I'm pretty sure what you say is correct, which means that the verbal agreement for equity also holds. It follows that if no equity is given, the contract is breached and the code can be taken elsewhere.
And if he breached, what would he have to give back to the founders that was given to him for the code?
Also, if the code was given in return for equity (or the promise of equity), then he is an owner and should have a say in the decision to accept the investment and negotiate the terms.
I agree that the final stock agreement depends on the investor's lawyers (provided everything works out), but how the equity is divided before that is between the founder and the coder.