feat(conformance): L2 tests derive their environment from the cluster, not a literal

Six L2 behavioural tests embedded `home.keithjackson.dev`. They are test INPUTS,
not reconciled manifests, so postBuild substitution never touched them — correct
while dev held the apex, wrong the moment prod came up on
prod.home.keithjackson.dev, and blocking §9's "suite passes green against prod".

Each test now asks the cluster what it is, via a test-level chainsaw binding over
flux-system/cluster-vars — the SAME ConfigMap Flux renders the platform from, so
a test cannot disagree with the cluster it runs on:

  bindings:
    - name: baseDomain
      value: (x_k8s_get($client,'v1','ConfigMap','flux-system','cluster-vars').data.BASE_DOMAIN)

Chosen over a flag or env var because there is nothing to forget at run time, and
test-level scope covers every step (step outputs/bindings are step-scoped).

THE APEX WAS NOT THE ONLY LEAK. dns-exposure and dns-internal-resolution also
hardcoded DEV'S Cilium LB range 192.168.1.53-.60; prod's is 192.168.2.20-.30, so
both were wrong for prod regardless of hostname. Replaced with assertions on the
OBSERVED value — the DNS answer must equal that cluster's GATEWAY_VIP, and the
public record must equal the LB IP the Service was actually assigned — which is
strictly STRONGER than the old range check as well as environment-independent.
sso-forward-auth held the literal only in prose (it talks over Service DNS).

PROVEN, NOT ASSERTED — and the positive control is the important half:
  * expressions extracted verbatim from the tracked files resolve to the correct,
    DIFFERENT values per cluster (dev home.keithjackson.dev / 192.168.1.53,
    prod prod.home.keithjackson.dev / 192.168.2.20);
  * the same assert with the HARDCODED apex passes on dev and FAILS on prod
    ("Invalid value: *.prod.home... Expected: *.home..."), so the harness is
    provably not blind — that is exactly the drift removed;
  * chainsaw lint VALID on all six; run.sh --lint clean over the whole tree.

END-TO-END L2 RUN AGAINST LIVE DEV: `dns-exposure` PASSED (42.6s) — the binding
produced conformance-dns.home.keithjackson.dev, external-dns published it, and the
probe Job asserted the record against the assigned LB IP. This is the first time
one of these tests has been executed since parameterization, and it exercises the
full path rather than just the binding.

FINDING FROM THAT RUN, worth recording: the test's teardown is ASYNCHRONOUS. It
reports PASS as soon as chainsaw deletes the namespace, but the Cloudflare record
is reaped later by external-dns's own --interval=1m sync. A zone query immediately
after PASS still showed conformance-dns.home.keithjackson.dev plus its owner=default
TXT registry entry. Harmless here, but it means a green dns-exposure does NOT prove
cleanup happened, and if external-dns were suspended the record would persist
silently. Verified separately that it clears.

conformance/incluster/rbac.yaml: its cluster-wide `get configmaps` is now
LOAD-BEARING for these bindings — narrowing it to the test namespace breaks five
tests. Commented so it is not "tidied" later.

l3-fault-injection/dr-restore: its KNOWN-GAPS block said off-host is unproven
because the MinIO shares a Proxmox host with dev's VMs. Still true as run, so the
text now says both — that the R2 move (32d6766) is what closes it, that this test's
pass is against MinIO, and that the ledger row proving R-STATE-03 PREDATES the move,
so off-host DR cannot be claimed until the drill is re-run against R2.

NOT VERIFIED, plainly: no full L2 suite run against prod, so "green against prod"
remains unproven — what is proven is that the tests now derive the CORRECT
expectation for whichever cluster they are pointed at. Whether prod SATISFIES them
(split-horizon, LE wildcard, Grafana's issuer) is untested.

VERIFIED: full CI gate PASS. flux-postbuild-substitution 260 assertions,
render-golden 10/10.

Refs R-TEST-01, R-TEST-02, R-TEST-03, R-TEST-04, R-ENV-02, R-DNS-01/02/03.

Co-Authored-By: Claude Opus 5 <[email protected]>

conformance/tests/README.md

@@ -93,6 +93,27 @@ and coverage extraction exact and robust.
   break the thing and assert fail-closed / no-data-loss, with `finally` restoring state.
 - **Never weaken a test to go green (R-TEST-06).** If the spec can't be met, escalate to
   the PM — do not relax the assertion or the requirement.
+- **Never write a per-environment value into a test (R-ENV-02).** No hostname suffix, no
+  Gateway VIP, no LB-pool range. One authored suite must run green against dev *and* prod,
+  so a test **asks the cluster it is pointed at** what it is. The mechanism is a chainsaw
+  binding over the same ConfigMap Flux substitutes from:
+
+  ```yaml
+  spec:
+    bindings:
+      - name: baseDomain
+        value: (x_k8s_get($client, 'v1', 'ConfigMap', 'flux-system', 'cluster-vars').data.BASE_DOMAIN)
+  ```
+
+  Declare it at **test level** (step `outputs`/`bindings` are step-scoped), then consume it:
+  `($baseDomain)` for a pod `env:` value, `(join('.', ['myhost', $baseDomain]))` where a
+  full hostname is needed — including inside a `fixtures/*.yaml` applied with `apply: file:`,
+  which chainsaw templates with the same bindings. Prefer reading the *actual* observed value
+  over restating a range (e.g. assert the DNS answer equals `GATEWAY_VIP`, or equals the LB IP
+  the Service was assigned) — it is both stricter and environment-independent. Never take the
+  environment from a CLI flag or an exported variable: a flag someone forgets is how a suite
+  ends up silently asserting the other cluster's expectations. L1 goldens are the one
+  exception: they are rendering fixtures and carry the literal `${BASE_DOMAIN}` token.
 
 Scaffolds in this tree carry `TODO(T-x.y)` markers where a fixture/assertion lands as a
 later roadmap phase delivers the capability under test. `lib/status.py` treats such a