openai/gpt-chat-latest → A (4:1)

Side A introduces lasting infrastructure by centralizing private-room route encoding/decoding (`room_route_segment`/`room_id_from_route_segment`), updating all routing and URL generation to use it, and adding URL normalization utilities (including canonicalization improvements and tests). Side B is a good targeted bug fix that correctly moves the zero-ratio guard before `ensure_item` and `voted_pairs.insert`, preventing ghost items and stale voted pairs, but its scope and long-term architectural impact are much smaller.