OK, so I found some info on cleaning out a hung/broken task via foreman-rake and I think I’m finally out of hot water. And then I was able to successfuly “unpromote” the newly-created (and likely hosed) incremental content views as well. I’m back to square 1 which is good.
The thing that caused this in the first place is an issue with incremental content views; a few of us all had the same issue (Unable to publish an incremental CV update - #9 by caseybea) and @iballou has confirmed a bug and so eventually there will be a fix.
Anyone else recently having this issue (attempt to create an incremental content view, things blow up) should watch that thread identified above for updates.