I'm totally disgusted by Steve's behavior, but you don't need a written contract to have a contract, regardless of what designs someone did or didn't do. A partner's level of input could be simply marketing or sales and have no technical expertise at all.
That being said, I agree with Mr. Sauer.
Take it to emails, phone calls, tete-a-tete meetings with your lawyers -- whatever.
I don't care to be subjected to your legal problems, your tongue-in-cheek pleadings for understandings, your millimeter thin false sincerity for honesty and disclosure.
It's not why I joined the community. I don't care what your reasons are, what your motivations may be. I don't care how right you are or how wrong you are.
I just don't want to hear it.