getDefaultUserPresence

Read this client's presence state out of the store: the default CreatePresenceStateDerivationOpts.getUserPresence.

Exported so a host that only wants to *adjust* the default — blank the cursor, add some meta — can call it and edit the result, rather than reimplementing the store reads and drifting out of step with them.

Returns null before the store has an instance record, i.e. before the editor has finished starting up: there is nothing meaningful to broadcast about a client that is not looking at anything yet.