; Sending <exec SOMECOMMAND RESTARTPOLICY> causes the command to be run.
;
?? <exec ?argv ?restartPolicy> [
  let ?id = timestamp
  let ?facet = facet
  let ?d = <temporary-exec $id $argv>
  <run-service <daemon $d>>
  <daemon $d {
    argv: $argv,
    readyOnStart: #f,
    restart: $restartPolicy,
  }>
  ? <service-state <daemon $d> complete> [$facet ! stop]
  ? <service-state <daemon $d> failed>   [$facet ! stop]
]

; If the restart policy is not specified, it is defaulted to `on-error`.
;
?? <exec ?argv> ! <exec $argv on-error>