This might have been answered elsewhere, and people alluded to it in previous posts, but...
What is the earliest turn in which a game can end? Assume no one quits.
For the sake of discussion, let there be "half turns". I.e. turn 1.0 would be {player 1 does actions, buys, cleans up, etc.}; turn 1.5 would be player 2 does that stuff; turn 2.0 is player 1 doe that stuff; and so on (yes, even though I'm a computer scientist, I'm starting counting at 1, not 0).
Shenanigans (Bakers, Nomad Camp, Black Market, Bane cards, etc.) are allowed.
EDIT: Assume 2 players. Of course the game can end in less than 1 turn if there are enough players.