You can also just use AI and keep the scale of your changes small rather than refactoring the whole app with a change? This isn't super-weird.

"In the discrete world of computing, there is no meaningful metric in which "small" changes and "small" effects go hand in hand, and there never will be." - E.W.Dijkstra (EWD1036)

As you know, the boundary ultimately depends on code quality. The problem is that AI generates code that looks high quality even outside my area of expertise, at least from my perspective. So now the boundary has to be redrawn. Refactoring usually ends up redefining those boundaries. At that point, the question becomes: do I rewrite my own code, or do I reject the AI code? Those are the two choices left.

In the end, an exceptionally skilled programmer might be able to keep their core domain intact, but I think the vast majority would find that very difficult. So it might be possible once you cross a certain threshold, but considering the sheer amount of code required to deliver a single modern program, it's hard to know which parts to focus on. However, my perspective might be different because I'm coming from the point of view of delivering a working program, not from the perspective of open source development