docs: public OperationResult executeCommand(long index, long sequence, long timestamp, RaftSession session, PrimitiveOperation operation) {
      // If the service has been deleted then throw an unknown service exception.
      if (deleted) {
        log.warn("Service {} has been deleted by another process", serviceName);
        throw new RaftException.UnknownService("Service " + serviceName + " has been deleted");
      }
  
      // If the session is not open, fail the request.
      if (!session.getState().active()) {
        log.warn("Session not open: {}", session);
        throw new RaftException.UnknownSession("Unknown session: " + session.sessionId());
      }
  
      // Update the session's timestamp to prevent it from being expired.
      session.setLastUpdated(timestamp);
  
      // Update the state machine index/timestamp.
      tick(index, timestamp);
  
      // If the command's sequence number is less than the next session sequence number then that indicates that
      // we've received a command that was previously applied to the state machine. Ensure linearizability by
      // returning the cached response instead of applying it to the user defined state machine.
      if (sequence > 0 && sequence < session.nextCommandSequence()) {
        log.trace("Returning cached result for command with sequence number {} < {}", sequence, session.nextCommandSequence());
        return sequenceCommand(index, sequence, session);
      }
      // If we've made it this far, the command must have been applied in the proper order as sequenced by the
      // session. This should be the case for most commands applied to the state machine.
      else {
        // Execute the command in the state machine thread. Once complete, the CompletableFuture callback will be completed
        // in the state machine thread. Register the result in that thread and then complete the future in the caller's thread.
        return applyCommand(index, sequence, timestamp, operation, session);
      }
    }