That's what they are actually doing.

I think quite opposite, agents need to come with all permissions possible, highlighting that it's actually the OS responsibility to constrain it.

It's kind of dumb to except a process to constrain itself.

A non-deterministic process at that. Coding agents are basically "curl into sh" pattern on steroids

	▲	Terr_ a day ago \| parent [-]
		Even worse, the sh portion is recursive. So the attacker doesn't need to send an evil-bit over the network, if they can trigger the system into dreaming up the evil-bit indirectly as its own output at some point.