I'm looking for a specific fic I read on ao3 several years ago. It was WinterIron eventually, and featured a Tony who'd been kidnapped by Hydra at some point and turned into a version of the Winter Soldier-possibly called the Mechanic?-the fic is set after the Avengers have formed. Tony knew Bucky, but when he escaped they were separated and Bucky remained the Winter Soldier. When Steve brings Bucky back to the Tower, he's locked in a holding cell for a while. I just remember a scene where Tony got Jarvis to let him into Bucky's cell and then lock the door so no one else could get in. It was written/set pre-Civil War and possibly also pre-AoU. Help?