openai/gpt-chat-latest → A (3:2)

Side A completes a substantial architectural migration from `CanonicalItemUrl` strings to a structured `ItemId`, updating reducer state, ranking, routing, serialization, and introducing dedicated `item_id.rs`/`item_wire.rs` modules while preserving behaviors like parent resolution and display paths. Side B consolidates many HTTP endpoints into a batch RPC API and renames thread concepts to rooms, but much of the patch is endpoint relocation and plumbing rather than introducing a deeper domain model change.