Function try_acquire_family 

pub async fn try_acquire_family(
    map: &AgentLockMap,
    pool: &Pool,
    state_dir: &Path,
    family: Family,
) -> Result<Option<AcquiredFamily>, Error>

Resolve + acquire a whole Family NON-BLOCKING, all-or-nothing, and partition it for the registry (AIH lock split out from the tag locks). Ok(None) if any member is busy. Used by spawn / deliver, which resolve the family up front and acquire it in one shot.