The root font-size was calc(16px * var(--font-scale)); a non-integer scale
(1.02 -> 16.32px) made every rem-derived box height fractional. When a filter
section's visible row count changes on a facet refetch, its fractional height
shifts everything below it by the sub-pixel remainder — a deterministic ~0.5px
CSS move that snaps to a visible 1px jitter of the whole filter rail at DPR=1.
round(calc(16px * var(--font-scale)), 1px) keeps the font-scale feature but
quantises the root to an integer pixel, so metrics land on integers and the
sub-pixel reflow jitter is gone app-wide. Verified: root 16.32->16px, chip row
26.453->26px, build + Lightning CSS pass round() through intact.
peter
61ee7af9e4