You're mistaken. The operating system largely prevents cross-process memory access. Of course, CPU vulnerabilities can circumvent these protections, but even then your micro services can run on distinct machines while monoliths can't.

> The only way this would be helpful is if your whole goal is to make something (breaking the contract) as hard to do as possible

Yeah, that's the idea. "defense in depth".

> And in that case, I really have to ask, who are your teammates that you trust them so little as to literally enforce separation this way? No healthy organization should have to resort to this kind of civil war.

(1) not all attackers are internal

(2) some attackers are internal and many very profitable organizations do restrict employee access to secrets (and in many cases this is required by compliance).