Function get_sync_service 

pub fn get_sync_service(
    service_name: &str,
    services: &ServiceCache,
    backend: &mut Backend,
) -> Option<Service>

Memoized getter for a Service record from the backend, populating the shared ServiceCache on a miss. The or_insert_with holds only the relevant DashMap shard during the one-time DB lookup (vs. the old whole-map Mutex), so concurrent lookups of other services are unblocked.