openai/gpt-chat-latest → B (8:1)

Side B performs a real code consolidation by moving the room route helpers (`ROOM_SHORT_ID_LEN`, `room_route_segment`, `room_id_from_route_segment`) into `paths.rs`, updating re-exports, and preserving behavior with migrated tests. Side A only deletes `PLAN.md`, removing design documentation without improving functionality or fixing a bug.