The window tree: splits, tabs and focus, expressed as rectangles.
There are no ratatui types here and no dependencies at all. A layout is a tree plus some
arithmetic, and keeping the terminal out of it is what lets the rules, where focus goes
when you press <C-w>l, what happens to a split's siblings when you close it, be tested
as plain functions.
The model is vim's, because the people who want a Temporal client in their terminal mostly have vim's window commands in their fingers already. It also means the diff feature is not a feature: two workflow histories in a side-by-side split is the comparison, and it works for any two views rather than a pair somebody anticipated.