Function reserve_local_addr 

pub fn reserve_local_addr() -> ChannelAddr

Reserve a local channel address that can be served later.

Local channels are backed by an in-process port registry, so reserving a concrete address is a synchronous allocation that does not require a Tokio runtime or an OS listener. Gateways use this to have a stable advertised local location immediately, including when the process-wide gateway is initialized from a std::sync::OnceLock. Serving is a separate step that binds the reserved port to a receiver.

Network transports do not have an equivalent reservation API here: their concrete addresses come from binding sockets and starting the corresponding channel server.