The less visible you are, the easier it is to throw you under the bus. For example, suppose you don't give any interviews, never sign anything for the company,

The less visible you are, the easier it is to throw you under the bus. For example, suppose you don't give any interviews, never sign anything for the company, never pitch to investors, etc. Then, it is easier for them to pretend you never existed later - even if you make the entire product. So, I suggest you be at least somewhat visible and offer to help your business partner with some of these things in addition to coding. Also make sure you agree in writing to a percentage of the company rather than a total number of shares, and make sure you're privy to the final cap table.