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

Side B fixes a real production bug — a tokio RwLock deadlock in room grant/create RPC handling caused by holding a read guard across nested read/write calls — and adds a regression test plus timeouts to prevent hangs, delivering concrete correctness value. Side A is a pure test-code refactor (deduplicating shared helpers into test.common/test.oauth) that improves maintainability but touches no production logic and provides no new functional guarantees.