Eshell: Patch INSIDE_EMACS.

.emacs.d/lisp/init-eshell.el

@@ -303,4 +303,6 @@ This should be faster then `seq-uniq'."
   (when (fboundp 'helm-fish-completion-make-eshell-source)
     (setq helm-esh-pcomplete-build-source-fn #'helm-fish-completion-make-eshell-source)))
 
+(require 'patch-eshell-inside-emacs)
+
 (provide 'init-eshell)

.emacs.d/lisp/patch-eshell-inside-emacs.el

@@ -0,0 +1,9 @@
+;;; Reported upstream, see #39596.
+(defun ambrevar/set-inside-emacs ()
+  "Export INSIDE_EMACS just like M-x shell does.
+This is useful for programs like Guix that take provisions for Emacs."
+  (setenv "INSIDE_EMACS" (format "%s;%s" emacs-version "eshell")))
+
+(add-hook 'eshell-mode-hook 'ambrevar/set-inside-emacs)
+
+(provide 'patch-eshell-inside-emacs)