Runs a create with its name claimed. Where nothing can race, run is
called synchronously with an idle claim; otherwise the claim is awaited, a
refusal goes to refuse, and run must settle the claim.
Parameters
what: unknown
{ username } or { group }, or null for no claim
run: (held:HeldClaim)=>any
the create, handed the claim
refuse: (held:HeldClaim)=>any
answers a refused claim
onThrow: (e:any)=>any
answers a throw out of run, after the claim is settled
as failed
Runs a create with its name claimed. Where nothing can race,
runis called synchronously with an idle claim; otherwise the claim is awaited, a refusal goes torefuse, andrunmust settle the claim.