feat: complete and prove the authorization chain end to end

Implements step 2 (access-engine POST /v1/check) and wires the whole
GH-DEC-2026-003 sequence together, then proves it against a live throwaway
OpenBao rather than only unit-level fakes.

- decision_check.check_decision performs the PDP call; an unreachable or
  non-200 PDP raises, since silence is never permission.
- approval_consume.authorize_action coordinates steps 1 and 2 and returns an
  AuthorizedAction. Both steps build the same CheckRequest via a shared
  _expected_request, since two descriptions of the action cannot produce
  corresponding digests.
- apply_unreachable_engine_stance takes authorized=. The published map
  defines fail_closed as no side effect WITHOUT a durable decision record,
  so holding a validated one means the residue does not apply. Not a bypass:
  both steps must have succeeded and CAS consume still precedes OpenBao.
  Unconfigured still returns None and fails closed.

The end-to-end test caught one more instance of the cross-vocabulary bug: a
leftover comparison of the claim's binding.action against ours. The claim
says secrets.kv.destroy where we say destroy, so it would have failed against
every real claim. Removed; the tie is pdp_digest.

Integration coverage asserts PIP-then-PDP ordering, that consume is the last
step before the backend, and that an unreachable PDP, denied decision,
invalid claim, missing pdp_digest, consume conflict and action mismatch each
stop before OpenBao. 284 tests pass; production still fails closed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01M65ovP3eiiPHubibvWs9mD

Assistant: claude-code
Assistant-Model: opus
Assistant-Process: 393550@bnt-lap001
Assistant-Session: 4bb359f9-1f12-4410-9e76-079cf23c82e4

src/secrets_engine/cli.py

@@ -35,6 +35,7 @@ from types import SimpleNamespace
 from secrets_engine import __version__
 from secrets_engine.apply import apply_plan
 from secrets_engine.approval_consume import (
+    authorize_action,
     require_production_consume,
     resolve_consume_binding,
 )
@@ -122,9 +123,19 @@ def _require_lane_approval(
     consume path. Build/test ``fail_open`` still requires the existing
     lane-approval check — a tracked gap until SECRETS-WP-0008-T02.
     """
-    stance = apply_unreachable_engine_stance(cfg, entry, action or "unknown")
+    # Steps 1 and 2 first: a validated claim and decision are what make the
+    # unreachable-engine residue inapplicable. Absent configuration returns
+    # None and production stays closed exactly as before.
+    authorization = authorize_action(
+        cfg, entry, action or "unknown", None, fields=fields
+    )
+    stance = apply_unreachable_engine_stance(
+        cfg, entry, action or "unknown", authorized=authorization is not None
+    )
     if evidence is not None:
         evidence.mark_stance(stance)
+        if authorization is not None:
+            evidence.detail.update(authorization.as_evidence())
     decision = None
     if entry.approval_required():
         decision = resolve_decision(
@@ -138,9 +149,7 @@ def _require_lane_approval(
     require_production_consume(
         cfg,
         entry,
-        binding=resolve_consume_binding(
-            cfg, entry, action or "unknown", decision, fields=fields
-        ),
+        binding=authorization.binding if authorization is not None else None,
         evidence=evidence,
     )
     return decision