Cynthia reveals Chancellor of the Annex from their opening hand. On Dave's first turn he plays an Island and passes the turn. On Cynthia's first turn she casts Faithless Looting. Dave casts Daze returning the Island to his hand, saying “float a blue”. Both players put their spells into the graveyard and Cynthia passes the turn, at which point Dave tries to cast Brainstorm with the floating blue. Cynthia says that the blue was spent to pay for the Chancellor trigger, while Dave claims the trigger was missed since Cynthia never said anything about it.

The MTR and the IPG both have lines that would seem to say that Dave is correct and the trigger was missed.

MTR 4.2
During the resolution of one of their spells or abilities, a player may not assume their opponent has taken a shortcut. They must seek confirmation that a choice with no visible impact was taken.

IPG 2.1
Even if an opponent is involved in the announcement or resolution of the ability, the controller is still responsible for ensuring the opponents make the appropriate choices and take the appropriate actions.

Do these lines apply here? Or are those meant for different situations and we should fall back on the philosophy of “Triggered abilities are assumed to be remembered until otherwise indicated, and the impact on the game state may not be immediately apparent.”, thus ruling with Cynthia that the trigger resolved and was paid for?



Official answer please.