Parse a persisted whiteboard payload (WhiteboardState.ToJSON output) into a
rehydrated engine instance. PURE + TOLERANT: any malformed input (empty, non-JSON,
JSON of the wrong shape) returns null instead of throwing — callers render an
empty state rather than breaking the surface they're embedded in.
Parse a persisted whiteboard payload (WhiteboardState.ToJSON output) into a rehydrated engine instance. PURE + TOLERANT: any malformed input (empty, non-JSON, JSON of the wrong shape) returns
nullinstead of throwing — callers render an empty state rather than breaking the surface they're embedded in.