Aha there is another issue. New mandatory things can be created after a player's shot at doing them has passed. I wonder if there's any way to actually do that. New optional things happen of course. A mandatory thing, well it would be a "while this is in play" paired with playing a card at a weird time, or "this turn" with a weird trigger. Let's say, "When you gain this, this turn, when any player buys a card, they get +1 VP." That doesn't look too real. But uh, I buy Messenger and hand those out; you gained it, it causes a trigger on my Messenger buy; we already finished resolving those, so which way the rules go determines whether or not I get the +1 VP.
I'm not getting it, because I don't see the connection between this and the ruling we're discussing. In this scenario there is no optional effect and no reacting.
As far as I understand it, we're still doing "when-buy" for your Messenger. After we're done with everything that follows from handing out the cards (to all your opponents), there is now another "when-buy" ability waiting, or several of them if several players gained that card. Why wouldn't you just get the +1 VP? You're the one who triggered the "+1 VP" effect by buying a card, so it's ordered (and resolved) by you on your turn.
If the rule is "when a trigger happens on my turn, we do all of my stuff, then B's, then C's," and B's thing creates a new effect for the same trigger, then we already did my stuff, so it doesn't happen.
To do the new thing, it would need to be that the rule was "we do all of my stuff, then B's, then C's, but if new stuff shows up for me, here is how to handle it."
Ok, I see the issue you're talking about. But I don't think your example illustrates it.
The trigger in this example is that you buy Messenger, and then we do all
your stuff from the trigger, then B's, then C's. But B and C don't have anything that triggers from that. First there is just Messenger's own when-buy. When we resolve that, all of this happens: You gain a hypothetical card ("Poet"), then B gains a Poet - which triggers Poet's when-gain, then C does the same. Poet's when-gain is that from now on, this turn, whenever someone buys a card, they get +1 VP. Ok, so now we're done with Messenger's when-buy ability. We haven't done any other when-buy abilities yet (and importantly, not for any other player), so we're still resolving when-buy abilities for you. Now there are two other when-buy abilities, both saying that you get +1 VP. (Actually, since
you gained a Poet too, there are three, so you're getting +3 VP.)
Trying to think of a scenario that works, but I don't think this can happen with purely mandatory abilities. (See bottom of post for the card abilities.)
(1) Let's say Bob has
Lancier in play. Alice plays an Attack, and then discards
Food Taster. The thing is that since Lancier's card-being-played ability is not optional for Bob, it works like Swamp Hag. Bob doesn't resolve it, it's resolved by Alice. She gets to order it and resolve it before we get to any of Bob's card-being-played abilities (like Moat). That's how I understand it anyway, from your explanations earlier in this thread. So again there's no question that Alice will get the +1 VP, no matter what the ruling is on ordering things.
(2) Let's go with a scenario with optional abilities too then. Bob has
Poleturner in hand. Alice plays an Attack, Bob reveals Poleturner, and Alice discards Food Taster as before. Now - according to the old ruling - by the time Bob chooses to reveal Poleturner, we're done with Alice's card-being-played abilities, so she doesn't get +1 VP. What about the new ruling? By the time we get to optional things for Bob, and he resolves something, Alice could jump in and resolve an
optional thing, but does she resolve a mandatory thing like Food Taster? I would say yes she does, she gets the +1 VP, because we're still resolving mandatory things for Alice. With the new ruling anybody can jump in with optional things, but mandatory things go in turn order.
(3) What about a scenario including a mandatory thing for Bob too? ...Actually I was not able to come up with a mandatory card for Bob, and I don't think it's possible. (If it were possible, the outcome would depend on whether Bob revealed Poleturner before or after the mandatory thing.) I thought of
Abbot, and Bob having it in play, but actually, since it's mandatory, Alice would be the one resolving it (again, like Swamp Hag). So this has the weirdety of having Alice choose when in the turn Bob gets +1 Coin token, but doesn't create a different scenario for ordering things.
Conclusion: So it seems that with the new ruling, Alice will always get the +1 VP; with the old ruling she doesn't get it if it's from Bob's mandatory thing, just from an optional thing.
Lancier: While this is in play, when another player plays an Attack, he discards one card.
Food Taster: When you discard this, this turn, when you play an Attack, +1 VP.
Poleturner: When another player plays an Attack, you may reveal this from your hand. If you do, that player discards down to 3 cards in hand.
Abbot: While this is in play, when another player plays an Attack, +1 Coin token.