Queue a rebuild that shows the panel for a new query/result set.
The panel is shown by _rebuild_options via call_next, not here, and
not at all if that rebuild hits its recovery path -- which hides and
abandons the search instead.
Empty-state message to show instead of rows, if any. It
replaces the rows rather than joining them, so passing both is
a caller error; titles is dropped in that case rather than
rendered underneath the message.
