ci: enable functional containment in pytest

.github/workflows/ci.yml

@@ -102,7 +102,8 @@ jobs:
 
   python-tests:
     name: Python tests (pytest)
-    runs-on: ubuntu-latest
+    # Keep the namespace/AppArmor setup tied to the audited Ubuntu release.
+    runs-on: ubuntu-24.04
     # Make Python test validation authoritative for the configured scope.
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
@@ -159,5 +160,55 @@ jobs:
           command -v ffmpeg
           ffmpeg -version | head -n 1
 
+      - name: Establish functional bubblewrap containment
+        if: steps.docs-check.outputs.docs_only != 'true'
+        shell: bash
+        run: |
+          set -euo pipefail
+          sudo apt-get update
+          sudo apt-get install -y --no-install-recommends bubblewrap
+          bwrap --version
+          sysctl kernel.unprivileged_userns_clone user.max_user_namespaces \
+            kernel.apparmor_restrict_unprivileged_userns
+          if [ "$(sysctl -n kernel.unprivileged_userns_clone)" != 1 ] || \
+             [ "$(sysctl -n user.max_user_namespaces)" -eq 0 ]; then
+            echo '::error::The pytest runner must allow unprivileged user namespaces; kernel namespace support is disabled.'
+            exit 1
+          fi
+
+          # Match containment._bwrap_available(): PID and mount namespaces,
+          # including fresh proc/dev mounts, as the unprivileged runner user.
+          bwrap_probe() {
+            timeout 3s bwrap --die-with-parent --unshare-pid --ro-bind / / \
+              --proc /proc --dev /dev /bin/true
+          }
+
+          if ! bwrap_probe && [ "$(sysctl -n kernel.apparmor_restrict_unprivileged_userns)" = 1 ]; then
+            # Ubuntu 24.04 restricts userns for unconfined applications. Allow
+            # only the distro bwrap entry point on this ephemeral pytest VM;
+            # retain the global restriction and all unrelated AppArmor policy.
+            sudo tee /etc/apparmor.d/odysseus-ci-bwrap > /dev/null <<'PROFILE'
+          abi <abi/4.0>,
+          include <tunables/global>
+          profile odysseus-ci-bwrap /usr/bin/bwrap flags=(unconfined) {
+            userns,
+          }
+          PROFILE
+            sudo apparmor_parser -r /etc/apparmor.d/odysseus-ci-bwrap
+          fi
+
+          if ! bwrap_probe; then
+            echo '::error::Functional bubblewrap PID/mount namespaces are required for pytest; containment setup failed.'
+            exit 1
+          fi
+          # Also gate on the runtime probe so a future requirements change
+          # cannot silently leave this job without real containment coverage.
+          python - <<'PY'
+          from src import containment
+          if not containment._bwrap_available():
+              raise SystemExit("::error::Runtime bubblewrap functionality probe failed; pytest must not start.")
+          print("Runtime bubblewrap PID/mount namespace probe passed.")
+          PY
+
       - run: python -m pytest -q -rs
         if: steps.docs-check.outputs.docs_only != 'true'