[Blackthorn]

> But it also creates this very accessible footgun:

Well, you said it yourself in the article though. There's always ways around the locking; C++ doesn't really give you the full ability to guarantee a field is locked when access. You'll need to either trust the users to some extent or use a style guide to disallow the pattern (I'd suggest only allowing use of auto x = state.locked() to avoid lifetime questions around state.locked()->x). You'd need to use compiler annotations to get any better.