Metafora was marking tasks as Done on Shutdown, now let Run decide

Also drop error return value as there was nothign for Metafora to do with it.

## FAQ

**Q. Will we regret only returning a bool from Run() when we want to add some automated error handling in the future?**

*A. Probably, but I'd rather fix it when it's broken than try to guess at the right implementation now. Let me know if you think that's foolish.*