If you're building a code base where AI is delivering on the the details of it, it's generally a bad thing if the code provided by AI provide safeguards WITHIN your code base.

Those kinds of safeguards should instead be part of the framework you're using. If you need to prevent SQL injection, you need to make sure that all access to the SQL type database pass through a layer that prevents that. If you are worried about the security of your point of access (like an API facing the public), you need to apply safeguards as close to the point of entry as possible, and so on.

I'm a big believer in AI generated code (over a long horizon), but I'm not sure the edge case robustness is the main selling point.

Sounds like we're talking about different kind of safeguards. I mean stuff like a character in a game ending up in a broken case due to something that is theoretically possible but very unlikely or where the consequence is not worth the effort. An AI has no problem taking those into account and write tedious safeguards, while I skip it.