Strongly Consistent Name Registration

[zicklag]

Right now, the way that we reserve usernames is built on Leaf's eventually consistent store.

This means that it's possible for one user to claim a username, think that it worked, and then, with very close timing, another user could claim the same name, and take it from the first user.

This window of time where it could be taken is probably in the milliseconds with a non-clustered Weird server, but with a clustered server, it could be prolonged if there was a network partition between the clustered servers.

The user would only find out that the username was taken by another user after the servers reconnected to each-other.

This is not that big a deal right now, but in the future, we should build some sort of strongly consistent layer on top of Leaf, possibly using multi-paxos or raft, to make sure that name registration is strongly consistent.