ui: the signal badge is the drag handle (to a plot row, or to reorder); the list rows stop dragging

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

src/ui_app.hpp

@@ -531,9 +531,6 @@ struct App {
   /// True while `sync_panel_switches()` is writing the switches: setting a `GtkSwitch` emits its own
   /// `notify::active`, and without this the program's own write would come back as a click.
   bool panel_switch_sync = false;
-  /// True while a drag has the overlaid sidebar hidden: what it was showing before, so `drag-end` puts it
-  /// back rather than guessing.
-  bool sidebar_hidden_for_drag = false;
   /// The channel a session's trigger names, until `rebuild_trigger_signals()` can resolve it: the
   /// file stores a *name* and the trigger needs an index into the acquired channels, which do not
   /// exist until the stream has been described. Empty means "nothing pending".
@@ -1166,11 +1163,11 @@ struct App {
   /// of them are streamed signals. The `MATH` divider and the math channels account for the rest, and
   /// `rows == signals + 1 + math` is the invariant the dump checks -- a list that lost its `+`.
   int dbg_signal_rows = 0;
-  /// How many rows of the list carry a `GtkDragSource`: `rows - 1`, the divider not being draggable.
+  /// How many rows of the list carry a `GtkDragSource`: 0 -- the signal badges are the drag handles now.
   int dbg_signal_drag_sources = -1;
-  /// The drag-with-an-overlaid-sidebar pair: the sidebar hid for the drag, and came back after it.
-  int dbg_drag_hid_sidebar = -1;
-  int dbg_drag_restored_sidebar = -1;
+  /// A drag begun through the first signal badge's source closed the open slide-over (1), or did not (0);
+  /// -1 when there is no badge to drag.
+  int dbg_drag_closed_slideover = -1;
   std::size_t dbg_signal_plain = 0;
   int dbg_side_column_after_hide = 1;
   std::string dbg_mode_triggered;
@@ -1852,10 +1849,6 @@ const char* trigger_mode_text(TriggerMode m);
 TriggerMode trigger_mode_from_text(const std::string& s);
 /// The panel's controls from the model, and the session's trigger into both.
 void write_trigger_widgets(App& app);
-/// Hides the sidebar for the length of a drag when it is *overlaid*, and puts it back after. With the
-/// split view collapsed the sidebar covers the plot, so a drag that starts in the signal list has nowhere
-/// to land: the pointer is over the sidebar, not over a drop target.
-void row_drag_sidebar(App& app, bool dragging);
 /// The compact line the trigger pane shows while it is locked, and the lock itself: the panes'
 /// bodies, their [edit] buttons and the signal list's rows all follow from `trigger_locked` and
 /// `signals_locked`.