Forum digest processing does not mark posts as read

As admin:

1. Ensure the Forum module setting "Manual message read marking" is disabled.
2. In a course, create a force-subscribed forum.
3. Enrol a student user in the course.
4. Configure the student user with forum digest type "complete", read tracking "yes", and "mark post as read" when sending post notifications.
5. Create a post in the forum with "no editing-time delay" set.
6. Log in as the student, view the forum and observe the unread post.
7. Run: php admin/tool/task/cli/schedule_task.php --execute='mod_forum\task\cron_task'
   Observe the task output reads "Queued 1 digests".
8. Fudge the queued adhoc tasks via SQL so they can be executed immediately:
   UPDATE mdl_task_adhoc SET nextruntime=1
9. Run: php admin/tool/task/cli/adhoc_task.php --execute
   Observe that the mod_forum\task\send_user_digests task ran.
10. While still logged in as the student, reload the same forum page.
    • Before fix: observe the same unread post remains.
    • After fix: observe no unread posts are shown.

Confirm the alternative behaviour. As admin:

1. Ensure the Forum module setting "Manual message read marking" is enabled.
2. Execute steps 2 through 9 from above.
3. While still logged in as the student, reload the same forum page.
   • Before fix: observe no unread posts are shown.
   • After fix: observe the same unread post remains.