So... add another presubmit test that fails when a test is removed. Require human reviews.

It's not like a human being always pushes correct code, my risk assessment for an LLM reading a small bug and just making a PR is that thinking too hard is a waste of time. My risk assessment for a human is very similar, because actually catching issues during code review is best done by tests anyways. If the tests can't tell you if your code is good or not then it really doesn't matter if it's a human or an LLM, you're mostly just guessing if things are going to work and you WILL push bad code that gets caught in prod.