Immunity to corruption isnt actually a necessity for a "trustworthy" government in my view. You need it to stay that way, sure, but literally all complex things are prone to some form of decay that requires they be maintained or replaced eventually. For example, can you trust an airplane to be reasonably safe to travel in? Yes, but only if you dont require that the aircraft be passively able to do this indefinitely, because if you do require that, you run into the issue that without repair and replacement of parts and eventually the whole thing, it will decay and eventually become unsafe to use. That is to say, I view corruption as something like the decay state of governments, I think you can theoretically have a trustworthy government if it is well designed- for a period of time after it is established, with that length of time depending on the efforts of the people living in that society to keep corruption out. When those efforts inevitably fail, it's in need to replacement or at least refurbishment, but that does not mean that the people that lived in the time before that corruption began to mount were unable to rely on it. That we cant design a society to be reliable forever after doesnt mean we cannot build one that is reliable to us and maybe the next generation, we just have to accept that at some point, it'll be the problem of people of the future to do the same.