Title Create E2E test plan for v1beta1, and implement missing tests

# Enhancement

**Why is this needed?**:

To graduate to v1beta1, we need to define and e2e test plan, get it approved, and implement all tests.

**Describe the solution you'd like in detail**:

**Describe alternatives you've considered**:

**Additional context**:

Start by reviewing the COSI v1beta1 API and the project's existing end-to-end test coverage. Define the graduation test plan, get it approved, then identify and implement every missing test. Done means the approved plan is complete and the full v1beta1 E2E suite passes.

Written by the indexing model from the issue text.