LLMs can add broken cells that never show output

[dlqqq]

Description

Claude Code can sometimes add "broken cells" that never show output:

Screen.Recording.2025-07-15.at.8.50.28.AM.mov

The browser console logs 404 responses from the /outputs endpoint:

This seems to occur because Claude Code added cells with invalid IDs that are not UUIDs:

  {
   "cell_type": "code",
   "execution_count": 20,
   "id": "gasm8x2jicg",
   "metadata": {},
   "outputs": [],
   "source": [
    "# Measure langchain-anthropic import time\n",
    "start_time = time.time()\n",
    "import langchain_anthropic\n",
    "end_time = time.time()\n",
    "langchain_import_time = (end_time - start_time) * 1000\n",
    "print(f\"langchain-anthropic import time: {langchain_import_time:.2f} ms\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "id": "gggbmd0ki2o",
   "metadata": {},
   "outputs": [],
   "source": [
    "# Measure litellm import time\n",
    "start_time = time.time()\n",
    "import litellm\n",
    "end_time = time.time()\n",
    "litellm_import_time = (end_time - start_time) * 1000\n",
    "print(f\"litellm import time: {litellm_import_time:.2f} ms\")"
   ]
  },

[dlqqq]

Even deleting the "id" property from the broken cells does not fix the issue. It is just replaced with a similar non-UUID for some reason. I was only able to fix this by copying the ID of another cell & changing the last character.