The settled outcome of dispatching a notification on a single channel.
One element is returned per requested channel, in request order, by
INotifier.sendSettled. A channel that failed reports ok: false
with the serialized error rather than throwing, so a caller can retry one
channel without re-sending the ones that succeeded.
{ readonly channel: string; readonly ok: true; }
| { readonly channel: string; readonly ok: false; readonly error: SerializedError; }