Three low-risk wins for large filtered feeds:
- content-visibility:auto on cards (.cv-card/.cv-row) so the browser skips
layout/paint for off-screen cards; contain-intrinsic-size keeps the scrollbar
stable and is remembered per card after first render.
- memo(VideoCard) + stable onState/onChannelFilter callbacks (onState reads the
loaded list via a ref) so appending a page only renders the ~60 new cards
instead of reconciling every card already on screen.
- Prefetch the next page earlier (sentinel rootMargin 800px → 1500px) so the
'Loading more…' flash is far less likely during fast scrolling.
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