> I have a personal aversion to defer as a language feature.

Indeed, `defer` as a language feature is an anti-pattern.

It does not allow the abstraction of initialization/de-initialization routines and encapsulating their execution within the resources, transferring the responsibility to manually perform the release or de-initialization to the users of the resources - for each use of the resource.

> I also dislike RAII because it often makes it difficult to reason about when destructors are run [..]

RAII is a way to abstract initialization, it says nothing about where a resource is initialized.

When combined with stack allocation, now you have something that gives you precise points of construction/destruction.

The same can be said about heap allocation in some sense, though this tends to be more manual and could also involve some dynamic component (ie, a tracing collector).

> [..] and also admits accidental leaks just like defer does.

RAII is not memory management, it's an initialization discipline.

> [..] what I would want is essentially a linear type system in the compiler that allows one to annotate data structures that require cleanup and errors if any possible branches fail to execute the cleanup. This has the benefit of making cleanup explicit while also guaranteeing that it happens.

Why would you want to replicate the same cleanup procedure for a certain resource throughout the code-base, instead of abstracting it in the resource itself?

Abstraction and explicitness can co-exist. One does not rule out the other.