Rivet currently allows a client to present the same resume token again while the preious transport is still being torn down. In normal recconects this is harmless, but during a fast network handoff two transports can briefly race to restore the same subscription state. This affects Northstar because its client reconnect flow can open the replacemnet transport before the previous one has fully disappeared. I'd like to agree on the contract at the Rivet boundary rather than relying on client-side timing.