Ok so remember when you met the Didact in Cryptum and he was executed? Well that was the Ur-Didact, or Original Didact. Bornstellar was just carrying the Ur-Didacts Conscious. So it turns out the Ur-Didact wasn't executed, but instead was abandoned in a flood-infested system, and although we don't know how, it looks like he got back to the forerunner empire. And yes, you were right aout that a couple months ago(virtual high-five!). And that monitor wasn't Spark, but just Chakas. Spark is one of multiple fragments of the Chakas monitor because he tells the science team(remember this is in 2558) "I see one of me has already caused you trouble." All the Ur-Didact info is from Cryptum, Primordium, and the official description for Silentium.