I would just put a PR_REVIEW.md file in the repo an have a CI agent run it on the diff/repo and decide pass or reject. In this file there are rules the code must be evaluated against. It could be project level policy, you just put your constraints you cannot check by code testing. Of course any constraint that can be a code test, better be a code test.

My experience is you can trust any code that is well tested, human or AI generated. And you cannot trust any code that is not well tested (what I call "vibe tested"). But some constraints need to be in natural language, and for that you need a LLM to review the PRs. This combination of code tests and LLM review should be able to ensure reliable AI coding. If it does not, iterate on your PR rules and on tests.