The kanban drawer had grown the only edge-aware masked scroller in the
tree, and the next surface that wants one would have copied it. Lift it
to components/ui as FadeScroll, export it on the plugin SDK, and leave
kanban's ScrollFade as a name its call sites already pass `max` to.
The mask math comes out as two pure functions. jsdom's CSS parser drops
any gradient containing calc(), so a rendered mask-image can't be read
back off the style attribute -- edgeMask/scrollEdges are testable for
real where the component's inline style is not.
Brooklyn Nicholson
15b0b95413