Like many of the comments have stated, his visions are not all powerful. His visions are more like he has to try and scope them out not just them coming to him- so at that point he wasn't looking for a vision of whether or not darth vader would kill him because he was sure he wouldn't betrayed. He had no reason to use his powers to foresee darth vader's trust. Also, even if he tried to foresee this, the future is always changing. For example, darth vader really did intend not to save luke but changed his mind at the last second after seeing luke tortured. It was a last minute decision and no vision could have predicted that fast enough.

Like many of the comments have stated, his visions are not all powerful. His visions are more like he has to try and scope them out not just them coming to him- so at that point he wasn't looking for a vision of whether or not Darth Vader would kill him because he was sure he wouldn't be betrayed. He had no reason to use his powers to foresee Darth Vader's trust. Also, even if he tried to foresee this, the future is always changing. For example, Darth Vader really did intend not to save Luke but changed his mind at the last second after seeing Luke tortured. It was a last minute decision and no vision could have predicted that fast enough.