When using the book of the dead trait, I’m supposed to be able to cast the first 2 spell gems that summon minions that I have equipped. However, when my artifact’s spell - that also summons minions - activates, it no longer will cast the second gem. Considering how many times I cast my spells, as I’m running a familiar build with the brush of muse, this means that it hardly ever works as I’d expected it to.
When it doesn’t cast my artifact spell after casting my first spel gem, however, it casts it as one would expect. My artifact spell can then also be cast if it happens to be triggered, as one would expect.
In summary, for some reason the trait counts a decidedly not spell gem towards it 2 spell limit, and I don’t think that that is intended considering the wording of the trait, so I hereby submit a bug report.
So, as the title implies, it turns out artifact slotted spells interrupt the creature’s actions. For example, the creature casted a spell, and then it triggers the artifact, and instead of later continuing what they were doing since they had additional casts, or postponing the artifact spell until later, it casts that artifact slot and then ends whatever was going to happen if it haddened casted. This includes start of battle effects.