ui: read the signal count under the lock in the badge bar; validate the drop payload

src/ui.cpp

@@ -4654,10 +4654,16 @@ void run_app_action(App& app, AppAction action) {
       toggle(app.cursors_toggle);
       break;
     case AppAction::ShowMeasure: dock_show_section(app, "measure"); break;
-    case AppAction::ShowSignals:
+    case AppAction::ShowSignals: {
       // The `+` badge is insensitive without signals; so is its shortcut.
-      if (!app.model->signals().empty()) slideover_toggle(app, "signals");
+      bool have_signals = false;
+      {
+        std::lock_guard<std::mutex> lock(app.model->mutex());
+        have_signals = !app.model->signals().empty();
+      }
+      if (have_signals) slideover_toggle(app, "signals");
       break;
+    }
     case AppAction::LayoutEditor:
       toggle(app.layout_toggle);
       break;

src/ui_badges.cpp

@@ -256,12 +256,17 @@ void sync_badge_bar(App& app) {
   set_text_if_changed(bb.trigger.state, trigger_badge_state(enabled, armed, pending, has_event));
   set_open(bb.trigger.button, slideover_page(app) == bb.trigger.page);
 
+  bool have_signals = false;
+  {
+    std::lock_guard<std::mutex> lock(app.model->mutex());
+    have_signals = !app.model->signals().empty();
+  }
   if (bb.plus.button != nullptr) {
-    gtk_widget_set_sensitive(bb.plus.button, !app.model->signals().empty());
+    gtk_widget_set_sensitive(bb.plus.button, have_signals);
     set_open(bb.plus.button, slideover_page(app) == "signals");
   }
   if (bb.overflow.button != nullptr) {
-    gtk_widget_set_sensitive(bb.overflow.button, !app.model->signals().empty());
+    gtk_widget_set_sensitive(bb.overflow.button, have_signals);
     // The overflow stands for every signal's badge too: a signal page opened from a list row marks it.
     set_open(bb.overflow.button,
              slideover_page(app) == bb.overflow.page || slideover_page(app).rfind("signal:", 0) == 0);

src/ui_signals.cpp

@@ -557,7 +557,11 @@ gboolean on_drop_channel(GtkDropTarget*, const GValue* value, double x, double y
   // Where the drop landed decides the row: one area covers them all.
   const int row = row_at(*app, x, y);
   const char* text = g_value_get_string(value);
-  const std::size_t signal = static_cast<std::size_t>(std::atoll(text ? text : "0"));
+  if (text == nullptr || *text == '\0') return FALSE;
+  char* end = nullptr;
+  const unsigned long long parsed = std::strtoull(text, &end, 10);
+  if (end == nullptr || *end != '\0') return FALSE;
+  const std::size_t signal = static_cast<std::size_t>(parsed);
   if (!assign_signal_to_row(*app, signal, row)) return FALSE;
   cancel_drag_on(*app, row);
   return TRUE;