papermill inserts "Starting Kernel..." text into output notebook

🐛 Bug

I noticed that papermill prepends the statement "Starting Kernel..." to the top of the output notebook. This occurs both when declaring an output notebook and when piping to stdout.

papermill -k xpython --no-progress-bar --log-level ERROR /path/to/qc_bx_stats.ipynb  > output.ipynb

# or #

papermill -k xpython --no-progress-bar --log-level ERROR /path/to/qc_bx_stats.ipynb  output.ipynb

And the top of the output notebook looks like:

Starting kernel...
{
 "cells": [
  {
   "cell_type": "markdown",
   "id": "a15b719a",
   "metadata": {
    "tags": [
     "papermill-error-cell-tag"
    ]
   },
   "source": [
    "<span style=\"color:red; font-family:Helvetica Neue, Helvetica, Arial, sans-serif; font-size:2em;\">An Exception was encountered at '<a href=\"#papermill-error-cell\">In [4]</a>'.</span>"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "716e29e7",
   "metadata": {
    "papermill": {
     "duration": 0.000372,
     "end_time": "2026-07-10T18:28:39.105932+00:00",
     "exception": false,
     "start_time": "2026-07-10T18:28:39.105560+00:00",
     "status": "completed"
    },
    "tags": []
   },
   "source": [
....