What is this checker Async going to look like? How does it wire into the completion stuff? This is why in my branch I was using the persist to wire the two together. So if you have a ```_check_context``` you will persist the Async which will then kick off the actual completion check without having to explicitly import anything from ```furious.extras/appengine/ndb_persistance```.

I'm just confused what this is going to look like in context.py that doesn't involve an Async with an explicit target into the persistence layer (Unless we do some config magic, if that is what you are suggesting).

```
def _get_tasks_by_queue(self):
    ....
    async.get_options()['_check_context'] = ???
```