Creator of Ante here, Ante inherits Rust's Send/Sync for thread-safety. `mut` refs and `Rc` which provides shared mutability don't implement either and thus can't be shared across threads. So shared mutability is only within a single thread.
What would be good is if effects are used to discharge the ownership obligations, that should dovetail well in Ante. BTW I appreciate the clear effects handling in Ante, very nice!
FYI - this article is written by the author of Vale