code: public function persistSeenCatItemIds($seenCatItemId)
      {
          $sessionId = $this->getTestSession()->getSessionId();
          $items = $this->getServiceManager()->get(ExtendedStateService::SERVICE_ID)->getCatValue(
              $sessionId,
              $this->getCatSection()->getSectionId(),
              'cat-seen-item-ids'
          );
          if (!$items) {
              $items = [];
          } else {
              $items = json_decode($items);
          }
  
          if (!in_array($seenCatItemId, $items)) {
              $items[] = $seenCatItemId;
          }
  
          $this->getServiceManager()->get(ExtendedStateService::SERVICE_ID)->setCatValue(
              $sessionId,
              $this->getCatSection()->getSectionId(),
              'cat-seen-item-ids',
              json_encode($items)
          );
      }
docs: Persist seen CAT Item identifiers.
  
  @param string $seenCatItemId