3643eccf added swarm_name: Option<Arc<str>> to AppState and updated
the production initializer, but not state_with_roster()'s test-only
one — main's --all-targets/test build has been broken since. None,
matching atlas's proposed shape: the roster/links tests this helper
backs don't read the display name, and the loading path already has
its own coverage (load_swarm_name_covers_missing_and_set).
Closes#3458.
02aa866e5b