Well, you can just treat them like they are anybody else. So, $1000 fine plus a point on the license of Waymo. And as suggested by another commenter in the thread, if the cars in the fleet (collectively) accumulate more than 4 points within 12 months, Waymo loses its license. As in, all cars operated by Waymo.

What would justify it? Full years salary of a developer plus their fringe benefits? Probably what $300k fine?

If this behavior actually is a prevalent issue, then there will be many fines that add up. If Google doesn't rack up many fines, then this problem is evidently rare.

Ticket and require a company lawyer and programmer to show up in traffic court for every infraction and explain current status of self-driving software.