You need a harness, yes, and you need quality gates the agent can't mess with, and that just kicks the work back with a stern message to fix the problems. Otherwise you're wasting your time reviewing incomplete work.
Your point being? A proper harness will mostly catch things like that. Even a low end model can be employed to do write tests plans and do consistency checks that mostly weed out stuff like that. Hence: You need a harness, or you'll spend your time worrying about dumb stuff like this.