It would be good to document the json format somewhere in this file, i.e. at least that we extract the events blob for the JSON request (which also contains a bunch of other metadata)

I think we should also have a second timestamp corresponding to the time the blob was received. Otherwise we can't do things like sanity check that the upload interval is correct (e.g., the client-side timestamp should be at least PULSE_INTERVAL away from the server-side timestamp, and we shouldn't be receiving really old events)