ReadonlyCONNECTION_At least one agent is connected.
ReadonlyCONNECTION_No agent is connected. Nothing the tunnel exposes is reachable.
ReadonlyCONNECTION_Proto3 zero value. A read of the tunnel never returns it; a mutation records it, because it reports the tunnel that was written.
Defines the static values of ConnectionState.