Fix HF cache path for torchao checkpoint CI

.ci/scripts/test_torchao_huggingface_checkpoints.sh

@@ -45,6 +45,15 @@ if [[ -z "${PYTHON_EXECUTABLE:-}" ]]; then
   PYTHON_EXECUTABLE=python3
 fi
 
+# OSDC runners may expose a read-only shared HF cache at /mnt/hf_cache.
+# Redirect hf downloads to a writable per-job cache before the first download.
+HF_CACHE_ROOT="${RUNNER_TEMP:-/tmp}/hf_cache"
+if [[ -z "${HF_HOME:-}" || "${HF_HOME}" == /mnt/hf_cache* ]]; then
+  export HF_HOME="${HF_CACHE_ROOT}"
+fi
+mkdir -p "${HF_HOME}" 2>/dev/null || export HF_HOME=/tmp/hf_cache
+mkdir -p "${HF_HOME}"
+
 MODEL_OUT=model.pte
 
 # Hugging Face Hub revisions, pinned. On OSDC runners HF_HUB_CACHE is a read-only

.github/workflows/trunk.yml

@@ -605,6 +605,12 @@ jobs:
         CONDA_ENV=$(conda env list --json | jq -r ".envs | .[-1]")
         conda activate "${CONDA_ENV}"
 
+        # OSDC mounts HF_HOME read-only at /mnt/hf_cache; redirect to a writable dir
+        # (RUNNER_TEMP, or /tmp when RUNNER_TEMP isn't writable inside the container).
+        export HF_HOME="${RUNNER_TEMP:-/tmp}/hf_cache"
+        mkdir -p "${HF_HOME}" 2>/dev/null || export HF_HOME=/tmp/hf_cache
+        mkdir -p "${HF_HOME}"
+
         PYTHON_EXECUTABLE=python bash .ci/scripts/setup-linux.sh --build-tool cmake
 
         if [[ "${{ matrix.backend }}" == "torchao" ]]; then