feat(cilium): export Plex's pre-SNAT client address via Hubble, scoped to tcp/32400

The requirement is log visibility only -- which address connected to Plex.

Plex's own log cannot show it. Every LoadBalancer Service here is
externalTrafficPolicy: Cluster, so the node holding the VIP's L2 lease SNATs
the client before forwarding to the backend pod. Measured: Plex had logged
3,214 requests from 10.0.1.x (lease holder k3s-prod-3's own address, Cilium
identity 1 = reserved:host) and ZERO from any 192.168.x address, ever. No
X-Forwarded-For either -- it serves raw tcp/32400, not HTTP via the Gateway.
Nothing on the router does this; there is no hairpin NAT. It is Cilium.

The address is not lost, only unrecorded. Cilium observes the flow at ingress,
BEFORE its own translation, so Hubble already has it:

  192.168.2.133 -> 10.0.0.135   real LAN client -> the Plex pod
  10.0.1.78     -> 10.0.0.135   same traffic post-SNAT, what Plex sees

What was missing is RETENTION: 4095/4095 flows at ~303/s is about thirteen
seconds of history, metrics disabled, no exporter configured.

So enable the static exporter, port-scoped, to the agent's stdout -- Alloy
already tails every pod into Loki, so this needs no new mount, no rotation
handling and no Alloy change.

  {namespace="kube-system", app="cilium"} |= "32400"

Scoped BY PORT, not namespace, on evidence: --to-namespace plex returned only
the post-SNAT flows; the record carrying the real client address did not match
it. A namespace filter would drop exactly what this exists to capture.

Rejected, with reasons: eTP:Local is incompatible with cilium 1.20's L2
announcer per upstream docs for this version ("may cause service IPs to be
announced on nodes without pods causing traffic drops") -- and the VIP is on
prod-3 while the pod is on prod-1, so it would black-hole 32400 immediately;
making it safe costs Plex its ability to reschedule. DSR: routing-mode is
vxlan, not native/geneve, and DSR returns bypass the ingress node, breaking
the router's stateful NAT on the remote path.

Also corrects the repo's own record: 2026-10-03 says the SNAT lands in
192.168.0.0/16 (the node's LAN address). It is 10.0.1.x, the cilium_host
inside the pod CIDR -- which is why LanNetworksBandwidth can never separate
local from remote while eTP is Cluster.

UNVERIFIED and stated in the handoff: nothing is reconciled; `filePath: stdout`
is taken from a verbatim upstream sentence but not confirmed against 1.20.1
source (a wrong notation is a silent no-op, with the file+Alloy fallback
documented); the port FlowFilter has no upstream example; and this change
ROLLS CILIUM -- prod-3 announces the Gateway, PiHole DNS and Plex VIPs, so a
lease move during the rollout could briefly interrupt LAN DNS.

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

platform/cilium/helmrelease.yaml

@@ -101,6 +101,60 @@ spec:
         enabled: true
       ui:
         enabled: true   # exposure gated behind oauth2-proxy forward-auth later (ADR-0014)
+      # --- STATIC FLOW EXPORT: persist the PRE-SNAT client address for Plex (2026-10-04) ---
+      # [parity] MUST equal Ansible: hubble.export.static.{enabled,filePath,allowList}
+      #
+      # WHY THIS EXISTS. Plex's own log cannot show who connected. Every LoadBalancer Service in
+      # this cluster is `externalTrafficPolicy: Cluster`, so the node holding the L2 lease for the
+      # VIP SNATs the client before forwarding to the backend pod. Measured 2026-10-04: Plex had
+      # logged 3,214 requests from `10.0.1.x` (the lease holder k3s-prod-3's own address, Cilium
+      # identity 1 = reserved:host) and ZERO from any 192.168.x address, ever. No X-Forwarded-For
+      # either -- it serves raw tcp/32400, not HTTP through the Gateway.
+      #
+      # THE ADDRESS IS NOT LOST, ONLY UNRECORDED. Cilium observes the flow at ingress, BEFORE its
+      # own translation, so Hubble already has the true source. Measured on the lease holder:
+      #     192.168.2.133 -> 10.0.0.135   (real LAN client -> the Plex pod)
+      #     10.0.1.78     -> 10.0.0.135   (the same traffic, post-SNAT -- what Plex sees)
+      # What was missing is RETENTION: the ring buffer was 4095/4095 flows at ~303 flows/s, i.e.
+      # about THIRTEEN SECONDS of history, with hubble metrics disabled and no exporter configured.
+      #
+      # WHY NOT FIX THE SNAT INSTEAD. `externalTrafficPolicy: Local` would preserve the address in
+      # Plex's own log, but cilium 1.20's L2 announcer is explicitly incompatible with it -- upstream
+      # docs for this exact version: "incompatible with the externalTrafficPolicy: Local on services
+      # as it may cause service IPs to be announced on nodes without pods causing traffic drops",
+      # and "L2 announcements isn't currently aware of this setting". Live proof that this is not
+      # theoretical: the VIP is announced by k3s-prod-3 while the pod runs on k3s-prod-1, so the
+      # flip would black-hole tcp/32400 immediately. Making it safe would mean pinning BOTH the pod
+      # and the announcement to one node and giving up Plex's ability to reschedule -- a real
+      # availability loss to buy a log field. (It is the same trap platform/crafty/service-l4.yaml
+      # documents from an 8-day Minecraft outage.) DSR was also rejected: routing-mode here is
+      # vxlan, not native/geneve, and DSR returns bypass the ingress node, which breaks the SOHO
+      # router's stateful NAT on the remote path.
+      #
+      # `filePath: stdout` RATHER THAN A FILE, deliberately. Grafana Alloy already runs as a
+      # DaemonSet tailing every pod's logs into Loki (platform/monitoring/alloy.yaml), so stdout
+      # reaches Loki with NO new hostPath mount, no file-rotation handling and no Alloy change.
+      # Upstream documents it: "To get Hubble flows directly exported to the logs instead of written
+      # to a rotated file, `stdout` can be defined as `hubble-export-file-path`." fileMaxSizeMb /
+      # fileMaxBackups are therefore left at chart defaults and do not apply.
+      #   Query:  {namespace="kube-system", app="cilium"} |= "32400"
+      #
+      # SCOPED BY PORT, NOT BY NAMESPACE -- and that is a measured decision, not a preference. A
+      # `--to-namespace plex` query returned ONLY the post-SNAT flows; the flow carrying the real
+      # client address did NOT match it, because at the point of observation the destination
+      # identity is not yet resolved to the plex pod. Filtering by namespace would therefore drop
+      # exactly the record this change exists to capture. Port it is.
+      #
+      # Both directions are listed so the return path is captured too. Volume is small (a few
+      # hundred to a few thousand lines a day); if it ever becomes noisy, narrow it with
+      # `fieldMask` rather than by removing a filter.
+      export:
+        static:
+          enabled: true
+          filePath: stdout
+          allowList:
+            - '{"destination_port":["32400"]}'
+            - '{"source_port":["32400"]}'
     # --- L2 announcement for the ingress VIP on the flat LAN (docs/09, OQ-1 resolved) ---
     # [parity] MUST equal Ansible: l2announcements.enabled: true. IP pool +
     # CiliumL2AnnouncementPolicy (reserved 10.73.0.240-.250) authored by WS-NET in Phase 2.

platform/cilium/values.yaml

@@ -38,6 +38,18 @@ hubble:
     enabled: true
   ui:
     enabled: true
+  # [parity] static flow export -> cilium-agent stdout -> Alloy -> Loki. Records the PRE-SNAT
+  # client address for Plex's raw tcp/32400, which Plex's own log cannot show (every LB Service here
+  # is externalTrafficPolicy: Cluster, so the VIP lease holder SNATs the client). Scoped BY PORT,
+  # not namespace: the flow carrying the real client IP does not match a namespace filter. Full
+  # rationale, measurements and the rejected alternatives are in helmrelease.yaml.
+  export:
+    static:
+      enabled: true
+      filePath: stdout
+      allowList:
+        - '{"destination_port":["32400"]}'
+        - '{"source_port":["32400"]}'
 # [parity] ingress VIP announcement on the flat LAN (docs/09, OQ-1)
 l2announcements:
   enabled: true