Yep, and part of that as needed/as assigned is to notify your supervisor that you are done with your assigned tasks and are ready for a new one, if they don’t have one for you great, play minesweeper, but if you’re done with your assignments (seriously who is ever in that position), and don’t say so, now you’re acting deceptively.

I don't see 'notify your supervisor when tasks are complete' as part of most contracts either; it wouldn't be there, really, because beyond really basic stuff that actually creates way too much information for the supervisor to go through.

Without it being in the terms, it's not a duty you have to fulfill. It's not deceptive not to do favors for your supervisor.