openai/gpt-chat-latest → B (4:1)

Side B introduces a unified batched RPC API (`/api/v0/rpc`), migrates the CLI to it, refactors validation into shared modules, and restructures the core data model from thread-centric to room/scope-aware (`room_id`, `thread_tag`, scoped reducer state). These are foundational architectural changes affecting server, client, events, reducer, types, and tests, whereas Side A primarily adds a new `/ui` endpoint with HTML UI actions, form-template handling, and reuses existing web-post logic to support progressive browser interactions.