This post is from the Activity iPhone Duo UIKit Q&A.
We have a CALayer subclass performing custom draw(in:) rendering (a radial gradient) behind a card view, resized via viewDidLayoutSubviews. For an ordinary rotation we sync it inside coordinator.animate(alongsideTransition:). If the fold/unfold transition doesn't go through viewWillTransition at all (per Q1), what is the recommended hook to animate custom CALayer content smoothly across this specific transition, given it appears to involve a scene relocation rather than a resize?