TEMP: probe 3.15 torchvision import under faulthandler in windows smoke

Diagnostic to surface the silent import crash on cp315 (no traceback in the
smoke test). Prints torch/numpy/torchvision versions and a C-level stack on
fault. To be reverted once the root cause is understood.

Author: atalman

.github/workflows/build_wheels_windows.yml

@@ -371,6 +371,13 @@ jobs:
           else
             ${CONDA_RUN} pip install "${{ inputs.repository }}/dist/$WHEEL_NAME"
           fi
+          # TEMP DEBUG (3.15): the smoke test crashes on import with no traceback.
+          # Probe imports under faulthandler to surface the real failure/C stack.
+          if [[ "${{ startsWith(matrix.python_version, '3.15') }}" == "true" ]]; then
+            echo "::group::3.15 import probe"
+            ${CONDA_RUN} python -X faulthandler -c "import sys, torch; print('TORCH', torch.__version__); import numpy; print('NUMPY', numpy.__version__); import torchvision; print('TORCHVISION', torchvision.__version__)" 2>&1 || echo "IMPORT_PROBE_FAILED rc=$?"
+            echo "::endgroup::"
+          fi
           if [[ ! -f "${{ inputs.repository }}"/${SMOKE_TEST_SCRIPT} ]]; then
             echo "${{ inputs.repository }}/${SMOKE_TEST_SCRIPT} not found"
             ${CONDA_RUN} "${{ inputs.repository }}/${ENV_SCRIPT}" python -c "import ${PACKAGE_NAME}; print('package version is ', ${PACKAGE_NAME}.__version__)"