openai/gpt-chat-latest → B (3:2)

Side B introduces a substantial architectural shift by consolidating many separate REST endpoints into a typed RPC layer, separating validation into its own module, and changing the data model from thread-centric to room-centric (`room_id` + `thread_tag`), with corresponding reducer, CLI, event, and test updates. Side A contains a valuable functional bug fix for the external garden index (`external_root_host_items`) and adds richer GitHub import card rendering, but much of its patch is feature work and module reorganization rather than the broad infrastructure change delivered by Side B.