lein re-frame generated a project.clj with the following clause:

:shell {:commands {"open" {:windows ["cmd" "/c" "start"]
                             :macosx  "open"
                             :linux   "xdg-open"}}}

is it possible that's part of lein-shell? there's some mention of :shell here: https://github.com/hypirion/lein-shell/blob/master/src/leiningen/shell.clj#L121 (along with a few other instances)

fwiw: https://github.com/hypirion/lein-shell/blob/master/doc/DOCUMENTATION.md#configuration