diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 3e17809..0ec0b4e 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -170,16 +170,18 @@ jobs:
       - name: task changelog:verify
         run: task changelog:verify
 
-  # SonarCloud: needs repo secret SONAR_TOKEN. Automatic Analysis must stay off
-  # (mutually exclusive with CI analysis + Go coverage). Non-blocking per OD-3 —
-  # quality gate is ERROR until E4-S02 clears duplication; continue-on-error so
-  # that does not block the remediating lanes.
+  # SonarCloud: needs repo secret SONAR_TOKEN. Automatic Analysis must stay OFF —
+  # it is mutually exclusive with CI analysis (the scanner exits 3) and it ignores
+  # sonar-project.properties, so the E4-S02 test exclusions silently would not
+  # apply. Blocking as of 2026-08-06 (OD-3 revisit): the continue-on-error escape
+  # hatch is gone AND sonar.qualitygate.wait=true is set, so both a scanner
+  # failure and an ERROR quality gate now fail this job. Fork PRs receive no
+  # secrets, so the scan step self-skips rather than failing.
   sonarqube:
     name: sonarqube
     runs-on: ubuntu-latest
     timeout-minutes: 20
     needs: [check]
-    continue-on-error: true
     steps:
       - name: Checkout
         uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
diff --git a/Taskfile.yml b/Taskfile.yml
index a17e67b..99ef467 100644
--- a/Taskfile.yml
+++ b/Taskfile.yml
@@ -103,6 +103,22 @@ tasks:
     cmds:
       - bash hack/pinned-actions.sh
 
+  guards:
+    desc: Run the hack/test/*.sh config regression guards
+    cmds:
+      - |
+        fail=0
+        for t in hack/test/*.sh; do
+          if bash "$t" >/dev/null 2>&1; then
+            echo "ok: $t"
+          else
+            echo "FAIL: $t" >&2
+            bash "$t" || true
+            fail=1
+          fi
+        done
+        exit "$fail"
+
   tools:git-cliff:
     desc: Download pinned git-cliff binary ({{.GIT_CLIFF_VERSION}})
     status:
@@ -135,7 +151,7 @@ tasks:
       - bash hack/verify-changelog.sh
 
   check:
-    desc: Local gate — fmt, lint, arch, coverage≥90%, gitleaks, build, REWE-trace, pinned-actions
+    desc: Local gate — fmt, lint, arch, coverage≥90%, gitleaks, build, REWE-trace, pinned-actions, guards
     cmds:
       - task: fmt-check
       - task: vet
@@ -146,6 +162,7 @@ tasks:
       - task: build
       - task: rewe-trace
       - task: pinned-actions
+      - task: guards
 
   docs:install:
     desc: Install the locked MkDocs toolchain into .venv-docs
diff --git a/hack/test/sonar_blocking_gate_test.sh b/hack/test/sonar_blocking_gate_test.sh
new file mode 100755
index 0000000..8260d91
--- /dev/null
+++ b/hack/test/sonar_blocking_gate_test.sh
@@ -0,0 +1,66 @@
+#!/usr/bin/env bash
+# Assert the SonarCloud job is a BLOCKING gate (OD-3 revisit, 2026-08-06).
+#
+# OD-3 made `sonarqube` non-blocking so the quality gate could not veto the very
+# lanes (E4-S01/E4-S02) that were fixing it. That gate went OK once Automatic
+# Analysis was disabled and CI analysis actually ran, so the escape hatch came
+# out. Blocking here means BOTH halves, because either alone is a false sense of
+# safety:
+#
+#   1. no `continue-on-error` — a scanner failure fails the job. Without this a
+#      hard exit 3 ("running CI analysis while Automatic Analysis is enabled")
+#      was swallowed for a day while the workflow reported success.
+#   2. `sonar.qualitygate.wait=true` — the scanner polls for the gate verdict
+#      instead of fire-and-forget. Without this the job goes green the moment the
+#      report is uploaded, so a gate that flips to ERROR is never noticed.
+#
+# Run: bash hack/test/sonar_blocking_gate_test.sh
+set -euo pipefail
+
+root="$(git rev-parse --show-toplevel 2>/dev/null || pwd)"
+wf="${root}/.github/workflows/ci.yaml"
+props="${root}/sonar-project.properties"
+
+fail=0
+
+# 1. No job or step in ci.yaml may opt out of failing the workflow. Deliberately
+#    whole-file: nothing in this workflow has a legitimate use for it today.
+#    Matches bare, quoted and expression forms.
+if grep -Eq "^[[:space:]]*continue-on-error:[[:space:]]*(\"?true\"?|'true'|\\\$\\{\\{)" "$wf"; then
+  echo "FAIL: continue-on-error opt-out still present in ci.yaml" >&2
+  grep -nE '^[[:space:]]*continue-on-error:' "$wf" >&2
+  fail=1
+else
+  echo "ok: no continue-on-error opt-out in ci.yaml"
+fi
+
+# 2. The sonarqube job must exist and keep needing `check` — the scan consumes
+#    coverage.out via the artifact that `check` uploads.
+if grep -Eq '^[[:space:]]{2}sonarqube:' "$wf"; then
+  echo "ok: sonarqube job present"
+else
+  echo "FAIL: sonarqube job missing from ci.yaml" >&2
+  fail=1
+fi
+
+if grep -Eq '^[[:space:]]*needs:[[:space:]]*\[[[:space:]]*check[[:space:]]*\]' "$wf"; then
+  echo "ok: sonarqube needs [check] (coverage artifact producer)"
+else
+  echo "FAIL: sonarqube no longer declares needs: [check]" >&2
+  fail=1
+fi
+
+# 3. The scanner must wait for the quality gate verdict, not merely upload.
+if grep -Eq '^sonar\.qualitygate\.wait[[:space:]]*=[[:space:]]*true' "$props"; then
+  echo "ok: sonar.qualitygate.wait=true"
+else
+  echo "FAIL: sonar.qualitygate.wait=true missing from sonar-project.properties" >&2
+  echo "      without it the job passes on upload and never sees an ERROR gate" >&2
+  fail=1
+fi
+
+if [[ "${fail}" -ne 0 ]]; then
+  echo "sonar_blocking_gate_test: RED" >&2
+  exit 1
+fi
+echo "sonar_blocking_gate_test: GREEN"
diff --git a/sonar-project.properties b/sonar-project.properties
index b6fc894..5409a15 100644
--- a/sonar-project.properties
+++ b/sonar-project.properties
@@ -13,6 +13,11 @@ sonar.tests=.
 sonar.test.inclusions=**/*_test.go
 sonar.go.coverage.reportPaths=coverage.out
 
+# Make the CI job actually ENFORCE the gate rather than fire-and-forget: without
+# this the scanner uploads and exits 0, so a quality gate that flips to ERROR
+# leaves the workflow green. Guarded by hack/test/sonar_blocking_gate_test.sh.
+sonar.qualitygate.wait=true
+
 # Belt-and-suspenders with source exclusion above (cpd.exclusions alone was
 # insufficient when tests were dual-indexed as sources).
 sonar.cpd.exclusions=**/*_test.go