That was wholly unexpected, throwing Tony's entire identity into question for a dark moment before he gathered his resources enough to remember this wasn't the first time Steve had tried to give up the shield. It just always bounced back, though, Tony couldn't be sure Steve ever really meant it to. Outside of the Avengers, Tony had a lot of good to take care of and occupy his hands. More than a decade after he woke up, Steve still didn't have a whole lot.
"I can build," Tony eventually said, grinning with confidence in that skill at least, but with his brow knit with concern. If he was good at anything, it was making a machine that worked with terrible efficiency. It was a lot easier if he knew what his tools were, though. "What do you mean, you're not...did I do something? Because if it's, if you're talking about 'before' like before I left, I'll apologize but I wouldn't change that. I should have given up the suit then, but I was sick and I'm bad at letting go, and I can see that now and I'm in a good place here." Tony didn't look like he believed it, but Steve didn't seem to be in a good position to argue with him so Tony took a bite of finality out of his burger, letting that note hang in the air for a moment. But this wasn't supposed to be about him. "What changed?" he rephrased to bring them back to the point. If Steve wasn't Captain America, who was he?