Is the fold/unfold transition a window resize, a scene relocation, or a completely new scene?

When toggling between cover and unfolded posture in the iPhone Duo simulator, we observe several seconds of black screen during the transition — much longer than a typical 0.3s rotation animation. Does viewWillTransition(to:with:) fire at all during this transition, or does the OS tear down and recreate the UIWindowScene/UIWindow on the other screen? We need to know which lifecycle hooks are guaranteed to fire so we can update UI state (search width, gradients, cached layout sizes) at the right time.