Change counts for diff, taken before it was clipped for display.
The prompt's +N -M header must not be recounted from diff: the
write_file and delete previews are built with max_lines=100, so a
recount describes the preview rather than the change, and on the delete path
that number gates destroying the file. The edit_file preview passes
max_lines=None and so is safe to recount — do not read that as a cap
covering all three.
