In Europe they call these things a "bus" or a "train". They are usually cheap, in Luxembourg all public transport is free.

You get into it, and it takes you to the destination. You can space out all you like.

Yes, it is slower than driving yourself, unless there is heavy traffic, but it tends to work well.

The car beeps and by the time the driver returns to earth and figures out what the fuck is going on, it will almost certainly be too late.

What you're really asking for is a car that predicts when it needs to beep. I'd imagine that in most of the serious situations, the maximum warning time will be shorter than the minimum spaced-out driver reorientation time. In fact, no meaningful scenario comes to mind where the car would want help but with a handful of seconds to spare.