Round-1 accounting rounded each .codeline span's own height to rows, but
in pre-wrap the newline text nodes between blocks each render as their own
anonymous row, so per-span height undercounts and gutter numbers drift
below their line's first visual row. Renumber now derives rows per line
from the rendered gap between consecutive line tops (wrapped rows plus the
newline row); the last line falls back to its own box height. Wrap-off
path unchanged.
fen