The checkpoint store uses optimistic concurrency to allow for only one winner when it tries to claim ownership. We do this properly when the ownership blob already exists.

When the blob does NOT already exist, however, we allow for the possibility of multiple winners. This isn't world-ending because we should eventually figure it out when we try to create the link (Event Hubs will also enforce ownership) but this will result in more flux than is needed, and we could head it all off by just passing If-None-Match "*" when attempting to create the blob/set metadata.

This will also introduce another failure condition when claiming but it's an "expected" error, so should be okay. (409 conflict).