[ceremony]

Interesting. Is this intended or is it a bug/quirk of the programming? The fact that you can use them for casting purposes in combat makes me suspect it's the latter, perhaps like the inability to lower province defense in the same turn that you buy it once you've selected a new friendly province. It seems that if you buy provincial defense, then close the window and select another province, and then come back to the original province and click on the Defense, you can take back the points you bought. However, if you select one of your own provinces in the interim and click on "Defense", your ability to change the provincial defense becomes locked, and you can only buy more defense, not reduce it to the level it had at the start of the turn. Because you can change spellcasting, recruiting, movement, and just about everything else until you actually click on "Host," it seems like this is a programming quirk. Maybe the game leaves the previously selected province (where you changed the defense) open for writing until you select a new province's Defense, whereupon the game saves the old one and opens the new one in preparation for you to change the defense level. It would make more sense as a programming quirk, because it's not consistent with the other game mechanics (where you can basically take back anything, even building purchases and gem expenditures) until you host the turn.

I'm curious as to whether or not this is related to the AI's ability to seemingly "see" provincial defense in the turn that you buy it. I've done numerous, repeated experiments with this and it appears that the AI reacts to you buying provincial defense in the same turn you purchase it, meaning that it could not be explained by the presence of scouts. I have saved game folders in which the AI attacked me in several provinces, and replayed the turns numerous times. Each time the AI attacked the same provinces. However, when I purchased provincial defense above a certain level in those provinces and re-loaded the game, the AI suddenly refrained from attacking. I've found that in solo play, it is possible to direct the AI to attack a certain province simply by leaving it with a low provincial defense while increasing the defense of surrounding provinces. I've had great success in solo games in channeling the AI once it gets behind my lines by simply leaving it with one movement option that has zero provincial defense. However, the AI is not looking at my moves themselves, because I can always ambush this movement with one or more of my armies. It's actually a good way to pick off marauding AI, assuming you have the gold to spend and an army to intercept with. The AI heads for the province with the least defense (this can sometimes be affected by priority targets like fortresses) but the key point is that you can absolutely change AI movement by purchasing provincial defense in that same turn.

Given that the game seems to be designed to allow you to make whatever changes you wish until you finally hit "Host", and provincial defense appears to violate this rule, and the AI doesn't cheat in the sense that it doesn't know your orders but it reacts to this defense purchase, I wonder if the AI is inadvertently getting information from you because of a save state, where the game gets information it is treating as being from a previous turn, but is actually from the current one.

Likewise, I'm curious if the blood slave thing is deliberate as well. I have no problem with it being a game mechanic: I like how everything is the game has a consequence, and that you can't just "undo" things (like disband units - once you buy them, you have to find a way to kill them). So if you have blood slaves and get into combat, you can't use them for rituals. But because they can be used in combat spellcasting, I wonder if there isn't some coincidence at work here.