Resumptions can escape without using raw ctl

[TimWhiting]

This causes at least one issue with finalizers being run twice: #641

I've noticed in general that resumptions do not have adequate escape analysis, though what is "adequate" and what is too restrictive could be two separate things. Given the fact that we have raw ctl for when we want to take full manual control, I think erring on the side of being more strict would be good.