A couple of things:
1. Direct the AI to look specifically into areas where I have a gut feel things might go wrong
2. An assessment by another model (eg Codex reviews Claude's work)
3. Manual testing
If you are unsure about the AI generated code, it's better to not ship a risky product. You can also use 3rd party services for the most vulnerable areas of your product.
I think the key is treating AI-generated code like code from a junior developer: review it carefully, test it thoroughly, and never assume it's correct just because it was generated.