paste-lines.js rebuilt the codebody with innerHTML but relied on the
server-side '\n' delimiters disappearing between the per-line blocks.
Under white-space: pre any whitespace-only text node that survives
(cached HTML, template drift) renders as a phantom row and drifts the
gutter numbers off their lines. splitLines() now strips whitespace-only
text nodes after rebuilding, keeping renumber() geometry intact.
fen