Lockout functions that take significant time and effort to defeat (when enabled) I take for granted, even though for decades the unlock code for all U.S. nuclear warhead firing circuits was a string of zeros.

Ha, I didn't know that one. Not sure what to make of it...I guess reality is crazier than fiction, as usual.

In the case of weapons eligible for export, I would only be a /little/ less confident that back doors are not included: One wants one's allies' weapons to work as advertised, and the blowback from discovered back doors would be very costly.

I don't know...For starters I'd suggest the US has no allies. But regardless, it seems semsible to only export weapons that can't easily be used against you. So backdooring them is the obvious thing to do. If your 'customers' manage to disabe the backdoors, tough luck. But the thing is, the people who can disable backdoors can probably build the weapons themselves, so they are not likely to buy from you. On the other hand people who have to buy a complex system most likely can't audit it.

As is done with proprietary trade secret operating systems etc., these back doors would be called "bugs" or "design flaws" when discovered,

"Bugs" are the perfect, 'plausibly deniable' way to fuck users.

and this hard to disprove canard would be widely accepted as fact. But when (not if) back doors weapons systems are discovered, that would be Bad For Business: Quality really counts when defending the interests of one's own billionaires from the servants of hostile overseas billionaires.

Maybe, so the pentagon will sell, say, sabotaged radars to the 'good' dictators so that they can bomb the 'bad' dictators, who bought stuff that's less capable than what the 'good' dictators have.

The consequences of back doors discovered /and/ exploited could include personal reprisals against parties considered responsible and major realignments of global power dynamics.

I don't know...I guess that could happen. But for the time being it looks as if the US can get away with virtually anything.