She isn't shown drawing a single rune in comic time. She doesn't actually show anything to us about how magic works and Reynir comes away from her class with no visible increase in skills. So we don't *see* a mage with expertise in the "show don't tell" sense.
Precisely. She has lots of experience in
teaching magic. In the "those who can't do it, teach it" sense ...
Anne was divinely gifted the ability to hold her sense of self for 90 years until help could be provided to save the lost souls. Despite having turned into a troll.
Like I don't know what other evidence is needed.
I can imagine it's possible that the christian god stomped their feet at first and refused to work with a heathen [...]
And honestly there's no reason in comic to believe that the gods are cranky about what the humans in an area believe or working together.
I'm not sure we're working from the same page here - according to Minnas statements, SSSS magic is a gift from the
old (pre-Christian) gods, who
abstain from interfering with humans who belong to another pantheon (mainly the old
Finnish gods', who reciprocrate). She even explained that the few Danes who
do have a magic talent got it as a gift from the
Nordic gods, not to mention
all of the Danes being equipped with a fylgja, a rather Nordic-specific piece of equipment, in spite of their disbelief in it. And Christianity dropped out of the post-Rash world to the point of Onni barely knowing it existed until they ran into Anne.
Yes so how is someone discovered?
Discovery isn't typically a passive process. There is a degree of language barrier since English isn't Minna's native language, but it seems unlikely that a process to identify mages wouldn't be a big priority.
To me, first and foremost, "discovery" is not what you call the expected results of a systematic screening. You
discover a bug in the software you've already shipped to X customers, but you don't "discover" a completely unresponsive device in the course of doing proper QA on the hardware. Also, that info page says that those discovered "
may enter a training program" - having the entire populace searched for those with potential doesn't sound like there'd be much "may" left in their future, even if only by peer pressure.
Frankly, I think that they don't
need to do organized searches. For most SSSS Icelanders, being a mage seems to hold prestige - and the promise of steady employment. I suspect that the Academy of Seiður is rather busy scanning the
applicants to keep the wannabes out ...
Historically there's stigma against men using seidr so it is possible that boys aren't tested or there's even social pressure for boys to ignore any signs.
No trace of that in the info page (or the comic) beyond saying that seiður are "
predominately [sic!] female". (And while Reynir
did make his gender into an awkward topic while visiting the academy, I'm not under the impression he would've gotten any stink-eye
before having embarrassed himself.)