The review's premise that the group-emptied arm could not be pinned was
incorrect; the same-group reap case already exercises it. This adds the missing
seam-observable case: dispose() while a setsid orphan holds the pipes and the
run is unresolved — settle kills the child, the group empties (the orphan is in
its own session), and the poll finalizes promptly instead of waiting out the
60 s grace. The v8 ignore on that arm is removed.