We use a PreferenceKey-based pattern to measure real per-row content height in a List (via an invisible .background(GeometryReader { ... }) per row), caching the result in @State keyed by row index, since a fixed height estimate wasn't reliable. This is a common SwiftUI technique, not iPhone-Duo-specific. Apple's guidance on GeometryProxy.reservedRegion covers fold-aware layout for regions affected by the hinge, but I haven't found guidance on whether a live pose change (open → folded, or vice versa, without a relaunch) automatically invalidates cached measurements taken via a PreferenceKey at first layout, or whether SwiftUI's dependency tracking doesn't propagate that kind of external geometry change and the cache needs to be explicitly cleared on a pose-change notification.
Is there a specific environment value or notification to observe for "the window's available geometry changed due to a fold event," separate from the standard horizontal/vertical size-class change?