sceneFromWire function
Read back what SceneDocument.toWire wrote — a PICTURE, not a document.
The wire's values are already composed (base folded with every fx writer), so they land in the authored slots here and draw exactly as sent. The one exception is the imposed transform block, which has no authored slot at all: it comes back as an fx contribution, which is where a transform lives on this side too.
Implementation
SceneDocument sceneFromWire(Map<String, Object?> root) =>
SceneDocument(_nodeFromWire(root) as FrameNode);