[Coldsaturn]

- "what is the chip actually controlling?"
His emotions, for one. He can't feel anything too strongly or the chip activates and gets him to reset. Normally it would mean resetting his memories (so that the trigger disappears entirely), whereas for Caleb it means he knows he needs to be extra careful the next time. The brainwashing caused by the chip would be enough to control soldiers, but with his arm we're also looking at body control in its entirety, once the project is complete. It's all controlled by the brain, after all.

- "did he develop this black-hole-in-my-brain defense as a child, due to EVER's experiments?"
I don't think he had any reason to have a black hole in his brain back then, despite everything. The chip is way more recent. Plus, I think that kind of evol control speaks of maturity. We know that Zayne already manifested his evol when he was a child, so it's entirely fair to assume that kids have it, but in a way that is difficult to control and possibly weaker.

- "why did EVER pick up Caleb?"
World Underneath texts go a bit into that.

- "we're from the same source"
Until we get more content in the main story, this sentence might be referring to Decoherence world specifically.
Writers have been careful to tie MC with each LI by something different, and they already stretched Sylus and Raf by going for the soul with one and the heart with the other. I doubt they'd do the soul again with Caleb.
But so long as we talk about the myth specifically, I can't give more details until you play it!

- "i still do think that the initial reaction was legit"
Yeah I agree with you on that! I think that's the version that puts together both your take and mine in a way that makes sense.

- "i have been pushed at Nier Automata a number of times as a game i *must* play but i just haven't gotten there"
It is a very long game, I totally get it. Back in the day I didn't even play it myself at first, I simply pulled up a complete walkthrough on youtube and strapped in for the journey. It's one of those gaming experiences that stay with you, I totally recommend it as well!
And I didn't know FFXIV had a Nier inspired raid series, that's amazing.
I'll call you when I'll finally walk into ffxiv and you'll do the same when you decide to pick up secret world legends again.

(running to listen to that song, and how dare you slap me in the face by mentioning Inner Universe out of the blue. That song took my entire spleen as hostage 20 years ago and never gave it back)