Renarin started his prescient visions in WoR, before he went to Urithiru.
He was writing on the walls before the Everstorm came and they knew to look for the Oathgate.
Those times when he played with his little box or whatever, he was probably talking with Glys.

Glys is, apparently a "corrupted" spren...
How hand when did this happen?

Was the corrupter unmade at the Shattered Plains?
Did Glys follow him from Alethkar?

What kind of spren was he before he was corrupted?
How has this corruption affected him?

Renarin apparently has the surge of progression, but does he have the surge of illusions? Or has the void precog thing replaced that?

Or is it the result of a weird resonance between his surges and the void-nature of his spren that his seizures allow to slip in?

Shallon does appear to have glimpses of far-seeing (remote viewing?) in her drawings is that caused by resonance?