Hrm. I'm not immediately impressed by the "Level<>" construct. That feels like a lot of new cognitive burden. It's also not at all obvious to me that multiple levels of mutex is a common pattern? I'm not sure I've ever encountered a situation where locking Account also and always requires locking Config? Heaven help you if you have 3 or more levels.

I dunno. I appreciate the opposition to "just be careful". But this feels to me like it's inducing bad design patterns. So it feels like it's wandering down the wrong path.