The agreement is simply a statement that they are your adventurer. A hearthperson is a human term for the core minions of a lord, it does not have any connection with adventurers at all; beyond the fact that adventurers can be hearth-people for all the little it effects the game.
Players can also have hearthpeople, provided they can find a way to become a lord. Generally you need to be the unchallenged claimant to a site I think.
Hearthpeopel can also get actual quests from the lord, that are also tracked as agreements. SO it
isn't just "they are adventuring with you" (yes this applies to adventurers too, you get a quest from your lord and it is tracked as an agreement in your Q screens “agreements” page abd you can turn it in and end the agreement and get some fame as a reward) I like goblincookie (and their mod, kinda inspired a mod in working on rn) however I dont think goblincookie gets how much content is in agreements now. I believe you can even assign hearthpeople to zones right now in player sites. Then there also the previous example of temporary agreements such as the guide me to a location agreement, and the "lets overthrow the goblins" agreement you can get during insurrections at goblin controlled sites.
Agreements are much more then "you are my companion" at the current juncture.
Not to say that they don't need work, but they are a very powerful new feature that is already leveraged for being employed by someone to do a quest for them. It is likely it will continue being expanded.
Not that I really feel like arguing with someone and throwing a nice thread like this off track. It’s just that I feel like certain people will benefit from this knowledge.Toady also explicitly stated that he WANTS adventure mode to be more “personal” then fort mode, I have a feeling that he will probably do employment (proper non-hearth non-lieutenant employment ) by leveraging some mix between the powerful agreement system and the new “group” stuff like performance troupes, and lordship .
As someone who plays mainly adventure mode I tend to mess with these mechanics in game a lot , for example it looks like whether you are a hearth or a lieutenant or not also factors into inheritance (if you become a lieutenant for a bandit, then kill all the other bandits, including the leader, you inherit their position and can get your own lieutenants) for example. Which means being a hearth or lieutenant does mean something more then “you can get quest agreements from me now”.
Sorry for my ramble. But yes more work needs to be done but the underlying stuff is there and not using that would be silly, he even said in df talk that that was the whole reason for agreements in the first place. So you can hire people to do things for you.