No doubt this has been asked and answered before; for the Imperial player, when does a special action constitute an attack (as far as the one attack per activation limit goes)?

I understand that the Elite Imperial Officer’s Executive Order doesn’t count as an attack. Some are unambiguous, like Tusken Cycler (“Perform a ‘range’ attack...”. How about Vader’s Force Choke? No attack dice are involved - is the use of attack dice by the figure the key factor?

Special action is an attack action (action containing at least one attack) if it allows the activating figure to perform one or more attacks.

Force Choke is listed in the rules reference guide as an example of an ability that causes the target to suffer damage, but isn't an attack.

Edit: note that there is no "one attack per activation limit". The limit is "one action containing one or more attacks per activation".

Attacks can be performed from abilities that are not actions without them counting towards the attack action limit (e.g. Heroic, Sustained Fire class card).