Open on the Home tab every launch, as in Excel (fixes #2329)

crates/ui-egui/src/lib.rs

@@ -117,6 +117,14 @@ impl Default for UiState {
 }
 
 impl UiState {
+    /// The state saved by an earlier run, as the app starts with it. The ribbon tab is written to
+    /// the preferences but not restored: Excel opens on Home every launch, so a contextual tab
+    /// (Table Design) cannot come back with nothing selected to justify it.
+    pub fn at_startup(mut self) -> Self {
+        self.ribbon_tab = "Home".into();
+        self
+    }
+
     pub fn theme_preference(&self) -> egui::ThemePreference {
         if self.system_theme {
             egui::ThemePreference::System

crates/ui-egui/tests/contextual_ribbon_tab.rs

@@ -72,3 +72,25 @@ fn leaving_the_table_while_on_table_design_returns_to_home() {
     h.run_steps(2);
     assert_eq!(h.state().ui.ribbon_tab, "Home");
 }
+
+#[test]
+fn startup_opens_on_home_not_the_saved_tab() {
+    let mut saved = gridcraft_ui_egui::UiState::default();
+    saved.ribbon_tab = "Table Design".into();
+    saved.dark = true;
+    let json = serde_json::to_string(&saved).unwrap();
+    assert!(json.contains(r#""ribbonTab":"Table Design""#), "{json}");
+    let restored = serde_json::from_str::<gridcraft_ui_egui::UiState>(&json).unwrap().at_startup();
+    assert_eq!(restored.ribbon_tab, "Home", "the saved tab is not restored");
+    assert!(restored.dark, "the other preferences are");
+}
+
+#[test]
+fn an_ordinary_tab_stays_put_in_a_session() {
+    let mut session = Session::new();
+    session.new_workbook();
+    let mut h = harness(session);
+    h.state_mut().ui.ribbon_tab = "Data".into();
+    h.run_steps(3);
+    assert_eq!(h.state().ui.ribbon_tab, "Data");
+}