Add governed test plane and close T04/T08

Encode fail-closed admission, target registrations, and a credential
broker that never returns secret values. Calibrate audit-core shaped
probes in-process. Send no packets and request no live credentials.

Assistant: grok
Assistant-Session: 01a02670-3345-76f2-a014-70fde8e2a2bb

plane/README.md

@@ -0,0 +1,27 @@
+# Governed test plane
+
+Contract only. This repository does not apply cluster objects, request
+credentials, or send packets. `ops-mason` provisions from these files after a
+**new, unretired** engagement ID exists. Cancelled IDs
+`WH-ENG-20260821-AUDIT-E2` and `WH-ENG-20260821-TENANT-E2` are terminal.
+
+## Controls
+
+1. Namespace `whitehat`, default-deny networking, explicit target egress.
+2. Immutable runner identity with required engagement labels and no standing
+   service-account token.
+3. Custody broker projects two short-lived tenant-scoped identities into the
+   runner mount and revokes them. Values never enter Git, chat, evidence or
+   State Hub.
+4. Pinned runner image digest on the engagement.
+5. Independently usable kill switch: create `plane/KILL` or set
+   `WHITEHAT_KILL_SWITCH=1`. Admission fails closed while it is engaged.
+6. Rate watcher and automatic lease cleanup in `whitehat_security.plane`.
+
+## Standing versus live
+
+`fixture-e2` is the in-process class already permitted by the rules of
+engagement. `live-e2` still needs a dated engagement, target-owner
+acknowledgement, plane namespace, pinned digest and a connected custody
+broker. `e3` and `capacity` are separate approval classes and will not be
+admitted by the E2 plane.