method DiscoveryProvider.watch DiscoveryProvider.watch(serviceName: string,listener: (instances: readonly ServiceInstance[]) => void): Promise<Unsubscribe> Subscribes to instance-list changes. Push-based where the backend supports it, interval-polled where it does not. The listener always receives the full list. Parameters serviceName: string Logical service name listener: (instances: readonly ServiceInstance[]) => void Called with the full instance list on every change Return Type Promise<Unsubscribe> Unsubscribe function that stops the underlying watch