+    s.execute("version.preview", &json!({"index": 0})).unwrap();
+    let err = s.execute("edit.cut", &json!({"ids": [a]})).unwrap_err();
+    assert!(matches!(err, EngineError::Disabled(..)), "{err:?}");
+    assert_eq!(roots(&s), vec![b], "failed edit.cut changed the clipboard");
+    assert!(std::sync::Arc::ptr_eq(s.clipboard.source.as_ref().unwrap(), &source));
+    assert_eq!(s.undo_depth(), depth, "history untouched");
+}