React SplitView: Restore Layout

[MidnightTinge]

I'm using a SplitView in a react project and am having problems (de)serializing its width for persistence. This is a simple two-pane layout with a treeview on the left and a content pane on the right. In the onReady callback I am attaching an onDidDimensionChange handler to the treeview panel and this works perfectly for saving the panel's width. It's restoration that I am unable to do.

I know that layout is not exported on the typescript type so maybe I went down the wrong rabbithole but digging through the source code it seems like layout is what I'm looking for. But when I use layout() on the panel within the onReady callback there's no change, same with setSize(). Is there another way to do this in React?

The following is a basic example of what I'm trying to do:
https://codesandbox.io/p/sandbox/cranky-austin-n6w96l?file=%2Fsrc%2FApp.tsx%3A30%2C21

If you open the codesandbox console (top-right of the preview window, lil terminal icon) you'll see that states are serialized correctly but just not being restored. The restoration logic is src/App.tsx line 29-34, you can swap which code block is commented to verify neither are working.