The paste gutter was pinned to a fixed 3ch width. With box-sizing:
border-box that leaves only ~19px of content after the 10px+10px side
padding, so 2+ digit line numbers overflow right into the code text
(owner-visible from line 10, worst at 100+).
paste-lines.js now sets the gutter width to calc(Nch + 20px), where N is
the digit count of the highest line number, via CSSOM (CSP forbids
inline style attributes). Numbers were already right-aligned; the column
now matches the width of the biggest number. The width is only written
when it changes, so the resize-observer/renumber loop keeps a stable
fixed point.
fen