Moat says you are unaffected by that card as a whole, which logically includes while-in-play portions.
Moat says you are unaffected by "that attack", which may mean either the card or its attacking part. By convention, a card is not an attack if its harmful effect does not happen on play, which, in my eyes, implies that harming you outside of the on-play part is not an "attack", and so Moat does not apply. It's not even important whether i'm right here (how would i ever prove that), just that official cards avoid diverting from this convention to avoid confusion, which is why i suggest the convention should be applied here, too.
As I've said above, I think these points have merit, but still disagree with your conclusion and have given reasons why. "That attack" logically refers to the card as a whole; that's why Enchantress has its own special keyword to refer to the on-play instructions only.
I think an issue with your argument is that the card ideas being discussed here
do have the attacking part happen on-play, because they can only ever be in play by being played. These aren't Attack-Reserves, which can be put into play without being played, so the confusion isn't an issue here.
In any case, I don't think Tollgate can safely exist while following that "convention". If it's not worth breaking the convention, then it should be scrapped as a whole.
What do you think of Factory, which
does follow the convention?
Mean Court Room - $6
Action-Attack
+4 Cards
+1 Buy
All other players draw a card.
All other players gain a curse.
I reveal moat. Do I draw a card? Imo: I do not.
Mean Fishing Village-$5
Action-Attack-Duration
+1Action
At the start of your next turn: +1 Action
All other players discard down to 3 Cards.
When this is in play: all cards cost $1 less.
I reveal moat when Mean Fishing Village is played. It's my turn: are cards cheaper for me? I am inclined to think they do.
But what if it said:
Mean Fishing Village-$5
Action-Attack-Duration
+1Action
At the start of your next turn: +1 Action
All other players discard down to 3 Cards.
When this is in play: all cards cost $1 less and when someone buys a card, they gain a curse.
Are cards now cheaper for me, when I revealed moat when it was played? Do I gain the curse?
Mean Court Room - no you don't, because you're unaffected by the card.
Mean Fishing Village (1) - It should say "Now an at the start of your next turn" and "while this is in play", but the answer should be no. You are unaffected by the card, which includes beneficial parts of it.
Mean Fishing Village (2) - The answer is still no. It has zero affect on you.