35 years ago, when I was a teenager, I remember having discussions with a couple of pilots, where one was a hobbyist pilot and engineer the other a former fighter pilot turned airline pilot.
Both claimed that computers would never be able pilot planes. The engineer gave a particularily bad (I thought) reason, claiming that turbulent air was mathematically chaotic, so a computer would never be able to fully calculate the exact airflow around the wings, and would therefore, not be able to fly the plane.
My objection at the time, was that the computer would not have to do exact calculations of the air flow. In the worst case, they would need to do whatever calculations humans were doing. More likely though, their ability to do many types of calculations more quickly than humans, would make them able to fly relatively well even before AGI became available.
A couple of decades later, drones flying fully autonomously was quite common.
My reasoning when it comes to robots contructing robots is based on the same idea. If biological robots, such as humans, can reproduce themselves relatively cheaply, robots will at some point be able to do the same.
At the latest, that would be when nanotech catches up to biological cells in terms of economy and efficiency. Before that time, though, I expect they will be able to make copies of themselves using our traditional manufacturing workflows.
Once they are able to do that, they can increase their manufacturing capacity exponentially for as long as needed, provided access to raw materials are met.
I would be VERY surprised if this doesn't become possible within 50 years of AGI coming online.
Both Teslas and military robots are designed with limited autonomy.
For a tesla to be able to drive without even a human in the car, is only a software update away. The same is the case for drones "loyal wingmen" any aircraft designed to be optionally manned.
Even if their current software currently requires a human in the killchain, that's a requirement that can be removed by a simple software change.
While fuel supply creates a dependency on humans today, that part, may change radically over the next 50 years, at least if my assumptions above about the economy of robots in general are correct.
Consider that biological cells are essentially nanotechnology, and consider the tradeoffs a cell has to make in order to survive in the natural world.