Notifications management: accessing and manipulating notification threads

There’s an old issue which is somewhat related.

The V3 (“REST”) API provides some support for manipulating notifications (unlike the V4 API), however when creating an issue or PR on behalf of a user there seems to be no good way to opt the user out of being notified: the only way to access a thread id seems to be by having received a notification, there looks to be no way to list “inactive” threads, or to access the notification thread from an object without listing them all and filtering by the ill/un-documented subject (that property looks to not be mentioned at all in the Activity page.