diff --git a/deploy/helm/certctl/templates/NOTES.txt b/deploy/helm/certctl/templates/NOTES.txt
index c0b296c..630c35c 100644
--- a/deploy/helm/certctl/templates/NOTES.txt
+++ b/deploy/helm/certctl/templates/NOTES.txt
@@ -72,3 +72,28 @@ IMPORTANT NOTES FOR PRODUCTION:
    - All containers run as non-root
    - Implement network policies to restrict traffic between components
    - Consider pod security policies or security standards for your cluster
+{{- /*
+  DEPL-006 closure (Sprint 3, 2026-05-16). Loud notice when the
+  operator runs a multi-replica deploy without crossing the two
+  required HA toggles. Per-pod rate-limit buckets and round-robin
+  load balancing both silently break correctness above replicas:1.
+*/}}
+{{- if gt (int .Values.server.replicas) 1 }}
+
+⚠️  HA MISCONFIGURATION WARNINGS (replicas={{ .Values.server.replicas }}):
+{{- $backend := .Values.server.rateLimiting.backend | default "memory" }}
+{{- if eq $backend "memory" }}
+   - server.rateLimiting.backend = "memory" with replicas > 1 gives each
+     pod its own bucket map, so the configured cap is effectively
+     multiplied by the replica count. Set
+     `--set server.rateLimiting.backend=postgres` (see DEPL-006 /
+     docs/operator/runbooks/ha.md).
+{{- end }}
+{{- if not .Values.server.service.sessionAffinity }}
+   - server.service.sessionAffinity is empty. Round-robin Service load
+     balancing routes login → /api/v1/auth/login → /api/v1/auth/csrf
+     across different pods, breaking the CSRF token + session cookie
+     handshake. Set
+     `--set server.service.sessionAffinity=ClientIP`.
+{{- end }}
+{{- end }}
diff --git a/deploy/helm/certctl/templates/server-deployment.yaml b/deploy/helm/certctl/templates/server-deployment.yaml
index e32eb62..36246c4 100644
--- a/deploy/helm/certctl/templates/server-deployment.yaml
+++ b/deploy/helm/certctl/templates/server-deployment.yaml
@@ -51,6 +51,20 @@ spec:
               containerPort: {{ .Values.server.port }}
               protocol: TCP
           env:
+            # DEPL-003 closure (Sprint 3, 2026-05-16). Pre-fix the
+            # CERTCTL_MIGRATIONS_VIA_HOOK env var was documented in
+            # values.yaml (L797-810) and migration-job.yaml comments
+            # but was never rendered into the server Deployment env
+            # block. With migrations.viaHook=true the operator's
+            # intent is "the pre-install/pre-upgrade Helm Job owns
+            # migrations" — but the server pods, missing the env,
+            # ran their own boot-time RunMigrations alongside the
+            # hook Job, racing on the schema lock. cmd/server/migrations.go
+            # only short-circuits when this env is "true" (line 144).
+            {{- if .Values.migrations.viaHook }}
+            - name: CERTCTL_MIGRATIONS_VIA_HOOK
+              value: "true"
+            {{- end }}
             - name: CERTCTL_SERVER_HOST
               value: "0.0.0.0"
             - name: CERTCTL_SERVER_PORT
diff --git a/deploy/helm/certctl/templates/server-service.yaml b/deploy/helm/certctl/templates/server-service.yaml
index 1de2383..dffd9c2 100644
--- a/deploy/helm/certctl/templates/server-service.yaml
+++ b/deploy/helm/certctl/templates/server-service.yaml
@@ -11,6 +11,23 @@ metadata:
   {{- end }}
 spec:
   type: {{ .Values.server.service.type }}
+  {{- /*
+    DEPL-006 closure (Sprint 3, 2026-05-16). Render the optional
+    sessionAffinity field. docs/operator/runbooks/ha.md instructs
+    operators to set sessionAffinity: ClientIP for replicas > 1 so
+    login + CSRF flows stay on the same pod; pre-fix the chart did
+    not actually pass the value through. sessionAffinityConfig
+    clientIP.timeoutSeconds renders only when set, otherwise
+    Kubernetes applies its default (10800s / 3h).
+  */}}
+  {{- if .Values.server.service.sessionAffinity }}
+  sessionAffinity: {{ .Values.server.service.sessionAffinity }}
+  {{- with .Values.server.service.sessionAffinityTimeoutSeconds }}
+  sessionAffinityConfig:
+    clientIP:
+      timeoutSeconds: {{ . }}
+  {{- end }}
+  {{- end }}
   ports:
     - port: {{ .Values.server.service.port }}
       targetPort: https
diff --git a/deploy/helm/certctl/values.yaml b/deploy/helm/certctl/values.yaml
index ad5db0e..d93c09c 100644
--- a/deploy/helm/certctl/values.yaml
+++ b/deploy/helm/certctl/values.yaml
@@ -160,6 +160,17 @@ server:
     type: ClusterIP
     port: 8443
     annotations: {}
+    # DEPL-006 closure (Sprint 3, 2026-05-16). Optional sticky-session
+    # routing. REQUIRED when server.replicas > 1 so login + CSRF token
+    # rows stay on the same pod for the duration of a session — the
+    # default round-robin load balancing breaks those flows. Set to
+    # "ClientIP" for production HA (see deploy/helm/examples/values-prod-ha.yaml).
+    # Leave empty for single-replica deploys.
+    sessionAffinity: ""
+    # When sessionAffinity is set, timeout window (in seconds) the
+    # Service maps a source IP to the same pod. Default null →
+    # Kubernetes applies its built-in default (10800s / 3h).
+    sessionAffinityTimeoutSeconds: null
 
   # Authentication configuration.
   # Valid types: "api-key" (production) or "none" (demo only — disables
diff --git a/deploy/helm/examples/values-prod-ha.yaml b/deploy/helm/examples/values-prod-ha.yaml
index 2c5042a..25eeeff 100644
--- a/deploy/helm/examples/values-prod-ha.yaml
+++ b/deploy/helm/examples/values-prod-ha.yaml
@@ -36,6 +36,14 @@ server:
 
   service:
     type: ClusterIP
+    # DEPL-006 closure (Sprint 3, 2026-05-16): with replicas:3, the
+    # default round-robin Service load balancing breaks login/CSRF
+    # flows because the session cookie + the CSRF token row land on
+    # different pods between requests. sessionAffinity: ClientIP
+    # routes every connection from a given source IP to the same
+    # pod for the configured timeout window. docs/operator/runbooks/ha.md
+    # documents this; pre-fix the chart did not actually render it.
+    sessionAffinity: ClientIP
     annotations:
       prometheus.io/scrape: "true"
       prometheus.io/port: "8443"
@@ -53,6 +61,14 @@ server:
   rateLimiting:
     rps: 500
     burst: 1000
+    # DEPL-006 closure (Sprint 3, 2026-05-16): replicas > 1 REQUIRES
+    # the postgres backend so per-key buckets are cross-replica-
+    # consistent. The default 'memory' backend gives each pod its
+    # own bucket map, so a 3-replica fleet effectively triples the
+    # configured cap (a client churning across pods bypasses the
+    # limit). See deploy/helm/certctl/values.yaml L217-226 for the
+    # canonical comment.
+    backend: postgres
 
 postgresql:
   enabled: true
diff --git a/scripts/ci-guards/B3-helm-chart-coherence.sh b/scripts/ci-guards/B3-helm-chart-coherence.sh
index b8f7de4..4c4ced2 100755
--- a/scripts/ci-guards/B3-helm-chart-coherence.sh
+++ b/scripts/ci-guards/B3-helm-chart-coherence.sh
@@ -152,10 +152,62 @@ if helm template c "$CHART" \
   failed=1
 fi
 
+# Check 8 — DEPL-006 (Sprint 3 closure): when
+# server.service.sessionAffinity is set, server-service.yaml MUST
+# render the field. Pre-fix the chart silently dropped the value
+# and docs/operator/runbooks/ha.md's instructions had no effect.
+if helm template c "$CHART" \
+      --set server.tls.existingSecret=ci \
+      --set postgresql.auth.password=p \
+      --set server.auth.apiKey=k \
+      --set server.service.sessionAffinity=ClientIP \
+      > "$TMP/affinity.yaml" 2> "$TMP/affinity.err"; then
+  if ! grep -q 'sessionAffinity: ClientIP' "$TMP/affinity.yaml"; then
+    echo "::error file=${CHART}::B3 regression (DEPL-006): server.service.sessionAffinity=ClientIP did not render. Round-robin Service routing will break login + CSRF flows."
+    failed=1
+  fi
+else
+  echo "::error file=${CHART}::B3 regression (DEPL-006): sessionAffinity mode failed to render."
+  cat "$TMP/affinity.err"
+  failed=1
+fi
+
+# Check 7 — DEPL-003 (Sprint 3 closure): when migrations.viaHook=true
+# is set, the server Deployment env block MUST render
+# CERTCTL_MIGRATIONS_VIA_HOOK=true. Without it the server runs
+# boot-time migrations alongside the pre-install/pre-upgrade hook
+# Job, racing on the schema lock.
+if helm template c "$CHART" \
+      --set server.tls.existingSecret=ci \
+      --set postgresql.auth.password=p \
+      --set server.auth.apiKey=k \
+      --set migrations.viaHook=true \
+      > "$TMP/viahook.yaml" 2> "$TMP/viahook.err"; then
+  if ! grep -q 'name: CERTCTL_MIGRATIONS_VIA_HOOK' "$TMP/viahook.yaml"; then
+    echo "::error file=${CHART}::B3 regression (DEPL-003): migrations.viaHook=true did not render CERTCTL_MIGRATIONS_VIA_HOOK in the server Deployment env block. Server pods will race the hook Job."
+    failed=1
+  fi
+  # Inverse: with viaHook unset (default), the env var MUST NOT render.
+  if helm template c "$CHART" \
+        --set server.tls.existingSecret=ci \
+        --set postgresql.auth.password=p \
+        --set server.auth.apiKey=k \
+        > "$TMP/noviahook.yaml" 2> "$TMP/noviahook.err"; then
+    if grep -q 'name: CERTCTL_MIGRATIONS_VIA_HOOK' "$TMP/noviahook.yaml"; then
+      echo "::error file=${CHART}::B3 regression (DEPL-003): default render (viaHook=false) leaked CERTCTL_MIGRATIONS_VIA_HOOK env var. Conditional template missing the {{- if }} guard."
+      failed=1
+    fi
+  fi
+else
+  echo "::error file=${CHART}::B3 regression (DEPL-003): migrations.viaHook=true mode failed to render."
+  cat "$TMP/viahook.err"
+  failed=1
+fi
+
 if [ "$failed" -ne 0 ]; then
   echo ""
   echo "${GUARD_NAME}: FAILED — Helm chart coherence regression."
   exit 1
 fi
 
-echo "${GUARD_NAME}: clean (default + external-Postgres + cert-manager + production hardening + 3 fail-fast gates all green)."
+echo "${GUARD_NAME}: clean (default + external-Postgres + cert-manager + production hardening + 3 fail-fast gates + DEPL-003 viaHook env render all green)."