Convenience factory for the dominant per-call case: route this request's
progress to cb (the verb mints a unique token), leaving progressToken
and logLevel unset. Spelled out so a single-callback caller need not pad
the leading positional fields with throwaway values.
Convenience factory for the dominant per-call case: route this request's progress to cb (the verb mints a unique token), leaving progressToken and logLevel unset. Spelled out so a single-callback caller need not pad the leading positional fields with throwaway values.