When staging lines (or doing anything that requires the main view to split into two)
we want to split vertically if there's not much width available in the window.
If there is enough width we will split horizontally. The aim here is to allow for
sufficient room in the side panel. We might need to tweak this or make it configurable
but I think it's set to a pretty reasonable default i.e. switching to split vertically
when the window width falls under 220
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