The 3♦ is probably not everyone's choice, but that's not the issue. As for my 4♥, if I have to guess I guess. Sometimes I guess right.
A partner (not the one in this hand) advocates 4♣ to deal with a 5-5 such as this, and this hand supports her views, but of course I sometimes just get dealt clubs. Is there consensus? For example, undiscussed, I would assume that an auction (3♦)-4♣-(Pass)-4♠ would say something like "Really glad to hear about your clubs and your values, I have a spade suit and I suggest we play this hand in 4♠" Or it could be that 4♠ is a try for a club slam. Or, if 4♣ is two suited, it could be that 4♠ announces a willingness to play in spades if that is my major, with clubs as the back-up plan.
This was pick-up, so of course I make my best guess. But if I wanted to have some agreements, what are your suggestions?