Function try_read_record 

pub fn try_read_record(
    suite: &Suite,
    service: &str,
) -> Result<Option<ServiceRecord>>

The published record, telling “absent” from “unreadable”.

Ok(None): there is no service.json (or it holds no record). Err: it could not be read right now, so whether a service exists is unknown. Treat that as “try again”, never as “no service”. Nothing here retries.