In the scriptures below you'll notice that words canst, could, and cannot are used as opposed to won't, would and will not. The question is: Is it that God "cannot" lie or that he "will not" lie? If he "cannot" lie - how does that not restrict his agency?
12 And he answered: Yea, Lord, I know that thou speakest the truth, for thou art a God of truth, and canst not lie.
(Book of Mormon | Ether 3:12)
6 And I, Enos, knew that God could not lie; wherefore, my guilt was swept away.
(Book of Mormon | Enos 1:6)
6 Behold, I, the Lord, have brought you together that the promise might be fulfilled, that the faithful among you should be preserved and rejoice together in the land of Missouri. I, the Lord, promise the faithful and cannot lie.
(Doctrine and Covenants | Section 62:6)
