split ~total ~count is an int list of length count, where each element is equal to total / count. If total mod count <> 0 then total mod count elements are eqaul to (total / count) + 1.

columns ~consumes items groups items into columns. A new column starts at each item whose predecessor does not consume. The concatenation of the result is items.

layout ~usable ~offset items is the canonical-space geometry of items arranged as full-height columns on a horizontal strip, in order. Column width is the head item's width_fac * usable width (min 1); windows within a column split the height evenly. Strip x offset is subtracted, so rects may lie outside usable. Callers apply Gaps.post.

scroll ~align ~viewport_w ~max_offset ~offset ~col:(x, w) is the strip offset after applying align to the focused column col, where x is its strip-relative position (offset-0 placement minus the usable origin), w its width. max_offset is the strip-relative x of the last column. For Left and Visible the result is clamped to 0, max 0 max_offset, so stale offsets self-heal and the tail column can anchor at the left edge.