I tried to undo my choice from an Amulet, but there was no dot at the start of my turn. Does this mean there's no way to undo a start-of-turn choice from a duration card?
undo should certainly work for all decisions... and I have used it to go back to the start of a turn before.
All the dots were in the other player's turn, so I don't know what I should have clicked to go back to the start of my turn.