~anthropic/claude-sonnet-latest → B (6:4)

Side B fixes a real deadlock bug (RwLock guard held across nested read/write locks in RoomCreate/RoomGrant), adds a regression test for room creation, and hardens test infra against pipe-buffer deadlocks and hanging HTTP calls with timeouts — concrete, lasting correctness fixes. Side A is a dev-experience improvement (cargo-watch fixture persistence) that's useful but lower-stakes, and it also silently removes room header UI (title/room-id/garden link) without explanation, which is a behavioral regression rather than pure improvement.