The feed takes its column count from main's clientWidth and its
thumbnails are aspect-ratio boxes, so the two feed each other once the
content height sits within a scrollbar's width of the viewport: the bar
appears, 15px goes, thumbs shorten, the content fits, the bar leaves,
and round again — every frame. Measured: scrollbar width alternating
0/15 and clientWidth 987/972 on consecutive frames. Reserving the gutter
holds clientWidth constant and breaks it.
peter
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