Terry, I don't think you fully appreciate the ability of an electric vehicle to monitor the traction of each driven wheel and adjust the power going to/from it. The left wheel can brake while the right wheel accelerates if that is what is needed at the moment. Torque vectoring allows for a level of control one simply does not have with a brake pedal pushing on a hydraulic master cylinder.
Trailer braking may be necessary at times and I'm sure there's an air compressor in the tractor. Trailer brakes may be individually controlled if that is needed. Running separate air lines is a small modification to the basic trailer brake system.
Cables from motors to batteries to carry the power from regen back to the batteries will be large enough since they carry enough power from the batteries to the wheels to accelerate a fully loaded trailer from 0 to 60 in 20 seconds and an unloaded trailer from 0 to 60 in 5 seconds.
Jackknifing can occur when the trailer brakes lock up, or when the cab brakes are used too heavily
That sounds like operator error to me. With properly written software those problems should not happen in an automated braking system. The computer will know the total rig weight (force needed to move the rig on level ground), the slope of the road ahead along with curves and their radius, the weather conditions, individual driven wheel traction levels. With properly written software the truck should keep itself within the limits of what is needed for a safe and controlled stop.
There may be, at times, the need for a panic stop. A boulder falling from a hillside. The truck will act faster than a human driver and will then use trailer brakes along with tractor reg and mechanical brakes to stop.
I'm aiming the rest of this comment only partially at you, Terry. I see a lot of other people engage in the same criticism/doubt.
Why do people think Tesla engineers and engineers working on self-driving systems at many other companies dumb?
Don't they realize that as part of the design process many engineers have dug through the available data on what causes crashes. They've talked to experienced drivers to get their take on the problems encountered when driving. They've done mathematical models of the physics involved in keeping trucks from running into stuff. They've built test systems and tested them.
Tesla has converted diesel rigs to battery powered trucks by taking out the engines/transmissions and replacing them with batteries and electric motors. They've been running loads from their Reno (up in the mountains) battery factory to their Fremont (down at sea level) car factory.
They've taken those rigs to test tracks, loaded up, and pushed the limits to see where traction and braking fail.
Being skeptical is fine. But if you don't know how to do something that experts say that they can do why not phrase it in terms of "I don't understand how this will work" rather than state that something won't work when you don't know that.