~x-ai/grok-latest → A (2:1)

A redesigns auth to return HTML fragments and morph the form via poem JS, removing redirect churn and a parallel auth_layout in favor of the shared layout—lasting UX/architecture. B only aligns thread_post_index to 0-based paths (drop +1/unwrap_or(0), expect, tests), a precise correctness fix but narrower in scope.