One thing that the Perl6/Raku project got right is: The test suite is the spec. If it passes the test suite, it's a correct compiler.

I think this is the right answer for nearly any software project. Especially in the days of AI. The test suite is the spec. If it's not in the test suite it's irrelevant. If your vibe code passes the test suite without changing it, it's correct.

New projects start with a failing set of tests that get approved.

This is the way.