fix(ui): persist the AutoSave preference across restarts

Closes #1901

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

crates/ui-egui/src/backstage.rs

@@ -969,9 +969,9 @@ fn options(app: &mut SheetApp, ui: &mut Ui) {
     }
     ui.add_space(18.0);
     section(ui, lang, "Options|Save");
-    let mut autosave = app.grid.autosave();
+    let mut autosave = app.ui.autosave;
     if ui.checkbox(&mut autosave, lang.tr("Save .xlsx workbooks automatically after every change")).changed() {
-        app.grid.toggle_autosave();
+        app.toggle_autosave();
     }
     let Some(calc) = app.session.active().map(|d| d.wb.calc.clone()) else { return };
     ui.add_space(18.0);

crates/ui-egui/src/grid.rs

@@ -119,7 +119,6 @@ pub struct GridState {
     pub glide: crate::selection_glide::SelectionGlide,
     pub last_click: Option<(CellRef, f64)>,
     pub hover_cell: Option<CellRef>,
-    pub autosave: bool,
     pub last_autosave: f64,
     pub last_border: String,
     pub last_fill: String,
@@ -179,15 +178,6 @@ impl WheelZoom {
     }
 }
 
-impl GridState {
-    pub fn autosave(&self) -> bool {
-        self.autosave
-    }
-    pub fn toggle_autosave(&mut self) {
-        self.autosave = !self.autosave;
-    }
-}
-
 /// Geometry of the grid for one frame (handles zoom and frozen panes).
 #[derive(Clone)]
 pub struct Geo {

crates/ui-egui/src/lib.rs

@@ -60,6 +60,9 @@ pub struct UiState {
     /// Enable AutoComplete for cell values (File ▸ Options ▸ Editing): typed text is completed
     /// from the one matching entry in the same column.
     pub autocomplete: bool,
+    /// AutoSave (the title-bar switch): save saved-to-file .xlsx workbooks shortly after every
+    /// change. A preference like the rest of this struct — it stays on across restarts (#1901).
+    pub autosave: bool,
     pub recent: Vec<String>,
     /// One-shot keytip request for a ribbon control: set when a keytip action resolves to
     /// [`keytips::Action::Control`], consumed (and cleared) by the control's render site.
@@ -103,6 +106,7 @@ impl Default for UiState {
             status_bar: true,
             animations: true,
             autocomplete: true,
+            autosave: false,
             recent: vec![],
             keytip_invoke: None,
             language: i18n::Language::En,
@@ -1128,6 +1132,12 @@ impl SheetApp {
         }
     }
 
+    /// Flip AutoSave (title-bar switch / Options ▸ Save). Persisted with the other UI
+    /// preferences, so it stays as the user left it across restarts (#1901).
+    pub fn toggle_autosave(&mut self) {
+        self.ui.autosave = !self.ui.autosave;
+    }
+
     /// Lays out the whole window.
     pub fn ui(&mut self, ui: &mut egui::Ui) {
         let ctx = ui.ctx().clone();
@@ -1190,7 +1200,7 @@ impl SheetApp {
         }
         self.perf.last = now;
         // AutoSave: save workbooks that have a file shortly after they change.
-        if self.grid.autosave
+        if self.ui.autosave
             && self.editor.is_none()
             && self.text_box_editor.is_none()
             && now - self.grid.last_autosave > 2000.0

crates/ui-egui/src/ribbon.rs

@@ -53,14 +53,14 @@ pub fn title_bar(app: &mut SheetApp, ui: &mut Ui) {
             ui.add_space(TITLE_LEFT_PAD);
             // AutoSave toggle (saves after each change when the workbook has a file).
             ui.label(egui::RichText::new("AutoSave").font(theme::ui_font(12.5)).color(t.text_dim));
-            let on = app.grid.autosave();
+            let on = app.ui.autosave;
             let (r, resp) = ui.allocate_exact_size(vec2(30.0, 16.0), Sense::click());
             ui.painter().rect_filled(r, 8.0, if on { t.accent } else { Color32::TRANSPARENT });
             ui.painter().rect_stroke(r, 8.0, Stroke::new(1.0, if on { t.accent } else { t.text_dim }), StrokeKind::Inside);
             let knob = if on { pos2(r.right() - 8.0, r.center().y) } else { pos2(r.left() + 8.0, r.center().y) };
             ui.painter().circle_filled(knob, 5.0, if on { Color32::WHITE } else { t.text_dim });
             if resp.on_hover_text("AutoSave: save after every change (workbooks saved to a file)").clicked() {
-                app.grid.toggle_autosave();
+                app.toggle_autosave();
             }
             ui.add_space(6.0);
             let __k = icon_button(ui, Icon::Home, t.text_dim, "Home", vec2(26.0, ch));

crates/ui-egui/tests/autosave_persist.rs

@@ -0,0 +1,26 @@
+//! #1901: AutoSave is a preference — it must survive a restart like the other UI settings.
+
+use gridcraft_engine::Session;
+use gridcraft_ui_egui::SheetApp;
+
+#[test]
+fn autosave_survives_a_restart() {
+    let mut app = SheetApp::new(Session::new(), Default::default());
+    assert!(!app.ui.autosave, "off by default");
+    app.toggle_autosave();
+    assert!(app.ui.autosave, "the toggle flips the persisted flag");
+    // What the desktop app writes to ui.json, and reads back on the next launch.
+    let saved = serde_json::to_string(&app.ui).unwrap();
+    let restored: gridcraft_ui_egui::UiState = serde_json::from_str(&saved).unwrap();
+    assert!(restored.autosave, "a saved ui.json restores AutoSave on (#1901)");
+    app.toggle_autosave();
+    assert!(!app.ui.autosave, "toggling back persists off too");
+}
+
+#[test]
+fn an_old_ui_json_without_autosave_still_loads() {
+    // Files saved by earlier versions have no autosave key; serde(default) reads them as off.
+    let restored: gridcraft_ui_egui::UiState = serde_json::from_str(r#"{"dark": true}"#).unwrap();
+    assert!(!restored.autosave);
+    assert!(restored.dark, "the rest of the old file still applies");
+}