feat: bind the destroy gate to approval_binding_digest and pdp_path

The vocabulary mapping this path was waiting on is not coming: gate-house
rejected it in GH-DEC-2026-008, because a translation can be confidently
wrong and fails open by accepting a claim approved for a different action.
The stronger option arrived instead, and both halves are enforced here.

flex-auth published binding.approval_binding_digest (FLEX-DEC-2026-007) to
fix the circularity this repo reported: a pdp_digest recorded at issue time
can never equal the request_digest of the request that carries the claim in
its hashed context, so with GH-DEC-2026-008 requiring that equality, destroy
would have failed closed forever on a check no correct record could pass.

- authorization.approval_binding_digest implements the published exclusion
  rule, including Go's context,omitempty behaviour when stripping empties
  the context; digest_material drops an empty context for the same reason.
- validate_decision_envelope recomputes the field rather than trusting it,
  refuses a claim-bearing request whose decision records none, and compares
  the claim's digest from step 1 against it -- never against request_digest,
  which still covers the claim so it stays a sound replay identity.
- validate_approval_claim requires binding.pdp_path true before using
  pdp_digest at all. Path intent is never inferred from a digest that
  happens to be present; pre-schema-v3 approvals carry pdp_path false
  regardless of any digest they hold.

Replay fixtures re-vendored from dd3ce4c. The destroy pins moved a second
and final time; approval_binding_digest did not, which is the point. The
fixture now demonstrates the property instead of asserting it: we rederive
fa07becf... from its own request through our canonical implementation,
proving we hash the same material flex-auth does rather than pinning a
constant we cannot reproduce.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E4tNMAYcSQmZWUE4wqP4ij

Assistant: claude-code
Assistant-Model: opus
Assistant-Process: 715726@bnt-lap001
Assistant-Session: 80a42b32-cba6-4b23-8be0-68819b1a6092

docs/approval-consumption.md

@@ -43,16 +43,62 @@ never compared to each other:
   of `{action, actor, principal, purpose, target}`.
 - `decision.binding.request_digest` — flex-auth canonical CheckRequest digest.
 
-`claim.binding.pdp_digest` is the **only** comparison usable today, and its
+`claim.binding.pdp_digest` is the **only** comparison usable, and its absence
-absence fails the action closed. The claim's `binding.action` and
+fails the action closed. The claim's `binding.action` and `binding.target` speak
-`binding.target` speak approval-engine's vocabulary (`secrets.kv.destroy`,
+approval-engine's vocabulary (`secrets.kv.destroy`, `{"id": ..., "stage": ...}`)
-`{"id": ..., "stage": ...}`) while ours speaks the catalog's (`destroy`,
+while ours speaks the catalog's (`destroy`, `catalog:<id>`). No mapping between
-`catalog:<id>`), and no mapping between them is published. flex-auth makes no
+them exists and none is coming: gate-house rejected one outright in
-cross-check either and states the correspondence is ours. Computing a native
+`GH-DEC-2026-008`, because a translation can be confidently wrong and fails
-digest from our own vocabulary would compare two different languages and never
+**open** by silently accepting a claim approved for a different action. An
-match, so this engine does not compute one. Closing that gap needs a published
+identity check cannot. So this engine computes no native digest.
-mapping co-authored by approval-engine and flex-auth; it is a prerequisite for
+
-`SECRETS-WP-0007-T04` making `destroy` reachable.
+### The two gates on the pdp path
+
+**1. `binding.pdp_path` must be `true`.** This is approval-engine's declaration
+(schema v3) that the approval was requested against a bound CheckRequest. Their
+`create()` refuses `pdp_path` true without a `pdp_digest`, so the declaration
+*guarantees* the digest. The converse does not hold, and we must not infer it: a
+digest recorded for some other reason is no declaration anybody made, and every
+approval issued before schema v3 carries `pdp_path` false regardless of any
+digest it holds.
+
+The cost is real and is ours to carry — an approval requested without a bound
+CheckRequest is not usable here and never becomes usable later. `GH-DEC-2026-008`
+holds that correct: an approval granted against an unspecified action does not
+become an approval for a specific one because a consumer later found a use for
+it. If a real destroy workflow cannot bind at issue, that is the falsifier
+gate-house wrote into the reversal, and it should be **raised**, not worked
+around.
+
+**2. The digest identity, against the right comparand.**
+
+```text
+claim.binding.pdp_digest == decision.binding.approval_binding_digest   correct
+claim.binding.pdp_digest == decision.binding.request_digest            can never pass
+```
+
+`pdp_digest` is recorded at *issue* time, and issue precedes the decision. A
+request that carries the claim inside its hashed `context` therefore has a
+different `request_digest` by construction — the claim is part of the material
+being hashed. This engine found that circularity against the T03 replay fixture;
+flex-auth fixed it in `FLEX-DEC-2026-007` by publishing
+`binding.approval_binding_digest`, the same canonical digest with
+`context.approval` removed, which is stable across attaching the claim.
+
+`approval_binding_digest` is **not** a replay identity. `request_digest` still
+covers the claim and still moves when it changes, because two requests differing
+only in which approval was presented must not share a replay identity — one
+allows, the other denies `dual_control_required`. Collapsing them would let an
+allow obtained with a valid claim be replayed against a request carrying none.
+
+Our own CheckRequest is claim-free today (`context` is `{"purpose": ...}`), so
+flex-auth emits no `approval_binding_digest` for it and the identity holds
+transitively: step 1 compares the claim's `pdp_digest` to the canonical digest of
+the exact claim-free request we are about to send, and step 2 confirms the
+decision's `request_digest` is that same value. `approval_binding_digest(request)`
+implements the published exclusion rule so that the check is already correct if
+we ever carry the claim in context; when the field is present it is recomputed
+and never taken on faith.
 
 ### What is hashed in the flex-auth digest
 

src/secrets_engine/approval_claim.py

@@ -150,11 +150,25 @@ def validate_approval_claim(
     # supplies a binding built in that vocabulary (see the note in
     # resolve_consume_binding about the missing mapping).
     if expected_pdp_digest:
+        # GH-DEC-2026-008 / approval-engine schema v3: pdp_path is the issuer's
+        # DECLARATION that this approval was requested against a bound
+        # CheckRequest, and it guarantees pdp_digest is non-null. Path intent is
+        # never inferred from a pdp_digest that merely happens to be present --
+        # a digest recorded for some other reason is not a declaration anybody
+        # made, and approvals issued before schema v3 carry pdp_path false
+        # regardless of any digest they hold.
+        if binding.get("pdp_path") is not True:
+            raise DecisionError(
+                "approval claim does not declare binding.pdp_path; it was not "
+                "issued against a bound CheckRequest and cannot authorize this "
+                "action (GH-DEC-2026-008). Request an approval bound at issue."
+            )
         if not pdp:
             raise DecisionError(
-                "approval claim records no pdp_digest, and no published mapping "
+                "approval claim declares pdp_path but records no pdp_digest, and "
-                "exists between approval-engine and secrets-engine action/target "
+                "no published mapping exists between approval-engine and "
-                "vocabularies; the claim cannot be tied to this exact action"
+                "secrets-engine action/target vocabularies; the claim cannot be "
+                "tied to this exact action"
             )
         if pdp != expected_pdp_digest:
             raise DecisionError("approval claim pdp digest does not match the request")

src/secrets_engine/approval_consume.py

@@ -326,6 +326,10 @@ def authorize_action(
         expected_request,
         accepted_policy_packages={package},
         accepted_policy_versions={version},
+        # The claim's pdp_digest, established in step 1. If this request carried
+        # the claim in context, the decision must name the same claim-free
+        # envelope in binding.approval_binding_digest (FLEX-DEC-2026-007).
+        expected_approval_binding_digest=binding.request_digest,
     )
     if validated.action != action:
         raise DecisionError("access-engine decision does not bind this action")

src/secrets_engine/authorization.py

@@ -8,6 +8,7 @@ from __future__ import annotations
 
 import hashlib
 import json
+import re
 import uuid
 from dataclasses import dataclass
 from datetime import datetime, timezone
@@ -16,6 +17,8 @@ from typing import Any
 from secrets_engine.catalog import CatalogEntry
 from secrets_engine.errors import DecisionError
 
+DIGEST_RE = re.compile(r"^sha256:[0-9a-f]{64}$")
+
 SCHEMA_VERSION = "0.1"
 CONTRACT_VERSION = "flex-auth.decision-record.v1"
 
@@ -171,7 +174,13 @@ def digest_material(request: object) -> dict[str, Any]:
     against every correctly issued decision.
     """
     canonical = canonical_check_request(request)
-    return {k: v for k, v in canonical.items() if k not in _UNHASHED_FIELDS}
+    material = {k: v for k, v in canonical.items() if k not in _UNHASHED_FIELDS}
+    # flex-auth tags Context `json:"context,omitempty"`, which drops the key for
+    # an empty map as well as a nil one. Keeping an empty object here would hash
+    # different material than the evaluator did.
+    if material.get("context") == {}:
+        del material["context"]
+    return material
 
 
 def request_digest(request: object) -> str:
@@ -182,6 +191,35 @@ def request_digest(request: object) -> str:
     return "sha256:" + hashlib.sha256(encoded).hexdigest()
 
 
+#: The context key an approval claim travels on, per flex-auth's
+#: ``ApprovalContextKey``.
+APPROVAL_CONTEXT_KEY = "approval"
+
+
+def approval_binding_digest(request: object) -> str:
+    """flex-auth's ``binding.approval_binding_digest`` for this request.
+
+    The same canonical digest with ``context.approval`` removed, so it is stable
+    across attaching the claim. A request that carries no claim has no separate
+    binding digest, and flex-auth returns the plain request digest there.
+
+    This exists because a ``pdp_digest`` recorded at approval-issue time can
+    never equal the ``request_digest`` of the request that later carries the
+    claim: the claim is part of the hashed context. See
+    ``flex-auth/docs/canonical-request-digest.md`` "The approval-binding digest"
+    and FLEX-DEC-2026-007. It is deliberately NOT a replay identity.
+    """
+    canonical = canonical_check_request(request)
+    context = canonical.get("context")
+    if not isinstance(context, dict) or APPROVAL_CONTEXT_KEY not in context:
+        return request_digest(request)
+    stripped = dict(canonical)
+    stripped["context"] = {
+        k: v for k, v in context.items() if k != APPROVAL_CONTEXT_KEY
+    }
+    return request_digest(stripped)
+
+
 def _require_exact_target_sets(request: dict[str, Any]) -> None:
     resource = _required_dict(request, "resource")
     attributes = resource.get("attributes", {})
@@ -199,12 +237,63 @@ def _require_exact_target_sets(request: dict[str, Any]) -> None:
             )
 
 
+def _check_approval_binding_digest(
+    binding: dict[str, Any],
+    expected: dict[str, Any],
+    expected_digest: str,
+) -> None:
+    """Tie an approval claim to this exact request (FLEX-DEC-2026-007).
+
+    ``binding.approval_binding_digest`` is the canonical request digest computed
+    with ``context.approval`` removed, and it appears only when the request
+    carried a claim there. It is the ONLY sound comparand for a claim's
+    ``pdp_digest``: a digest recorded at issue time can never equal the
+    ``request_digest`` of the request that carries the claim, because the claim
+    is part of the hashed material. Comparing against ``request_digest`` fails
+    closed forever; comparing against nothing fails open.
+
+    It is deliberately NOT a replay identity -- two requests differing only in
+    which approval was presented share it while their decisions differ -- so it
+    is checked here in addition to ``request_digest``, never instead of it.
+
+    When our own request is claim-free the field is absent by contract, and the
+    identity already holds transitively: step 1 compared the claim's pdp_digest
+    to this same canonical digest of the claim-free request.
+    """
+    present = binding.get("approval_binding_digest")
+    if present is not None:
+        if not isinstance(present, str) or not DIGEST_RE.fullmatch(present):
+            raise DecisionError("flex-auth approval binding digest is malformed")
+        if present != approval_binding_digest(expected):
+            raise DecisionError(
+                "flex-auth approval binding digest does not match this request "
+                "with the approval claim removed"
+            )
+    if expected_digest:
+        if present is None:
+            context = expected.get("context")
+            if not isinstance(context, dict) or APPROVAL_CONTEXT_KEY not in context:
+                # Claim-free request: no approval_binding_digest is emitted and
+                # step 1 already bound the claim to this canonical digest.
+                return
+            raise DecisionError(
+                "request carried an approval claim but the decision records no "
+                "approval_binding_digest; the claim cannot be tied to it"
+            )
+        if present != expected_digest:
+            raise DecisionError(
+                "approval claim pdp digest does not match the decision's "
+                "approval binding digest"
+            )
+
+
 def validate_decision_envelope(
     envelope: object,
     expected_request: object,
     *,
     accepted_policy_packages: set[str],
     accepted_policy_versions: set[str],
+    expected_approval_binding_digest: str = "",
     now: datetime | None = None,
 ) -> ValidatedDecision:
     """Validate a flex-auth DecisionEnvelope against the proposed action.
@@ -264,6 +353,7 @@ def validate_decision_envelope(
         raise DecisionError("flex-auth decision binding does not match request")
     if binding.get("request_digest") != request_digest(expected):
         raise DecisionError("flex-auth request digest does not match request")
+    _check_approval_binding_digest(binding, expected, expected_approval_binding_digest)
     if _subject_ref(envelope.get("subject")) != expected["subject"]:
         raise DecisionError("flex-auth decision subject does not match request")
     if _resource_ref(envelope.get("resource")) != expected["resource"]:

tests/authorization_stub.py

@@ -40,6 +40,9 @@ class AuthorizationStub:
         self.claim_valid_now = True
         self.claim_reason_code = "ok"
         self.include_pdp_digest = True
+        #: approval-engine schema v3 declares whether the approval was
+        #: requested against a bound CheckRequest; false is the pre-v3 shape
+        self.claim_pdp_path = True
         self.effect = "allow"
         self.consume_status = 200
         self._pdp_digest = ""
@@ -118,6 +121,7 @@ class AuthorizationStub:
             "target": {"id": "lane-under-test", "stage": "prod"},
             "digest": "sha256:" + "3" * 64,
         }
+        binding["pdp_path"] = self.claim_pdp_path
         if self.include_pdp_digest:
             binding["pdp_digest"] = self._pdp_digest
         return {

tests/fixtures/flex-auth-replay/PROVENANCE.md

@@ -8,16 +8,29 @@ published `secrets-engine.catalog-lane.lifecycle` v1 package via
 Vendored so the digest contract test is hermetic. Regenerate upstream and
 re-copy if the contract version changes.
 
-Re-copied 2026-09-06 after flex-auth regenerated `decision_destroy_dual_control`
+Re-copied 2026-09-06 (twice, both upstream regenerations):
-to carry a **complete** approval-claim on `context.approval` (including the
+
-now-required `binding.pdp_digest`). Because `context` is part of the digest
+1. commit `9f3e7e3` completed the approval-claim on `context.approval`. Because
-material, completing the claim changed both the request digest and the context
+   `context` is hashed material, completing the claim moved the request digest.
-input-claim digest. The pins below are the post-regeneration values.
+2. commit `dd3ce4c` (`FLEX-DEC-2026-007`) published
+   `binding.approval_binding_digest` and set the embedded claim's
+   `binding.pdp_digest` to it with `binding.pdp_path` true. The request digest
+   moved once more with the claim's contents; the approval-binding digest did
+   **not**, which is the property the fixture now demonstrates rather than
+   asserts.
+
+`decision_rotate.json` is unchanged and carries no `approval_binding_digest` —
+the field is omitted on claim-free decisions rather than duplicated onto them.
 
 **Pinned here** (stable across runs, per the upstream README):
-`binding.request_digest`, `provenance.policy_package_digest`,
+`binding.request_digest`, `binding.approval_binding_digest`,
-`provenance.registry_snapshot_digest`, and the presence/absence of
+`provenance.policy_package_digest`, `provenance.registry_snapshot_digest`, and
-`provenance.input_claim_digests.context`.
+the presence/absence of `provenance.input_claim_digests.context`.
+
+`approval_binding_digest` is not only pinned but **rederived** by
+`test_pdp_digest_equals_the_published_approval_binding_digest`: our canonical
+implementation must reproduce it from the fixture's own request. A pin asserts
+the constant; rederiving it proves we hash the same material flex-auth does.
 
 **Never pin:** `id`, `provenance.decision_time`, `lifetime.not_before`,
 `lifetime.expires_at` — all move with the clock.

tests/fixtures/flex-auth-replay/decision_destroy_dual_control.json

@@ -1,5 +1,5 @@
 {
-  "id": "decision:395efe37c5066e8a",
+  "id": "decision:44a40c339a020772",
   "contract_version": "flex-auth.decision-record.v1",
   "request_id": "check:secrets-engine-destroy",
   "effect": "allow",
@@ -72,7 +72,8 @@
           "action": "secrets.kv.destroy",
           "actor": "agt-secrets-engine",
           "digest": "sha256:3f3f3f3f3f3f3f3f3f3f3f3f3f3f3f3f3f3f3f3f3f3f3f3f3f3f3f3f3f3f3f3f",
-          "pdp_digest": "sha256:570d112890586d3cbf00c0e81c85ae7806f40f00afa1a2c0a23fd5e077a27f56",
+          "pdp_digest": "sha256:fa07becfaa471394d06aee5fa3cd66352bf0cc69ef24900240489684cda8cd56",
+          "pdp_path": true,
           "principal": "bernd",
           "purpose": "rotate-exposed-key",
           "target": {
@@ -98,13 +99,14 @@
         }
       }
     },
-    "request_digest": "sha256:fc155dba88f8ab18b3032ed086ba2f455158c6981106e7829d520ab7b036bdf3"
+    "request_digest": "sha256:c749ee2dc3cdf927a70a3e5b27cff4d97a438d3264153b4b2e3bcacbaf82091a",
+    "approval_binding_digest": "sha256:fa07becfaa471394d06aee5fa3cd66352bf0cc69ef24900240489684cda8cd56"
   },
   "lifetime": {
     "kind": "ttl",
     "ttl": "15m",
-    "not_before": "2026-09-06T12:18:21Z",
+    "not_before": "2026-09-06T12:51:16Z",
-    "expires_at": "2026-09-06T12:33:21Z"
+    "expires_at": "2026-09-06T13:06:16Z"
   },
   "diagnostics": {
     "action": "destroy",
@@ -122,9 +124,9 @@
     "policy_package_digest": "sha256:fe0070b79f66442ae6c218697a49c470c6c8f670aa57a30c078a5284d097bd8c",
     "registry_snapshot_digest": "sha256:f5a309bc0b36721fd6d9ad7f53eb21222162bc2eac62a0ab0802a9a1d51340bb",
     "input_claim_digests": {
-      "context": "sha256:b0d2203cd2b43a9ba573c21c038154c131afba4255e313affd7ecf810e2cc221"
+      "context": "sha256:8b73d29ecef286d42e03d2420531d6c45219f325a7ae004c1ecfc781203a2800"
     },
-    "decision_time": "2026-09-06T12:18:21Z"
+    "decision_time": "2026-09-06T12:51:16Z"
   },
   "caring": {
     "profile": "caring-0.4.0-rc2",

tests/test_approval_claim.py

@@ -122,6 +122,7 @@ def test_principal_falls_back_to_actor_when_absent():
 def test_pdp_digest_is_preferred_when_the_issuer_recorded_one():
     claim = _claim()
     claim["binding"]["pdp_digest"] = "sha256:" + "a" * 64
+    claim["binding"]["pdp_path"] = True
     claim["binding"]["digest"] = "sha256:" + "b" * 64  # native no longer matches
     assert _validate(claim, expected_pdp_digest="sha256:" + "a" * 64)
 

tests/test_consume_binding_join.py

@@ -84,6 +84,7 @@ def _served(entry=None, action="deactivate", fields=("api_token",), **over):
             # comparison usable today: the native digest speaks
             # approval-engine's vocabulary and no mapping to ours is published.
             "pdp_digest": request_digest(request),
+            "pdp_path": True,
         },
         "freshness": {
             "observed_at": now.strftime("%Y-%m-%dT%H:%M:%SZ"),
@@ -191,6 +192,30 @@ def test_superseded_claim_fails_closed(tmp_path):
         _resolve(_Cfg(_token(tmp_path)), _entry(), _served(valid_now=False, reason_code="superseded"))
 
 
+def test_claim_without_pdp_path_fails_closed(tmp_path):
+    """pdp_path is a declaration, and it is never inferred from a digest.
+
+    approval-engine schema v3 refuses to issue pdp_path true without a
+    pdp_digest, so a true declaration guarantees the digest. The converse does
+    not hold: a digest recorded for some other reason is not a statement that
+    this approval was requested against a bound CheckRequest, and approvals
+    issued before v3 carry pdp_path false regardless of any digest they hold
+    (GH-DEC-2026-008).
+    """
+    claim = _served()
+    claim["binding"]["pdp_path"] = False
+    with pytest.raises(DecisionError, match="does not declare binding.pdp_path"):
+        _resolve(_Cfg(_token(tmp_path)), _entry(), claim)
+
+
+def test_claim_omitting_pdp_path_fails_closed(tmp_path):
+    """An absent declaration is not a true one."""
+    claim = _served()
+    claim["binding"].pop("pdp_path")
+    with pytest.raises(DecisionError, match="does not declare binding.pdp_path"):
+        _resolve(_Cfg(_token(tmp_path)), _entry(), claim)
+
+
 def test_claim_without_pdp_digest_fails_closed_naming_the_missing_mapping(tmp_path):
     """No published vocabulary mapping means the claim cannot be tied to this action.
 

tests/test_decision_replay.py

@@ -17,6 +17,7 @@ from pathlib import Path
 import pytest
 
 from secrets_engine.authorization import (
+    approval_binding_digest,
     digest_material,
     request_digest,
     validate_decision_envelope,
@@ -37,9 +38,9 @@ CASES = {
     },
     "destroy": {
         "file": "decision_destroy_dual_control.json",
-        "digest": "sha256:fc155dba88f8ab18b3032ed086ba2f455158c6981106e7829d520ab7b036bdf3",
+        "digest": "sha256:c749ee2dc3cdf927a70a3e5b27cff4d97a438d3264153b4b2e3bcacbaf82091a",
         "action": "destroy",
-        "context_claim_digest": "sha256:b0d2203cd2b43a9ba573c21c038154c131afba4255e313affd7ecf810e2cc221",
+        "context_claim_digest": "sha256:8b73d29ecef286d42e03d2420531d6c45219f325a7ae004c1ecfc781203a2800",
     },
 }
 
@@ -180,14 +181,19 @@ def test_embedded_claim_uses_approval_engine_vocabulary_not_ours():
     assert claim["binding"]["target"]["id"] != envelope["resource"]["id"]
 
 
+APPROVAL_BINDING_DIGEST = (
+    "sha256:fa07becfaa471394d06aee5fa3cd66352bf0cc69ef24900240489684cda8cd56"
+)
+
+
 def test_embedded_claim_pdp_digest_cannot_equal_the_carrying_request_digest():
     """Carrying the claim inside a hashed context makes the two unequal.
 
     context is part of the digest material, so embedding an approval-claim
     changes the request digest of the very request that carries it. A
     pdp_digest recorded at issue time therefore cannot equal the final digest
-    of the dual-control request. Raised with approval-engine and flex-auth; this
+    of the dual-control request. This is why comparing pdp_digest against
-    test records the property so a future change is visible rather than silent.
+    request_digest can never pass and would fail destroy closed forever.
     """
     envelope = _envelope("destroy")
     binding = envelope["binding"]
@@ -195,8 +201,112 @@ def test_embedded_claim_pdp_digest_cannot_equal_the_carrying_request_digest():
     request = _request_from(envelope)
     assert request_digest(request) == binding["request_digest"]
     assert pdp != binding["request_digest"]
-    without_claim = dict(request)
+
-    without_claim["context"] = {
+
-        k: v for k, v in binding["context"].items() if k != "approval"
+def test_pdp_digest_equals_the_published_approval_binding_digest():
-    }
+    """FLEX-DEC-2026-007 closed the circularity, and we reproduce the value.
-    assert pdp != request_digest(without_claim)
+
+    ``approval_binding_digest`` is the canonical digest with context.approval
+    removed. Recomputing it here from our own canonical implementation is the
+    hermetic proof that this engine hashes the same material flex-auth does --
+    a pin alone would only assert the constant, not that we can derive it.
+    """
+    envelope = _envelope("destroy")
+    binding = envelope["binding"]
+    pdp = binding["context"]["approval"]["binding"]["pdp_digest"]
+    assert binding["approval_binding_digest"] == APPROVAL_BINDING_DIGEST
+    assert pdp == APPROVAL_BINDING_DIGEST
+
+    assert approval_binding_digest(_request_from(envelope)) == APPROVAL_BINDING_DIGEST
+
+
+def test_approval_binding_digest_is_not_a_replay_identity():
+    """It must not collapse into request_digest, or an allow becomes replayable.
+
+    Two requests differing only in which approval was presented share an
+    approval_binding_digest while their decisions differ -- one allows, one
+    denies dual_control_required. The fixture asserts the two digests disagree
+    on a claim-bearing request so the distinction stays real.
+    """
+    envelope = _envelope("destroy")
+    binding = envelope["binding"]
+    assert binding["approval_binding_digest"] != binding["request_digest"]
+
+
+def test_ordinary_decision_carries_no_approval_binding_digest():
+    """The field is omitted, not duplicated, on a claim-free decision."""
+    binding = _envelope("rotate")["binding"]
+    assert "approval" not in binding.get("context", {})
+    assert "approval_binding_digest" not in binding
+
+
+def test_embedded_claim_declares_the_pdp_path():
+    """pdp_path is the issuer's declaration, and it is what our PEP requires.
+
+    Path intent is never inferred from a pdp_digest that happens to be present;
+    approvals issued before approval-engine schema v3 carry pdp_path false
+    regardless of any digest they hold.
+    """
+    claim = _envelope("destroy")["binding"]["context"]["approval"]
+    assert claim["binding"]["pdp_path"] is True
+
+
+def test_decision_validation_ties_the_claim_to_the_approval_binding_digest():
+    """Step 2 checks the identity against the real envelope, not a local guess.
+
+    The PEP knows the claim's pdp_digest from step 1. When the request it sent
+    carried that claim, the decision must name the same claim-free envelope, or
+    the approval was issued against some other request.
+    """
+    envelope = _refresh_lifetime(_envelope("destroy"))
+    request = _request_from(envelope)
+    result = validate_decision_envelope(
+        envelope,
+        request,
+        accepted_policy_packages={"secrets-engine.catalog-lane.lifecycle"},
+        accepted_policy_versions={"v1"},
+        expected_approval_binding_digest=APPROVAL_BINDING_DIGEST,
+    )
+    assert result.action == "destroy"
+
+    with pytest.raises(DecisionError, match="approval binding digest"):
+        validate_decision_envelope(
+            envelope,
+            request,
+            accepted_policy_packages={"secrets-engine.catalog-lane.lifecycle"},
+            accepted_policy_versions={"v1"},
+            expected_approval_binding_digest="sha256:" + "c" * 64,
+        )
+
+
+def test_claim_bearing_request_without_a_binding_digest_fails_closed():
+    """A decision that records no binding digest cannot tie the claim to itself.
+
+    Comparing against request_digest instead would be the fail-open direction
+    the whole field exists to prevent, so the absence is refused outright.
+    """
+    envelope = _refresh_lifetime(_envelope("destroy"))
+    request = _request_from(envelope)
+    del envelope["binding"]["approval_binding_digest"]
+    with pytest.raises(DecisionError, match="records no approval_binding_digest"):
+        validate_decision_envelope(
+            envelope,
+            request,
+            accepted_policy_packages={"secrets-engine.catalog-lane.lifecycle"},
+            accepted_policy_versions={"v1"},
+            expected_approval_binding_digest=APPROVAL_BINDING_DIGEST,
+        )
+
+
+def test_a_forged_binding_digest_is_recomputed_not_trusted():
+    """The field is verified against our own canonical digest, never taken on faith."""
+    envelope = _refresh_lifetime(_envelope("destroy"))
+    request = _request_from(envelope)
+    envelope["binding"]["approval_binding_digest"] = "sha256:" + "d" * 64
+    with pytest.raises(DecisionError, match="does not match this request"):
+        validate_decision_envelope(
+            envelope,
+            request,
+            accepted_policy_packages={"secrets-engine.catalog-lane.lifecycle"},
+            accepted_policy_versions={"v1"},
+        )

workplans/SECRETS-WP-0007-production-lifecycle-hardening.md

@@ -481,13 +481,75 @@ to end; what remains is deployment only.
   pattern: unit tests with self-consistent fakes hid all three, and each was
   found only by a real artifact or a real chain.
 
+Destroy gate closed 2026-09-06 (inbound `FLEX-DEC-2026-007`, `GH-DEC-2026-008`,
+approval-engine schema v3). The vocabulary mapping this task was waiting on is
+not coming, and it should not have been waited on: gate-house rejected it
+outright, for the reason flex-auth and approval-engine both gave independently —
+a translation can be confidently wrong and fails **open** by accepting a claim
+approved for a different action. The stronger option arrived instead, and both
+halves of it are now enforced here.
+
+- **The circularity we reported is fixed at source.** A `pdp_digest` recorded at
+  approval-issue time can never equal the `request_digest` of a request that
+  carries the claim in its hashed context. With `GH-DEC-2026-008` requiring that
+  equality on the PDP path, destroy would have been permanently un-allowable,
+  failing closed forever on a check no correct record could pass. flex-auth
+  published `binding.approval_binding_digest` (commit `dd3ce4c`): the same
+  canonical digest with `context.approval` removed, stable across attaching the
+  claim. The comparison is against that field, never `request_digest`.
+- **`request_digest` deliberately still covers the claim**, so the two digests
+  disagree on a claim-bearing request and that disagreement is load-bearing: two
+  requests differing only in which approval was presented must not share a
+  replay identity, or an allow obtained with a valid claim could be replayed
+  against a request carrying none. `approval_binding_digest` is not a replay
+  identity and is not used as one.
+- `authorization.approval_binding_digest` implements the published exclusion
+  rule, including flex-auth's `json:"context,omitempty"` behaviour of dropping a
+  context that strips empty. `digest_material` now drops an empty context for the
+  same reason. `validate_decision_envelope` recomputes the field when present
+  rather than trusting it, refuses a claim-bearing request whose decision records
+  none, and takes the claim's digest from step 1 as `expected_approval_binding_digest`.
+- **`binding.pdp_path` is required true** before `pdp_digest` is used at all.
+  It is approval-engine's declaration that the approval was requested against a
+  bound CheckRequest; their `create()` refuses `pdp_path` true without a digest,
+  so the declaration guarantees the digest. The converse is not inferred: a
+  digest present for some other reason is no declaration, and pre-v3 approvals
+  carry `pdp_path` false regardless of any digest they hold.
+- The cost is accepted rather than engineered around: an approval requested
+  without a bound CheckRequest is not usable on this path and will not become
+  usable later. If a real destroy workflow cannot bind at issue, that is the
+  falsifier gate-house wrote into the reversal and it gets raised, not
+  worked around.
+
+The replay fixtures are re-vendored from `dd3ce4c`, and the pins moved a second
+and final time (`request_digest` `sha256:c749ee2d…`, context input-claim digest
+`sha256:8b73d29e…`; `approval_binding_digest` `sha256:fa07becf…`, which did
+**not** move — that is the point). The fixture now demonstrates the property
+instead of asserting it: `test_pdp_digest_equals_the_published_approval_binding_digest`
+rederives `fa07becf…` from the fixture's own request through our canonical
+implementation, which is a hermetic proof that this engine hashes the same
+material flex-auth does. A pin alone would only have asserted the constant.
+`decision_rotate.json` is unchanged and carries no `approval_binding_digest`;
+a test pins that omission so the field is not silently duplicated onto ordinary
+decisions.
+
+Our own CheckRequest stays claim-free (`context` is `{"purpose": …}`), so the
+identity holds transitively today; the code is already correct for the day we
+carry a claim in context.
+
+Still open and still ours: the T04 consumer-shape question flex-auth has asked
+twice — operator CLI reaching an in-cluster pin, a workload we do not have yet,
+or no pin at all. It is a deployment-shape answer, not engine work, and it is
+the reply owed on that thread.
+
 Remaining to go live is configuration and deployment, not engine work:
 `SECRETS_ENGINE_PDP_URL`/`_PDP_TOKEN_FILE` (awaiting the `flex-auth-secrets-engine`
 pin, `FLEX-WP-0021-T04`/`T05`), `SECRETS_ENGINE_APPROVAL_URL`/`_TOKEN_FILE`
 (awaiting `APPROVAL-WP-0002-T03`), the policy pin (published but not to be set
 until T05), a KeyCape RS256 credential in place of the static Bearer token, and
-`approval.authorization_id` on each lane. Destroy additionally needs the
+`approval.authorization_id` on each lane. Destroy's additional requirement is
-vocabulary mapping or a `pdp_digest` guarantee.
+now met in code: the `pdp_path` + `approval_binding_digest` identity replaced the
+vocabulary mapping that was never going to exist.
 
 Define and enforce the decision contract needed by production commands. A
 resolved approval must bind at least: