OFSC filter combination for one activity at a time

Summary

I'm having quite a bit of trouble with the following task:

Content

Hello,

Say we have a specific user type 'worker'.
Users of type 'worker' should only see one activity at a time in one's 'Edit/View Activity' screen.
A 'started' activity should take precedence and 'pending' activities come second, ordered by position in route.
Any other activity status should not be shown.

So, all my efforts at coming up with combinations of filters and filter conditions have been fruitless.
Have anyone of you ever been able to accomplish something like this? If so, how?

Thanks in advance

Tiago Murer