Hidden chat frames kept fading their lines, a scroll frame recomputed its range on every read and fired `OnScrollRangeChanged` on every `UpdateScrollChildRect`, hidden or not, and `OnUpdateModel` fired for panes with no size or off screen.
In the reference, each of these runs in the frame's own update slot, only while shown: message frames trim and fade there; a scroll frame recomputes a range its writers marked, stores it and notifies only on a real move. The model paint fires only for a resolved rect whose screen-clamped viewport has size.
Message frames and scroll frames are now walk kinds, the range is stored and marked, and the paint applies the rect and viewport gates. benilla's options scroll measures its body's own overhang.
Tests pin the hidden fades, the stored range and its notify, and the paint gates.
Fixes#182Fixes#175Fixes#892
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>