The Driver asked for the arrow on the people-group grid and on the regions list.
Those needed different wiring, and the reason is worth recording because it is
not a preference.
The regions dashboard owns its scroller: .rd-scroll has overflow-y:auto, so the
plugin mounts the button itself and drives its own element. It deliberately does
not touch the page's scroll — this renders inside a shadow root in someone
else's page, and their scroll is not ours to move.
The people-group grid owns no scroller at all. .pgg-root sets no overflow and
.pgg-body has no rule; the grid simply grows and something outside it scrolls.
In this shell that something is .vtl-host, which lives in the layout, outside
every plugin's shadow root, so the grid could not reach it even if it should.
So the arrow for that surface belongs in the layout, beside the circle the
layout already owns, driving the pane it already owns. The grid is untouched.
.vtl-host is per tab, so the arrow follows `active` rather than binding one ref,
or it would scroll whichever pane rendered last.
One component, two consumers, and each drives a scroller it actually owns.
Checked that this adds nothing to the hardcoded-English census: 256 before, 256
after — the three regions entries there are PosterWall prop literals and predate
this.
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