feat(vpn-ingress): WireGuard remote access on udp/51820 (hostNetwork, declarative peers)

Lets the operator's Android / Linux / Windows / macOS devices dial in from
anywhere and behave like LAN machines: full reach to 192.168.2.0/24 plus
internet egress out the house WAN. Opposite direction to platform/vpn-egress,
which sends pods OUT through PIA; the two share nothing but the word "VPN".

WireGuard because it is the only option with a first-party client on all four
named platforms, and because its handshake MAC is keyed with the responder's
own public key: an unauthenticated packet gets NO reply, so udp/51820 is
indistinguishable from a closed port. That, not "it is encrypted", is what
makes an unfiltered WAN port defensible, and why there is no source allowlist.

hostNetwork: true is REQUIRED, not convenient. A pod-networked server must SNAT
clients to its own pod IP, so every remote client would carry that pod's Cilium
identity -- and a pod-sourced request to the shared Gateway VIP returns 403 from
Envoy for ALL 16 hostnames (measured 2026-10-04), because Cilium's Gateway
preserves the original source identity and enforces the destination's ingress
policy. The obvious build would have shipped a healthy-looking tunnel on which
every cluster web UI was 403 and *.home.keithjackson.dev did not even resolve.
In the host netns traffic is SNATed to the node and arrives as host/remote-node,
exactly like a LAN client. It also sidesteps the unsafe ip_forward sysctl, the
L2-announcement lease lottery, and double encapsulation (hence MTU 1420).
Permitted by restrict-host-namespaces' own carve-out for platform namespaces.
The cost is stated in networkpolicy.yaml rather than papered over: no
NetworkPolicy constrains a hostNetwork pod.

A DaemonSet so the hand-made WAN forward cannot be invalidated by a reschedule;
all three nodes answer the same keys, so failover is a one-line router change.

Peer PUBLIC keys are plaintext in peers.yaml, which makes "who can get into my
house" a reviewable PR diff. The only secret -- the server's private key -- is
an out-of-band Secret: an agent must not mint a long-lived private key, and the
two halves are joined only at pod start into a tmpfs that dies with the pod.

Ships INERT-BUT-HEALTHY with zero peers. THREE off-repo manual steps remain
(kernel module, server key, WAN forward) -- runbooks/vpn-remote-access.md.

Touches clusters/** , so ci/approval-policy.sh will block pending the
operator's /approve-override. Deliberately not posted by me (CLAUDE.md §1).

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

clusters/base/vpn-ingress.yaml

@@ -0,0 +1,56 @@
+---
+# Flux Kustomization: WireGuard remote-access VPN — reconciles ./platform/vpn-ingress.
+#
+# POST-PLATFORM TIER (dependsOn platform-config), NON-GATING (wait:false). Not a line in
+# platform/kustomization.yaml, for the standard reason plus one specific to this component:
+#
+#   * STANDARD: a leaf must never sit in the gating `platform` tier. While `platform` is not-Ready
+#     NOTHING downstream reconciles — the incident behind the headlamp/oauth2-proxy/homepage moves
+#     (DECISIONS-LOG: "Headlamp gating stall").
+#   * SPECIFIC, AND THE REASON THIS IS NOT A JUDGEMENT CALL: this DaemonSet cannot start until the
+#     operator creates the out-of-band `wg-server-key` Secret (runbooks/vpn-remote-access.md
+#     step 1). That is the correct fail-closed state — an unenrolled VPN must not come up — but in
+#     the gating tier it would have been a self-inflicted platform-wide outage ON MERGE, with the
+#     cause (a missing manual step) invisible from any Flux condition.
+#
+# WHY dependsOn platform-config AND NOT cilium. This component needs no Gateway, no TLS cert, no
+# Keycloak and no LB-IPAM pool — it has no HTTPRoute and no LoadBalancer Service, and hostNetwork
+# means it does not even need a Cilium endpoint. It could legally reconcile much earlier. It is
+# pinned behind platform-config anyway so that the ONE thing remote clients actually consume
+# through it — split-horizon DNS and the shared Gateway — exists by the time the tunnel does.
+# A tunnel that comes up before the things on the far side of it is a support call, not a feature.
+#
+# wait:false: nothing in the graph dependsOn this, and its pods are legitimately not-Ready whenever
+# the server key is absent or the `wireguard` kernel module has not been loaded on a node. Neither
+# condition should be able to gate anything else, even if a future resource is mistakenly pointed
+# at it.
+apiVersion: kustomize.toolkit.fluxcd.io/v1
+kind: Kustomization
+metadata:
+  name: vpn-ingress
+  namespace: flux-system
+spec:
+  interval: 10m
+  retryInterval: 2m
+  timeout: 5m
+  prune: true
+  wait: false
+  dependsOn:
+    - name: platform-config
+  sourceRef:
+    kind: GitRepository
+    name: flux-system
+  path: ./platform/vpn-ingress
+  # REQUIRED, not boilerplate: platform/vpn-ingress/daemonset.yaml renders ${WG_CLIENT_CIDR} into
+  # the config-assembly script. Without this block that token becomes the EMPTY STRING and the
+  # Kustomization still reports Ready (Flux's substitution fails OPEN — ci:
+  # flux-postbuild-substitution), leaving an initContainer that derives a server address of ".1/"
+  # and a MASQUERADE rule with no source. Both fail loudly at pod start, but the Kustomization
+  # would look healthy.
+  postBuild:
+    substituteFrom:
+      - kind: ConfigMap
+        name: cluster-vars
+  # NO `decryption:` stanza is needed in the overlays: this path carries no *.sops.yaml. The server
+  # key is an out-of-band Secret (platform/vpn-ingress/kustomization.yaml says what to do if that
+  # ever changes).