openai/gpt-chat-latest → B (3:5)

Side B adds durable developer infrastructure: the walkthrough fixture now uses persistent `fixture-data/`, prefers a stable port with fallback via `pick-port-prefer`, runs through `cargo watch`, reuses seeded data when available, and updates URLs when reloading, substantially improving iterative development. Side A simplifies Kaocha configuration by replacing manually enumerated test namespaces with a single auto-discovered `^test\..+` suite, reducing maintenance and ensuring new tests run automatically, but its scope is narrower than the broader workflow improvements in Side B.