> I’d say that, in all the ways that matter, I understand the code. Sure, if I had to hand-edit it now, there’d be a serious learning curve. But I won't have to. And more importantly, I can reason about the system, share perspectives with my colleagues, and guide agents on future work.

If there's a serious learning curve to editing code then you don't understand the code. We used to call that 'on-boarding' when you brought a new engineer on the team as they got up to speed as to how the codebase worked.