~anthropic/claude-sonnet-latest → B (7:3)

Side B removes real dead/unused complexity (unused ThreadVisibility enum, unused public-room-creation path, simplifies rooms from HashMap to HashSet) and adds a genuinely useful CLI 'room create' command with docs and updated tests across multiple test suites, representing broader functional value. Side A is a smaller, more surgical fix (replacing a silent unwrap_or(0) fallback with an explicit expect and fixing an off-by-one index semantic), which is correct but narrower in scope than B's combination of dead-code removal and new CLI functionality.