With the planned 'stolen artifact recovery squads', what's the range of the artifacts you'll be able to send people out to recover? Artifacts stolen from your fortress? Artifacts stolen from your civ hundreds of years ago? Artifacts not stolen from you at all but your mayor thought they'd look pretty good on his shelf after hearing a drunken elven bard sing about them? Will there be an actual 'game' element to this (recover artifacts to deal with noble demands, cure a depressed population or something) or is it just something fun to do?
and...
When the new spies come to check out your artifacts, will there be any way of working out who they are? Will the fortress guard or other diligent dorfs notice them acting suspiciously and accuse them?
Oh, also...
You mentioned peddlers on Twitter the other day, will they also turn up in fortress mode? Does this mean you're replacing the old merchant system finally or will both systems remain for now?
It's just a guess, of course, but I imagine peddlers as merchants with more exquisite/valuable things to sell, and without season fixations, unlike caravans, they could show up in your fortress just like normal visitors
Pretty good adition by the way, Adds a more tasteful realism to the game, and remind me of the tinkers from the kingkiller's chronicle, which is comfy
As for the other questions
-It should make sense that you had to know about an artifact to command someone to look for it, apart from that, you should be able to send anybody to look out for any trinket you want, atleast until law and diplomacy hits in (ex. your king considering the recovery of an artifact a personal matter and prohibits any vasal to look for it without his permission). Now, the important bit, is that they might not come back. For example if the artifact has been lost for centuries, the chance of finding it is considerably lower than normal, something to take in consideration
-For the spies. Again, a wild guess, but although I want specially dumb dwarves to unmask themselves as criminals for mistakes, I suppose firts-update agents will work similarly as vampires, they do stuff, you start being suspicious, and you find him
It would be interesting if one noble could be asigned to see who makes certain questions about artifacts, that way you could know who 'might' be a spy, and act acordingly
Now, obtaining the info for whom does he work is kinda hard without torture, and I dont think its gonna be added soon, or ever