openai/gpt-chat-latest → B (4:1)

Side B extracts substantial duplicated test infrastructure into shared utilities (`test.common` and `test.oauth`), adding reusable helpers such as `run-cargo-build-release!`, `slug-server-env`, `complete-registration!`, configurable mock Google OAuth, and centralized assertion/output logic while updating multiple test suites to use them. Side A improves Kaocha configuration by replacing manually enumerated test namespaces with a single auto-discovered suite, which reduces maintenance, but its impact is confined to test discovery rather than broadly improving the test architecture.