Comment 2 for bug 1873556

it's trying to address the issue of reproducbility but probably in a not-so-great way.
It may be enough at this point that we're binding the counter around each toplevel form. And also around a file as a whole which may be redundant.
I don't think an intended use of gensym is to let you remove the "#:" and have the resulting form "just work" when read back in. *gensym-counter* does say "*... can be either assigned or bound at any time"

I prefer that any invocation of a setf expander starts numbering its gensyms from 1, but this case does look wonky. Maybe other devs have a strong opinion that binding is expressly the wrong thing.