Split the paste codebody into per-line block spans (paste-lines.js) and
rebuild the gutter from each line's wrapped height so numbers count
visual rows, not logical lines. Pinned the gutter width (flex 0 0 auto,
3ch) so its row count no longer feeds back into the code column width.
ResizeObserver renumbers on wrap toggle / resize; wrap-off behavior is
unchanged (one number per newline).
fen