The dots indicator: one circular <button> per page inside a clipped viewport
track. The active dot carries aria-current="page"; every dot exposes its page
name via aria-label (the circle is decorative). Click navigates through the
brain, gated while busy. For large counts the track glides (CSS transform
transition) to keep the active dot centred, iOS page-control style, instead of
reshuffling the DOM. Dot DOM + windowing live here, not in a shared atom.