openai/gpt-chat-latest → B (3:2)

Side B introduces a lasting architectural change by consolidating many REST endpoints into a typed batch RPC interface (`RpcCommand`/`RpcResult`), refactoring the CLI to use it, and restructuring reducer/event models around room and thread separation (`room_id` + `thread_tag`). Side A makes a useful URL refactor—centralizing private room route encoding/decoding with `room_route_segment` and adding URL normalization helpers—but it is narrower in scope and primarily updates routing and URL handling rather than the project's core API and state model.