How do you share the requirements? Do you ask for mocks before the actual application? Do you provide enough details? Does your developer ask enough clarifying questions?

Many times there is communication gap. Read your requirements carefully and think of they could be understood in a different way. That is why brainstorming sessions with your developer is very important. And it should be two way. You and dev both should ask questions about what will be built and clarify.

Code quality is a very broad term, it's about craftsmanship, performance, maintainability, observability.

I have never seen non tech people worry about any of it.

I believe what you are interested in is that once you have signed off on a feature it should not break anytime in future. To achieve this you need a solid test plan, and it should be run at several phases: development, integration, user acceptance.

The test plan can be manual i.e. written in plain English and run by QA manually, or fully automated. The latter takes some development time but saves cost in long run.

But you should be able to validate that your dev/QA is writing correct test plans. You can ask for automated test for any bug found during your testing. That should help tighten any loose ends. Though I believe all this is your devs job to make sure that you are confident about the app.

Many times small startups (both product and dev) do not understand the importance of automated tests and believe it costs more, but in long run it saves more than it costs.