The subdued edge-fade the rail and side panels use now hints at more content on
the page scroller too, which the feed, the channel page and Plex all scroll
inside. Both <main>s move into one PageScroller so the invariants they share —
the load-bearing scrollbar gutter, and the bar staying visible because hiding it
would zero that gutter — are stated once.
Two fixes the hook needed first: it set fresh state on every scroll event, which
above a page tree would re-render it per frame; and it watched a single child
captured at mount, so a lazy page swapping out its Suspense fallback left the
observer on a detached node and the fade frozen at its pre-load value (measured
on the Plex page: no bottom fade over a 3119px list).
peter
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