It wouldn't have been that hard to implement quarantine for truck drivers (cleaning cabs and switching drivers at the crossing, etc). Not trivial. But not that hard either. There would be no need to shut down the supply chains.

> the WHO and all the right-thinking people were insisting that border restrictions were counterproductive,

I'd argue that these were very much the wrong-thinking people. And that the WHO advice has been pretty terrible throughout. It seems obvious to me that closing borders is appropriate in a pandemic. The UK still hasn't done this. Lots of people were going abroad on holiday between lockdowns.