What I find is actually necessary for me to have a mental model of the system is not typing out the definitions of the classes and such, but rather operating and debugging the system. I really do need to try to do things, and dig into logs, and figure out what's going on when something is off. And pretty much always ends up requiring reading and understanding a bunch of the implementation. But whether I personally typed out that implementation, or one of my colleagues, or an AI, is less important.
I mean, I already had to be able to build a mental model of a system that I didn't fully implement myself! I essentially never work on anything that I have developed in its entirety on my own.