ui: cap and cheapen the dock's events rebuild

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

src/ui_events.cpp

@@ -782,10 +782,8 @@ void attach_preview_zoom(GtkWidget* frame, const std::string& path) {
                         GConnectFlags(0));
 }
 
-/// A row's first line: when the event was latched, how long it is, and whether it is the one on
-/// screen. One function because two callers write it -- the row builder and the in-place
-/// re-mark -- and a mark that reads differently depending on which of them last ran would be
-/// worse than no mark.
+/// Whether the event is the one on screen: the one question the title's "(on screen)" and the dock's
+/// filled mark both ask.
 bool event_on_screen(const App& app, const EventRecord& r) {
   return std::string(app.waveform_name) == r.file;
 }
@@ -797,6 +795,10 @@ bool event_in_group(const App& app, const EventRecord& r) {
                      [&](const EventRecord& g) { return g.file == r.file; });
 }
 
+/// A row's first line: when the event was latched, how long it is, and whether it is the one on
+/// screen. One function because two callers write it -- the row builder and the in-place
+/// re-mark -- and a mark that reads differently depending on which of them last ran would be
+/// worse than no mark.
 std::string event_row_title(App& app, const EventRecord& r) {
   const std::time_t t = static_cast<std::time_t>(r.wall_time);
   std::tm tm{};
@@ -828,7 +830,7 @@ void mark_events_on_screen(App& app) {
 /// the whole pane describes whichever event happens to be newest rather than the one being read. The
 /// numbers are one line each: a list that has to load the samples to describe an event is a list that
 /// cannot show thirty of them.
-static void rebuild_events_pane_list(App& app) {
+static void rebuild_events_pane_list(App& app, std::vector<EventRecord>& records) {
   if (app.events_list == nullptr) return;
   while (GtkWidget* child = gtk_widget_get_first_child(app.events_list)) {
     gtk_list_box_remove(GTK_LIST_BOX(app.events_list), child);
@@ -838,8 +840,8 @@ static void rebuild_events_pane_list(App& app) {
   // the one that finds out.
   app.events_thumb = nullptr;
   if (app.event_store == nullptr) return;
-  // Not const: a record whose preview had to be redrawn learns its thumbnail's path here.
-  std::vector<EventRecord> records = app.event_store->list();
+  // `records` is the caller's list, not const: a record whose preview had to be redrawn learns its
+  // thumbnail's path here.
   if (records.empty()) {
     GtkWidget* empty = gtk_label_new("no events yet -- arm the trigger");
     gtk_widget_add_css_class(empty, "dim-label");
@@ -975,8 +977,12 @@ static void rebuild_events_pane_list(App& app) {
 /// Both views of the cache, rebuilt from the same list: the pane's rows (with their pictures) and the
 /// dock's compact ones. The dock follows even when the pane's list does not exist.
 void refresh_events_pane(App& app) {
-  rebuild_events_pane_list(app);
-  dock_rebuild_events(app);
+  // One read of the cache directory for both views (none without a store, which the pane's rebuild
+  // and the dock's both treat as nothing to list).
+  std::vector<EventRecord> records;
+  if (app.event_store != nullptr) records = app.event_store->list();
+  rebuild_events_pane_list(app, records);
+  if (app.event_store != nullptr) dock_rebuild_events(app, records);
 }
 
 /// Clicking a row replays it: the same loader `--open` uses, on the event's file. The acquisition is