test(rest): measure the two authorization-input absorb seams in computeExecCtx

Phase-1 MEASUREMENT — no production code changed. Drives, with positive
controls beside every fault leg:

- tenancy posture (kernelManager path): a healthy isolated posture refuses an
  ex-member org-stamped API key (organization_membership_ended, 401 on the
  wire); a tenancy service that is REGISTERED AND FAILS to construct skips the
  refusal and the same key is served 200 — the permissive path is reachable.
  "Registered and failed" and "never registered" answer byte-identically.
- tenancy posture (single-kernel provider path): the local `kernel` is only
  assigned on kernelManager branches, so the posture probe is never issued —
  a healthy, wall-enforcing tenancy service is NEVER INVOKED (recorded), and
  the same deployment facts answer 401 via kernelManager and 200 via the
  shipped provider wiring. The always-undefined claim holds as the normal
  state of that wiring.
- ADR-0069 auth gate: an active gate blocks the gated user (403 + gate code);
  an inactive gate, a throwing probe, and a failed session re-read are
  byte-indistinguishable at the ExecutionContext field and at enforceAuth.
- Section 0 pins the enumeration criterion in-file (flags the two seams,
  never wiredEngineOrLoud); the historical control (same criterion flagging
  the provider engine seam pre-13910, 10 sites before / 9 after) is recorded
  on the card.

Pins are measurements, not endorsements.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015YPiiDdw96RGS25WLctCQP

Author: claude