> +  (define (sanitize path-fragment)
> +    (escape-special-chars
> +     ;; GNU tar strips the leading slash off of absolute paths before applying
> +     ;; the transformations, so we need to do the same, or else our
> +     ;; replacements won't match any paths.
> +     (string-trim path-fragment #\/)
> +     ;; Escape the basic regexp special characters (see: "(sed) BRE syntax").
> +     ;; We also need to escape "/" because we use it as a delimiter.
> +     "/*.^$[]\\"
> +     #\\))

I'm not such a fan of using blacklist.  Those can easily get out of sync and
nobody notices.  But in this case I guess people take care not to extend
basic regexp special characters in sed (tar) without the user specifying a flag
requiring it.

LGTM!