The coverage lane flagged transcript.ts line 63 (diffContentLines' empty-text
return) uncovered: the same-file diff test only fed newline-terminated sides.
Add a third hunk removing a line with an empty added side (a full deletion), so
the empty arm runs and the footer proves the empty side draws no `+ ` row
(+2 -1 · 1 file). Raise the test's line budget so every hunk row stays visible.