D&D 5E - Command + Warcaster + Booming blade = 8d8+str?

So let's see, booming blade says that if the target moves it takes damage. The OA itself happens when a creature leaves your reach but before it actually does so. Basically you're asking if the effect being placed on a creature during the act of moving out of your reach would treat the triggering movement which allowed the OA in the first place to also proc the extra damage. It's an interesting question no doubt. I can see it 2 ways:

1. The movement is interrupted by the OA meaning that the creature attacked, after resolving the OA, can decide to keep moving or not since it now knows that if it does it will take more damage. The movement which triggers the OA can't also proc the bonus damage since the action to move was taken before the OA triggers and the effect of booming blast comes into play.

2. The movement is interrupted by the OA, true, but the movement has already been taken which means it can't be stopped and since the effect is now in place before the movement is completed it triggers the secondary damage instance.

hm.

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