ui: the sidebar is two tabs, and a toggle disables its pane

Replace the sidebar's five-panel scrolling column with an AdwViewStack
carrying two pages — Measure (cursors + measurements) and Signals
(trigger + math + channel list) — with an AdwViewSwitcher above it. The
trigger and cursors toggles change from "reveal/hide my pane" to
"enable/disable my feature, leaving the pane insensitive", following the
disable-not-hide principle. The keys probe loses a duplicate registration
that was toggling the sidebar back on before the exit probe captured its
state; the exit-probe captures now read adw_overlay_split_view_get_show_
sidebar() instead of gtk_widget_get_visible(), which AdwOverlaySplitView
never changes.

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

src/ui_app.hpp

@@ -139,18 +139,21 @@ struct App {
   /// what we synced is ours -- GTK only notifies on a change, so the user cannot produce it.
   int window_sync_unit = -1;
   GtkWidget* trigger_toggle = nullptr;
-  GtkWidget* trigger_revealer = nullptr;
   /// The trigger panel's own box, kept so the defaults probe can read its spin buttons without
   /// walking the window for them.
   GtkWidget* trigger_panel = nullptr;
-  GtkWidget* signal_toggle = nullptr;
-  GtkWidget* signal_revealer = nullptr;
   GtkWidget* signal_panel = nullptr;
   GtkWidget* side_box = nullptr;
+  /// The sidebar's tab stack and its switcher. The stack is what chooses which panels are on
+  /// screen; a feature's own on/off never does (it sets its panel's sensitivity instead).
+  GtkWidget* side_stack = nullptr;
+  GtkWidget* side_switcher = nullptr;
+  /// The page name the stack is showing, and the one value the session file persists about the
+  /// sidebar. "signals" on a first run.
+  std::string side_tab = "signals";
   GtkWidget* arm_button = nullptr;
   GtkWidget* trigger_signal_drop = nullptr;
   GtkWidget* sidebar_toggle = nullptr;
-  GtkWidget* side_scroll = nullptr;
   GtkWidget* trigger_edge_drop = nullptr;
   GtkWidget* trigger_type_drop = nullptr;
   GtkWidget* trigger_cmp_drop = nullptr;
@@ -211,10 +214,10 @@ struct App {
   /// *titlebar*, not a child of the window, so walking down from the window does not reach it.
   GtkWidget* toolbar = nullptr;
   GtkWidget* cursors_reset = nullptr;
-  /// The cursors pane: revealed with the toggle, and listing what the instruments
-  /// read -- T0/T1/dT always, per row an Y1/Y2/dY where rulers are up, and in `mix` mode
-  /// the value each cursor crosses each trace at.
-  GtkWidget* cursors_revealer = nullptr;
+  /// The cursors panel's root, kept because cursors-off disables it rather than hiding it.
+  GtkWidget* cursors_panel = nullptr;
+  /// The cursors pane: listing what the instruments read -- T0/T1/dT always, per row an Y1/Y2/dY
+  /// where rulers are up, and in `mix` mode the value each cursor crosses each trace at.
   GtkWidget* cursors_mode_drop = nullptr;
   GtkWidget* cursors_body = nullptr;
   /// One line per row (rulers) and one per bound trace (`mix`), in the order the body
@@ -237,16 +240,12 @@ struct App {
   /// price the frame tick should pay).
   std::vector<Measure> measures;
   std::vector<MeasureResult> measure_results;
-  GtkWidget* measures_revealer = nullptr;
   GtkWidget* measures_list = nullptr;
-  GtkWidget* measures_toggle = nullptr;
   // --- math channels --------------------------------------------------------
   /// The app's copy of the math channels, and the source of truth for the pane. Every change goes
   /// through `apply_math_channels()`, which writes this and hands it to the model -- the model's own
   /// copy is what the producer evaluates.
   std::vector<MathChannel> math;
-  GtkWidget* math_toggle = nullptr;
-  GtkWidget* math_revealer = nullptr;
   GtkWidget* math_list = nullptr;
   /// The math editor's builder. The editor's window belongs to the builder's object list, so the builder is
   /// held for as long as the window is up and cleared on the *next* opening rather than with the window --
@@ -358,7 +357,6 @@ struct App {
   /// that memory reused and the read is a **SIGSEGV** in the middle of the dump.
   int dbg_measures_pane_w = -1;
   int dbg_measures_pane_h = -1;
-  bool measures_revealed = false;
   /// The measurement dialog while one is open (null otherwise). A probe needs a handle on it:
   /// it is a window of its own, so the main window's widget tree does not reach its buttons.
   GtkWidget* measure_dialog = nullptr;
@@ -508,7 +506,6 @@ struct App {
   /// True once the renderer's `Style` has been stated (see `tick()`): the renderer does not
   /// exist until the area is realized, so the one-shot has to be a tick's job.
   bool style_stated = false;
-  bool signals_panel_initialised = false;
   /// Set once the user edits the trigger level, so the panel stops defaulting it
   /// into the middle of the declared range.
   bool trigger_level_touched = false;
@@ -690,7 +687,7 @@ struct App {
   /// over a run that acquired anything -- that is what "it blinks" means, and a badge
   /// stuck lit looks identical to a working one in a screenshot.
   int dbg_badge_frames[4] = {0, 0, 0, 0};
-  int dbg_reset_visible = -1;
+  int dbg_reset_sensitive = -1;
   std::vector<std::uint64_t> last_stored;
   std::uint64_t dbg_latches_at_disarm = 0;
   std::uint64_t dbg_seq_at_disarm = 0;
@@ -738,12 +735,12 @@ struct App {
   int dbg_signal_row_h = 0;
   int dbg_trigger_w = 0;
   int dbg_trigger_h = 0;
-  int dbg_signal_revealed = 0;
-  int dbg_trigger_revealed = 0;
+  int dbg_signal_page_current = 0;
+  int dbg_trigger_sensitive = 0;
   int dbg_side_visible = 0;
   int dbg_trigger_items = 0;
   int dbg_trigger_selected = -1;
-  int dbg_side_scroll_after_hide = 1;
+  int dbg_side_column_after_hide = 1;
   std::string dbg_mode_triggered;
   std::string dbg_window_text;
   double dbg_marker_x = 0.0;
@@ -751,8 +748,8 @@ struct App {
   double dbg_trigger_time = 0.0;
   int dbg_trigger_time_valid = -1;
   std::string dbg_mode_live;
-  int dbg_toggles_visible = 0;
-  int dbg_trigger_revealed_default = 0;
+  int dbg_switcher_visible = 0;
+  int dbg_trigger_sensitive_default = 0;
 
   /// The detail string the popover and the exit dump read. The dump used to read the label,
   /// which no longer carries these fields.
@@ -1336,7 +1333,6 @@ void rebuild_math_pane(App& app);
 GtkWidget* build_measures_panel(App& app);
 GtkWidget* build_cursors_panel(App& app);
 void on_cursors_toggled(GtkToggleButton* button, gpointer user);
-void on_signals_toggled(GtkToggleButton* button, gpointer user);
 void on_fit_clicked(GtkButton*, gpointer user);
 void on_fit_x_clicked(GtkButton*, gpointer user);
 void on_cursors_reset(GtkButton*, gpointer user);
@@ -1359,6 +1355,8 @@ void row_menu_fill(RowMenuState& st);
 GtkWidget* open_row_menu(App& app, int row, double x, double y, GtkWidget* parent, bool autohide = true);
 void on_right_click(GtkGestureClick* gesture, int, double x, double y, gpointer user);
 gboolean on_drop_channel(GtkDropTarget*, const GValue* value, double x, double y, gpointer user);
+void on_side_tab_changed(GObject*, GParamSpec*, gpointer user);
+void select_side_tab(App& app, const char* name);
 void update_side_visibility(App& app);
 void on_sidebar_toggled(GtkToggleButton* button, gpointer user);
 void rebuild_signal_panels(App& app);