At the risk of shining the spotlight back om this thread, I was directly asked a few questions and would like to respond:
snip I'm curious and would like you to further clarify if your reference to "your table being big" means your post is citable as a coy but official ruling for SRM?
Unofficial, I have a team and we'll run it by them. It's honestly not something any of us thought to be a 'thing'.
And since in your view the first paragraph doesn't mean what it says about covering "all magic", are there other sorts of magic that also get unstated exclusions? The line "Any form of magic (conjuring, spellcasting, enchanting, magical lodges, spirits, etc.)" absolutely means those explicitly listed things are governed by the rule, and the "etc" at the end of the list undeniably says the list is not exhaustive/there are more things than those explicitly listed that are governed by the rule. In your view "et cetera" doesn't cover Sustained Spells. In your view does anything else not make the list of things governed by the rule? Perhaps active Foci, as asked about a few posts upthread?
So, understand that my answer is a compromise between the fluff and the practicality of Shadowrun Core mechanics.
So, I'm going to break down the fluff so we can get to the meat of the mechanics.
"Magic is rarely subtle" By what measure are we determining subtlety and b what perspective. Being invisible isn't subtle by any stretch of the imagination. But that doesn't mean it's detectable by those unaffected by the spell or should be detectable via any other means. The guy that's invisible knows, for sure though. Mindnet? There is nothing subtle about a dude talking in your head. But that doesn't mean anyone outside of that net should have any clue whatsoever that magic has been used except that... (to be continued below)
"Any form of magic changes the world around it." ANY. There are no exceptions. But what defines change? To what extent. again, with Mindlink the change is present in the ability to communicate telepathically. That's a change and it's in the world around the magic. Detect Enemies? That's a change personally, but it also changes in ways that aren't immediately recognizable, the world for your enemies. Who thought they were about to surprise you, but inexplicable are not.
"Sometimes it’s obvious through a magician’s gestures or incantations" and sometimes not.
"Spirits sometimes cause the air to shimmer, even from astral space." And sometimes they don't? I mean it doesn't say ALL the time.
"People have reported feeling chills, dread, or other unnatural sensations they can’t quite put their finger on when magic is in the area." And, at any given moment, any number of magical effects could be, and probably are, occurring at any given location.
So, basically, the fluff tells me that anything is potentially detectable as a magical effect. What it DOESN'T tell me is that it's because of some latent glowey magic field or because you can somehow see magic like heatwaves rising off of asphalt to whatever. A lot of discussion in this thread has been around hypothetically shimmery fields or whatever. But the fluff tells me that I'm seeing a spell being cast because I LITERALLY SEE the wizard in the ACT of casting the spell, not because of some pseudo astral vision.
So, extrapolate that to any other spell and the 'sustained' effect. I can detect a sustained invisibility spell if I HEAR someone two feet in front of me but don't see anyone. Or if they bump into me.
I 'detect' a Mindnet because of the preternatural coordination in the tactics of three absolutely silent individuals.
I 'detect' Mind Control when my companions start behaving in ways completely counter to their nature.
I detect a fireball because there's a gorram fireball.
The fluff tells me that magic makes things happen and that the effects of those things are things that can be seen, heard, or felt. But not necessarily in the moment, maybe in hindsight. It's pretty amorphous and meant to be... well... fluff. A way to bring our collection of crunchy mechanics to life.
SO... at the end of the day, there are mechanics in place for detecting active spellcasting and going through a ward (which is probably a balance thing, really). But everything else is just good intuition and storytelling and outside of the scope of the mechanics. Which is why it was included as fluff.