RAG debugging is harder than I expected

I've started building a vector database to learn modern vector search for the AI era. In my professional work, I maintain Jepsen/Antithesis tests for distributed databases and blockchain systems. These tests check system correctness through transactional behaviors under real-world failures. When working on a vector database, I started wondering: what does "correctness" even mean in vector search? By definition, ANN results don't have to exactly match exact search. Some level of approximation is