> The problem is to end up at "noindex site" thinking that the "noindex site" is a competitor site
And there is no solution for that, it seems. The solution for the problem <red in address line>'hey, that's noindex site!'</red> is obvious and simple.
> And I don't see how such deception is possible without the backbutton-bug
You told it yourself - 'you can just call the URL directly in browser'. And there are many ways and scenarios how that clicking on a link could happen.
And there is no solution for that, it seems. The solution for the problem <red in address line>'hey, that's noindex site!'</red> is obvious and simple.
> And I don't see how such deception is possible without the backbutton-bug
You told it yourself - 'you can just call the URL directly in browser'. And there are many ways and scenarios how that clicking on a link could happen.