Function pin_exists_in_atlas 

async fn pin_exists_in_atlas(
    atlas: &mut AtlasClient,
    pin: &str,
    contract: &str,
) -> bool

True iff atlas currently has a provider whose id (or namespace) matches the pin AND it provides contract over GRPC. Used at chat startup to detect stale pins from a prior deploy whose audio provider has since been renamed or removed — caller drops the pin and re-prompts the picker instead of silently letting voice fail with “no provider”.