This DEV-only field was added in 836331ba5f69f2cc53b273ec073fae116db14302 by @sebmarkbage but it's not being used anymore to my knowledge.
if (current === null) {
    
    const freshCache = requestCacheFromPool(renderLanes);
    const initialState: CacheComponentState = {
      parent: parentCache,
      cache: freshCache,
    };
    workInProgress.memoizedState = initialState;
    initializeUpdateQueue(workInProgress);
    pushCacheProvider(workInProgress, freshCache);
  } else {
    
    if (includesSomeLane(renderLanes, updateLanes)) {
      cloneUpdateQueue(current, workInProgress);
      processUpdateQueue(workInProgress, null, null, renderLanes);
    }
    const prevState: CacheComponentState = current.memoizedState;
    const nextState: CacheComponentState = workInProgress.memoizedState;
    
    
    if (prevState.parent !== parentCache) {
      
      const derivedState: CacheComponentState = {
        parent: parentCache,
        cache: parentCache,
      };
      
      
      workInProgress.memoizedState = derivedState;
      if (workInProgress.lanes === NoLanes) {