diff --git a/.github/workflows/code-hygiene-self-test.yml b/.github/workflows/code-hygiene-self-test.yml
index 907c789..a90ea23 100644
--- a/.github/workflows/code-hygiene-self-test.yml
+++ b/.github/workflows/code-hygiene-self-test.yml
@@ -9,6 +9,7 @@ on:
       - 'actions/referencing-check/**'
       - 'actions/secrets-check/**'
       - 'actions/boj-cartridge-check/**'
+      - 'actions/manifest-check/**'
       - '.github/workflows/code-hygiene-self-test.yml'
   pull_request:
     paths:
@@ -17,6 +18,7 @@ on:
       - 'actions/referencing-check/**'
       - 'actions/secrets-check/**'
       - 'actions/boj-cartridge-check/**'
+      - 'actions/manifest-check/**'
       - '.github/workflows/code-hygiene-self-test.yml'
 
 permissions:
@@ -39,3 +41,37 @@ jobs:
       - run: bash actions/referencing-check/test.sh
       - run: bash actions/secrets-check/test.sh
       - run: bash actions/boj-cartridge-check/test.sh
+      - name: Create manifest controls
+        id: fixtures
+        shell: bash
+        run: |
+          root="$RUNNER_TEMP/manifest-controls"
+          mkdir -p "$root/valid" "$root/bad-a2ml" "$root/bad-k9"
+          printf '%s\n' '# SPDX-License-Identifier: MPL-2.0' 'agent-id = "ci-control"' 'version = "1.0.0"' > "$root/valid/control.a2ml"
+          printf '%s\n' 'K9!' '# SPDX-License-Identifier: MPL-2.0' 'pedigree = {' '  metadata = { name = "ci-control", version = "1.0.0" },' "  security = { leash = 'Kennel }," '}' > "$root/valid/control.k9.ncl"
+          printf '%s\n' 'invalid manifest' > "$root/bad-a2ml/control.a2ml"
+          # K9-suffixed library modules are outside pedigree validation. Give
+          # this negative control a real contract marker and omit its pedigree.
+          printf '%s\n' 'K9!' '# SPDX-License-Identifier: MPL-2.0' 'invalid manifest' > "$root/bad-k9/control.k9.ncl"
+          echo "root=$root" >> "$GITHUB_OUTPUT"
+      - name: Valid manifests must pass
+        uses: ./actions/manifest-check
+        with:
+          path: ${{ steps.fixtures.outputs.root }}/valid
+      - name: Invalid A2ML must fail
+        id: bad-a2ml
+        continue-on-error: true
+        uses: ./actions/manifest-check
+        with:
+          path: ${{ steps.fixtures.outputs.root }}/bad-a2ml
+      - name: Invalid K9 Nickel manifest must fail
+        id: bad-k9
+        continue-on-error: true
+        uses: ./actions/manifest-check
+        with:
+          path: ${{ steps.fixtures.outputs.root }}/bad-k9
+      - name: Verify both negative controls failed
+        env:
+          A2ML_OUTCOME: ${{ steps.bad-a2ml.outcome }}
+          K9_OUTCOME: ${{ steps.bad-k9.outcome }}
+        run: test "$A2ML_OUTCOME" = failure && test "$K9_OUTCOME" = failure
diff --git a/actions/manifest-check/action.yml b/actions/manifest-check/action.yml
index 1f668db..75c14be 100755
--- a/actions/manifest-check/action.yml
+++ b/actions/manifest-check/action.yml
@@ -1,27 +1,28 @@
+# SPDX-License-Identifier: MPL-2.0
 name: 'Manifest Validation Gate'
-description: 'Strict parsing of .a2ml and .k9 files to guarantee they align with grammars and are fully populated.'
+description: 'Validate A2ML/DEED and K9 manifest structure using the maintained format validators.'
+inputs:
+  path:
+    description: 'Directory containing manifests to validate.'
+    required: false
+    default: '.'
+  strict:
+    description: 'Promote validator warnings to failures.'
+    required: false
+    default: 'false'
 runs:
   using: 'composite'
   steps:
-    - name: Run Manifest Check
-      shell: bash
-      run: |
-        echo "Validating A2ML and K9 manifests..."
-        
-        # We would use the a2ml-tool or k9-validate here
-        manifests=$(find . -name "*.a2ml" -o -name "*.k9" 2>/dev/null)
-        if [ -n "$manifests" ]; then
-          for m in $manifests; do
-             echo "Checking $m..."
-             # Check for unpopulated null points
-             if grep -qE '""|\[\]|\{\}|null' "$m"; then
-               echo "::warning::Manifest $m contains empty or null points. Ensure it is fully populated with explicit values or null markers."
-             fi
-             
-             # Placeholder for actual parser invocation
-             # a2ml-tool validate "$m" || exit 1
-          done
-          echo "Manifest validation passed."
-        else
-          echo "No .a2ml or .k9 manifests found."
-        fi
+    - name: Validate A2ML and DEED manifests
+      uses: hyperpolymath/deed-ecosystem/validate-action@f7a40a4d5cc82b2e73f861119baa6818d77a448d
+      with:
+        path: ${{ inputs.path }}
+        strict: ${{ inputs.strict }}
+    - name: Validate K9 manifests
+      uses: hyperpolymath/k9-ecosystem/validate-action@2ee51eed590b4722efcdca2fe4685ef24600bced
+      with:
+        path: ${{ inputs.path }}
+        strict: ${{ inputs.strict }}
+# These validators check manifest structure. Executable Nickel contracts need
+# a separate Nickel evaluation step; neither an empty-field grep nor this
+# structural check establishes that a contract evaluates or a proof holds.