My memories have become a bit foggy, but I distinctly remember
that at least some source in the game claims it was stolen from Vlaakith, who I think never leaves her base of power in Tu'narath and always keeps her secrets close. There are no Crèches in Astral Space as they're specifically used to do things that are physically impossible in the astral, like raising young or growing food. In the Astral Sea time doesn't pass by itself, only by observation, cause and effect. The same is true for space. The Planescape books call it something like the "backstage of the multiverse". That's why Githyanki can show up almost everywhere without long travelling times. In 2e they can just plane shift at will.
If I remember the Emperor's part correctly, he was sent to retrieve it by the Cult of the Absolute, came under the influence of the prism and suddenly had a better idea, improvising with what he had. The Sharrans may have been manipulated to go steal the artifact by Gortash and then taken under mental domination by the elder brain. Maybe the Emperor was their backup plan or even deployed as support. Looking at his personality, I wouldn't even rule out that it was given to him by the Absolute to be a more plausible ally to the Sharrans, but then its tether snapped.
