test: assert the digest-unconfirmed caveat on the success line
Address nh13 review: the no-digest test checked the stderr warning and
that the success line still prints, but not that the line carries the
"(digest unconfirmed)" caveat - the point of the feature. Assert it so
a regression to an unqualified success message is caught.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
