This question has been boiling in my brain for quite a long time.

Consider a hypothetical scenario where one spy chinese or russian programmer working in Google or Meta might have siphoned off (copied and uploaded) all the important code (Monorepo) to the Mothership and all of us are now sitting ducks.

I am sure, this question might have crossed your minds. I have no idea. if blueprints for the TPU chip design could get leaked, imagine what might have already happened?

That kinda happened already in 2009. See https://en.wikipedia.org/wiki/Operation_Aurora

Industrial espionage also was publicly disclosed around the plans for the joint strike fighter. https://www.usni.org/magazines/proceedings/2017/july/chinas-...

I’m sure in the classified arena there are a lot more examples.

Minor point but this doesn't only have to be russian/chinese spies but rather this can be anybody including say the UK/Israel or even countries which can be considered "allies"

I'd also be surprised if this code isn't already available with the US forces too and sometimes the enemy can be from within too.