Experimental Sorbet feature enabled by `T::Helpers` and `requires_ancestor { Klass }`. Lets a module declare that it must be mixed into a specific class (e.g. a `UserDependency` module that only makes sense inside `User`), so Sorbet can resolve calls to the host class's methods without forcing casts or `T.bind(self, …)`. Erwin Kroon strongly recommends enabling it ('life is so much harder without it') when adopting Sorbet in real Ruby codebases that use modules as dependencies rather than interfaces.