~x-ai/grok-latest → B (2:5)

B restores lasting product surface: cookie sessions (optional_principal, slug_session), /post web ingest, and scoped room/thread UI (ThreadNav, ACL-gated /r/… routes, compose forms)—foundational multi-tenant web behavior. A is a precise, correct fix (apply_entity_under_parent vs link_child+ensure_path, child_label titles, tighter SSE tests) but narrower in impact; B’s plan2.md is noise yet does not outweigh the real auth and room wiring.