fix(render): keep a cursor parked on an axis bound inside and visible

include/plot/render/renderer.hpp

@@ -455,8 +455,13 @@ class Renderer {
   /// The cursors, both orientations: one stroke per cursor, placed at the coordinate its own
   /// orientation owns (`Plot::cursor_screen_coordinate()`) and spanning the other axis' whole
   /// range, in its own colour -- or in the accent at handle width while it is hovered or
-  /// grabbed, which is the same cue a region's hot bound gets. A cursor at the far edge of
-  /// its range is skipped rather than drawn as half a stroke over the strip beside it.
+  /// grabbed, which is the same cue a region's hot bound gets. A cursor more than half a
+  /// stroke outside its range's mapped span (a marker scrolled past the right edge, a ruler
+  /// past the bottom) is skipped; one on or within half a stroke of a bound is drawn, with
+  /// its stroke centre held half a stroke inside the rect -- so a marker parked on an edge
+  /// stays visible there instead of losing its outside half, and the inside sliver of it, to
+  /// the clip, and a range maximum that undershoots the edge by a ulp is not mistaken for
+  /// off the plot.
   void draw_cursors(const Plot& plot, const PlotLayout& layout);
   /// One cursor's label: the caller's caption for either orientation, and for a horizontal
   /// ruler the value itself, written in its y axis' own tick format (`Axis::format_value()`)