diff --git a/clusters/base/cilium.yaml b/clusters/base/cilium.yaml
new file mode 100644
index 0000000..2ba18e1
--- /dev/null
+++ b/clusters/base/cilium.yaml
@@ -0,0 +1,60 @@
+---
+# Flux Kustomization: CILIUM (the CNI) — reconciles ./platform/cilium.
+# Serves R-PLAT-01 (platform components reconciled by GitOps) and R-GITOPS-01/03.
+#
+# WHY CILIUM HAS ITS OWN KUSTOMIZATION (split out of `platform`, 2026-09-01)
+#
+# This is the MIRROR IMAGE of the oauth2-proxy / headlamp splits, not a repeat of them. Those are
+# leaves that must NEVER gate a tier, so they left `platform` and run `wait: false` below it.
+# Cilium is the one component that legitimately SHOULD gate everything — but inside the shared
+# `platform` Kustomization its health was indistinguishable from eleven unrelated components:
+#
+#   * `platform`'s Ready condition could not tell you "the CNI is down" from "longhorn is slow".
+#   * The only emergency valve was `flux suspend kustomization platform` — freezing the ENTIRE
+#     tier (storage, TLS, DNS, ingress, monitoring, Keycloak, KubeVirt) to stop touching the CNI.
+#     `flux suspend kustomization cilium` now freezes exactly the CNI and nothing else, which is
+#     the valve the 2026-09-01 substitution incident wanted and did not have.
+#   * `platform`'s 10m interval + 5m timeout are wrong for a CNI: a 3-node DaemonSet rollout with
+#     `wait: true` can exceed 5m, and re-rendering the CNI every 10m buys nothing.
+#
+# GATING IS PRESERVED, NOT WEAKENED: `wait: true` here plus `platform.dependsOn: [cilium]` means
+# nothing in the graph reconciles until the CNI is healthy — the same guarantee as before, now
+# expressed as an explicit edge instead of an accident of co-tenancy.
+apiVersion: kustomize.toolkit.fluxcd.io/v1
+kind: Kustomization
+metadata:
+  name: cilium
+  namespace: flux-system
+spec:
+  # A CNI does not need a 10m re-render cadence. A git push still reconciles immediately —
+  # kustomize-controller is source-triggered; `interval` is only the drift-correction floor.
+  interval: 1h
+  retryInterval: 2m
+  # 10m (not the 5m `platform` uses): a 3-node Cilium DaemonSet rollout under `wait: true`,
+  # rolled ONE NODE AT A TIME (maxUnavailable: 1, P2), legitimately exceeds 5m.
+  timeout: 10m
+  prune: true
+  # TRUE, deliberately: this is the ONE component whose health should gate the whole platform.
+  wait: true
+  # Same revision-gating reason `platform` has it (2026-09-01 incident): `cluster-vars` is APPLIED
+  # by the root `flux-system` Kustomization, and this Kustomization SUBSTITUTES from it. `dependsOn`
+  # is revision-gated (kustomize-controller v1.4.0 `checkDependencies`), so this cannot render
+  # revision N of helmrelease.yaml against the revision N-1 `cluster-vars`. That race is exactly how
+  # `k8sServiceHost: ""` once reached the Cilium HelmRelease and took down 2/3 agents.
+  dependsOn:
+    - name: flux-system   # the ROOT Kustomization (sync.yaml) that applies cluster-vars
+  sourceRef:
+    kind: GitRepository
+    name: flux-system
+  path: ./platform/cilium
+  # MANDATORY, not decorative: platform/cilium/helmrelease.yaml references ${K3S_API_HOST}.
+  # kustomize-controller now runs --feature-gates=StrictPostBuildSubstitutions=true, so without
+  # this stanza an undefined ${K3S_API_HOST} FAILS this Kustomization outright (it no longer
+  # renders empty). That is the intended fail-closed behaviour — but it means the stanza is
+  # load-bearing for the CNI coming up at all. Do not remove it.
+  postBuild:
+    substituteFrom:
+      - kind: ConfigMap
+        name: cluster-vars
+  # No `decryption` stanza: platform/cilium carries no SOPS-encrypted resource (unlike
+  # oauth2-proxy/headlamp/crafty/velero, whose overlays patch one in by name).
diff --git a/clusters/base/kustomization.yaml b/clusters/base/kustomization.yaml
index 85aa5a6..b1db32b 100644
--- a/clusters/base/kustomization.yaml
+++ b/clusters/base/kustomization.yaml
@@ -5,6 +5,13 @@ apiVersion: kustomize.config.k8s.io/v1beta1
 kind: Kustomization
 resources:
   - flux-system.yaml     # GitRepository (reconciliation source)
+  # Cilium (the CNI) — its OWN Kustomization, split OUT of `platform` (2026-09-01). The mirror image
+  # of the oauth2-proxy/headlamp splits: those are leaves that must never gate a tier (wait:false);
+  # Cilium is the one component that legitimately SHOULD gate everything, so it keeps wait:true and
+  # `platform` dependsOn it. Splitting it out buys a per-CNI Ready condition, CNI-appropriate
+  # interval/timeout, and `flux suspend kustomization cilium` as an emergency valve that does not
+  # freeze the other eleven platform components. See clusters/base/cilium.yaml.
+  - cilium.yaml          # Flux Kustomization -> ./platform/cilium (dependsOn flux-system, wait:true)
   - platform.yaml        # Flux Kustomization -> ./platform (CONTROLLERS: HelmReleases / CRDs)
   - platform-config.yaml # Flux Kustomization -> ./platform-config (CONFIGS: CRs; dependsOn platform)
   # App tier, split into dependency-ordered WAVES (was the single ./apps `apps` Kustomization).
diff --git a/clusters/base/platform.yaml b/clusters/base/platform.yaml
index 02251e1..394f0cd 100644
--- a/clusters/base/platform.yaml
+++ b/clusters/base/platform.yaml
@@ -11,7 +11,27 @@ spec:
   interval: 10m
   retryInterval: 2m
   timeout: 5m
-  prune: true          # drift correction: delete resources removed from git (R-GITOPS-03)
+  # ======================= TEMPORARY — prune:false TRANSITION STATE =======================
+  # RESTORE TO `prune: true` IN THE VERY NEXT MERGE. This is step 1 of the documented Flux
+  # procedure for MOVING RESOURCES BETWEEN KUSTOMIZATIONS (fluxcd.io/flux/faq: "set spec.prune to
+  # false, sync, move the manifests, then re-enable pruning"), used here to move ./platform/cilium
+  # out of this tier and into its own `cilium` Kustomization (clusters/base/cilium.yaml).
+  #
+  # WHY IT IS NOT OPTIONAL: `platform/cilium/namespace.yaml` is the ONLY declaration of
+  # Namespace/kube-system anywhere under ./platform, and the live object carries
+  # `kustomize.toolkit.fluxcd.io/name=platform`. The moment ./platform/cilium leaves this
+  # Kustomization's rendered path, Namespace/kube-system + the Cilium HelmRepository/HelmRelease
+  # become STALE in this Kustomization's inventory. With prune:true that is not "uninstall the
+  # CNI" — it is `kubectl delete namespace kube-system`, which takes the whole cluster.
+  #
+  # A SECOND, INDEPENDENT PROTECTION IS ALSO IN PLACE (belt and braces, deliberately):
+  # kustomize-controller's pruner passes `Inclusions: GetOwnerLabels(platform, flux-system)`, so it
+  # only deletes objects whose LIVE labels still say they belong to `platform`. The new `cilium`
+  # Kustomization relabels all three objects to `name=cilium` when it applies them, and the
+  # `dependsOn: [cilium]` edge below is REVISION-gated — `platform` cannot reconcile revision N
+  # until `cilium` has APPLIED revision N. So the relabel provably precedes the prune. Neither
+  # mechanism is trusted alone for an object of this blast radius.
+  prune: false         # <-- TEMPORARY; see block above. Normal value: true (R-GITOPS-03)
   wait: true           # block `apps` until platform is healthy
   # ORDERING FIX (2026-09-01 incident: a substitution race that failed OPEN broke Cilium).
   #
@@ -40,6 +60,13 @@ spec:
   # health-gates its own children (see clusters/dev/sync.yaml).
   dependsOn:
     - name: flux-system   # the ROOT Kustomization (sync.yaml) that applies cluster-vars
+    # THE CNI GATES THE TIER. Cilium was split out of ./platform into its own Kustomization
+    # (clusters/base/cilium.yaml, wait:true) so its health has its own Ready condition and its own
+    # suspend valve. This edge preserves the ordering that co-tenancy used to provide implicitly:
+    # nothing in `platform` — and therefore nothing anywhere downstream — reconciles until the CNI
+    # is healthy. It is also revision-gated, which is what makes the prune-safety argument above
+    # deterministic rather than a race.
+    - name: cilium
   sourceRef:
     kind: GitRepository
     name: flux-system
diff --git a/platform/kustomization.yaml b/platform/kustomization.yaml
index b0dcedd..78a07e0 100644
--- a/platform/kustomization.yaml
+++ b/platform/kustomization.yaml
@@ -12,7 +12,15 @@ kind: Kustomization
 resources:
   # ---- Phase 2 — Platform Core: Network, Storage, TLS, DNS, Ingress ----
   - kyverno            # admission enforcer FIRST — policies present before other components reconcile
-  - cilium             # CNI (adopts the running Ansible-installed release; parity verified)
+  #      cilium (the CNI) is DELIBERATELY NOT here: it now reconciles in its OWN Flux Kustomization
+  #      (clusters/base/cilium.yaml, dependsOn flux-system, wait:true), and `platform` dependsOn IT.
+  #      Not the headlamp/oauth2-proxy rationale (a leaf that must not gate) but its mirror image:
+  #      the CNI is the one component that SHOULD gate everything, and inside this shared tier its
+  #      health was indistinguishable from eleven unrelated components, the only emergency valve was
+  #      freezing the whole tier, and the tier's 10m/5m interval/timeout are wrong for a 3-node
+  #      DaemonSet rollout. Gating is preserved via the explicit `platform.dependsOn: [cilium]` edge.
+  #      NOTE: platform/cilium/namespace.yaml is the ONLY declaration of Namespace/kube-system in
+  #      this tree — that is why the move required a prune-disabled transition. See DECISIONS-LOG.
   - longhorn           # replicated block storage / CSI
   - external-snapshotter  # CSI snapshot CRDs + snapshot-controller (VolumeSnapshot API; CDI smart-clone)
   - cert-manager       # Let's Encrypt DNS-01 wildcard — needs SOPS `cloudflare-api-token`