DF-5822 control run (churn thread disabled-by-failure: initial scaffold was
mode 4555 so setegid(0) failed with EPERM for the whole run - an accidental
perfect control: same poll loop, no cred replacement, 719,556 iterations).

  setegid0: Operation not permitted            (x many, churn inert)
  poll iterations      : 719556
  iterations w/ rows   : 0
  root rows observed   : 0 while euid=1001

This is the transcript of the first guest run (rig output captured before
the run.log files were switched on); it matches run.log/run.2.log's
3-second in-band control phases (which also show zero control-phase hits).