The body has letter-spacing: -0.011em (~-0.176px at 16px) for typography
refinement. xterm's DOM renderer measures cell width with that spacing
inherited (~7.83px), then sets an inline letter-spacing override on
.xterm-rows that cancels the body inherit, leaving glyphs to render at
their natural ~8.00px width.
The mismatch — measured 7.83px cells vs rendered 8.00px glyphs —
accumulates as cols grow, eventually overflowing .xterm-rows > div and
getting clipped by its overflow: hidden. At 124 cols the drift was
~21px, chopping ~3 chars off the right edge.
Resetting letter-spacing on .xterm makes both phases agree and reduces
the drift to sub-pixel rounding (~2px worst case at any reasonable
cols).
ddf9732a3e