ci: require persistent Pages mount

.gitea/workflows/build.yml

@@ -43,7 +43,12 @@ jobs:
             *..*|/*|*/|*//* ) echo "unsafe repository slug: $ORG_REPO" >&2; exit 1 ;;
           esac
           test -f build/index.html
-          destination="/gondor-v1-gitea-pages/$ORG_REPO"
+          pages_root="/gondor-v1-gitea-pages"
+          if ! mountpoint -q "$pages_root"; then
+            echo "$pages_root is not a persistent host mount inside the Gitea Actions job container" >&2
+            exit 1
+          fi
+          destination="$pages_root/$ORG_REPO"
           rm -rf -- "$destination"
           mkdir -p "$destination"
           cp -a build/. "$destination/"