By definition, a prenuptial agreement only covers entering into the marriage. Future assets, especially in community property states, usually have to be specifically disclaimed by the other party in the marriage before they can be considered separate property. For example: A prenup can't specify that a house bought after marriage is separate property, but the non-owning spouse can voluntarily sign away rights to that property as a recorded instrument. This is why some deeds say "John A. Doe, Grantee, a married man as his sole and separate property." (Some states allow for property purchased with separate assets to remain separate inside the marriage but the paper trail on this better be meticulous if a divorce ever happens.)
Editorializing: Why would a spouse be no less entitled to reap the rewards generated by the other spouse's start-up? A relationship, especially a marriage, is inherently two people acting as a unit, so just because one spouse didn't sling PHP and research lambdas all night doesn't mean that either spouse's contribution is more or less valuable. If my spouse accomplished something like this, I'd be thrilled at the success and genuinely looking forward to our life together with much less time and stress investment from both of us, since that means that I was also picking up a lot more of the "home life."