fix(vpn-ingress): keep the server key in source through SOPS, not as an out-of-band Secret

Operator correction: secrets are kept in source through sops. #55 shipped the
WireGuard server private key as a Secret to `kubectl create` by hand. Two real
costs, not just a convention break:

  * R-SEC-01 / spec docs/07 -- secrets live in source, SOPS-encrypted, and
    reach the cluster only through Flux.
  * It broke DR for the one credential that cannot be re-derived. A rebuild
    restores everything in git; it does not restore a hand-made Secret, and
    losing this key means re-enrolling EVERY device, because each client
    profile pins its public half. #55 papered over that with "keep a copy in
    your password manager".

(Note secret-provenance did NOT forbid the original shape -- it scopes to
app-namespace=true and vpn-ingress is deliberately a platform namespace. The
rule broken was the written requirement, not an enforced control.)

An agent still must not mint a long-lived private key (CLAUDE.md §6), so the
file is committed ALREADY ENCRYPTED with `privatekey: REPLACE-ME`. That makes
the wiring complete and green from the first commit -- resource line plus both
overlay decryption patches -- leaving the operator exactly one act: replace the
value. A commented-out resource to uncomment later is the "in git, no generator
entry, reviewed, merged, still broken" shape this repo keeps hitting.

The init guard is now a validation rather than an emptiness check: the value is
piped through `wg pubkey`, which accepts only a real curve25519 private key, and
the pod names which case it hit -- placeholder, empty, mangled, or (the silent
one) still `ENC[` ciphertext because an overlay is missing its decryption patch,
which otherwise applies cleanly with every Flux condition green.

Second, independent finding that also fixes #55's step 2: `wg` is on the HOST
only and `sops` is in the CONTAINER only, so `sops -d | wg pubkey` cannot run in
one shell -- the command #55 documented could not have worked. Every step is now
split by where it runs, and the written key is verified by comparing sha256
digests rather than printing anything. `qrencode` is on neither, so the QR step
says so and gives the install command.

Touches clusters/** and adds a **/*.sops.yaml, so approval-policy will block
pending the operator's /approve-override. Deliberately not posted by me.

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

decisions/2026-10-05-vpn-server-key-in-sops.md

@@ -0,0 +1,146 @@
+---
+date: 2026-10-05
+branch: fix/vpn-server-key-in-sops
+title: VPN server key moves into SOPS-encrypted git — the out-of-band Secret broke R-SEC-01 and the DR story
+---
+
+## What changed
+
+**Operator correction (2026-10-05): "secrets are kept in source through sops".** They are right, and
+#55 shipped the WireGuard server private key the wrong way: as a Secret the operator was told to
+`kubectl create` out of band, referenced by name only. This branch moves it into the tree as
+`platform/vpn-ingress/wg-server-key.sops.yaml`, where every other secret in this repo lives.
+
+**Why the original choice was wrong, not merely unconventional.** Two concrete costs, both of which
+#55's own README half-admitted and then shipped anyway:
+
+1. **R-SEC-01 / spec docs/07 says secrets live in source, SOPS-encrypted, reaching the cluster only
+   through Flux.** An out-of-band Secret is outside the GitOps tree by construction.
+2. **It broke DR for the one credential that cannot be re-derived.** A cluster rebuild restores
+   everything in git; it does not restore a hand-made Secret. Losing this key means **re-enrolling
+   every device**, because each client profile pins its public half. #55 papered over this with
+   "keep a copy in your password manager", which is a workaround for a self-inflicted gap.
+
+Note `platform/kyverno/admission/secret-provenance.yaml` did **not** forbid the original shape —
+it scopes to `app-namespace=true` namespaces and `vpn-ingress` is deliberately a platform namespace,
+so admission would have accepted the hand-applied Secret. The rule it violated was the written
+requirement, not an enforced control. Recording that because "the gate let it through" was never
+evidence it was correct.
+
+**How the unfillable-key problem is solved.** An agent still must not mint a long-lived private key
+(CLAUDE.md §6), so the file is committed **already encrypted, with `privatekey: REPLACE-ME`**. That
+makes the wiring complete and the gate green from the first commit — the resource line and both
+overlay decryption patches are present — and leaves the operator exactly one act: replace the value.
+The alternative, a commented-out resource line to uncomment later, is precisely the "file in git with
+no generator entry: reviewed, merged, apparently done, still broken" shape this repo keeps getting
+bitten by (`alert-runbooks-resolvable` exists because of it).
+
+**The init-container guard is now a validation, not an emptiness check.** It was `[ -z "$key" ]`.
+Because the committed placeholder is non-empty, the likely failure is now a value that is present
+and *wrong*, so the guard pipes the value through `wg pubkey` — which accepts only a real 32-byte
+curve25519 private key — and names which of four cases it hit:
+
+| case | why it matters |
+|---|---|
+| `REPLACE-ME` placeholder | the expected fresh-install state |
+| empty | blanked value |
+| **starts with `ENC[`** | **the Secret reached the cluster UNDECRYPTED.** A missing overlay decryption patch applies cleanly and leaves every Flux condition green — this is the silent failure the guard exists for |
+| rejected, none of the above | mangled value, or a *public* key pasted by mistake |
+
+Files:
+
+- `platform/vpn-ingress/wg-server-key.sops.yaml` (new) — SOPS-encrypted to the repo's age recipient,
+  `stringData.privatekey` only, placeholder value.
+- `platform/vpn-ingress/wg-server-key.sops.yaml.example` (new) — plaintext template + operator
+  hand-off, following the `crafty-oauth2-proxy-credentials.sops.yaml.example` convention.
+- `platform/vpn-ingress/kustomization.yaml` — the resource added; the "DELIBERATELY ABSENT: a
+  Secret" block replaced with the overlay-patch warning.
+- `platform/vpn-ingress/daemonset.yaml` — the `wg pubkey` guard; volume comment rewritten.
+- `clusters/dev/kustomization.yaml`, `clusters/prod/kustomization.yaml` — **the `vpn-ingress`
+  `decryption:` patch, in both.** This is the load-bearing half: #55's own kustomization comment
+  predicted that forgetting it applies ciphertext cleanly.
+- `clusters/base/vpn-ingress.yaml` — its "NO decryption stanza is needed" comment was now false.
+- `platform/vpn-ingress/README.md`, `runbooks/vpn-remote-access.md` — step 2 rewritten.
+- `infra/vpn-ingress/new-peer.sh` — stale "step 1" pointer.
+
+**A second finding, which changes the procedure independently of SOPS: `wg` and `sops` are not in
+the same place.** Measured: `wg` is on the **host** only (`/usr/bin/wg`, absent from the dev
+container); `sops` is in the **container** only (`/usr/local/bin/sops`, absent from the host). So
+`sops -d … | wg pubkey` cannot be run in one shell, and #55's step 2 — which assumed it could —
+would have failed. The runbook and the `.example` now split every command by where it runs, and
+verify the written key by comparing **sha256 digests** of the decrypted value and the operator's
+local copy, which never puts key material on a terminal. `qrencode` is on neither, so the QR
+instruction now says so and gives the install command.
+
+**SENSITIVE PATHS — this PR touches `clusters/**` (two overlays) AND adds a `**/*.sops.yaml`, so
+`ci/approval-policy.sh` will BLOCK it.** It needs the operator's `/approve-override <reason>` as a
+PR **review** of type "Comment". I have deliberately not posted it (CLAUDE.md §1).
+
+## What I verified
+
+- **The encrypted file is real and correctly targeted.** `sops -e -i` in the pinned toolbox
+  produced `stringData.privatekey: ENC[AES256_GCM,...]` with cleartext keys, `encrypted_regex
+  ^(data|stringData)$`, and exactly one age recipient:
+  `age175l8mdpdfu7hq0aml3exs3gykarwjmuvr23sq56s3wjejnyk44wsp4mfzg` — the recipient in the root
+  `.sops.yaml`, i.e. the key Flux holds as `sops-age`.
+- **Round-trip, without exposing anything**: `sops -d` then a Python read of key names only →
+  `stringData keys: ['privatekey']`, and `value is still the placeholder: True`.
+- **Both overlay patches are present and name the right Kustomization** (`name: vpn-ingress`,
+  `namespace: flux-system`, `decryption.secretRef.name: sops-age`), inserted after each overlay's
+  `velero` stanza, mirroring headlamp/crafty/velero.
+- **`kubectl kustomize platform/vpn-ingress` builds** and now emits five objects — Namespace,
+  ConfigMap, **Secret**, DaemonSet, NetworkPolicy — with `${WG_CLIENT_CIDR}` still an unexpanded
+  token for Flux.
+- **`wg` / `sops` / `qrencode` locations**, measured on both host and container, as described above.
+- **Toolbox gate** from an isolated worktree: **rc 3**, with `spec-immutability`, `decisions-log`,
+  `lint`, `l0`, `render-golden`, `l1` and `approval-policy` all **pass**; rc 3 is the two
+  environmental skips (`gitea-settings` — no local token; conformance L2/L3 — no cluster).
+  **Not green. Reported as rc 3, not as pass.**
+- **The L0 gate caught THREE real defects in this branch before it could merge — including one
+  in the fix for another — and I had asserted one of them was fine without running it.** Both are recorded because the gate's value here is the
+  whole point of the exercise:
+  1. **`no-plaintext-secrets` FAILED**: "`wg-server-key.sops.yaml.example`: an unencrypted .example
+     template is referenced by a kustomization — it would be applied as a plaintext Secret". My
+     kustomization named the template in a *comment*, and the check matches comments too (correctly:
+     naming one is how a plaintext Secret gets applied by accident). `platform/crafty/kustomization.yaml`
+     never names its own example either — the convention was there to copy and I missed it. Fixed by
+     not naming the file; the hand-off lives inside the example, where it belongs.
+     **An earlier draft of this entry claimed this check passed. It did not. The claim was written
+     from expectation rather than from a run.**
+  2. **`flux-postbuild-substitution` FAILED** on `${key#ENC[}` in my new guard
+     (`daemonset.yaml:155`), flagged `[SILENT-EMPTY]`: envsubst consumes every `${...}`, so my
+     shell prefix-strip would have rendered to the empty string — the ciphertext branch of the guard
+     would never have fired, which is precisely the silent failure the guard was added to catch.
+     Rewritten with `case`, which uses no braces and so has nothing to escape.
+  3. **And then it failed a THIRD time, on the fix's own comment** — `[FATAL-PARSE]
+     daemonset.yaml:156 ${...}`, the prose explaining the rule, written with the literal form. That
+     class is worse than it looks: a `FATAL-PARSE` hazard fails the **entire** Kustomization, every
+     resource in the path, not just the line. Rewritten as "dollar-brace expansion". This is the
+     second time in this component that writing the hazard literally inside a comment about the
+     hazard has been the defect (the first was in #55), so the habit to build is: **in any
+     substituted path, describe the construct in words, never type it.**
+- **After both fixes, `no-plaintext-secrets` and `flux-postbuild-substitution` pass** (446 and 198
+  assertions respectively), and `l0` is green.
+
+## What I did NOT verify
+
+- **That Flux decrypts this file on prod.** The overlay patches have never reconciled. This is the
+  whole risk of the change and it has exactly one observable outcome: after merge the pods should
+  CrashLoop reporting the **`REPLACE-ME` placeholder** (proving decryption worked), *not* reporting
+  **`ENC[`** (which would prove a patch is wrong). I built the guard to tell those apart because I
+  cannot test them.
+- **That `wg pubkey` accepts the operator's real key through this path.** The guard is reasoned from
+  `wg pubkey`'s behaviour and has never run — `wg` is absent from both this workstation's container
+  and the gate, so the first execution will be in the pod.
+- **The `sops set` command in the hand-off.** I verified `sops -e -i` and `sops -d` in the toolbox;
+  I did **not** run `sops set` with the quoting shown, and nested quoting inside
+  `dev.sh run bash -c` is exactly where a documented command tends to break. If it misbehaves, the
+  editor form (`sops <file>`) is the fallback and does not depend on quoting.
+- **The sha256 comparison in step 2 step 4** is untested end to end (it needs the real key).
+- **Whether anything else in #55 assumed a tool is available where it is not.** I checked `wg`,
+  `sops` and `qrencode` because step 2 depended on them. I did not audit every command in the
+  runbook the same way — and that class of defect has now produced two corrections in a row
+  (`site.sh`, then `sops | wg`), so assume more remain until each step has actually been run.
+- **The live VPN still carries no traffic**, and the earlier gaps stand unchanged: the
+  iptables-vs-nftables question, `allowPrivilegeEscalation: false` versus the image's s6 init, and
+  any off-LAN reachability.