only way that seems possible is if another deal is in the works to unload a contract or two (mara? metro? those would be the easiest)
otherwise, it would put us right on the cap threshold (4.2 season cap hit coming in vs ~1.2 going out, with injuries and the ~2.3 cap space we had, it might fit, but it would be tight)
also, for next year, it would make things very difficult without unloading other contracts.
but as far as a straight up deal, it's not terrible.
I'd hate to give up on S.Kost so early, because he could be a good one, but from a roster makeup pov, Hartnell brings the kind of physical presence that can play in the top 6 that we sorely lack (mind you, he is prone to the bad penalties, so there is a risk of him quickly becoming a lighting rod for criticism if he doesn't produce right away).
losing Halak is pretty much inevitable, and getting an established vet that fills such a big hole is a pretty decent return... better than a 2nd round pick, or an average prospect...