openai/gpt-chat-latest → A (4:1)

Side A introduces a new structural `ItemId` type, extracts shared wire-normalization into `item_wire`, and propagates the new identity model through reducer state, ranking, routing, HTML, RPC, and tests, replacing pervasive `CanonicalItemUrl` usage with a stronger abstraction. Side B usefully separates identity and path normalization into dedicated modules and cleans up API semantics around usernames/delegates, but it is primarily an architectural reorganization and wire-format adjustment rather than the broad foundational data-model change implemented in Side A.