TypeAlias.PreferredLocale

type PreferredLocale = NonNullable<AuthUser["preferredLocale"]>;

The set of locales accepted by the user-update API, derived from the canonical AuthUser model (non-null). Persisting a value outside this set is a type error, so callers must narrow an app-local string locale (e.g. via isSupportedEmailLocale) before calling persistPreferredLocale.