anchor.diff:                          controller: frontScrollController,
                           scrollDirection: widget.scrollDirection,
                           reverse: widget.reverse,
  -                        cacheExtent: _cacheExtent(constraints),
  +                        cacheExtent: cacheExtent,
                           alignment: frontAlignment,
                           physics: widget.physics,
                           addSemanticIndexes: widget.addSemanticIndexes,
  
positive.code:                     ),
                    ),
                  ),
                ),
              if (_showFrontList)
                PostMountCallback(
                  key: const ValueKey<String>('Front'),
                  callback: startAnimationCallback,
                  child: FadeTransition(
                    opacity: opacity,
                    child: NotificationListener<ScrollNotification>(
                      onNotification: (_) {
                        return scrollNotificationCallback?.call() ==
                            _ListDisplay.front;
                      },
                      child: LayoutBuilder(
                        builder: (context, constraints) => PositionedList(
                          itemBuilder: widget.itemBuilder,
                          separatorBuilder: widget.separatorBuilder,
                          itemCount: widget.itemCount,
  
negative.code:   }
  
    @override
    Widget build(BuildContext context) {
      return LayoutBuilder(
        builder: (context, constraints) {
          final cacheExtent = _cacheExtent(constraints);
          return GestureDetector(
            onPanDown: (_) => cancelScrollCallback?.call(),
            excludeFromSemantics: true,
            child: Stack(
              children: <Widget>[
                if (_showBackList)
                  PostMountCallback(
                    key: const ValueKey<String>('Back'),
                    callback: startAnimationCallback,
                    child: FadeTransition(
                      opacity: ReverseAnimation(opacity),
                      child: NotificationListener<ScrollNotification>(
                        onNotification: (_) {
                          return scrollNotificationCallback?.call() ==
                              _ListDisplay.back;
                        },
                        child: PositionedList(
                          itemBuilder: widget.itemBuilder,
                          separatorBuilder: widget.separatorBuilder,
                          itemCount: widget.itemCount,
  