stored_loopback_port

Return the stored loopback redirect URI port, if one is reusable.

DCR registers client_id against a specific redirect_uri. If the callback server binds a fresh random port on a later launch, the authorize request will carry a redirect_uri that no longer matches the one registered with the persisted client_id, and the authorization server will reject it ("invalid or missing redirect_uri"). Reusing the persisted port keeps the registration valid across runs.