Does emacs supports concurrent sessions of ielm / private session?

Question

concurrent sessions - two sessions of ielm running independently
private session - running emacs-lisp code without effecting emacs variables/functions

Answer 1

NO, emacs doesn't support two concurrent sessions of elisp. only one session of elisp will be running inside emacs and all elisp code blocks are executed under the same session

so the org-mode :session header args is also ignored for elisp code block