Search API + Facets: Overwrite facet output and conditionally alter query condition based on active filter

I have a date field on hundreds of nodes indexed. I created a facet for the date field but it displays all dates available (ew). Instead, we'd like a filter for "Available Now" nodes and "Available in Future" nodes.

Facet Solution: create a custom processor to replace the facet results (hundreds of timestamps) with "Available Now" and "Available in the Future".

/**
 * Provides a processor for Availability.
 *
 * @FacetsProcessor(
 *   id = "availability_processor",
 *   label = @Translation("Availability Processor"),
 *   description = @Translation("Now vs Future Availability"),
 *   stages = {
 *     "build" = 14
 *   }
 * )
 */
class DateProcessorHandler extends UrlProcessorHandler implements BuildProcessorInterface {

  /**
   * {@inheritdoc}
   */
  public function build(FacetInterface $facet, array $results) {
    /** @var \Drupal\facets\Utility\FacetsUrlGenerator $url_generator */
    $url_generator = \Drupal::service('facets.utility.url_generator');

    /** @var ResultInterface $now_result */
    $now_result = new Result($facet, 'now', 'Available Now', 1);
    $now_url = $url_generator->getUrl([$facet->id() => ['now']]);
    $now_result->setUrl($now_url);

    /** @var ResultInterface $future_result */
    $future_result = new Result($facet, 'future', 'Available in the Future', 1);
    $future_url = $url_generator->getUrl([$facet->id() => ['future']]);
    $future_result->setUrl($future_url);

    $new_results = [$now_result, $future_result];
    $facet->setResults($new_results);

    return $new_results;
  }
}

Works great so far; links on the facet add and remove the "now" and "future" url parameters as expected.

However, the results show 0. I tried subscribing to SearchApiEvents::QUERY_PRE_EXECUTE and altering the query to modify the condition:

protected function alterExploreQuery(QueryPreExecuteEvent $query_event) {

  $availability_active_facet = ?????

  $now = \Drupal::service('datetime.time')->getRequestTime();
  $operator = $availability_active_facet === 'now' ? '=<' : '>';
  $query->getConditionGroup()->addCondition('field_date', $now, $operator);
}

This event is fired long before any processors set the active facet items so how do I get the active facet value?

Also, is there any way to output the "Available Now/Future" links in place of dates besides using a custom processor? Reason I ask, the custom processor shows up as an option on all facets, not just the date one I want it to.