The description for Aegis of the Hearth is much more detailed in DE and clarified some points - but I still have two questions on how casting tokens work:
"Participating magi, and only participating magi, can invite other individuals into the Aegis. This involves giving the individual a token that was designated as part of the ritual."
It's not stated explicitly - does the casting token need to be present during the ritual? Or is an arcane connection sufficient to designate it? The reason I am asking is that all Presiding Quaesitors hold casting tokens for Magvillus’s Aegis of the Hearth ritual (HoH:TL p.44). Those need to be renewed every year, so the question is whether all Presiding Quaesitors have to travel to Magvillus once a year to present their tokens at the ritual. (The casting tokens are powerful magic items, so I am assuming that they are not created anew every year and sent to the Presiding Quaesitors.)
"Any participating magus can also revoke an invitation, whether issued by themselves or by someone else. They do not need to retrieve the token in order to do this."
It's not stated how exactly an invitation is revoked. I imagine that a) the magus revoking the invitation has to be inside the Aegis and b) that it can be done as quickly and easily as saying out loud "I revoke the invitation of X to this Aegis of the Hearth". Is this what others are assuming as well?
Aegis tokens I would expect to be present and expressly ritually designated as a token during the ritual by those casting it. You couldn't for instance sneak an object you want to use as a token into your pouch/pocket and have it present, but not handled during the ritual. Tokens I would expect to generally be tracked/known by the Magi of a Covenant, often limited to a specific number per participant barring special arrangements for say a magical Custos etc. For the Presiding Q's I'd expect that facilitating these events does require special arrangements of some sort, likely with magic/assistance made available by the House for this purpose.
We don't really have much in the way of guidance but I think being inside the Aegis is likely unnecessary, but I could see the argument for it. I am also not sure I'd require verbalization. A conscious willing (like an act of spell concentration, spent trying to direct the Aegis) would likely be enough to me. If the individual in question was a participant in the Aegis they effectively count as a caster of the spell and I'd argue that means they have an intrinsic connection to it as an active effect of their own magic.
I think a 'token' needs to be present (and specifically included in the ritual as a token) at the casting -- and any previously issued tokens which are not brought back & renewed simply expire. At the same time, designating a token does not seem to be like enchanting any kind of item -- there is minimal time spent, no special expenditure of Vis, no lab text generated, etc. So the Aegis of Magvillus just has a number of 'spare tokens' created every year -- the tokens the Presiding Quaesitors have are a non-issue, and they can pick up (or even send for) their new 'current' token at any time.
Very much this. Each casting of an Aegis is a unique spell/ritual being cast. Tokens must be present for any given ritual to count as tokens for that instance of an Aegis.
In “Shadow & Flame,” which is totally unofficial, one magus revokes a casting token silently and without anyone noticing. The bearer of the token was wounded and distracted, and didn’t realize the Aegis was affecting them again until they tried to cast a spell.
Thats how I interpreted the new language about revocation. At any time, simply by wishing to do so.
I agree that it makes sense to require the casting tokens to be physically present during the ritual.
There are basically two ways to accomplish this. The first is an annual gathering of the complete council when the Aegis is renewed. The advantage here is that it makes in-game sense to have this annual gathering to exchange information and discuss Quaesitor matters, as otherwise the council would only be an emergency thing. The disadvantage is that it either takes time to travel or the members incur warping points, which might inconvenience very old magi.
The second option is that every year, every member sends their casting token to Magvillus by Redcap express. This means that every year for the same two days the item is not available to them. This is probably not a problem, but feels less interesting. There is of course the potential for stories that involve stealing those items, but the fact that they can be destroyed remotely creates complications.
The reason I wrote "The casting tokens are powerful magic items" is this: "Members of the outer tier [...] are provided with invested devices capable of transporting them and companions, to a reception house outside the Magvillus fortress. This device includes a signal effect to inform the member of a meeting and another that destroys the device, both can be remotely activated by the Guernicus Primus. These devices are used as casting tokens for Magvillus’s Aegis of the Hearth ritual." (HoH:TL p.44) I don't think it's a good use of resources to create two dozen spare invested items. Even worse, it would be boring. Would it be a good idea for every council member to have one of those items and use a mundane item as a casting token? Sure, but that's not how they do it.
Revoking an invitation
I like the explanation that the participants count as the caster and can change the spell's effects by concentrating on it. My explanation where you "command" the Aegis is more "item-like".
It's not clear from the novel alone how the token was revoked - Dominicus might have revoked it somewhere private where he could not be overheard. But if you say he did it silently, then that's how it happened.