When the FBI comes to you, an executive at a printer manufacturer, and says “implement tracking dots or we will discover criminal images on your son’s laptop” or some similar situation the existence or lack thereof of any legal requirement is irrelevant.

Blackmail an Executive? That's a complete overkill.

It's so much easier just to "recruit" the direct manager of the firmware engineering team. Convince them it's their patriotic duty to add "tracking dots" to the design requirements without drawing attention to where the requirement came from.

The engineers implementing it will assume the requirement came from somewhere above, or another engineering team. And if the executives ever notice, they will assume it came from somewhere below. Both will probably assume the legal department was responsible, and that there is some kind of law somewhere requiring them to implement that functionality.

I hear sentiment like this occasionally and I genuinely wonder if this is conspiracy theory stuff or if this sort of thing actually happened in the past.

I'm aware of the programs Snowden revealed, Tempora / XKeyscore / Longhaul / the like, plus I've heard J. Edgar Hoover did bad things and lots of CIA meddling internationally was bad. Still, these seem qualitatively different to the explicit blackmail you're referring to.

Do you (or someone else reading this) know of historical examples that demonstrate a pattern of this sort of thing? You can interpret "this sort of thing" as you wish.

That's a lot to ask for on the spot, so if not, I would be interested in what generally makes you approach the situation from this cynical angle, especially given that it's the FBI. In my experience, which is fairly limited but is as a US citizen, most of the time the US government mostly follows the law and doesn't do this sort of thing to citizens.