Focus-based split + keyboard shortcuts — iTerm's 50-year pattern, not a new one
First split UX put a button in the toolbar that always split the root. Replaced with focused-pane split + ⌘D / ⌘⇧D / ⌘W, matching what every terminal user has had muscle memory for since the 1970s.
What was wrong
The initial Split button operated on the root of the mosaic tree, not on the currently focused pane. After a couple of splits you couldn't tell which pane the next click would affect — and there were no keyboard shortcuts at all.
What landed
- Split is now scoped to the focused pane:
⌘D(horizontal split),⌘⇧D(vertical),⌘W(close). - Startup-level navigation:
⌘1..9(jump),⌘⇧[/⌘⇧](prev/next). - Focus is tracked at the pane id level, not the mosaic path level, so it survives remounts.
Commit df83a6b (focus-based split), 341bf28 (startup shortcuts), 4f72b48 (actually patched the keydown handler in App.tsx — the first attempt only wired the menu).
Pattern
For a category as old as terminal multiplexers, the right defaults already exist — iTerm, tmux, and screen converged on the same shortcuts decades ago. The wedge is not in reinventing the bindings; it's in everything around them (multi-startup, persistence, BYO Claude Code). Saved a long argument with myself by copying conventions instead of designing them.