in-every-mind-each-lesson-learned
The obvious next step would be to just - pull the info out of Primary-Friend's mind directly. As soon as it was confident that the matter-creation ability was truly novel, Mediator attempted to grab everything it could out of Primary-Friend's brain.
Which was - nothing. Primary-Friend's thoughts and memories appear to be totally impervious to being accessed by Mediator. Its first hypothesis was that this was maybe the result of damage from the collision that entangled them, or the extremely unusual interface between them, but then Primary-Friend spontaneously manifested the brain-hardware for a standard interface (which should also not be possible!), and Mediator was still denied access. The other shards it's asked ran into the same problem, including Negotiator, who specializes in this kind of thing.
Another one of Primary-Friend's mysterious powers at work, Mediator concludes, and it starts shifting gears towards passive observation, until Negotiator forwarded a packet of data it received as a byproduct of its own failed attempt, along with instructions for Mediator on how to get similar feedback from its own failures...