+1 to `propagateIfFatal` now, thanks (both here and above)

as for `abort2Qon2F` remember the tasks are sequential so if there is a failure in a secondary task, none of the subsequent ones will yet have been queued; the runner just aborts with the remaining tasks unsubmitted.  (and in fact a caller can submit them later and it works, they is maybe a bit dangerous.)  so the `cs` is not still running and i think we're safe.  but it is worth javadoc on the fields.  (having the fields is a huge step forward too!  :) )