SPEC-DASHBOARD-KIT D3, and the last of the three decided-not-built items. The bus
carried two coordinated channels — filterSet NARROWS scope, selectionSet MARKS
individuals — and was missing the third: hoverKey POINTS at the one record under
the pointer. It is how a reader sweeps a table and watches the map answer without
choosing anything, and kepler.gl treats hover as a configured interaction beside
filters for the same reason.
IT IS A PLAIN ref AND NOT A SET, AND THAT IS THE WHOLE DESIGN. Hover fires on
every mousemove across a 2,107-row table. selectionSet had to become a plain Set
with a version counter precisely because a reactive collection fires per element;
a single ref has none of that problem — one dependency, one write, no iteration.
A repeat is a no-op, so an unchanged value never wakes a panel.
HOVER IS NOT SELECTION, AND MUST NEVER BECOME IT. The cheap implementation is to
put the key in selectionSet "just while hovering", and every consequence of that
is bad while none is obvious at the call site: useSelectionCamera watches
selectionVersion, so a hover would fly the camera at every mousemove — the
resize-strobe bug wearing a new hat, on a Driver who is photosensitive. The CSV
exporter reads selection > filter > all, so a hover would silently change what an
export contains. The table's selection pill and the shell's live region both
report selection counts, and both would narrate the pointer. So a panel may fade
or outline on hover; it may not fly, select or filter.
NO PANEL IS WIRED, deliberately, and I want that on the record rather than left
to be noticed. D3 says panels opt in, and the first opt-in belongs with a
consumer that has a reason: wiring one into Big Picture speculatively would be a
visual change to the flagship that no reader asked for, landed while the kit
stack is paused. That does leave a channel nothing uses — the same criticism I
made of the unmounted filter chips — so the difference has to be earned rather
than asserted: this is a documented, gated contract with its first consumer
named, not a component that was quietly orphaned. check:hover-channel is what
makes it a contract instead of dead code; the first panel to use it inherits the
rules instead of inventing them.
Three mutants, all caught: routing setHover through selectionSet, dropping the
equality guard, and removing hoverKey from the returned surface.
SOURCE ONLY. Stacked on landing 2. No rebuild needed — nothing renders it yet.
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