This was hard to debug. It manifested in nodes that had been collapsed
into their parent. When a node was dragged over the recently-collapsed
node, the placeholder would show the action as if the flex direction was
reversed. It turns out useDrag has trouble tracking changes to the
LayoutNode objects. For now, I am just finding the nodes again in the
computeMoveNode function. Later when I redo the drag system, I will fix
this better.