Distributed notification center not notifying distributedly

In a deamon, I register using:

[[NSDistributedNotificationCenter defaultCenter] addObserver:loader
    selector:@selector(getNotifications:)
    name:kProxyStartNotification
    object:@"MyProxy"];

In the transparent proxy provider, I post using:

static let dnc = DistributedNotificationCenter.default()
// later
Self.dnc.postNotificationName(.proxyStart,
                                      object:"MyProxy",
                                      deliverImmediately:true)

(I also tried putting the same observer code in the containing app, just to be sure.)

(Also, btw: the automatic conversion of kProxyStartNotification to Notification.Name.proxyStart is really sweet.)

I'm not getting the notification in other processes. I tried putting an observer in the extension, and sure enough that did get the notification, so it is being generated. Just... not leaving my process.

I tried checking for sandbox violations, using Quinn's instructions, but see nothing.

I also tried

[[NSDistributedNotificationCenter defaultCenter] addObserver:loader
    selector:@selector(getNotifications:)
    name:nil
    object:@"MyProxy"];

(and the same in Swift, for the network extension), and -- as can be guessed by my still asking this question -- no luck.