diff --git a/.github/workflows/e2e.yml b/.github/workflows/e2e.yml
index bc46cdb..266ce55 100644
--- a/.github/workflows/e2e.yml
+++ b/.github/workflows/e2e.yml
@@ -132,3 +132,36 @@ jobs:
           args=(-v -ra --color=yes)
           [ -n "$MARKERS" ] && args+=(-m "$MARKERS")
           uv run --project tests/e2e pytest tests/e2e "${args[@]}"
+
+  # Alert Slack when any e2e leg does not succeed. Runs only on the nightly
+  # schedule — manual dispatch is interactive, so the operator already sees the
+  # result. `result != 'success'` covers both failures and cancellations (the
+  # 30-min job timeout cancels rather than fails), so timed-out nightly runs
+  # still alert. Needs the SLACK_WEBHOOK_URL repo secret (a Slack Incoming
+  # Webhook URL; the target channel is fixed by the webhook). Self-skips if the
+  # secret is unset.
+  notify:
+    name: notify-slack-on-failure
+    needs: e2e
+    if: ${{ always() && github.event_name == 'schedule' && needs.e2e.result != 'success' }}
+    runs-on: ubuntu-latest
+    steps:
+      - name: Post failure to Slack
+        env:
+          SLACK_WEBHOOK_URL: ${{ secrets.SLACK_WEBHOOK_URL }}
+          RUN_URL: ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}
+          REPO: ${{ github.repository }}
+        run: |
+          if [ -z "$SLACK_WEBHOOK_URL" ]; then
+            echo "::warning::SLACK_WEBHOOK_URL not set — skipping Slack alert"
+            exit 0
+          fi
+          # Build the payload with jq so RUN_URL/REPO are JSON-escaped, never
+          # interpolated into the shell or the JSON string by hand.
+          payload="$(jq -n \
+            --arg repo "$REPO" \
+            --arg url "$RUN_URL" \
+            '{text: ("🔴 Nightly e2e failed for *" + $repo + "*\n<" + $url + "|View run>")}')"
+          curl --proto '=https' --tlsv1.2 -sSf --retry 3 \
+            -X POST -H 'Content-Type: application/json' \
+            -d "$payload" "$SLACK_WEBHOOK_URL"