Does a wet dream invalidate the fast if one sleeps certain that he will have a wet dream, or if he surrenders to the wet dream until ejaculation occurs? What is the expiation for it, and how is that day to be made up?

The sleeping person is not held accountable. A wet dream does not affect the validity of a fasting person's fast, even if he anticipates it, because it is an involuntary act beyond his control. The emission of semen due to thought while awake does not invalidate the fast according to the majority of scholars. However, if the emission of semen is caused by deliberate action while awake, the fasting person must make up the day and repent, but expiation is not required.