fix run-list size calculation, accounting for advance vs. end pad

src/font_cache/font_cache.c

@@ -839,6 +839,7 @@ f_push_run_from_string(Arena *arena, F_Tag tag, F32 size, F32 base_align_px, F32
     }
     run.dim = dim;
     run.dim.x += last_piece_end_pad;
+    run.end_pad = last_piece_end_pad;
     run.ascent  = hash2style_node->ascent;
     run.descent = hash2style_node->descent;
   }

src/font_cache/font_cache.h

@@ -71,6 +71,7 @@ struct F_Run
 {
   F_PieceArray pieces;
   Vec2F32 dim;
+  F32 end_pad;
   F32 ascent;
   F32 descent;
 };