Symbols: a dragged 9-slice guide moves with Real-time Drawing off

With Performance > Real-time Drawing and Editing off, tool previews are
applied only on release. A ruler guide being dragged was already exempt;
a symbol's 9-slice guide, a symbol.options preview that sets only
nineSliceGuides, now is too, so the dotted guide follows the pointer
while it is dragged. The release still leaves one Symbol Options step.

crates/engine/src/tests/prefs.rs

@@ -1658,6 +1658,30 @@ fn real_time_drawing_off_still_shows_a_dragged_guide() {
     assert_eq!((s.doc().unwrap().doc.guides[0].pos, s.doc().unwrap().history.undo.last().map(|e| e.label.as_str())), (150.0, Some("Move Guide")));
 }
 
+/// With Real-time Drawing off, a 9-slice guide of the edited symbol moved with the Selection tool
+/// still moves while it is dragged, and the release leaves one Symbol Options undo step.
+#[test]
+fn real_time_drawing_off_still_shows_a_dragged_nine_slice_guide() {
+    let mut s = Session::new();
+    s.execute("file.new", &json!({"width": 400, "height": 400})).unwrap();
+    s.execute("shape.rectangle", &json!({"x": 100, "y": 100, "width": 100, "height": 100})).unwrap();
+    s.execute("symbol.new", &json!({"name": "Box", "nineSlice": true})).unwrap();
+    s.execute("symbol.edit", &json!({})).unwrap();
+    let v = ViewInfo::default();
+    s.select_tool("selection", v).unwrap();
+    set_pref(&mut s, "realTimeDrawing", json!(false));
+    let left = |s: &Session| s.doc().unwrap().doc.symbol_nine_slice("Box").unwrap().left;
+    assert_eq!(left(&s), 0.25);
+    let steps = s.doc().unwrap().history.undo.len();
+    s.pointer(&PointerEvent::new(PointerKind::Down, 125.0, 150.0), v).unwrap();
+    s.pointer(&PointerEvent::new(PointerKind::Drag, 110.0, 150.0), v).unwrap();
+    assert!((left(&s) - 0.1).abs() < 1e-9, "the guide moves while dragged: {}", left(&s));
+    s.pointer(&PointerEvent::new(PointerKind::Up, 110.0, 150.0), v).unwrap();
+    let d = s.doc().unwrap();
+    assert!((left(&s) - 0.1).abs() < 1e-9);
+    assert_eq!((d.history.undo.len(), d.history.undo.last().map(|e| e.label.as_str())), (steps + 1, Some("Symbol Options")));
+}
+
 /// Real-time Drawing turned on mid-drag still applies the deferred preview on commit.
 #[test]
 fn real_time_drawing_turned_on_mid_drag_still_commits_deferred_preview() {

crates/engine/src/tooling.rs

@@ -65,6 +65,13 @@ fn rgb(hex: &str, fallback: [u8; 3]) -> [u8; 3] {
     })
 }
 
+/// Whether a tool preview of `cmd` with params `p` sets only a symbol's 9-slice guides: a
+/// `symbol.options` whose params hold `nineSliceGuides` and nothing besides `name`.
+fn nine_slice_guide_preview(cmd: &str, p: &Value) -> bool {
+    cmd == "symbol.options"
+        && p.as_object().is_some_and(|m| m.contains_key("nineSliceGuides") && m.keys().all(|k| k == "name" || k == "nineSliceGuides"))
+}
+
 /// Requests from tools that only the frontend can fulfil.
 #[derive(Clone, Debug, PartialEq)]
 pub enum UiRequest {
@@ -784,8 +791,9 @@ impl Session {
                 Action::Preview(cmd, p) => {
                     // Performance › Real-time Drawing and Editing (#394): off, remember the latest
                     // params and apply them once on Commit instead of every move. A ruler guide
-                    // being dragged still shows: the guide is all there is to see (#4646).
-                    if !self.prefs.real_time_drawing && !matches!(cmd.as_str(), "guide.add" | "guide.move") {
+                    // being dragged still shows: the guide is all there is to see (#4646). So does a
+                    // symbol's 9-slice guide being dragged.
+                    if !self.prefs.real_time_drawing && !matches!(cmd.as_str(), "guide.add" | "guide.move") && !nine_slice_guide_preview(&cmd, &p) {
                         self.clear_deferred_overlay_cache();
                         let st = self.doc_mut()?;
                         if let Some(it) = &mut st.interaction {