A Pane Is an Object, Not a Rectangle
A native split is a tree. Each node is either a split (horizontal or vertical, with a divider) or a leaf (a pane bound to one PTY and one terminal view). Nested splits are just deeper nodes. That sounds like window-manager trivia. It is the difference between "I can move this job" and "I can screenshot this job." An object has identity: title, color, focused descendant, the process attached to it. A rectangle in a byte stream has cells.
Because the pane is an object, the app can ask it questions without parsing the screen. Which pane has focus. Which process is in the foreground. What directory it was born in. A sibling that wants a new split to the right of this object asks the tree, not a multiplexer. Selection copies text from the view, not a scraped grid. The first track's seam was expensive because none of those questions had an object to land on.
Linked Dividers and Maximize
Dividers are part of the tree, not decorations. Adjacent splits that share an edge can share a divider, so dragging one does not leave a jagged gap. That is layout, owned, not a luck of pixel alignment. Maximize is also a tree operation: the focused leaf takes the tab's frame, the other leaves remember their ratios, restore puts the tree back. Maximize is not "hide the other PTYs." The jobs keep running. Only the projection of the sibling leaves is borrowed.
If maximize killed the unfocused jobs, it would be a close wearing a zoom icon. If maximize discarded the tree and rebuilt a single pane, restore would rematerialize instead of revealing. The tree has to survive being visually one leaf. That is the same lesson as detach: the drawing is allowed to change without the ownership changing.
Navigate the Objects
Keyboard navigation walks leaves: next, previous, and left/right/up/down by nearest rectangle that overlaps on the other axis. That directional pick is how Smolder actually moves focus — geometry on objects, not a parsed screen. Parent-split and swap-with-neighbor are not verbs here. The tree still owns the leaves, which is the tree you will drag in the next lesson.
Focus is singular inside a window. One leaf is the focused pane. Chrome can show that without painting the world orange — a rail, a mark, a word in the title. The next lessons will put identity in that chrome and let TUI colors stay standard. Here the only claim is: there is a focused object, the tree knows which, and navigation moves that knowledge, not a pixel highlight that forgot the model.