Who owns the code I pay you to write?

You do, fully. When you pay us to build an extension, the source code is yours under a written assignment-of-IP clause in the contract. You can put it on your own GitHub, sell it, modify it, take it to another developer, open-source it — anything. We retain the right to reuse generic patterns (e.g. our boilerplate module skeleton, our PHPUnit test scaffolding) but never anything specific to your business logic, data, or branding.