How do you get the attachment image from a local notification on the Watch?

Been at this for ages now, getting nowhere, thanks to Swift and the betas...

The iOS app schedules a local notification that has a userInfo dictionary, and one small JPEG image attachment.

Objective-C in iOS app:

content.attachments	= @[[UNNotificationAttachment attachmentWithIdentifier:myIdentifier URL:[imageURL filePathURL] options:@{UNNotificationAttachmentOptionsTypeHintKey : UTTypeJPEG} error:&error]];

This works fine. The notification is correctly scheduled.

If I ignore the Watch and let the notification appear on my phone's Lock Screen, the image is there.

Going back to the Watch. The Watch app receives the notification, and the didReceive method is called in the NotificationController.

No matter what I try, I can't get the image from the notification.

NotificationController.swift: (image is sent to the NotificationView to use as the background.)

guard let attachment = notification.request.content.attachments.first
else {
	print("Couldn't get the first attachment, using default")
	image = Image.init(kDefaultImage)
	return
}

// We get here, so we know there's an attachment
if attachment.url.startAccessingSecurityScopedResource() {
	let imageData = try? Data.init(contentsOf: attachment.url)
	if let imageData = imageData {
		image = Image(uiImage: UIImage(data: imageData) ?? UIImage.init(imageLiteralResourceName: kDefaultImageMasked))
	}
	attachment.url.stopAccessingSecurityScopedResource()

} else {
  // << I ALWAYS HIT THIS BIT >>
	print("Couldn't access the file, using default")
	image = Image.init(kDefaultImageMasked)
}

I always get told I can't access the file in the security scoped bit.

If I take out that check I get Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value because the code doesn't put anything into image. Obviously I would put the default image in there, but once the Watch app crashes the notification that's shown on the Watch shows the correct image, but it's obviously not using my NotificationView because that crashed.

How the hell do I get the image from the attachment? This was simple to do in the old WatchKit extension stuff, look:

NSArray *attachments = notification.request.content.attachments;
if(attachments.count == 1) {
	[_groupAll setBackgroundImage:attachments[0]];
}

No problems there; it always worked.

Thanks.