openai/gpt-chat-latest → B (5:1)

Side B replaces the pervasive `CanonicalItemUrl` string wrapper with a structured `ItemId` type across the reducer, ranking, routing, RPC, path handling, and tests, while adding dedicated `item_id`/`item_wire` modules and updating APIs to use the stronger abstraction. Side A is a useful, well-tested UX improvement that makes ranked child-group pin icons submit the existing unpin flow and adjusts CSS, but its scope is limited to a single interaction whereas Side B establishes a foundational identity model used throughout the project.