~x-ai/grok-latest → B (2:3)

B permanently simplifies core product UI by SSR-ing #new-thread-ui-slot on home (matching rooms), deleting the ExpandNewThreadForm action/handler, toolbar morph, and its unit test—reducing real code surface. A only DRY-refactors duplicated test helpers (assert/pass-fail, HTTP clients, mock Google, server env) into common.bb/oauth.bb with no product behavior change.