fix(notebook): install hf_transfer + clear HF_HUB_ENABLE_HF_TRANSFER to fix Colab download crash

notebooks/fathom_train.ipynb

@@ -45,7 +45,11 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "!pip install -q 'huggingface_hub>=0.28' openenv-core fastapi 'uvicorn[standard]' pydantic RestrictedPython tiktoken httpx hydra-core omegaconf wandb tyro\n",
+    "# Colab sets HF_HUB_ENABLE_HF_TRANSFER=1 but often lacks the package.\n",
+    "# Install it first, then clear the flag as a safety net so downloads never fail.\n",
+    "import os; os.environ.pop('HF_HUB_ENABLE_HF_TRANSFER', None)\n",
+    "\n",
+    "!pip install -q hf_transfer 'huggingface_hub>=0.28' openenv-core fastapi 'uvicorn[standard]' pydantic RestrictedPython tiktoken httpx hydra-core omegaconf wandb tyro\n",
     "!pip install -q transformers==4.56.2 accelerate==1.5.2 peft==0.14.0 bitsandbytes==0.45.1 datasets==4.7.0\n",
     "!pip install -q --no-deps trl==1.2.0\n",
     "!pip install -q safetensors sentencepiece einops scipy xxhash protobuf pyyaml fsspec aiohttp dill multiprocess pyarrow\n",
@@ -64,6 +68,7 @@
    "outputs": [],
    "source": [
     "import os\n",
+    "os.environ.pop('HF_HUB_ENABLE_HF_TRANSFER', None)  # ensure still cleared after pip restart\n",
     "from huggingface_hub import snapshot_download, hf_hub_download\n",
     "REPO = 'Pratham-math/fathom-code'\n",
     "snapshot_download(repo_id=REPO, repo_type='model', local_dir='/content/fathom')\n",
@@ -100,10 +105,10 @@
     "    answer_regex='<answer>(.*?)</answer>'\n",
     ")\n",
     "\n",
-    "good             = '<answer>Paris</answer>'\n",
+    "good              = '<answer>Paris</answer>'\n",
     "format_only_wrong = '<answer>Berlin</answer>'\n",
-    "no_format        = 'Paris'\n",
-    "padded           = '<answer>Paris</answer>' + ' '*5000\n",
+    "no_format         = 'Paris'\n",
+    "padded            = '<answer>Paris</answer>' + ' '*5000\n",
     "\n",
     "for label, completion in [\n",
     "    ('correct',             good),\n",