Is there a way for JS to see the attributes for each value? Because presumably setting an expire time in the past and iterating over every used set of attributes would get the job done to delete the cookie. Iterating over all possible (plausible?) attributes may also work, but knowing the specific attributes set would narrow that list of erasing writes to issue.

No, there isn't. All you get a list of values that are valid for the current page. Same on the server side.

If you're ever in a situation where you need to invalidate all possible instances of a cookie, it's easier to just use a different name.