You and Luke Sky Walker are commanders in the rebel army preparing to attack Darth Vader and his Death Star. By yourselves, neither you nor Luke possesses enough fire power to defeat Darth Vader, but together you can destroy the Death Star. However, you must come to agreement on the precise moment to attack, but you cannot communicate using the normal communications else your presence and location will be detected by Darth Vader.

But you each possess an unlimited number of R2D2 messenger droids that you can use to send messages to each other. But, the droids may be destroyed by the enemy's PatrolBots, so you have no way of knowing if your message gets through unless Luke sends a droid back to you with a confirmation message.

Suppose your droid gets through to Luke and Luke sends a droid back to you with a confirmation message agreeing to the time to attack, but it is destroyed by a PatrolBot? Should he attack? You haven't received a confirmation, so what will you do?

Is there a protocol that you and Luke can use to avoid defeat? If not, explain why not. If there is a protocol that would work, please explain it.