docs: private void validate() {
          long delayedEventCount = delayedEvents.size();
  
          long outstandingAgents = config.agents - agentsAvailable.size();
          long outstandingPhones = config.numbers - phoneNumbersAvailable.size();
  
          if (outstandingAgents != outstandingPhones) {
              throw new RuntimeException(
                      String.format("outstandingAgents (%d) != outstandingPhones (%d)",
                              outstandingAgents, outstandingPhones));
          }
          if (outstandingAgents != delayedEventCount) {
              throw new RuntimeException(
                      String.format("outstandingAgents (%d) != delayedEventCount (%d)",
                              outstandingAgents, delayedEventCount));
          }
      }