diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 339ff99..2de7121 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -82,6 +82,7 @@ jobs:
       - name: Run Entry Check
         env:
           GH_TOKEN: ${{ github.token }}
+          CODEQL_DEFAULT_SETUP_GUARDRAIL_TOKEN: ${{ secrets.CODEQL_DEFAULT_SETUP_GUARDRAIL_TOKEN }}
         run: bash -euo pipefail tools/ci/bin/run.sh preflight
       - name: Upload Artifact
         if: always()
diff --git a/.github/workflows/codeql-default-setup-guardrail.yml b/.github/workflows/codeql-default-setup-guardrail.yml
new file mode 100644
index 0000000..620e99f
--- /dev/null
+++ b/.github/workflows/codeql-default-setup-guardrail.yml
@@ -0,0 +1,45 @@
+name: codeql-default-setup-guardrail
+
+on:
+  schedule:
+    # Daily drift detection for security settings that cannot be protected by branch rules.
+    - cron: "17 4 * * *"
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  issues: write
+
+concurrency:
+  group: codeql-default-setup-guardrail
+  cancel-in-progress: false
+
+defaults:
+  run:
+    shell: bash
+
+jobs:
+  guardrail:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+
+      - name: Read CodeQL Default Setup State
+        id: state
+        env:
+          GH_TOKEN: ${{ github.token }}
+          CODEQL_DEFAULT_SETUP_GUARDRAIL_TOKEN: ${{ secrets.CODEQL_DEFAULT_SETUP_GUARDRAIL_TOKEN }}
+        run: bash tools/ci/codeql-default-setup-guardrail/get_state.sh
+
+      - name: Open Issue On Drift (idempotent)
+        if: steps.state.outputs.drift == 'true'
+        env:
+          GH_TOKEN: ${{ github.token }}
+          GITHUB_REPOSITORY: ${{ github.repository }}
+          CODEQL_DEFAULT_SETUP_GUARDRAIL_TOKEN: ${{ secrets.CODEQL_DEFAULT_SETUP_GUARDRAIL_TOKEN }}
+        run: bash tools/ci/codeql-default-setup-guardrail/ensure_issue.sh
+
+      - name: Fail Run On Drift (fail-closed)
+        if: steps.state.outputs.drift == 'true'
+        run: exit 1
diff --git a/docs/security/010_CODEQL_DEFAULT_SETUP_GUARDRAIL.MD b/docs/security/010_CODEQL_DEFAULT_SETUP_GUARDRAIL.MD
new file mode 100644
index 0000000..9ac1f64
--- /dev/null
+++ b/docs/security/010_CODEQL_DEFAULT_SETUP_GUARDRAIL.MD
@@ -0,0 +1,30 @@
+# CodeQL Default Setup Guardrail
+
+## Ziel
+Dieses Repository nutzt ein **CodeQL Advanced Setup** (`.github/workflows/codeql.yml`) fuer C# (build-mode `manual`).
+GitHub **CodeQL Default Setup** muss deshalb **deaktiviert** sein (`state=not-configured`), sonst werden Advanced-SARIF Uploads abgelehnt.
+
+## Verifikation
+```bash
+gh api repos/{owner}/{repo}/code-scanning/default-setup --jq '{state,updated_at,schedule}'
+```
+
+Erwartung:
+- `state: "not-configured"`
+
+## Guardrails
+- Merge-Gate (fail-closed): `tools/ci/check-codeql-default-setup.sh` ist Teil von `preflight`.
+- Drift Detection: `.github/workflows/codeql-default-setup-guardrail.yml` laeuft taeglich und erstellt bei Drift ein Issue.
+
+## Token / Permissions (wichtig)
+Der GitHub API Endpoint `GET /repos/{owner}/{repo}/code-scanning/default-setup` ist in GitHub Actions mit dem standardmaessigen `GITHUB_TOKEN` in diesem Repo nicht erreichbar (typisch: `HTTP 403 Resource not accessible by integration`).
+
+Damit der Guardrail in PR-CI und im scheduled Workflow deterministisch funktioniert, ist ein Fine-Grained PAT als Repo-Secret erforderlich:
+- Secret-Name: `CODEQL_DEFAULT_SETUP_GUARDRAIL_TOKEN`
+- Minimalrechte (Repository permissions):
+  - Administration: Read-only
+  - Security events: Read-only
+
+Wiring:
+- PR-CI: `.github/workflows/ci.yml` setzt `CODEQL_DEFAULT_SETUP_GUARDRAIL_TOKEN` als env fuer `preflight`.
+- Scheduled: `.github/workflows/codeql-default-setup-guardrail.yml` nutzt `CODEQL_DEFAULT_SETUP_GUARDRAIL_TOKEN`, falls vorhanden.
diff --git a/tools/ci/bin/run.sh b/tools/ci/bin/run.sh
index e19635b..4b5d57b 100755
--- a/tools/ci/bin/run.sh
+++ b/tools/ci/bin/run.sh
@@ -179,6 +179,7 @@ run_preflight() {
   run_or_fail "CI-PREFLIGHT-001" "Label engine tests" node "${ROOT_DIR}/tools/versioning/test-compute-pr-labels.js"
   run_or_fail "CI-PREFLIGHT-001" "PR governance checks" bash "${ROOT_DIR}/tools/ci/check-pr-governance.sh"
   run_or_fail "CI-PREFLIGHT-001" "Code scanning tools open alerts must be zero" bash "${ROOT_DIR}/tools/ci/check-code-scanning-tools-zero.sh"
+  run_or_fail "CI-CODEQL-001" "CodeQL default setup must be not-configured" bash "${ROOT_DIR}/tools/ci/check-codeql-default-setup.sh"
   run_or_fail "CI-PREFLIGHT-001" "Doc consistency drift guard" python3 "${ROOT_DIR}/tools/check-doc-consistency.py"
   run_or_fail "CI-PREFLIGHT-001" "Doc shell compatibility guard" python3 "${ROOT_DIR}/tools/check-doc-shell-compat.py"
   run_or_fail "CI-PREFLIGHT-001" "Docs checker unit tests" python3 -m unittest discover -s "${ROOT_DIR}/tools/tests" -p "test_*.py" -v
diff --git a/tools/ci/check-codeql-default-setup.sh b/tools/ci/check-codeql-default-setup.sh
new file mode 100755
index 0000000..50f5806
--- /dev/null
+++ b/tools/ci/check-codeql-default-setup.sh
@@ -0,0 +1,114 @@
+#!/usr/bin/env bash
+set -euo pipefail
+IFS=$'\n\t'
+export LC_ALL=C
+
+ROOT_DIR="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")/../.." && pwd)"
+OUT_DIR="${ROOT_DIR}/artifacts/ci/preflight/codeql-default-setup-guardrail"
+RAW_LOG="${OUT_DIR}/raw.log"
+SUMMARY_MD="${OUT_DIR}/summary.md"
+RESULT_JSON="${OUT_DIR}/result.json"
+DEFAULT_SETUP_JSON="${OUT_DIR}/default-setup.json"
+
+mkdir -p "${OUT_DIR}"
+: > "${RAW_LOG}"
+
+BASE_GH_TOKEN="${GH_TOKEN:-}"
+CODEQL_TOKEN="${CODEQL_DEFAULT_SETUP_GUARDRAIL_TOKEN:-}"
+
+log() {
+  printf '%s\n' "$*" | tee -a "${RAW_LOG}" >/dev/null
+}
+
+fail() {
+  local reason="$1"
+  log "FAIL: ${reason}"
+  {
+    echo "# CodeQL Default Setup Guardrail"
+    echo
+    echo "- status: fail"
+    echo "- reason: ${reason}"
+  } > "${SUMMARY_MD}"
+  if [[ -f "${DEFAULT_SETUP_JSON}" ]]; then
+    jq -n --arg reason "${reason}" \
+      '{schema_version:1,check_id:"codeql-default-setup-guardrail",status:"fail",reason:$reason,evidence_paths:["artifacts/ci/preflight/codeql-default-setup-guardrail/raw.log","artifacts/ci/preflight/codeql-default-setup-guardrail/default-setup.json","artifacts/ci/preflight/codeql-default-setup-guardrail/summary.md"]}' \
+      > "${RESULT_JSON}"
+  else
+    jq -n --arg reason "${reason}" \
+      '{schema_version:1,check_id:"codeql-default-setup-guardrail",status:"fail",reason:$reason,evidence_paths:["artifacts/ci/preflight/codeql-default-setup-guardrail/raw.log","artifacts/ci/preflight/codeql-default-setup-guardrail/summary.md"]}' \
+      > "${RESULT_JSON}"
+  fi
+  exit 1
+}
+
+if ! command -v gh >/dev/null 2>&1; then
+  fail "gh fehlt"
+fi
+if ! command -v jq >/dev/null 2>&1; then
+  fail "jq fehlt"
+fi
+
+REPO="${GITHUB_REPOSITORY:-}"
+if [[ -z "${REPO}" ]]; then
+  origin_url="$(git -C "${ROOT_DIR}" remote get-url origin 2>/dev/null || true)"
+  if [[ "${origin_url}" =~ github.com[:/]([^/]+/[^/.]+)(\.git)?$ ]]; then
+    REPO="${BASH_REMATCH[1]}"
+  fi
+fi
+if [[ -z "${REPO}" ]]; then
+  fail "Repository-Slug konnte nicht bestimmt werden"
+fi
+if [[ ! "${REPO}" =~ ^[A-Za-z0-9_.-]+/[A-Za-z0-9_.-]+$ ]]; then
+  fail "Ungueltiger Repository-Slug: '${REPO}' (erwartet owner/name)"
+fi
+
+gh_api() {
+  local -r endpoint="$1"; shift
+  if [[ -n "${CODEQL_TOKEN}" ]]; then
+    GH_TOKEN="${CODEQL_TOKEN}" GH_REPO="${REPO}" gh api "${endpoint}" "$@"
+  else
+    GH_REPO="${REPO}" gh api "${endpoint}" "$@"
+  fi
+}
+
+attempt=1
+delay=2
+max_attempts=3
+while true; do
+  if gh_api "repos/{owner}/{repo}/code-scanning/default-setup" > "${DEFAULT_SETUP_JSON}" 2>> "${RAW_LOG}"; then
+    break
+  fi
+  if (( attempt >= max_attempts )); then
+    if grep -qF "Resource not accessible by integration (HTTP 403)" "${RAW_LOG}"; then
+      fail "GitHub API 403 fuer CodeQL Default Setup. GITHUB_TOKEN reicht hier nicht aus; setze Secret CODEQL_DEFAULT_SETUP_GUARDRAIL_TOKEN (Fine-Grained PAT, Repo: Administration Read, Security Events Read)."
+    fi
+    fail "GitHub API fuer CodeQL Default Setup fehlgeschlagen"
+  fi
+  log "WARN: API-Fehler, retry ${attempt}/${max_attempts}"
+  sleep "${delay}"
+  attempt=$((attempt + 1))
+  delay=$((delay * 2))
+done
+
+state="$(jq -r '.state // empty' "${DEFAULT_SETUP_JSON}")"
+if [[ -z "${state}" ]]; then
+  fail "Ungueltige API-Antwort: state fehlt"
+fi
+
+if [[ "${state}" != "not-configured" ]]; then
+  fail "CodeQL Default Setup ist aktiv (state=${state}). Advanced-Setup erfordert state=not-configured."
+fi
+
+{
+  echo "# CodeQL Default Setup Guardrail"
+  echo
+  echo "- status: pass"
+  echo "- repo: ${REPO}"
+  echo "- state: ${state}"
+} > "${SUMMARY_MD}"
+
+jq -n \
+  '{schema_version:1,check_id:"codeql-default-setup-guardrail",status:"pass",state:"not-configured",evidence_paths:["artifacts/ci/preflight/codeql-default-setup-guardrail/raw.log","artifacts/ci/preflight/codeql-default-setup-guardrail/default-setup.json","artifacts/ci/preflight/codeql-default-setup-guardrail/summary.md"]}' \
+  > "${RESULT_JSON}"
+
+log "PASS: CodeQL Default Setup ist not-configured."
diff --git a/tools/ci/codeql-default-setup-guardrail/ensure_issue.sh b/tools/ci/codeql-default-setup-guardrail/ensure_issue.sh
new file mode 100755
index 0000000..ec8ae5f
--- /dev/null
+++ b/tools/ci/codeql-default-setup-guardrail/ensure_issue.sh
@@ -0,0 +1,108 @@
+#!/usr/bin/env bash
+set -euo pipefail
+IFS=$'\n\t'
+export LC_ALL=C
+
+repo="${GITHUB_REPOSITORY:-${REPO:-}}"
+if [[ -z "${repo}" ]]; then
+  echo "ERROR: missing GITHUB_REPOSITORY/REPO env (expected owner/name)." >&2
+  exit 2
+fi
+if [[ ! "${repo}" =~ ^[A-Za-z0-9_.-]+/[A-Za-z0-9_.-]+$ ]]; then
+  echo "ERROR: invalid repo slug: '${repo}' (expected owner/name)." >&2
+  exit 2
+fi
+
+CODEQL_TOKEN="${CODEQL_DEFAULT_SETUP_GUARDRAIL_TOKEN:-}"
+
+retry() {
+  local -r max="${1}"; shift
+  local -r base_sleep="${1}"; shift
+  local attempt=1
+  local sleep_s="${base_sleep}"
+  while true; do
+    if "$@"; then
+      return 0
+    fi
+    if [[ "${attempt}" -ge "${max}" ]]; then
+      return 1
+    fi
+    echo "WARN: command failed (attempt ${attempt}/${max}); retrying in ${sleep_s}s..." >&2
+    sleep "${sleep_s}"
+    attempt="$((attempt + 1))"
+    sleep_s="$((sleep_s * 2))"
+  done
+}
+
+gh_api() {
+  local -r endpoint="$1"; shift
+  if [[ -n "${CODEQL_TOKEN}" ]]; then
+    GH_TOKEN="${CODEQL_TOKEN}" GH_REPO="${repo}" gh api "${endpoint}" "$@"
+  else
+    GH_REPO="${repo}" gh api "${endpoint}" "$@"
+  fi
+}
+
+state=""
+if ! state="$(retry 4 1 gh_api "repos/{owner}/{repo}/code-scanning/default-setup" --jq .state)"; then
+  echo "ERROR: failed to query CodeQL default-setup state via GitHub API." >&2
+  exit 3
+fi
+if [[ -z "${state}" ]]; then
+  echo "ERROR: invalid API response (missing state)." >&2
+  exit 3
+fi
+
+if [[ "${state}" == "not-configured" ]]; then
+  echo "INFO: state is not-configured; no drift issue required."
+  exit 0
+fi
+
+title="SECURITY: CodeQL Default Setup ist aktiviert (Guardrail)"
+marker="<!-- codeql-default-setup-guardrail -->"
+
+body=$'Der CI-Guardrail hat festgestellt, dass **GitHub CodeQL Default Setup** aktiv ist.\n\n'
+body+=$'Impact:\n- Advanced CodeQL Workflow (`.github/workflows/codeql.yml`) kann dadurch keine SARIF-Ergebnisse wie erwartet verarbeiten.\n\n'
+body+=$'Fix:\n- In GitHub UI: Settings -> Code security and analysis -> CodeQL -> Default setup deaktivieren\n- Oder per API: `PATCH /repos/{owner}/{repo}/code-scanning/default-setup` mit `state=not-configured`\n\n'
+body+=$'Evidence:\n- Siehe Workflow-Logs und `artifacts/ci/preflight/codeql-default-setup-guardrail/`.\n\n'
+if [[ ! "${state}" =~ ^[a-z-]+$ ]]; then
+  state="unknown"
+fi
+body+="Observed state: \`${state}\`"$'\n\n'
+body+="${marker}"$'\n'
+
+existing="$(gh_api "repos/{owner}/{repo}/issues?state=open&per_page=100" --paginate --slurp | jq -r --arg t "${title}" '[.[] | .[] | select(.pull_request? | not) | select(.title == $t) | .number][0] // empty')"
+if [[ -n "${existing}" ]]; then
+  echo "INFO: drift issue already open (#${existing}); nothing to do."
+  exit 0
+fi
+
+issue_number=""
+if ! issue_number="$(gh_api "repos/{owner}/{repo}/issues" -X POST -f title="${title}" -f body="${body}" --jq .number)"; then
+  # Benign race: another run may have created the issue after our initial check.
+  existing_after_create="$(gh_api "repos/{owner}/{repo}/issues?state=open&per_page=100" --paginate --slurp | jq -r --arg t "${title}" '[.[] | .[] | select(.pull_request? | not) | select(.title == $t) | .number][0] // empty')"
+  if [[ -n "${existing_after_create}" ]]; then
+    issue_number="${existing_after_create}"
+    echo "INFO: drift issue was created concurrently (#${issue_number}); proceeding."
+  else
+    echo "ERROR: failed to create drift issue in ${repo}." >&2
+    exit 4
+  fi
+fi
+
+echo "INFO: created drift issue #${issue_number}."
+
+# Best-effort labels: only add labels that already exist, otherwise the API call would hard-fail.
+desired_labels=("security" "area:pipeline")
+labels_available="$(gh label list -R "${repo}" -L 200 --json name 2>/dev/null || echo '[]')"
+for label in "${desired_labels[@]}"; do
+  if jq -er --arg label "${label}" '.[] | select(.name == $label) | true' <<<"${labels_available}" >/dev/null 2>&1; then
+    if gh issue edit "${issue_number}" -R "${repo}" --add-label "${label}" >/dev/null 2>&1; then
+      echo "INFO: added label '${label}'."
+    else
+      echo "WARN: failed to add label '${label}' to issue #${issue_number}." >&2
+    fi
+  else
+    echo "INFO: label '${label}' not present in repo; skipping."
+  fi
+done
diff --git a/tools/ci/codeql-default-setup-guardrail/get_state.sh b/tools/ci/codeql-default-setup-guardrail/get_state.sh
new file mode 100755
index 0000000..0fbe265
--- /dev/null
+++ b/tools/ci/codeql-default-setup-guardrail/get_state.sh
@@ -0,0 +1,69 @@
+#!/usr/bin/env bash
+set -euo pipefail
+IFS=$'\n\t'
+export LC_ALL=C
+
+repo="${GITHUB_REPOSITORY:-${REPO:-}}"
+if [[ -z "${repo}" ]]; then
+  echo "ERROR: missing GITHUB_REPOSITORY/REPO env (expected owner/name)." >&2
+  exit 2
+fi
+if [[ ! "${repo}" =~ ^[A-Za-z0-9_.-]+/[A-Za-z0-9_.-]+$ ]]; then
+  echo "ERROR: invalid repo slug: '${repo}' (expected owner/name)." >&2
+  exit 2
+fi
+
+CODEQL_TOKEN="${CODEQL_DEFAULT_SETUP_GUARDRAIL_TOKEN:-}"
+
+retry() {
+  local -r max="${1}"; shift
+  local -r base_sleep="${1}"; shift
+  local attempt=1
+  local sleep_s="${base_sleep}"
+  while true; do
+    if "$@"; then
+      return 0
+    fi
+    if [[ "${attempt}" -ge "${max}" ]]; then
+      return 1
+    fi
+    echo "WARN: command failed (attempt ${attempt}/${max}); retrying in ${sleep_s}s..." >&2
+    sleep "${sleep_s}"
+    attempt="$((attempt + 1))"
+    sleep_s="$((sleep_s * 2))"
+  done
+}
+
+gh_api() {
+  local -r endpoint="$1"; shift
+  if [[ -n "${CODEQL_TOKEN}" ]]; then
+    GH_TOKEN="${CODEQL_TOKEN}" GH_REPO="${repo}" gh api "${endpoint}" "$@"
+  else
+    GH_REPO="${repo}" gh api "${endpoint}" "$@"
+  fi
+}
+
+state=""
+# Backoff schedule for max=4, base=1s: 1s, 2s, 4s.
+if ! state="$(retry 4 1 gh_api "repos/{owner}/{repo}/code-scanning/default-setup" --jq .state)"; then
+  echo "ERROR: failed to query CodeQL default-setup state via GitHub API." >&2
+  exit 3
+fi
+if [[ -z "${state}" ]]; then
+  echo "ERROR: invalid API response (missing state)." >&2
+  exit 3
+fi
+
+drift="false"
+if [[ "${state}" != "not-configured" ]]; then
+  drift="true"
+fi
+
+echo "INFO: default-setup state='${state}', drift='${drift}'."
+
+if [[ -n "${GITHUB_OUTPUT:-}" ]]; then
+  {
+    echo "state=${state}"
+    echo "drift=${drift}"
+  } >> "${GITHUB_OUTPUT}"
+fi