The selection bridge built at bind time.
The navigation position, or null when the cursor left the
chart — which clears every bound worksheet, since nothing else signals that
the selection ended and a stale highlight would follow the reader to another
panel.
A promise that settles once the selection (or clear) has been requested. It never rejects: a selection failure disables the layer and clears, and a clear failure is logged.
Mirror MAIDR's cursor into the viz as a Tableau mark selection.