~x-ai/grok-latest → B (2:5)

B introduces a lasting routing design (`ItemId::browse_href` / `/~/…`), removes the theme cookie/CSS machinery, and wires real browse handlers with tests—foundational product structure. A is a correct but narrow consistency fix (0-based `thread_post_index`, `expect` instead of silent `unwrap_or(0)`, always-on post links) with supporting asserts, so it matters less overall.