SPV3-1434: Multiple erosion runs are dispatched in parallel

Dan, I wrote a whole novella on the architecture and state of the R2 server-stuff in the ticket. Felt like it had to get recorded somewhere. Feel free to paste it into a requirements doc if you think that will help.

I still don't have any automated tests that really work this thing, I suppose I could put some in Integration Tests because that's really what they would be.