I can't see any rule for one PC trying to help another. Say a Player calls for a Task and another says "I'll help!" - and it's a situation where parallel attempts dont make sense (I admit I also don't like "me too" rolls of same thing by multiple players).

If I'm right and there isn't, is the easiest solution to make it a prolonged task - for 2 characters lower target number by 2, make it 3 checks (a failure means that particular PC can't check again)? In narration, whoever makes the most contribution is actually the one who "shone" and the other the "helper".

Rob

Prolonged tasks covers assisting.

TOR assumes that an instant task is to quick to have another PC provide any benefit, and I think there is some logic in that and it helps limit PC dog piles on many tasks

For the most part, I agree. But there are cases when people can work together.

How about if two characters sing a duet? Or try to break down a door with a battering ram?

These aren't extended actions that will eventually succeed when enough successes are accrued. They'll pass or fail based on a joint effort.

vs

I would consider both of those prolonged actions, or at the very least capable of being expressed through prolonged actions. In general, if another PC is getting involved then the extra spotlight time of prolonged actions rules seems appropriate.