feat: a reserved hole is shaded, so a sub-pixel gap is still a report

src/plot_host.hpp

@@ -12,6 +12,8 @@
 #include <map>
 #include <memory>
 #include <string>
+#include <utility>
+#include <vector>
 
 namespace udpscope {
 
@@ -179,6 +181,18 @@ class RowSet {
   /// and status line all describe the same display: the producer can open or close a
   /// capture between any two reads of `ScopeModel::display_mode()`.
   void bind(ScopeModel& model, DisplayMode mode);
+  /// Publishes `model.holes()` to every row as shading, in display coordinates.
+  ///
+  /// Separate from `bind()` and called *after* the display epoch has been written, because the
+  /// epoch the band needs is this frame's: `ui.cpp` recomputes it from the newly bound traces'
+  /// live edge, and the previous frame's value is a whole production interval stale -- a third
+  /// of the screen at 1 MS/s over a 50 ms window, which would put the band beside the gap
+  /// rather than over it.
+  ///
+  /// Shading only in `Live` and `Capturing`. A `Held` or `Paused` snapshot carries its own
+  /// stamps and its own x offset, and the live hole table does not address it; shading it would
+  /// accuse whichever samples happened to land under those coordinates.
+  void set_invalid_spans(ScopeModel& model, DisplayMode mode);
   /// Publishes the live buffer's new samples.
   void acquire(ScopeModel& model) { model.acquire_all(); }
 
@@ -487,6 +501,8 @@ class RowSet {
   /// an absent entry means "the palette decides", which is what keeps a new CONFIG's signals
   /// coloured without anything having to seed them.
   std::map<std::string, plot::u32> signal_colors_;
+  /// Reused across frames by `set_invalid_spans()`: see there.
+  std::vector<std::pair<f64, f64>> spans_;
   CursorMode cursor_mode_ = CursorMode::Vertical;
   bool cursors_on_ = false;
   bool relative_x_ = false;