help: the search block's (i) on its header, a 12 px mark, and a real search page

src/ui_app.hpp

@@ -246,6 +246,9 @@ struct App {
   GtkWidget* search_marks_label = nullptr;
   GtkWidget* search_prev_button = nullptr;
   GtkWidget* search_next_button = nullptr;
+  /// The expander the block lives in, so the probe can read its collapsed state when it reads the
+  /// header hint.
+  GtkWidget* search_exp = nullptr;
   /// Set true when the last `search_jump()` produced an empty cut — the hit was so close to the
   /// oldest retained sample that `publish_pause_view()` held nothing. Cleared at every jump.
   bool search_jump_empty = false;
@@ -284,10 +287,14 @@ struct App {
   GtkWidget* status_row = nullptr;
   GtkWidget* window_control_slot = nullptr;
   /// The hint hosts that are *not* a pane's heading row: a specific control's own row, so the "?" sits
-  /// beside the thing it explains -- the "record events" switch, the search block's action row, and the
+  /// beside the thing it explains -- the "record events" switch, the pre-trigger share row, and the
   /// signals pane's hint line (whose box exists so a hint can join it beside the text).
   GtkWidget* trigger_record_row = nullptr;
   GtkWidget* trigger_pre_row = nullptr;
+  /// The search block's expander *header* -- the box the contextual help's "trigger_search" hint joins
+  /// as its last child. The header, not the block: the expander's child is out of the widget-parent
+  /// chain until the block is expanded, so a hint there is invisible while it is collapsed.
+  GtkWidget* trigger_search = nullptr;
   GtkWidget* signals_note = nullptr;
   /// The guided tour. `tour.overlay` is a `GtkOverlay` inserted above the window's content, and the
   /// four dim rectangles, the spotlight and the card are its overlay children; `tour.plan` is the