As of 1.0.3, when two clients start the same one-shot service, the one
that loses the race never sees the value that was produced by the
‘start’ method.

  herd start one-shot & herd start one-shot

Here one of the ‘herd start’ processes will wrongfully fail with “failed
to start service one-shot”.

Instead, it calls ‘service-running-value’ but that always returns #f
because the one-shot service was stopped in the meantime.  I’m referring
to this bit of ‘start-service’:

      (match (get-message reply)
        (#f
         ;; We lost the race: SERVICE is already running.
         (service-running-value service))   ;<- here
        …)

Attached is a reproducer.

Ludo’.