I believe the problem is structural to all traditional class-based inheritance models.

The sort of situation I described is almost impossible with trait/typeclass-based polymorphism. You have to go very far out of the idiom with a weird mix of required and provided methods to achieve it, and I have never seen anyone do this in practice. The idiomatic way is for whatever consumes the trait to pass in a context type. There is a clear separation between the call-forward and the callback interfaces. In Rust, & and &mut mean that there's an upper limit to how tangled the interface can get.

I'm fine with inheritance if there's rigorous enforcement of one-directional calls in place (which makes it roughly equivalent to trait-based composition). The Liskov stuff is a terrible distraction from this far more serious issue. Does anyone do this?

> You shouldn't have to duplicate code or nest structures to attain those ergonomics.

What's wrong with nesting structures? I like nesting structures.