Xantcha, Sleeper Agent

Xantha, Sleeper Agent

*Xantha (opponent = owner and under my control) versus Ghostly prison, I am still forced to attack when I do not pay for Ghostly prison, and then can not proceed combat.
*Xantha (opponent = owner and under my control) and Teferi's protection. She did not return and wasn't found anywhere. The game for the owner froze.
*Xantha and Mystic Barrier. If the barriers direction is chosen to attack Xantha's owner Xantha is forced to attack still and game freezes.

No files, tests, or entry points are named. Reproduce the three Xantcha scenarios with Ghostly Prison, Teferi's Protection, and Mystic Barrier, then trace the related card and combat interactions; done means these cases no longer force an invalid attack, lose Xantcha, or freeze the game.

Written by the indexing model from the issue text.