Even less is needed to generate danger: I found myself checking my phone twice during a car trip because when listening to music through the USB-C to Jack dongle, it believes I am blasting music at full volume through my ears and decides to cut off the volume to 10% after 20 minutes.

Don't, and I mean DON'T decide things for the user.

Can't you let your phone know that the USB-C is not connected to headphones?