The coverage lane caught a regression in the prior commit: FileMutationRow now
passes the tool's raw path to the injected openFile (which resolves against cwd
in apply.ts), but diff-card.spec still asserted the row pre-resolved. Assert on
the raw path instead. Also fix the built-boot diff assertion to match on the
line body and footer text — the `+ ` prefix is a CSS ::before, absent from
textContent.