This DEV-only field was added in 836331ba5f69f2cc53b273ec073fae116db14302 by @sebmarkbage but it's not being used anymore to my knowledge.
current: Fiber | null,
  workInProgress: Fiber,
  renderLanes: Lanes,
) {
  const nextProps: OffscreenProps = workInProgress.pendingProps;
  const nextChildren = nextProps.children;
  const prevState: OffscreenState | null =
    current !== null ? current.memoizedState : null;
  
  
  
  let spawnedCachePool: SpawnedCachePool | null = null;
  if (
    nextProps.mode === 'hidden' ||
    nextProps.mode === 'unstable-defer-without-hiding'
  ) {
    
    if ((workInProgress.mode & ConcurrentMode) === NoMode) {
      
      const nextState: OffscreenState = {