Guardrails can and do help but they don't prevent hallucinations entirely. I generate trivia questions for my app. Questions are true/false and I tell it you must include an explanation of why the question is true for false. I also tell it to give me supporting links which validate its claim. I've had it make up explanations and invent plausible looking URLs. But I wrote a checker that pulls the content of the URL and asks a different model if the URL supports the claim. LLM's are much better at something like that than pulling a trivia question out of thin air. Reviewing diffs can be much the same. It isn't having to write the code but just evaluate if it matches what the commit comments claim it does. You are right, though. Without good comments on PR's and commits (i.e. context) the diff review is going to be a lot of assumptions made by the AI which is where hallucinations get more common.