> rather than let the LLM do the entire structure, I take the time to create the full hierarchy of abstractions and actors that I want my code to do. I decide, at the UML level, how abstractions will sit and interact — and then I make the LLM implement those gaps.

Do you do this with every repository that's brand-new to you? You refuse to, for example, use an agent to learn where the feature should generally live? This seems absurdly slow for that purpose, because even though humans can still get a deeper understanding of a codebase after several months, an agent can get a much deeper understanding over a timeline of the initial few days. Unless everything is already meticulously documented for you, I suppose.