~x-ai/grok-latest → A (3:1)

A replaces the stringly CanonicalItemUrl newtype with a structural ItemId enum (plus item_wire split), then propagates it through reducer maps, ranking, VoteData, RPC, and HTML—removing CanonicalItemUrl and encoding identity vs presentation in the domain model. B improves theme persistence (cookie + POST /theme + server-side layout) and adds room-aware RPC path helpers, which is useful polish and a real private-room URL fix, but is mostly presentation/wiring rather than lasting core design.