Legitimate question. In my projects, where I do have a ton of files, but kind of suspect not nearly as you have, I do occasionally instruct agent to review old files and decisions and archive them or delete.

Sometimes it is useful to know how we came about some decision or feature, but in general you often don't need them and they would contain prose that would confuse agent. So you remove it.

I don't use Claude Code mostly because it always loved to generate reports and there is no way I will read it's lengthy reports. I try to have documents I can actually read if I want to.

Hope this helps, but some lifecycle of your documents and requirements is useful to have.