Character: Reset Panel closes only the undo group it opens

Reset Panel ended its undo step with end_undo_group, which closes the
open undo group of every document. An undo group open in another
document, such as an MCP batch, was closed by a reset in this one, and
inside an undo group already open in this document the reset closed
that group too.

Reset Panel now opens its own group only when the active document has
none open, and closes only that group. Inside an open undo group the
reset is part of that group's step.

crates/ui-egui/src/panels/character.rs

@@ -867,11 +867,15 @@ pub fn menu(app: &mut VectorcraftApp, ui: &mut Ui) {
 /// kerning, no baseline shift, 100% scales, no rotation, no underline or strikethrough, All Caps
 /// and Small Caps off, the normal position (neither superscript nor subscript), Roman Baseline
 /// character alignment, Proportional Metrics off and the Default digits, whether or not Show
-/// East Asian Options and Show Indic Options are on.
+/// East Asian Options and Show Indic Options are on. Inside an undo group that is already open,
+/// the reset is part of that group's step.
 fn reset_panel(app: &mut VectorcraftApp) {
     // Typing in progress stays an undo step of its own.
     end_typing(app);
-    app.session.begin_named_undo_group(Some("Reset Panel".into()));
+    let open = app.session.active().is_some_and(|st| st.undo_group.is_some());
+    if !open {
+        app.session.begin_named_undo_group(Some("Reset Panel".into()));
+    }
     let d = CharStyle::default();
     style(app, json!({"tracking": 0, "leading": "auto"}));
     format(
@@ -883,7 +887,11 @@ fn reset_panel(app: &mut VectorcraftApp) {
         }),
     );
     set_anti_alias(app, TypeAntiAlias::Sharp);
-    app.session.end_undo_group(false);
+    // Closes the active document's undo group only, so an undo group open in another document
+    // stays open.
+    if !open && let Some(st) = app.session.active_mut() {
+        st.undo_group = None;
+    }
 }
 
 #[cfg(test)]
@@ -1247,6 +1255,43 @@ mod tests {
         assert_eq!((method(&app, a), tracking(&app)), (TypeAntiAlias::Strong, Some(50.0)), "one undo step");
     }
 
+    /// Reset Panel closes only the undo group it opens: in an undo group that is already open,
+    /// the reset is part of that group's step, and an undo group open in another document stays
+    /// open, with that document's later edits part of its step.
+    #[test]
+    fn reset_panel_closes_only_its_own_undo_group() {
+        let mut app = VectorcraftApp::new(Session::new(), Default::default());
+        app.run("file.new", json!({"width": 300, "height": 200})).unwrap();
+        let a = app.run("text.create", json!({"x": 20, "y": 50, "text": "A"})).unwrap()["id"].clone();
+        let steps = |st: &vectorcraft_engine::DocState| (st.history.undo.len(), st.history.undo.last().map(|e| e.label.clone()));
+        // An undo group open in the same document (MCP `command_batch` with `atomic`).
+        app.run("edit.undoGroup.begin", json!({"label": "Batch"})).unwrap();
+        app.run("text.setFormat", json!({"id": a, "antiAlias": "crisp"})).unwrap();
+        reset_panel(&mut app);
+        assert!(app.session.active().unwrap().undo_group.is_some(), "the batch's undo group stays open");
+        app.run("text.setFormat", json!({"id": a, "antiAlias": "strong"})).unwrap();
+        app.run("edit.undoGroup.end", json!({})).unwrap();
+        let a_steps = steps(app.session.active().unwrap());
+        assert_eq!(a_steps.1, Some("Batch".to_string()), "the reset is part of the Batch step");
+        // An undo group open in another document.
+        app.run("edit.undoGroup.begin", json!({"label": "Batch"})).unwrap();
+        app.run("text.setFormat", json!({"id": a, "antiAlias": "none"})).unwrap();
+        let a_steps = steps(app.session.active().unwrap());
+        app.run("file.new", json!({"width": 300, "height": 200})).unwrap();
+        assert_eq!(app.session.active_index(), Some(1));
+        let b = app.run("text.create", json!({"x": 20, "y": 50, "text": "B"})).unwrap()["id"].clone();
+        app.run("select.set", json!({"ids": [b]})).unwrap();
+        let b_steps = steps(app.session.active().unwrap()).0;
+        reset_panel(&mut app);
+        assert_eq!(steps(app.session.active().unwrap()), (b_steps + 1, Some("Reset Panel".to_string())));
+        assert!(app.session.active().unwrap().undo_group.is_none());
+        assert!(app.session.documents()[0].undo_group.is_some(), "the other document's undo group stays open");
+        app.session.set_active(0);
+        app.run("text.setFormat", json!({"id": a, "antiAlias": "crisp"})).unwrap();
+        app.run("edit.undoGroup.end", json!({})).unwrap();
+        assert_eq!(steps(app.session.active().unwrap()), a_steps, "the later edit is part of the Batch step");
+    }
+
     /// Character Alignment and Proportional Metrics are in the panel menu with the East Asian
     /// options only (as Mojikumi Set and Top-to-Top Leading are in the Paragraph panel).
     #[test]