This would require the shards to quantify magic first. Which is... Well. If they could do that then the cycle wouldn't really be a thing.
There's compromises. Maybe they've observed it, understand what the magic does, but can't replicate it. Or like, they've observed practitioners, but not the spirits, so they're really bad at copying it (and magic systems are different on each planet subtly, so the shards don't build up as much useful info as they'd like.)
Two points.
Firstly, what little definition Pact gives us on its magical system tells us that Pact is
metaphysically operating on real physics logic, but even more depressing: you can't get something without giving something in exchange, and on the whole the world trends toward spiraling down the drain. As such, there's no reason to think Pact's magic is any kind of escape from entropy -in a lot of ways Pact seems to be a world where supernatural entropy is
considerably faster than real-life physics entropy. So if the Entities know about magic, it wouldn't help them beat entropy.
Secondly, there's no reason to expect magic to be an out-of-context problem to Entities in terms of blocking precognition. An out-of-context problem in terms of Scion having no reason to think, on his own, that agreeing to give "something" in a backpack to a Fey in exchange for (whatever) is going to result in his name and therefore his identity stolen, certainly, but not out-of-context in terms of Entity precognition just failing to predict magical stuff. Worm precognition only seems to work when something
foils it -so higher spirits in Pact might have the power and protections in place to ward off the Entities, but magic wouldn't be invisible by default. Even if the invisibility to their senses applied, that really ought to be directly overturned by plugging into human senses -that is, Scion himself might be 100% clueless to magic, but the shards plugged into humans really ought to be aware of magic just from hitting hosts that are aware of magic.
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Re: the Quest itself, I'm not a fan of how
long the updates go on. I get that Blake is an established character, but I have trouble feeling invested in a Quest if it feels like I'm contributing only occasionally, and only a little, with most of what actually happens being about the Questmaster writing characters interacting and so on without any input from the audience. Like, Wormwood seems to me like it might be an interesting
fanfic, but it's not grabbing me as a
Quest.
I'm also skeptical of the idea that magic is "new" in Wormwood's setting. Pact's magical system is very reliant on precedent and history shaping perceptions that shape reality that shape perceptions. If you plugged in the basic idea into Worm and then had it grow organically, I have doubts you'd end up with Pact's magical system in anything but the most general of details, and it's my impression that Wormwood intends to cleave more closely to Pact's system as presented, not use it as a conceptual launching off point.
I like the idea of this Quest, but I find it sketchy so far, unfortunately.