Scrolled up from the end of a chat (more than 40 px), a pill floats over the composer, on a phone above the drawer's handle, in the composer's tone with only a hairline shadow: "see new messages" once the end has changed since the reader left it (a new last block, or more of a live reply; older pages loading above do not count), "back to latest" until then. It runs back to the end in 250 ms however far (the browser's smooth scroll crawls over a long chat), re-measuring the end each frame, and a wheel or touch takes over. Signed-off-by: dawn <90008@klbr.net>