start using markers for tracking where the user’s prompt is

codex.el

@@ -61,6 +61,8 @@
   (setq-local truncate-lines t)
   (setq-local codex--busy nil))
 
+(defvar-local codex--prompt-start nil)
+
 (defun list->hash-set (list &optional test)
   "Return a hash table whose keys are the elements of LIST."
   (let ((ht (make-hash-table :test (or test #'equal))))
@@ -79,7 +81,8 @@
 (defun user-prompt ()
   (prompt-delimiter)
   (insert "User:")
-  (newline))
+  (newline)
+  (setq codex--prompt-start (point-marker)))
 
 (defun codex--write-to-chat (msg)
   (with-codex-buffer
@@ -153,12 +156,10 @@
            (kill-buffer)))))))
 
 (defun codex--get-current-user-prompt ()
-  (with-current-buffer codex-buffer-name
-    (let* ((haystack (buffer-string))
-           (needle "---\nUser:\n")
-           (index
-            (cl-search needle haystack :from-end t)))
-      (substring haystack (+ (length needle) index)))))
+  (with-codex-buffer
+    (unless codex--prompt-start
+      (error "No current prompt start"))
+    (buffer-substring-no-properties codex--prompt-start (point-max))))
 
 (defun codex-send ()
   (interactive)
@@ -181,7 +182,7 @@
      (pop-to-buffer buf)
      (unless (derived-mode-p 'codex-mode)
        (codex-mode))
-     (insert "---\nUser:\n")
+     (user-prompt)
      (goto-char (point-max)))))
 
 (defun codex--read-sessions-file ()