rustfmt and `git diff` close every coloured run with `ESC ( B` (designate G0
as ASCII) and write it after the newline, ahead of the SGR reset. With no arm
for nF escapes the parser fell through to "two-char escape", ate `ESC (` and
left the `B` as text, so each diff line in the feed read `B+ added line`.
Intermediates 0x20-0x2f now run to a final 0x30-0x7e, and an unterminated
sequence stops where the CSI arm would.
8907766b5b