>Maybe things will evolve into projects having a well-defined, hard boundary between agents generated code and human generated code.

The only way things will evolve is towards maximizing AI generated code and minimizing human involvement because that is the most efficient mode for getting product to market. Any trend to the contrary is temporary, paperclip maximizer will maximize. Any code that humans touch directly will be considered implicitly too risky to run in any production environment.

We'll just have to hope things don't break too much and when they do, we'll just have to accept it because no human will be able to (or allowed to, or even trusted to) fix it.