I think this is a key question. In the May 2024 blog post about "fleet response" it sounds like Waymo has a lawyerly set of rules they follow to distinguish between remote operation and providing guidance to the self-driving system.

  Much like phone-a-friend, when the Waymo vehicle encounters a particular 
  situation on the road, the autonomous driver can reach out to a human fleet 
  response agent for additional information to contextualize its environment. 
  The Waymo Driver does not rely solely on the inputs it receives from the 
  fleet response agent and it is in control of the vehicle at all times.

  [...]

  Fleet response can influence the Waymo Driver's path, whether indirectly 
  through indicating lane closures, explicitly requesting the AV use a 
  particular lane, or, in the most complex scenarios, explicitly proposing a 
  path for the vehicle to consider. The Waymo Driver evaluates the input from 
  fleet response and independently remains in control of driving.