Google explicitly denied voluntarily cooperating or working with the NSA in such a manner. While their denial was picked apart (just as the Apple one is, everyone declaring exclusions and perceived disclaimers), Google's statement effectively eliminated the possibility of an NSL silencing them. An NSL bars you from talking about something, but can't compel you to publicly lie (nor do I think a company with the might and influence of Google be bullied too easily).

Of course this is all talking about Google as a corporation voluntarily doing something. Was someone in Google (or Apple or any other company) working on behalf of the NSA? There was early debates about whether that could even be legal, but at this point it seems that "anything goes" is the pattern, so possibly.

There's absolutely nothing stopping the NSA/CIA from hiring a foreign national to work on their behalf, just like the DGSE could pay an American national in Palo Alto. Whether those employees could operate domestically w/o breaking the laws of their spymaster, maybe not.

It's sorta telling to me that Google decided to go encryption on all intra-data after Snowden. No doubt they would have been briefed by agencies that they cooperate with about what the exposures would be.

It's more likely that whatever chipsets common across smartphones or routers is the point of exploit. So the NSA and Samsung or whomever have to have a private agreement. Apple/Google don't have a need to know, but you think a few engineers might be curious.