diff --git a/.gitattributes b/.gitattributes
index 96a0d0a..36ad0f5 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -13,7 +13,6 @@
 
 LICENSE   text eol=lf
 
-.github/        export-ignore
 .gitignore      export-ignore
 .gitattributes  export-ignore
 SECURITY.md     export-ignore
diff --git a/.github/.module b/.github/.module
new file mode 100644
index 0000000..e69de29
diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index fd4848b..dc623ad 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -21,6 +21,28 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
+  layout-marker:
+    name: Repo layout marker
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    permissions:
+      contents: read
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          fetch-depth: 1
+          persist-credentials: false
+      - name: Validate repo layout marker
+        shell: bash
+        run: |
+          set -euo pipefail
+          count=0
+          [ -f .github/.script ] && count=$((count+1))
+          [ -f .github/.module ] && count=$((count+1))
+          if [ "$count" -ne 1 ]; then
+            echo "::error::Repo layout marker invalid: exactly one of .github/.script or .github/.module must exist (found $count)."
+            exit 1
+          fi
   actionlint:
     name: actionlint
     runs-on: ubuntu-latest
diff --git a/.gitignore b/.gitignore
index 73c1e95..e09f04a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -15,6 +15,8 @@
 # CI and repo metadata
 !/.github/
 !/.github/CODEOWNERS
+!/.github/.script
+!/.github/.module
 !/.github/workflows/
 !/.github/workflows/*.yaml