1) Yes, we know Charlie wants to be involved, but we also know everyone is hostile to him, every nearby kingdom in fact.
2) Everyone, including the coalition will be on the lookout for veils, not least of all because GK has a foolmancer. In order to sneak GK's dwagon army in, they had to disguise it as a regular army, and fair enough. But what we apepar to be getting set up for is a literal "Archons invisibly snuck up to Spacerock, and are there now". If the plot doesn't go this way, all for the good, but I feel that's where it is headed. You have to wonder why GK wouldn't do this with massive forces if it's possible.
3) Especially because Jack is a master class foolmancer. A few replies I see try to tone him down, but so far we have him veiling whole cities from hostiles for years (however many turns that is, over 700 it seems), to the point nobody knew they existed. The reaction to his abilities from respected warlords like Caesar was complete incredulity. He's been very impressive to date, and it's really unlikely there is an Archon equivalent as good or better. Let alone lots of them.
4) If the Archons aren't in the battle space, then they're basically useless. So either the story is headed in a very different way, of they are somehow hidden in the battle space of Spacerock, and none of Jetstone's many warlords has noticed them at all, despite the fact that foolmancy needs to leave traces. Absurd.
5) The explanations for how they could have entered the battlespace without alerting others to their presence via the turn system are wholly unsatisfying. Jillian added them to the alliance without telling anyone? WTF? What authority does she have to do that? It also seems complete ridiculous. They don't use a turn? That's false, we saw in book 1.
Well for one thing, i think your assumptions for HOW warlords spot a veil are incorrect. From what i can tell you assume that the warlords have a percent chance of spotting a viel; so just having a bunch of warlords is enough for them to spot a veil... however, the way i think they spot a veil is just by noticing something out of place and weird... noticing rocks that were not there before or seeing clouds that are moving unusually fast. That's why it takes a "lucky/smart Warlord" to spot a veil, as they either have to stumble upon it by chance or be preceptive enough to notice even the slightest things wrong.
In the case of the archons, what if they were veiled as Faq infantry or giants? Jetstone would not suspect that they were veiled troops and just assume they were ordinary Faq troops... or another possibility, what if one of those megalogwiffs is actually a bunch of archons huddled together and vieled? Again jetstone would never even think of checking if they was a viel at work... hell they could be disguised as clouds hovering high above the city, and none of the warlords are perceptive enough to notice that there is something "wrong" about those clouds... there are any number of possibilities for how the archons might be veiled, without jetstone noticing...
As for Jillian adding charlie to the alliance without anyone knowing, who the hell ever said she couldn't?
I don't recall the mechanics of the alliance being discussed in detail... She is the queen of Faq and a full member of the alliance, who the hell says she needs anyone elses permission to invite another side into the alliance... Hell maybe she and charlie joined forces first and the allaince took chalrie in when they took jillian in without realizing it... who ever said that the mechanics of erfworld made it so that other sides are automatically aware of every side that joins them, and don't have to be told... you are pretty much talking about mechanics that may not even exist and are just your assumptions
Most importantly, the action from here on is likely to be silly, though I'll reserve judgement until I see it, because Jack, the archons, etc, should all pick up on the army of Archons before they get too close. This is a problem because if the Archons are overwhelming and can beat GK, then GK will be able to retreat, and can't be followed.
Well one thing that would help before passing judgement here is seeing HOW they are hidden... some of the stuff i mentioned above might not work, but those aren;t the only options... for all we know they could be within the hex but right outside the castle walls; namely on the OPPOSITE side of the castle... maybe they are making use of displacement magic; hiding their real bodies within the walls, invisible, behind the towers to keep out of sight, while at the same time projecting their fake bodies into trees outside the castle walls... so not only are they vieled but also hidden from sight... this is a wait and see kind of thing