You must use ns_job_done on persistent jobs.
Persistent I/O job callbacks will not be called when the client closes the connection. You cannot depend on being able to call ns_job_done on the persistent job when the connection is closed and the read callback is called. For non-persistent I/O jobs, the read callback will be called when the connection is closed by the client. We need to make sure this behavior is documented - or perhaps it is only a libevent thing?