diff --git a/conformance/lib/merge_junit.py b/conformance/lib/merge_junit.py
new file mode 100644
index 0000000..d488d0d
--- /dev/null
+++ b/conformance/lib/merge_junit.py
@@ -0,0 +1,84 @@
+#!/usr/bin/env python3
+"""Merge several Chainsaw JUnit reports into one.
+
+run.sh splits the L2/L3 run into a LIGHT pass (concurrent) and a HEAVY pass
+(serial, parallel=1) so the storage/VM-heavy tests never spike embedded-etcd
+while other tests are mid-setup (see run.sh `run_chainsaw`). Each pass writes its
+own JUnit file; this stitches them back into the single stable artifact CI
+collects (`_artifacts/report.junit.xml`) so the split is invisible downstream.
+
+Chainsaw emits `<testsuites>` with one `<testsuite>` per test. Merging is a
+concatenation of the child `<testsuite>` elements plus a recomputed roll-up of
+tests/failures/errors/time on the root, so the combined report totals exactly the
+sum of the passes (no double counting, no dropped cases). Inputs that don't exist
+are skipped (a pass may legitimately select zero tests); at least one must exist.
+"""
+from __future__ import annotations
+
+import argparse
+import sys
+import xml.etree.ElementTree as ET
+from pathlib import Path
+
+
+def _int(el: ET.Element, attr: str) -> int:
+    try:
+        return int(el.get(attr, "0") or "0")
+    except ValueError:
+        return 0
+
+
+def _float(el: ET.Element, attr: str) -> float:
+    try:
+        return float(el.get(attr, "0") or "0")
+    except ValueError:
+        return 0.0
+
+
+def main() -> int:
+    ap = argparse.ArgumentParser(description=__doc__)
+    ap.add_argument("--out", type=Path, required=True, help="merged JUnit path")
+    ap.add_argument("--name", default="chainsaw-report", help="root testsuites name")
+    ap.add_argument("inputs", nargs="+", type=Path, help="JUnit files to merge (missing ones skipped)")
+    args = ap.parse_args()
+
+    merged = ET.Element("testsuites", {"name": args.name})
+    tests = failures = errors = skipped = 0
+    total_time = 0.0
+    found = 0
+
+    for path in args.inputs:
+        if not path.exists() or path.stat().st_size == 0:
+            continue
+        found += 1
+        root = ET.parse(path).getroot()
+        # Accept either a <testsuites> wrapper or a bare <testsuite>.
+        suites = [root] if root.tag == "testsuite" else list(root.findall("testsuite"))
+        for suite in suites:
+            merged.append(suite)
+            tests += _int(suite, "tests")
+            failures += _int(suite, "failures")
+            errors += _int(suite, "errors")
+            skipped += _int(suite, "skipped")
+            total_time += _float(suite, "time")
+
+    if found == 0:
+        print(f"merge_junit: none of the input reports exist: {args.inputs}", file=sys.stderr)
+        return 1
+
+    merged.set("tests", str(tests))
+    merged.set("failures", str(failures))
+    merged.set("errors", str(errors))
+    if skipped:
+        merged.set("skipped", str(skipped))
+    merged.set("time", f"{total_time:.6f}")
+
+    args.out.parent.mkdir(parents=True, exist_ok=True)
+    ET.ElementTree(merged).write(args.out, encoding="unicode", xml_declaration=False)
+    print(f"merge_junit: merged {found} report(s) -> {args.out} "
+          f"(tests={tests} failures={failures} errors={errors} skipped={skipped})")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())
diff --git a/conformance/run.sh b/conformance/run.sh
index bea1715..8a4d84e 100755
--- a/conformance/run.sh
+++ b/conformance/run.sh
@@ -137,7 +137,56 @@ select_dirs() {
   fi
 }
 
+# --- HEAVY tests: the storage/VM/DR tests whose KubeVirt-CDI imports + Longhorn volume ops
+#     spike embedded-etcd I/O on the small dev VMs. Run SERIALLY (parallel=1) in their own
+#     pass so their etcd spikes never coincide with ANOTHER test's setup — the coincidence
+#     that made a single heavy test's apiserver blip fail-close Kyverno admission and abort
+#     every in-flight test's 0.01s setup (see config/chainsaw-config.yaml). Keyed by the test
+#     DIRECTORY basename (stable); override via CONF_HEAVY_TESTS to add/remove without code
+#     changes. Listed here even for tests still scaffolded (vm-lifecycle, dr-restore, ...) so
+#     the serialization is already correct the moment they grow real KubeVirt/Longhorn bodies.
+CONF_HEAVY_TESTS="${CONF_HEAVY_TESTS:-vm-lifecycle vm-data-survival vm-default-deny data-survival dr-restore}"
+
+conf_is_heavy_dir() {
+  # $1 = test dir; true if its basename is in the heavy set.
+  local base t
+  base="$(basename "$1")"
+  for t in ${CONF_HEAVY_TESTS}; do [ "$base" = "$t" ] && return 0; done
+  return 1
+}
+
+# One Chainsaw invocation over a specific set of dirs, at a given parallelism, writing to a
+# named report file. Returns chainsaw's rc (0=all passed) WITHOUT aborting run.sh (callers
+# collect both passes' rc so a light-pass failure still lets the heavy pass run, and vice
+# versa). failFast stays false (config) so every test in the pass runs regardless.
+run_chainsaw_pass() {
+  local report_name="$1" parallel="$2"; shift 2
+  local -a dirs=("$@")
+  local -a test_dir_args=()
+  local d
+  for d in "${dirs[@]}"; do test_dir_args+=(--test-dir "$d"); done
+  # Chainsaw writes JUnit per config/chainsaw-config.yaml (report.* under _artifacts).
+  # --report-path is passed ABSOLUTE (overriding the config's relative `_artifacts`) so the
+  # report write succeeds regardless of the caller's CWD. --report-name/--parallel override
+  # the config per-pass so the two passes don't clobber each other's report and the heavy
+  # pass forces serial execution.
+  local rc=0
+  chainsaw test \
+    --config "${CONF_ROOT}/config/chainsaw-config.yaml" \
+    --report-path "${ARTIFACTS}" \
+    --report-name "${report_name}" \
+    --parallel "${parallel}" \
+    "${test_dir_args[@]}" || rc=$?
+  return $rc
+}
+
 # --- Execute the Chainsaw suite against a live cluster ---------------------------------
+# Split into a LIGHT pass (concurrent, config parallelism) and a HEAVY pass (serial,
+# parallel=1). Robust single-pass green: the heavy etcd spikes are isolated in time from the
+# light tests' setup, so a heavy test's transient apiserver blip can no longer cascade into
+# mass fail-closed setup-aborts of unrelated tests. The two JUnit reports are stitched back
+# into the one stable artifact CI collects (report.junit.xml) via lib/merge_junit.py, so the
+# split is invisible to everything downstream.
 run_chainsaw() {
   local -a dirs
   mapfile -t dirs < <(select_dirs)
@@ -145,28 +194,52 @@ run_chainsaw() {
     log "No tests match the selection (layer=${LAYER} reqs='${REQS}')."
     return 0
   fi
-  local -a test_dir_args=()
-  for d in "${dirs[@]}"; do test_dir_args+=(--test-dir "$d"); done
 
-  log "Running Chainsaw over ${#dirs[@]} test dir(s) with pinned ${CHAINSAW_VERSION}"
-  # Chainsaw writes JUnit per config/chainsaw-config.yaml (report.* under _artifacts).
-  # --report-path is passed ABSOLUTE (overriding the config's relative `_artifacts`) so the report
-  # write succeeds regardless of the caller's CWD — otherwise chainsaw's relative path resolves
-  # against $PWD and fails ("open _artifacts/chainsaw-report.xml: no such file") when run.sh is
-  # invoked from the repo root instead of conformance/.
+  local -a light=() heavy=()
+  local d
+  for d in "${dirs[@]}"; do
+    if conf_is_heavy_dir "$d"; then heavy+=("$d"); else light+=("$d"); fi
+  done
+
   mkdir -p "${ARTIFACTS}"
-  chainsaw test \
-    --config "${CONF_ROOT}/config/chainsaw-config.yaml" \
-    --report-path "${ARTIFACTS}" \
-    "${test_dir_args[@]}"
+  local light_report="${ARTIFACTS}/chainsaw-report-light.xml"
+  local heavy_report="${ARTIFACTS}/chainsaw-report-heavy.xml"
+  rm -f "${light_report}" "${heavy_report}"
+  local light_rc=0 heavy_rc=0
 
-  # Normalize whatever chainsaw named the report to a stable path CI collects.
-  local produced
-  produced="$(find "${ARTIFACTS}" -maxdepth 1 -name 'chainsaw-report*.xml' -o \
-                   -name 'report*.xml' 2>/dev/null | grep -v report.junit.xml | head -1 || true)"
-  if [ -n "${produced}" ] && [ "${produced}" != "${JUNIT_OUT}" ]; then
-    cp "${produced}" "${JUNIT_OUT}"
+  # Determine the light pass's parallelism from the shared config (single source of truth),
+  # falling back to 2 if unreadable — so bumping the config on prod-class hw needs no run.sh edit.
+  local light_parallel
+  light_parallel="$(sed -nE 's/^[[:space:]]*parallel:[[:space:]]*([0-9]+).*/\1/p' \
+                      "${CONF_ROOT}/config/chainsaw-config.yaml" | head -1)"
+  [ -n "${light_parallel}" ] || light_parallel=2
+
+  if [ "${#light[@]}" -gt 0 ]; then
+    log "LIGHT pass: ${#light[@]} test(s), parallel=${light_parallel} (pinned ${CHAINSAW_VERSION})"
+    run_chainsaw_pass "chainsaw-report-light" "${light_parallel}" "${light[@]}" || light_rc=$?
+  else
+    log "LIGHT pass: no tests selected."
   fi
+
+  if [ "${#heavy[@]}" -gt 0 ]; then
+    log "HEAVY pass: ${#heavy[@]} test(s) SERIAL (parallel=1) — ${heavy[*]##*/}"
+    run_chainsaw_pass "chainsaw-report-heavy" 1 "${heavy[@]}" || heavy_rc=$?
+  else
+    log "HEAVY pass: no heavy tests selected."
+  fi
+
+  # Stitch both passes' JUnit into the one stable artifact CI collects.
+  "${PYTHON}" "${CONF_ROOT}/lib/merge_junit.py" \
+    --out "${JUNIT_OUT}" --name chainsaw-report \
+    "${light_report}" "${heavy_report}"
+
+  # Overall result is the union: fail if EITHER pass had a failing/erroring test. Real
+  # failures still surface (nothing is masked); the split only changes WHEN heavy tests run.
+  if [ "${light_rc}" -ne 0 ] || [ "${heavy_rc}" -ne 0 ]; then
+    log "Chainsaw reported failures (light rc=${light_rc}, heavy rc=${heavy_rc})."
+    return 1
+  fi
+  return 0
 }
 
 # --- L1 rendering: cluster-INDEPENDENT render checks (docs/14) --------------------------
diff --git a/conformance/tests/l3-fault-injection/alerting/fixtures/smtp-sink.yaml b/conformance/tests/l3-fault-injection/alerting/fixtures/smtp-sink.yaml
new file mode 100644
index 0000000..f500465
--- /dev/null
+++ b/conformance/tests/l3-fault-injection/alerting/fixtures/smtp-sink.yaml
@@ -0,0 +1,121 @@
+# =============================================================================
+# T-4.1 — Hermetic SMTP capture sink for the L3 "alerting" conformance test
+# (R-OBS-02, R-OBS-04).
+#
+# The alerting test injects a fault, Alertmanager fires and routes an email, and
+# the test asserts the email arrived. To keep the test hermetic (no real inbox,
+# ADR-0011 reproducibility), Alertmanager's email route is pointed at THIS
+# in-namespace sink instead of a real MTA. The sink is Mailpit: it speaks SMTP
+# for delivery and exposes an HTTP API the test polls for the captured message.
+#
+# Contract the alerting test relies on (chainsaw injects the ephemeral namespace,
+# so these are intentionally namespace-less):
+#   * Service name .............. smtp-sink        (stable DNS the test/AM target)
+#   * SMTP port (delivery) ...... 1025             (Alertmanager `smarthost`)
+#   * HTTP port (query/API) ..... 8025             (test polls for the message)
+#   * Query endpoint ............ GET http://smtp-sink:8025/api/v1/messages
+#                                 -> JSON: .messages[].Subject / .To / .From
+#     (health: GET /api/v1/messages returns 200 once the sink is up; a delivered
+#      alert appears as a message whose Subject matches the fired alertname.)
+#
+# Mailpit stores messages in memory (no PVC, no persistence) — a leaked namespace
+# leaves nothing behind, and chainsaw's per-test namespace teardown removes it.
+# =============================================================================
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: smtp-sink
+  labels:
+    app.kubernetes.io/name: smtp-sink
+    app.kubernetes.io/part-of: conformance-alerting
+    conformance.home.k3s/fixture: smtp-sink
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app.kubernetes.io/name: smtp-sink
+  template:
+    metadata:
+      labels:
+        app.kubernetes.io/name: smtp-sink
+        app.kubernetes.io/part-of: conformance-alerting
+    spec:
+      # Hermetic, disposable capture sink — no state worth protecting.
+      automountServiceAccountToken: false
+      securityContext:
+        runAsNonRoot: true
+        runAsUser: 1000
+        seccompProfile:
+          type: RuntimeDefault
+      containers:
+        - name: mailpit
+          image: axllent/mailpit:v1.21.8
+          imagePullPolicy: IfNotPresent
+          env:
+            # Bind SMTP + HTTP UI/API on the well-known conformance ports.
+            - name: MP_SMTP_BIND_ADDR
+              value: "0.0.0.0:1025"
+            - name: MP_UI_BIND_ADDR
+              value: "0.0.0.0:8025"
+            # In-memory store: no disk, cleared on pod restart (hermetic per-run).
+            - name: MP_MAX_MESSAGES
+              value: "500"
+          ports:
+            - name: smtp
+              containerPort: 1025
+              protocol: TCP
+            - name: http
+              containerPort: 8025
+              protocol: TCP
+          readinessProbe:
+            httpGet:
+              path: /readyz
+              port: http
+            initialDelaySeconds: 2
+            periodSeconds: 3
+            timeoutSeconds: 2
+          livenessProbe:
+            httpGet:
+              path: /livez
+              port: http
+            initialDelaySeconds: 5
+            periodSeconds: 10
+          resources:
+            requests:
+              cpu: 25m
+              memory: 32Mi
+            limits:
+              cpu: 100m
+              memory: 128Mi
+          securityContext:
+            allowPrivilegeEscalation: false
+            readOnlyRootFilesystem: true
+            capabilities:
+              drop:
+                - ALL
+          volumeMounts:
+            - name: tmp
+              mountPath: /tmp
+      volumes:
+        - name: tmp
+          emptyDir: {}
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: smtp-sink
+  labels:
+    app.kubernetes.io/name: smtp-sink
+    app.kubernetes.io/part-of: conformance-alerting
+spec:
+  selector:
+    app.kubernetes.io/name: smtp-sink
+  ports:
+    - name: smtp
+      port: 1025
+      targetPort: smtp
+      protocol: TCP
+    - name: http
+      port: 8025
+      targetPort: http
+      protocol: TCP