The rule about @escaping closures being non-isolated was never great: it's always been an heuristic to try to deal with the world where @Sendable has yet to be fully adopted. So instead of making this heuristic part of the actors design, to be removed at some later point, we've removed it from the proposal. Instead, we'll need to rely on dynamic checking where actor code interacts with non-@Sendable`-enforcing code.