lazy-scroll-helper-kit

Four small lazy-list utilities worth carrying between apps — scroll-direction as derived state, centre-an-item scrolling that waits a frame before measuring, an item's visible percentage, and a lookup into the visible window — with the trap each one hides. Use when a hide-on-scroll bar flickers or sticks, when scrolling to an item lands it at the edge or does nothing, or when viewport arithmetic returns values for…