Yes we all know they were creating more tension as that's my point. There is no good in story reason to drag this out.
There is no need to catch him off guard if ultimately it was a fake trial to begin with because his fate was sealed once Bran told them the truth. So the drama here is artificial as it's drama to please the audience. Not drama that makes sense in the story. In the story if they simply intended to rail road and murder him then the con is unnecessary.
He's going to die with or without the con.
Your operating under the assumption that Sansa/Arya tension all season long was just a long con, and I don't think that is the case. I believe the tension was real. It was not until episode 7 that Sansa put all the pieces together, using LF's own methods described here:
[video=youtube_share;h5iH26NAftE]https://youtu.be/h5iH26NAftE[/video]
LF clearly doesn't breakdown until after Bran interjects Lf's complicity in the murder of Ned Stark. Yes he does admit to killing Lyssa, who was a "Troubled Woman" but strongly denies all the other allegations against him. As soon as Bran interjects, Lf gets that whole "shit, I am fucked look". He could have still maintained his innocence, asking for proof, but the proof could be found, and LF knows it.
Your hinging a lot of your arguments on Lord Royce, who himself had his life threatened by LF, and has first hand knowledge of how he operates. It would only make sense that Sansa had talked to him prior to the trial, admitted what really happened at the Vale, and Lord Royce accepted her explanation of events. I am not so quick as you as to think Lord Royce was at all out of character, quite the opposite.
As for proof, I can tell you a few scenes did end up on the editing room floor, and Sansa did have proof in the original draft. The Maester at WF had ever scroll every sent to WF in storage, including some sent by LF to Ramsay.
