debug: add sys.path debugging and isolate pytest environment

Author: felixweinberger

.github/workflows/shared.yml

@@ -82,15 +82,25 @@ jobs:
           echo "=== Testing import from anyio with uv run ==="
           uv run --no-project --no-sync python -c "from anyio._backends import _asyncio; print('Import successful')" || echo "Import failed"
 
+          echo "=== Checking sys.path from venv Python ==="
+          .venv/bin/python -c "import sys; import pprint; pprint.pprint(sys.path)"
+
+          echo "=== Checking where anyio is loaded from ==="
+          .venv/bin/python -c "import anyio; print('anyio location:', anyio.__file__)"
+
       - name: Run pytest
         shell: bash
         run: |
           if [ "${{ matrix.dep-resolution.name }}" == "lowest-direct" ]; then
             # Run pytest directly from venv to avoid any uv resolution issues
+            # Isolate the Python environment completely
+            export PYTHONNOUSERSITE=1
+            export PYTHONPATH=""
+            export UV_PYTHON_PREFERENCE=only-system
             if [ "$RUNNER_OS" == "Windows" ]; then
-              .venv/Scripts/python -m pytest
+              .venv/Scripts/python -m pytest -v
             else
-              .venv/bin/python -m pytest
+              .venv/bin/python -m pytest -v
             fi
           else
             uv run --frozen --no-sync pytest