the only thing i'm uncertain of is if Margaery was in on it (when she fed him the pie), or was it Granny Tyrell and the cup.

initially it looked like Sansa was knowingly in on it but it would make no sense, since *if* Granny had given her something, she would have had to assume the unlikely chain of events that put Sansa in that position to get the cup. Also, the Fool only grabbed Sansa and took her away specifically because she was unaware of her part in this.

Watching Granny Tyrell's conversation with Sansa closely, it's pretty clear.