I want to attack with my cr90 side arc at long range.
I...
Gather attack dice to form the attack
pool and roll those dice. Gather only the dice that are appropriate for the range of the attack as indicated by the icons on the range ruler.
The attack is not obstructed so I roll my red die. I roll an accuracy and the attack follow to the next step.
I rolled against the Solar Corona so before anything I remove my red die. But I already go through the Roll Attack Dice step and I had at least one die so the attack was no canceled. So, technically, I could resolve my effects. CF needs a die so nothing to do with it until I had some color to copy but I have Ackbar as well and he simply add two red dice.
Could I add his dice?
I mean, I am pretty sure the attack is not cancelled unless I am missing some timing little aspect here.
The FAQ and the RRG let clear the attack is cancelled during the Roll Attack Dice step if there are no dice gathered. And I gather 1 die and also roll it. Before Resolve Attack Effects is not During the Roll Attack Dice step so I think I have that clear.
At first I would say it would be possible to add Ackbar and any add dice effect but the CF (until there is at least another die). But I also read that Attack Pool entry:
During an attack, the attack pool is comprised of all dice being used for that attack. This includes the dice gathered prior to rolling as well as the dice after they are rolled.
Cancelled dice are not the attack pool. They are removed from it. Ackbar and other add effects add to the attack pool but is there any attack pool? Is it possible for an attack pool to have 0 dice?
I think this would be a really restricted read of the Attack Pool but I acknowledge that someone could argue that if it is the dice and there is no dice, there's not an attack pool and Ackbar must add dice to an attack pool.