[BUG] ob-python hangs on second start [9.5.4 (release_9.5.4-763-g06373a @ ~/emacs/org-mode/lisp/)]

[Peter Mao <peter.mao@gmail.com>]

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Expectation:  When running ob-python code blocks, I should be able to
kill the python session in the *Python* buffer and run another code
block (or the same one).

Problem:  ob-python works fine on the first execution, but after
`exit()`ing the python session, it hangs without executing the code.
After a `C-g`, the prompt in the *Python* session shows up, but one then
has to re-execute the code block, as none of it has run.

The following three code blocks demonstrate the problem.  I have
bisected the problem, finding 06373a64 as the first bad commit.  I tried
to reproduce the problem on Emacs 28.2, but this commit of Org won't
compile on Emacs 28.2 for me.

#+begin_src elisp :results none
  (org-babel-do-load-languages 'org-babel-load-languages '((python . t)))
  (setq-local org-confirm-babel-evaluate nil)
#+end_src

#+begin_src python :results output
  print("Running first, this one issues a warning but competes
successfully.")
  exit()
#+end_src

#+begin_src python :results output
  print("Running second, this one hangs until user enters C-g.")
  print("None of the code executes.")
  exit()
#+end_src



Emacs  : GNU Emacs 29.1 (build 2, x86_64-pc-linux-gnu, GTK+ Version
3.24.33, cairo version 1.16.0)
 of 2023-07-31
Package: Org mode version 9.5.4 (release_9.5.4-763-g06373a @
/home/peterm/emacs/org-mode/lisp/)

current state:
==============
(setq
 org-link-elisp-confirm-function 'yes-or-no-p
 org-bibtex-headline-format-function #[257 "\300 \236A\207" [:title] 3
"\n\n(fn ENTRY)"]
 org-persist-after-read-hook '(org-element--cache-persist-after-read)
 org-export-before-parsing-hook '(org-attach-expand-links)
 org-cycle-tab-first-hook '(org-babel-hide-result-toggle-maybe
   org-babel-header-arg-expand)
 org-archive-hook '(org-attach-archive-delete-maybe)
 org-cycle-hook '(org-cycle-hide-archived-subtrees
org-cycle-show-empty-lines
 org-cycle-optimize-window-after-visibility-change)
 org-persist-before-read-hook '(org-element--cache-persist-before-read)
 org-mode-hook '(#[0 "\300\301\302\303\304$\207"
  [add-hook change-major-mode-hook org-fold-show-all append
   local]
  5]
#[0 "\300\301\302\303\304$\207"
  [add-hook change-major-mode-hook org-babel-show-result-all
   append local]
  5]
org-babel-result-hide-spec org-babel-hide-all-hashes)
 org-babel-load-languages '((python . t))
 org-confirm-shell-link-function 'yes-or-no-p
 outline-isearch-open-invisible-function 'outline-isearch-open-invisible
 org-agenda-before-write-hook '(org-agenda-add-entry-text)
 org-babel-tangle-lang-exts '(("python" . "py") ("emacs-lisp" . "el")
     ("elisp" . "el"))
 org-src-mode-hook '(org-src-babel-configure-edit-buffer
    org-src-mode-configure-edit-buffer)
 org-confirm-elisp-link-function 'yes-or-no-p
 org-speed-command-hook '(org-speed-command-activate
 org-babel-speed-command-activate)
 org-fold-core-isearch-open-function 'org-fold--isearch-reveal
 org-persist-before-write-hook '(org-element--cache-persist-before-write)
 org-tab-first-hook '(org-babel-hide-result-toggle-maybe
     org-babel-header-arg-expand)
 org-link-shell-confirm-function 'yes-or-no-p
 org-babel-pre-tangle-hook '(save-buffer)
 org-agenda-loop-over-headlines-in-active-region nil
 org-occur-hook '(org-first-headline-recenter)
 org-metadown-hook '(org-babel-pop-to-session-maybe)
 org-link-parameters '(("attachment" :follow org-attach-follow :complete
org-attach-complete-link)
      ("id" :follow org-id-open)
      ("eww" :follow org-eww-open :store org-eww-store-link)
      ("rmail" :follow org-rmail-open :store
org-rmail-store-link)
      ("mhe" :follow org-mhe-open :store org-mhe-store-link)
      ("irc" :follow org-irc-visit :store org-irc-store-link
:export org-irc-export)
      ("info" :follow org-info-open :export org-info-export
:store org-info-store-link :insert-description
org-info-description-as-command)
      ("gnus" :follow org-gnus-open :store
org-gnus-store-link)
      ("docview" :follow org-docview-open :export
org-docview-export :store org-docview-store-link)
      ("bibtex" :follow org-bibtex-open :store
org-bibtex-store-link)
      ("bbdb" :follow org-bbdb-open :export org-bbdb-export
:complete org-bbdb-complete-link :store
org-bbdb-store-link)
      ("w3m" :store org-w3m-store-link)
      ("doi" :follow org-link-doi-open :export
org-link-doi-export)
      ("file+sys") ("file+emacs")
      ("shell" :follow org-link--open-shell)
      ("news" :follow
#[514 "\301\300\302 Q \"\207"
 ["news" browse-url ":"] 6 "\n\n(fn URL ARG)"]
)
      ("mailto" :follow
#[514 "\301\300\302 Q \"\207"
 ["mailto" browse-url ":"] 6 "\n\n(fn URL ARG)"]
)
      ("https" :follow
#[514 "\301\300\302 Q \"\207"
 ["https" browse-url ":"] 6 "\n\n(fn URL ARG)"]
)
      ("http" :follow
#[514 "\301\300\302 Q \"\207"
 ["http" browse-url ":"] 6 "\n\n(fn URL ARG)"]
)
      ("ftp" :follow
#[514 "\301\300\302 Q \"\207" ["ftp" browse-url ":"]
 6 "\n\n(fn URL ARG)"]
)
      ("help" :follow org-link--open-help :store
org-link--store-help)
      ("file" :complete org-link-complete-file)
      ("elisp" :follow org-link--open-elisp))
 org-metaup-hook '(org-babel-load-in-session-maybe)
 )

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