Keyset pagination is strictly serial (a page needs the previous page's cursor)
and the read-ahead only fired within a fixed 4 rows of the loaded end, pulling
one 60-item page per cycle. A fast free-spin flick (MX Master & co.) out-scrolls
that tiny lookahead, lands on an empty bottom, and waits out a chain of serial
round-trips — the multi-second "Load more" hang. Scale the lookahead to the
rendered row count (PREFETCH_VIEWPORTS screenfuls); since the effect re-runs when
a page settles it chains, keeping a couple of screens buffered ahead of the fold
so the content is usually already there. Bounded, and a no-op for finite lists.
peter
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