ui: the cursors and measure pages are insensitive until the stream has signals

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/ui.cpp

@@ -2866,16 +2866,32 @@ void on_right_click(GtkGestureClick* gesture, int, double x, double y, gpointer
   open_row_menu(*app, row, x, y, widget);
 }
 
+/// The availability of everything that does nothing until the stream has signals: the dock and the two
+/// slide-over pages that were once in it (Cursors, Measurements). "Disable, do not hide": a page may be
+/// opened by its key before the first CONFIG, and shows its controls insensitive until then. The signal
+/// list is read under the model's mutex, as the producer replaces it on a CONFIG.
+bool update_signal_availability(App& app) {
+  bool have_signals = false;
+  {
+    std::lock_guard<std::mutex> lock(app.model->mutex());
+    have_signals = !app.model->signals().empty();
+  }
+  if (app.side_box != nullptr) gtk_widget_set_sensitive(app.side_box, have_signals);
+  if (app.cursors_panel != nullptr) gtk_widget_set_sensitive(app.cursors_panel, have_signals);
+  if (app.measures_panel != nullptr) gtk_widget_set_sensitive(app.measures_panel, have_signals);
+  return have_signals;
+}
+
 /// The dock is on when the user's sidebar button is in -- from the start, with or without signals; the
 /// two panel buttons appear as soon as a CONFIG describes any signal at all.
 void update_side_visibility(App& app) {
   if (app.side_box == nullptr) return;
-  const bool have_signals = !app.model->signals().empty();
+  const bool have_signals = update_signal_availability(app);
   // `sidebar_wanted` is the user's last word, which is why it is kept apart from the button's own state:
   // a swipe that hides the sidebar fires the button's handler (the binding is bidirectional), so a gesture
   // is a choice too. "Disable, do not hide": the dock is on screen from the start and does nothing until
   // the stream has signals, so the signals decide its *sensitivity* and never whether it is there.
-  gtk_widget_set_sensitive(app.side_box, have_signals);
+  // (`update_signal_availability()` above set it, and the two slide-over pages' with it.)
   gtk_widget_set_sensitive(app.sidebar_toggle, TRUE);
   const bool want_column = app.sidebar_wanted;
   // The split view owns the sidebar's visibility: it animates it, and when the window is too narrow it
@@ -3990,7 +4006,7 @@ gboolean tick(gpointer user) {
     // whether the dock is there; having signals decides only whether it does anything ("disable, do not
     // hide"): a dock that is on screen from the start does not jump in when the first CONFIG arrives.
     const bool want = app->sidebar_wanted;
-    gtk_widget_set_sensitive(app->side_box, !app->model->signals().empty());
+    update_signal_availability(*app);
     gtk_widget_set_sensitive(app->sidebar_toggle, TRUE);
     if (adw_overlay_split_view_get_show_sidebar(ADW_OVERLAY_SPLIT_VIEW(app->side_view)) != want) {
       adw_overlay_split_view_set_show_sidebar(ADW_OVERLAY_SPLIT_VIEW(app->side_view), want);
@@ -5137,9 +5153,10 @@ void on_activate(GtkApplication* application, gpointer user) {
   app->side_box = side;
 
   // Built in the order the panels have always been (cursors, measurements, trigger, signals); each is a
-  // page of the slide-over, reached by its badge, its key or the header's Cursors toggle.
+  // page of the slide-over, reached by its badge or its key (the Cursors page by the dock's Edit button;
+  // the header's Cursors toggle only switches the cursors on and mirrors the switch inside the page).
   app->cursors_panel = build_cursors_panel(*app);
-  GtkWidget* measures_panel = build_measures_panel(*app);
+  app->measures_panel = build_measures_panel(*app);
   app->trigger_panel = build_trigger_panel(*app);
   // Top-aligned: the page's scroller gives the child the page's height, and a form that stretched to it
   // would spread its rows (or draw its frame) over empty space under the last one.
@@ -5152,9 +5169,9 @@ void on_activate(GtkApplication* application, gpointer user) {
   // `c` / the header toggle drive the cursors themselves; this page is where they are configured and read
   // in full. `m` toggles the measurements page.
   gtk_widget_set_valign(app->cursors_panel, GTK_ALIGN_START);
-  gtk_widget_set_valign(measures_panel, GTK_ALIGN_START);
+  gtk_widget_set_valign(app->measures_panel, GTK_ALIGN_START);
   slideover_add_page(*app, "cursors", "Cursors", app->cursors_panel);
-  slideover_add_page(*app, "measure", "Measurements", measures_panel);
+  slideover_add_page(*app, "measure", "Measurements", app->measures_panel);
   // The dock is the compact readouts alone (step 4 adds the events to it).
   gtk_box_append(GTK_BOX(app->dock_page), build_readouts_dock(*app));