diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e056f59..a0817e5 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -29,6 +29,17 @@ jobs:
             echo "tag/commit mismatch unexpectedly accepted" >&2
             exit 1
           fi
+          if sh scripts/verify-release-ref.sh v0.0.0-m11.2 "$GITHUB_SHA" invalid-mode; then
+            echo "invalid verification mode unexpectedly accepted" >&2
+            exit 1
+          fi
+          parent="$(git rev-parse HEAD^)"
+          git tag v0.0.0-m11.5-audit "$parent"
+          if sh scripts/verify-release-ref.sh v0.0.0-m11.5-audit "$parent"; then
+            echo "strict mode unexpectedly accepted historical tag" >&2
+            exit 1
+          fi
+          sh scripts/verify-release-ref.sh v0.0.0-m11.5-audit "$parent" --allow-head-mismatch-for-audit
 
       - name: Verify exact-digest policy
         run: |
diff --git a/.github/workflows/post-release-audit.yml b/.github/workflows/post-release-audit.yml
new file mode 100644
index 0000000..7adc507
--- /dev/null
+++ b/.github/workflows/post-release-audit.yml
@@ -0,0 +1,166 @@
+name: Post-release audit
+
+on:
+  workflow_run:
+    workflows: [Release]
+    types: [completed]
+  workflow_dispatch:
+    inputs:
+      tag:
+        description: Existing release tag to audit
+        required: true
+        type: string
+
+permissions:
+  contents: read
+  packages: read
+  id-token: write
+
+env:
+  IMAGE_NAME: ghcr.io/ploos-as/soju
+
+jobs:
+  audit:
+    if: >-
+      github.event_name == 'workflow_dispatch' ||
+      github.event.workflow_run.conclusion == 'success'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262
+        with:
+          fetch-depth: 0
+
+      - name: Select release bound to producer commit
+        id: release
+        env:
+          GH_TOKEN: ${{ github.token }}
+          INPUT_TAG: ${{ github.event_name == 'workflow_dispatch' && inputs.tag || '' }}
+          PRODUCER_SHA: ${{ github.event_name == 'workflow_run' && github.event.workflow_run.head_sha || '' }}
+        shell: bash
+        run: |
+          set -euo pipefail
+          git fetch --force --tags origin
+          tag="$INPUT_TAG"
+          if [[ -z "$tag" ]]; then
+            while IFS= read -r candidate; do
+              [[ -n "$candidate" ]] || continue
+              commit="$(git rev-list -n 1 "$candidate" 2>/dev/null || true)"
+              if [[ "$commit" == "$PRODUCER_SHA" ]]; then
+                tag="$candidate"
+                break
+              fi
+            done < <(gh release list --repo "$GITHUB_REPOSITORY" --limit 100 --json tagName,isDraft --jq '.[] | select(.isDraft == false) | .tagName')
+          fi
+          [[ -n "$tag" ]]
+          tag_commit="$(git rev-list -n 1 "$tag")"
+          if [[ -n "$INPUT_TAG" ]]; then
+            sh scripts/verify-release-ref.sh "$tag" "$tag_commit" --allow-head-mismatch-for-audit
+          else
+            sh scripts/verify-release-ref.sh "$tag" "$tag_commit"
+          fi
+          release_json="$(gh release view "$tag" --repo "$GITHUB_REPOSITORY" --json tagName,isDraft,isPrerelease)"
+          jq -e --arg tag "$tag" '.tagName == $tag and .isDraft == false' <<<"$release_json" >/dev/null
+          if [[ -n "$PRODUCER_SHA" ]]; then
+            test "$tag_commit" = "$PRODUCER_SHA"
+          fi
+          echo "tag=$tag" >> "$GITHUB_OUTPUT"
+          echo "commit=$tag_commit" >> "$GITHUB_OUTPUT"
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@c7c53464625b32c7a7e944ae62b3e17d2b600130
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@8d2750c68a42422c14e847fe6c8ac0403b4cbd6f
+
+      - name: Log in to GHCR
+        uses: docker/login-action@c94ce9fb468520275223c153574b00df6fe4bcc9
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Resolve immutable release digest and verify platforms
+        id: image
+        env:
+          TAG: ${{ steps.release.outputs.tag }}
+        shell: bash
+        run: |
+          set -euo pipefail
+          image_tag="${IMAGE_NAME}:${TAG#v}"
+          docker manifest inspect "$image_tag" > /tmp/manifest.json
+          jq -e 'any(.manifests[]; .platform.os == "linux" and .platform.architecture == "amd64")' /tmp/manifest.json >/dev/null
+          jq -e 'any(.manifests[]; .platform.os == "linux" and .platform.architecture == "arm64")' /tmp/manifest.json >/dev/null
+          docker pull --platform linux/amd64 "$image_tag" >/dev/null
+          repo_digest="$(docker image inspect "$image_tag" --format '{{index .RepoDigests 0}}')"
+          digest="${repo_digest##*@}"
+          sh scripts/verify-exact-digest-runtime.sh "$IMAGE_NAME" "$digest" >/dev/null
+          echo "digest=$digest" >> "$GITHUB_OUTPUT"
+
+      - name: Install Cosign
+        uses: sigstore/cosign-installer@d7543c93d881b35a8faa02e8e3605f69b7a1ce62
+
+      - name: Verify exact-digest signature
+        env:
+          IMAGE_DIGEST: ${{ steps.image.outputs.digest }}
+        shell: bash
+        run: |
+          set -euo pipefail
+          cosign verify \
+            --certificate-oidc-issuer https://token.actions.githubusercontent.com \
+            --certificate-identity-regexp '^https://github.com/Ploos-AS/soju/.github/workflows/release.yml@refs/tags/v.*$' \
+            "${IMAGE_NAME}@${IMAGE_DIGEST}" > /tmp/cosign-verification.json
+          jq -e 'length > 0' /tmp/cosign-verification.json >/dev/null
+
+      - name: Verify immutable labels and runtime after release
+        env:
+          IMAGE_DIGEST: ${{ steps.image.outputs.digest }}
+          TAG: ${{ steps.release.outputs.tag }}
+          RELEASE_COMMIT: ${{ steps.release.outputs.commit }}
+        shell: bash
+        run: |
+          set -euo pipefail
+          image_ref="${IMAGE_NAME}@${IMAGE_DIGEST}"
+          docker pull --platform linux/amd64 "$image_ref" >/dev/null
+          revision="$(docker image inspect "$image_ref" --format '{{index .Config.Labels "org.opencontainers.image.revision"}}')"
+          version="$(docker image inspect "$image_ref" --format '{{index .Config.Labels "org.opencontainers.image.version"}}')"
+          test "$revision" = "$RELEASE_COMMIT"
+          test "$version" = "$TAG"
+          test "$(docker run --rm --platform linux/amd64 --entrypoint id "$image_ref" -u)" = "1000"
+          test "$(docker run --rm --platform linux/amd64 --entrypoint id "$image_ref" -g)" = "1000"
+          mkdir -p data-audit run-audit
+          sudo chown 1000:1000 data-audit run-audit
+          cid=$(docker run -d --rm --platform linux/amd64 \
+            -v "$PWD/data-audit:/var/lib/soju" \
+            -v "$PWD/run-audit:/run/soju" \
+            "$image_ref")
+          trap 'docker logs "$cid" 2>&1 || true; docker rm -f "$cid" >/dev/null 2>&1 || true' EXIT
+          for i in $(seq 1 30); do
+            if docker ps --filter "id=$cid" --format '{{.ID}}' | grep -q . \
+              && test -f data-audit/main.db \
+              && test -S run-audit/admin; then
+              healthy=true
+              break
+            fi
+            sleep 1
+          done
+          test "${healthy:-false}" = true
+          docker rm -f "$cid"
+          trap - EXIT
+
+      - name: Record post-release audit summary
+        env:
+          TAG: ${{ steps.release.outputs.tag }}
+          IMAGE_DIGEST: ${{ steps.image.outputs.digest }}
+        run: |
+          {
+            echo '### M11.5 post-release audit'
+            echo
+            echo "- release: $TAG"
+            echo "- immutable digest: $IMAGE_DIGEST"
+            echo '- GitHub Release/tag/commit binding: verified'
+            echo '- linux/amd64 + linux/arm64 manifest coverage: verified'
+            echo '- Cosign keyless signature and release workflow OIDC identity: verified'
+            echo '- OCI revision/version labels: verified'
+            echo '- non-root UID/GID 1000: verified'
+            echo '- exact-digest post-publication SQLite + admin-socket runtime: verified'
+          } >> "$GITHUB_STEP_SUMMARY"
diff --git a/scripts/verify-release-ref.sh b/scripts/verify-release-ref.sh
index 1c6c644..c374c6a 100644
--- a/scripts/verify-release-ref.sh
+++ b/scripts/verify-release-ref.sh
@@ -3,12 +3,21 @@ set -eu
 
 tag=${1:-${GITHUB_REF_NAME:-}}
 expected_sha=${2:-${GITHUB_SHA:-}}
+mode=${3:-strict}
 
 if [ -z "$tag" ] || [ -z "$expected_sha" ]; then
-  echo "usage: verify-release-ref.sh <tag> <expected-commit-sha>" >&2
+  echo "usage: verify-release-ref.sh <tag> <expected-commit-sha> [--allow-head-mismatch-for-audit]" >&2
   exit 2
 fi
 
+case "$mode" in
+  strict|--allow-head-mismatch-for-audit) ;;
+  *)
+    echo "invalid verification mode: $mode" >&2
+    exit 2
+    ;;
+esac
+
 if ! printf '%s\n' "$tag" | grep -Eq '^v(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)(-[0-9A-Za-z-]+(\.[0-9A-Za-z-]+)*)?(\+[0-9A-Za-z-]+(\.[0-9A-Za-z-]+)*)?$'; then
   echo "invalid release tag: $tag" >&2
   exit 1
@@ -24,10 +33,12 @@ if [ "$actual_sha" != "$expected_sha" ]; then
   exit 1
 fi
 
-head_sha=$(git rev-parse HEAD)
-if [ "$head_sha" != "$expected_sha" ]; then
-  echo "checkout/commit mismatch: HEAD=$head_sha expected=$expected_sha" >&2
-  exit 1
+if [ "$mode" = "strict" ]; then
+  head_sha=$(git rev-parse HEAD)
+  if [ "$head_sha" != "$expected_sha" ]; then
+    echo "checkout/commit mismatch: HEAD=$head_sha expected=$expected_sha" >&2
+    exit 1
+  fi
 fi
 
-printf 'release ref verified: tag=%s commit=%s\n' "$tag" "$expected_sha"
+printf 'release ref verified: tag=%s commit=%s mode=%s\n' "$tag" "$expected_sha" "$mode"