StickToBottomState

"Stick to bottom" for a chat list (the idea behind AI Elements' use-stick-to-bottom), for a normal top-to-bottom LazyListState:

• While following, every layout change that leaves content below the viewport — a streamed token, a Markdown block finishing parsing, a Mermaid or KaTeX WebView reporting its height, an image decoding, the keyboard opening — pins the list back to the bottom, instantly (no animation to fall behind the stream).

• The moment the user drags toward older content, following stops. Growth happens below the viewport, so what they are reading never moves.

• Scrolling back to the very bottom, or jumpToLatest, resumes following.

Anything that moves the list away from the bottom that we didn't do ourselves — a drag or fling, but also accessibility scroll actions, keyboard paging or app code calling scrollToItem — stops following, so pinning never fights whoever is scrolling.