diff --git a/SCOPE.md b/SCOPE.md
index c7dc4b7..09e00ba 100644
--- a/SCOPE.md
+++ b/SCOPE.md
@@ -28,7 +28,7 @@ decision gate, in plain terms; (4) build, only after approval.
 
 - Deciding *whether* access should exist — that's architecture/founder,
   ops-mason builds what's already decided
-- Runtime authorization decisions — flex-auth
+- Runtime authorization decisions — access-engine
 - Identity/MFA — key-cape/Keycloak
 - Routing consumers to lanes once built — ops-warden
 - SSH certificate issuance — ops-warden
@@ -38,9 +38,28 @@ decision gate, in plain terms; (4) build, only after approval.
 
 ## Current State
 
-Charter only (`INTENT.md`). `MASON-WP-0001` scopes the four-phase
-pipeline and its first real exercise: the `rein-openweights` OpenBao
-AppRole that `glas-harness/GLAS-WP-0002-T02` is blocked on. No code yet.
+The four-phase construction process, OpenBao AppRole/Kubernetes-auth builders,
+metadata inventory, and guarded Kubernetes-plane CLI are implemented and tested.
+Construction plans and build evidence live in `plans/` and `docs/evidence/`.
+
+OpenBao builds require an approved plan whose machine-readable specification
+and approved digest match the supplied execution inputs. Existing policies are
+content-pinned before reuse. AppRole credentials are delivered through private,
+exclusive files; the builders do not read downstream KV values. See
+`docs/construction-plan-format.md` for review and execution requirements.
+
+Kubernetes apply enforces pinned readiness tiers, the explicit whitehat
+placement, the dated policy-nexus transition, and recorded emergency activation.
+See `docs/kubernetes-plane.md`.
+
+The layer declaration is `Staff`, with PEP-shaped behavior, in `INTENT.md`.
+The founder-approved plan-approval exception and direct-contact gaps remain
+explicitly declared; this is not a claim of full layer-model conformance.
+
+Remaining work is held in existing blocked workplans: credential descriptions
+(MASON-WP-0004), the attended Telegram credential lane (MASON-WP-0005), and the
+2026-12-21 readiness/approval review (MASON-WP-0006-T06). `WORK-RECORDS.md` is
+the generated index; workplan files remain the source of task status.
 
 ## Getting Oriented
 
diff --git a/docs/construction-plan-format.md b/docs/construction-plan-format.md
index bde70fa..f45844c 100644
--- a/docs/construction-plan-format.md
+++ b/docs/construction-plan-format.md
@@ -95,3 +95,93 @@ section does not exist until phase 4 has run.
 See `plans/rein-openweights-openrouter-approle.md` once T01 is
 implemented against this format — the first real plan, not a synthetic
 one, per `MASON-WP-0001`'s own scoping.
+
+## Binding OpenBao approval to execution inputs
+
+The AppRole and Kubernetes-auth builders additionally require two frontmatter
+fields: `build_spec` and `approved_spec_sha256`. `build_spec` is the complete
+value-free output of `ops_mason.executor.build_spec_document(spec)`. It includes
+the engine, exact policy/role/path and identity bindings, token bounds, policy
+reuse and content pin, delivery destination, audit destination, and executable.
+`credential_type` must match its `engine`.
+
+During drafting, render the specification and its digest for review:
+
+```python
+from pathlib import Path
+from ops_mason.executor import AppRoleKVSpec, build_spec_document, build_spec_digest
+
+spec = AppRoleKVSpec(
+    policy_name="workload-kv-read-example",
+    kv_path="platform/workloads/example/runtime",
+    approle_name="example",
+    token_num_uses=8,
+    delivery_dir=Path("/home/consumer/.local/example/approle"),
+    audit_log_path=Path("/home/builder/ops-mason/audit/build-log.jsonl"),
+)
+document = build_spec_document(spec)  # put this mapping under build_spec
+candidate_digest = build_spec_digest(document)  # present alongside the review
+```
+
+The digest is SHA-256 of UTF-8 JSON with sorted keys, compact separators and
+no NaN values. Paths render as absolute strings; tuples render as lists. All
+specification fields, including explicit defaults and null values, participate.
+After the founder approves that exact specification, record the digest as
+`approved_spec_sha256` alongside `approved_by`, `approved_at` and
+`status: approved`. Quote approval dates in YAML. A candidate digest alone
+is not approval, and the digest is an integrity marker, not a signature.
+
+Before any OpenBao command, the builder reloads the plan from disk, checks
+approval and engine, validates the specification, and compares both the
+frontmatter mapping and approved digest to the actual inputs. Duplicate YAML
+keys, missing build specifications, changed scope or changed destinations are
+refused. Editing the mapping without renewing its approval digest cannot reuse
+the previous approval. The plan file remains the trust boundary: this does not
+protect against someone authorized to rewrite the approval record itself.
+
+Historical plans stay historical. They are not automatically given new
+specifications or approvals. Before re-executing one, draft and review the exact
+new inputs through the existing four-phase process. No live lane was changed
+by this format migration.
+
+### Input and policy constraints
+
+The existing AppRole engine creates only exact KV-v2 read lanes: one literal
+entry path, `read` on data and metadata, no wildcard, empty/parent path segment,
+HCL injection, or write capability. OIDC matrix writers remain a separate,
+blocked contract under MASON-WP-0005. Role and policy names must be single
+literal names; Kubernetes service-account names/namespaces must be explicit,
+nonempty, unique DNS labels. Token use counts must be explicit nonnegative
+integers (zero is deliberately unlimited when approved); TTLs are positive
+integer durations in `s`, `m` or `h`, with maximum TTL at least initial TTL.
+`secret_id_ttl: "0"` remains an explicit reviewable choice.
+
+For `AppRoleKVSpec(reuse_policy=True)`, also provide
+`reuse_policy_sha256`. For `KubernetesKVSpec`, provide `policy_sha256`, since
+that builder always binds an existing policy. During the scoped structure
+survey, hash the exact UTF-8 output of `bao policy read <name>`, including its
+trailing newline, and review that policy's full scope. The builder reads only
+policy text, checks its hash before auth-role writes, and refuses drift. A
+reused policy may deliberately cover more than the AppRole's nominal KV path;
+its reviewed contents, not that path field alone, define the grant. Rechecking
+a pin is not an atomic lock against later administrative policy changes.
+
+### Credential delivery and failed builds
+
+AppRole delivery requires an absolute directory. Every directory component is
+opened without following symlinks; missing directories are created privately.
+An existing final directory must belong to the executing account with mode
+0700. Both credential files are reserved exclusively at mode 0600 before any
+policy/auth write or credential issuance. Existing files, hardlinks and symlink
+paths are refused rather than overwritten or permission-repaired. Delivery
+uses the held file descriptors and flushes credentials to disk.
+
+OpenBao error and timeout output is suppressed so a failed credential command
+cannot echo sensitive material. Audit output contains object names, the
+approved specification digest and approval attribution, never credentials.
+A failed build can leave private empty or partially delivered files, and may
+have changed policy/auth structure or issued a credential before failing.
+Do not blindly retry or delete them: inspect structure and audit metadata,
+resolve/revoke any partial issuance through the scoped custody procedure, and
+review a fresh delivery destination before retrying. The executor does not
+claim transactional rollback or automatically widen its revocation authority.
diff --git a/intakes/intakes.md b/intakes/intakes.md
index 2e267fe..6fa5ed4 100644
--- a/intakes/intakes.md
+++ b/intakes/intakes.md
@@ -36,7 +36,8 @@ id: MASON-IN-0002
 kind: intake
 title: 'Declaration requested: state this repository''s layer in INTENT.md (security
   layer model §11)'
-status: open
+status: closed
+outcome: absorbed
 origin: cross-repo
 origin_ref: net-kingdom security-layer-model_v0.4 §11
 priority: low
@@ -61,5 +62,12 @@ description: 'A conformance sweep on 2026-08-28 found this repository has no lay
   If the proposed layer is wrong for what this repository actually does, that is more
   useful to us than a label added to close a checkbox. Standard: net-kingdom/canon/standards/security-layer-model_v0.4.md.'
 created: '2026-08-28T21:03:29.920563Z'
-updated: '2026-08-28T21:03:29.920563Z'
+updated: '2026-09-28T09:54:34.065401Z'
+notes: >-
+  Closed against the repository-authored Staff / pep-shaped declaration in
+  INTENT.md, dated 2026-09-21. That declaration names access-engine as the
+  authorization decision point and explicitly records direct Tooling contacts
+  and the founder-accepted plan-approval exception. The declaration request is
+  fulfilled; the accepted conformance gaps and their 2026-12-21 review remain
+  declared and are not marked conformant by this intake closure.
 ```
diff --git a/src/ops_mason/executor.py b/src/ops_mason/executor.py
index 6f1208f..3ba2eb8 100644
--- a/src/ops_mason/executor.py
+++ b/src/ops_mason/executor.py
@@ -18,13 +18,18 @@ printable form beyond confirmation that delivery happened.
 
 from __future__ import annotations
 
+import hashlib
+import json
 import os
+import re
+import stat
 import subprocess
-from dataclasses import dataclass, field
+from contextlib import contextmanager
+from dataclasses import asdict, dataclass, replace
 from pathlib import Path
 
 from ops_mason.audit import record_build
-from ops_mason.plan import ConstructionPlan
+from ops_mason.plan import ConstructionPlan, PlanError
 
 
 class BuildRefused(RuntimeError):
@@ -56,6 +61,7 @@ class AppRoleKVSpec:
     # When True the named policy already exists (and may grant more than one
     # KV path). Do not rewrite it — AppRole bind only.
     reuse_policy: bool = False
+    reuse_policy_sha256: str | None = None
 
 
 @dataclass
@@ -64,21 +70,21 @@ class KubernetesKVSpec:
     role_name: str
     service_account_names: tuple[str, ...]
     service_account_namespaces: tuple[str, ...]
+    policy_sha256: str = ""
     token_ttl: str = "15m"
     audit_log_path: Path | None = None
     bao_bin: str = "bao"
 
 
 def _run(bao_bin: str, args: list[str], input_text: str | None = None) -> str:
-    proc = subprocess.run(
-        [bao_bin, *args],
-        input=input_text,
-        capture_output=True,
-        text=True,
-        timeout=30,
-    )
+    try:
+        proc = subprocess.run(
+            [bao_bin, *args], input=input_text, capture_output=True, text=True, timeout=30,
+        )
+    except (OSError, UnicodeError, subprocess.TimeoutExpired):
+        raise BuildError("OpenBao command unavailable or timed out; output suppressed") from None
     if proc.returncode != 0:
-        raise BuildError(f"`{bao_bin} {' '.join(args)}` failed: {proc.stderr.strip()[:300]}")
+        raise BuildError(f"OpenBao command failed (exit {proc.returncode}); output suppressed")
     return proc.stdout
 
 
@@ -93,6 +99,12 @@ def _policy_hcl(kv_path: str, capabilities: tuple[str, ...]) -> str:
     OpenBao evaluates policy against the real `data/`-prefixed path, not
     the one a caller might naively check capabilities against.
     """
+    if not isinstance(kv_path, str) or len(kv_path.split("/")) < 2:
+        raise BuildRefused("KV path must contain a mount and a literal entry")
+    for part in kv_path.split("/"):
+        _name(part, "KV path segment")
+    if not isinstance(capabilities, tuple) or capabilities != ("read",):
+        raise BuildRefused("this KV read-lane engine permits only the read capability")
     mount, _, rest = kv_path.partition("/")
     caps = ", ".join(f'"{c}"' for c in capabilities)
     return (
@@ -101,57 +113,214 @@ def _policy_hcl(kv_path: str, capabilities: tuple[str, ...]) -> str:
     )
 
 
+def _name(value: str, label: str) -> None:
+    if not isinstance(value, str) or not re.fullmatch(r"[a-zA-Z0-9][a-zA-Z0-9_.-]*", value):
+        raise BuildRefused(f"{label} must be one literal name, without wildcards or separators")
+
+
+def _duration(value: str, label: str, *, allow_zero: bool = False) -> int:
+    if allow_zero and value == "0":
+        return 0
+    if not isinstance(value, str) or not re.fullmatch(r"[1-9][0-9]*[smh]", value):
+        raise BuildRefused(f"{label} must be a positive duration in s, m or h")
+    return int(value[:-1]) * {"s": 1, "m": 60, "h": 3600}[value[-1]]
+
+
+def _hash(value: str) -> None:
+    if not isinstance(value, str) or not re.fullmatch(r"[0-9a-f]{64}", value):
+        raise BuildRefused("reused policy requires an exact SHA-256 content pin")
+
+
+def _validate_spec(spec: AppRoleKVSpec | KubernetesKVSpec) -> None:
+    _name(spec.policy_name, "policy name")
+    _duration(spec.token_ttl, "token_ttl")
+    if not isinstance(spec.bao_bin, str) or not spec.bao_bin.strip():
+        raise BuildRefused("bao_bin must name an executable")
+    if spec.audit_log_path is not None and not isinstance(spec.audit_log_path, Path):
+        raise BuildRefused("audit_log_path must be a Path")
+    if isinstance(spec, AppRoleKVSpec):
+        _name(spec.approle_name, "AppRole name")
+        _policy_hcl(spec.kv_path, spec.kv_capabilities)
+        if type(spec.token_num_uses) is not int or spec.token_num_uses < 0:
+            raise BuildRefused("token_num_uses must be an explicit nonnegative integer")
+        if _duration(spec.token_max_ttl, "token_max_ttl") < _duration(spec.token_ttl, "token_ttl"):
+            raise BuildRefused("token_max_ttl must not be shorter than token_ttl")
+        _duration(spec.secret_id_ttl, "secret_id_ttl", allow_zero=True)
+        if type(spec.reuse_policy) is not bool:
+            raise BuildRefused("reuse_policy must be boolean")
+        if spec.reuse_policy:
+            _hash(spec.reuse_policy_sha256)
+        elif spec.reuse_policy_sha256 is not None:
+            raise BuildRefused("policy pin is only used with reuse_policy")
+        if not isinstance(spec.delivery_dir, Path) or not spec.delivery_dir.is_absolute():
+            raise BuildRefused("credential delivery requires an explicit absolute directory")
+        if ".." in spec.delivery_dir.parts:
+            raise BuildRefused("credential delivery path must not contain parent traversal")
+        if spec.audit_log_path is not None and spec.audit_log_path.absolute() in {
+            spec.delivery_dir, spec.delivery_dir / "role_id", spec.delivery_dir / "secret_id"
+        }:
+            raise BuildRefused("audit path must not overlap credential delivery")
+    else:
+        _name(spec.role_name, "Kubernetes role name")
+        _hash(spec.policy_sha256)
+        for values in (spec.service_account_names, spec.service_account_namespaces):
+            if not isinstance(values, tuple) or not values:
+                raise BuildRefused("Kubernetes role requires explicit service account bindings")
+            for value in values:
+                if not isinstance(value, str) or not re.fullmatch(r"[a-z0-9](?:[a-z0-9-]*[a-z0-9])?", value) or len(value) > 63:
+                    raise BuildRefused("service account bindings must be literal DNS labels")
+            if len(set(values)) != len(values):
+                raise BuildRefused("duplicate service account binding")
+
+
+def build_spec_document(spec: AppRoleKVSpec | KubernetesKVSpec) -> dict:
+    """Render the complete, value-free execution input for phase-3 review."""
+    _validate_spec(spec)
+    fields = asdict(spec)
+    for key, value in fields.items():
+        if isinstance(value, Path):
+            fields[key] = str(value.absolute())
+        elif isinstance(value, tuple):
+            fields[key] = list(value)
+    return {
+        "engine": "openbao-approle-kv" if isinstance(spec, AppRoleKVSpec) else "openbao-kubernetes-kv",
+        **fields,
+    }
+
+
+def build_spec_digest(document: dict) -> str:
+    """Hash canonical JSON; this is an integrity marker, not a signature."""
+    try:
+        encoded = json.dumps(document, sort_keys=True, separators=(",", ":"), allow_nan=False).encode()
+    except (TypeError, ValueError) as exc:
+        raise BuildRefused("build specification is not canonical JSON") from exc
+    return hashlib.sha256(encoded).hexdigest()
+
+
+def _approved_build(plan: ConstructionPlan, spec) -> ConstructionPlan:
+    # The file is authoritative, so revoking approval after load takes effect.
+    try:
+        current = ConstructionPlan.load(plan.path)
+    except (OSError, PlanError) as exc:
+        raise BuildRefused("cannot reload construction-plan approval") from exc
+    if current.id != plan.id or not current.is_approved():
+        raise BuildRefused("construction plan is not approved; refusing to build")
+    document = build_spec_document(spec)
+    if current.credential_type != document["engine"]:
+        raise BuildRefused("credential_type does not match the build engine")
+    if not isinstance(current.build_spec, dict) or not current.approved_spec_sha256:
+        raise BuildRefused("plan requires build_spec and approved_spec_sha256")
+    expected = build_spec_digest(document)
+    if build_spec_digest(current.build_spec) != expected or current.approved_spec_sha256 != expected:
+        raise BuildRefused("build specification does not match the approved specification digest")
+    return current
+
+
+def _verify_policy(bao_bin: str, name: str, expected: str) -> None:
+    content = _run(bao_bin, ["policy", "read", name])
+    if hashlib.sha256(content.encode()).hexdigest() != expected:
+        raise BuildRefused("live reused policy does not match the approved content pin")
+
+
+@contextmanager
+def _delivery_files(path: Path):
+    """Reserve private files before Bao writes, without following any symlink.
+
+    Hold directory/file descriptors throughout delivery. Existing files are
+    never opened or overwritten. Failed issuance leaves private partial files
+    for explicit recovery; retries must use a newly reviewed destination.
+    """
+    directory = os.open("/", os.O_RDONLY | os.O_DIRECTORY)
+    files = {}
+    try:
+        for component in path.parts[1:]:
+            try:
+                os.mkdir(component, 0o700, dir_fd=directory)
+            except FileExistsError:
+                pass
+            child = os.open(component, os.O_RDONLY | os.O_DIRECTORY | os.O_NOFOLLOW, dir_fd=directory)
+            os.close(directory)
+            directory = child
+        info = os.fstat(directory)
+        if info.st_uid != os.geteuid() or stat.S_IMODE(info.st_mode) != 0o700:
+            raise BuildRefused("delivery directory must be owned by the caller with mode 0700")
+        # Check both first so a pre-existing destination never causes a write.
+        for name in ("role_id", "secret_id"):
+            try:
+                os.stat(name, dir_fd=directory, follow_symlinks=False)
+            except FileNotFoundError:
+                continue
+            raise BuildRefused("credential destination already exists; refusing overwrite")
+        for name in ("role_id", "secret_id"):
+            files[name] = os.open(name, os.O_WRONLY | os.O_CREAT | os.O_EXCL | os.O_NOFOLLOW,
+                                  0o600, dir_fd=directory)
+            os.fchmod(files[name], 0o600)
+    except (OSError, BuildRefused) as exc:
+        for fd in files.values():
+            os.close(fd)
+        os.close(directory)
+        if isinstance(exc, BuildRefused):
+            raise
+        raise BuildRefused("cannot reserve safe credential delivery files") from None
+    try:
+        yield files
+    finally:
+        for fd in files.values():
+            os.close(fd)
+        os.close(directory)
+
+
+def _write_credential(fd: int, value: str) -> None:
+    if not value or "\n" in value or "\r" in value or "\x00" in value:
+        raise BuildError("credential command returned an invalid response")
+    with os.fdopen(os.dup(fd), "w") as stream:
+        stream.write(value + "\n")
+        stream.flush()
+        os.fsync(stream.fileno())
+
+
 def build_approle_kv_lane(plan: ConstructionPlan, spec: AppRoleKVSpec) -> dict[str, str]:
     """Create the policy + AppRole for an `openbao-approle-kv` plan, deliver role_id/secret_id.
 
     Refuses unless plan.is_approved(). Returns object names only (no
     secret material) and appends a metadata-only audit record.
     """
-    if not plan.is_approved():
-        raise BuildRefused(
-            f"plan {plan.id!r} is not approved "
-            f"(status={plan.status!r}, approved_by={plan.approved_by!r}, "
-            f"approved_at={plan.approved_at!r}) — refusing to build"
+    spec = replace(spec)
+    plan = _approved_build(plan, spec)
+    if spec.reuse_policy:
+        _verify_policy(spec.bao_bin, spec.policy_name, spec.reuse_policy_sha256)
+    with _delivery_files(spec.delivery_dir) as files:
+        if not spec.reuse_policy:
+            policy_hcl = _policy_hcl(spec.kv_path, spec.kv_capabilities)
+            _run(spec.bao_bin, ["policy", "write", spec.policy_name, "-"], input_text=policy_hcl)
+
+        _run(
+            spec.bao_bin,
+            [
+                "write",
+                f"auth/approle/role/{spec.approle_name}",
+                f"token_policies={spec.policy_name}",
+                f"token_ttl={spec.token_ttl}",
+                f"token_max_ttl={spec.token_max_ttl}",
+                f"token_num_uses={spec.token_num_uses}",
+                f"secret_id_ttl={spec.secret_id_ttl}",
+            ],
         )
 
-    if not spec.reuse_policy:
-        policy_hcl = _policy_hcl(spec.kv_path, spec.kv_capabilities)
-        _run(spec.bao_bin, ["policy", "write", spec.policy_name, "-"], input_text=policy_hcl)
+        role_id = _run(
+            spec.bao_bin, ["read", "-field=role_id", f"auth/approle/role/{spec.approle_name}/role-id"]
+        ).strip()
+        secret_id = _run(
+            spec.bao_bin,
+            ["write", "-field=secret_id", "-f", f"auth/approle/role/{spec.approle_name}/secret-id"],
+        ).strip()
 
-    _run(
-        spec.bao_bin,
-        [
-            "write",
-            f"auth/approle/role/{spec.approle_name}",
-            f"token_policies={spec.policy_name}",
-            f"token_ttl={spec.token_ttl}",
-            f"token_max_ttl={spec.token_max_ttl}",
-            f"token_num_uses={spec.token_num_uses}",
-            f"secret_id_ttl={spec.secret_id_ttl}",
-        ],
-    )
-
-    role_id = _run(
-        spec.bao_bin, ["read", "-field=role_id", f"auth/approle/role/{spec.approle_name}/role-id"]
-    ).strip()
-    secret_id = _run(
-        spec.bao_bin,
-        ["write", "-field=secret_id", "-f", f"auth/approle/role/{spec.approle_name}/secret-id"],
-    ).strip()
-
-    delivered_to = ""
-    if spec.delivery_dir is not None:
-        spec.delivery_dir.mkdir(parents=True, exist_ok=True)
-        os.chmod(spec.delivery_dir, 0o700)
-        role_id_path = spec.delivery_dir / "role_id"
-        secret_id_path = spec.delivery_dir / "secret_id"
-        role_id_path.write_text(role_id + "\n")
-        secret_id_path.write_text(secret_id + "\n")
-        os.chmod(role_id_path, 0o600)
-        os.chmod(secret_id_path, 0o600)
-        delivered_to = str(spec.delivery_dir)
+        _write_credential(files["role_id"], role_id)
+        _write_credential(files["secret_id"], secret_id)
+    delivered_to = str(spec.delivery_dir)
 
     objects = {
+        "approved_spec_sha256": plan.approved_spec_sha256,
         "policy_name": spec.policy_name,
         "approle_name": spec.approle_name,
         "kv_path": spec.kv_path,
@@ -172,14 +341,9 @@ def build_kubernetes_kv_lane(
     plan: ConstructionPlan, spec: KubernetesKVSpec
 ) -> dict[str, str]:
     """Create a policy-bound Kubernetes auth role without handling secret values."""
-    if not plan.is_approved():
-        raise BuildRefused(
-            f"plan {plan.id!r} is not approved "
-            f"(status={plan.status!r}, approved_by={plan.approved_by!r}, "
-            f"approved_at={plan.approved_at!r}) — refusing to build"
-        )
-    if not spec.service_account_names or not spec.service_account_namespaces:
-        raise BuildRefused("Kubernetes role requires explicit service account bindings")
+    spec = replace(spec)
+    plan = _approved_build(plan, spec)
+    _verify_policy(spec.bao_bin, spec.policy_name, spec.policy_sha256)
 
     _run(
         spec.bao_bin,
@@ -193,6 +357,7 @@ def build_kubernetes_kv_lane(
         ],
     )
     objects = {
+        "approved_spec_sha256": plan.approved_spec_sha256,
         "policy_name": spec.policy_name,
         "kubernetes_role_name": spec.role_name,
         "service_account_names": ",".join(spec.service_account_names),
diff --git a/src/ops_mason/plan.py b/src/ops_mason/plan.py
index 83ad6b9..72f4229 100644
--- a/src/ops_mason/plan.py
+++ b/src/ops_mason/plan.py
@@ -19,6 +19,23 @@ class PlanError(RuntimeError):
     pass
 
 
+class _PlanLoader(yaml.SafeLoader):
+    """Reject ambiguous approval documents rather than keeping the last key."""
+
+
+def _unique_mapping(loader, node, deep=False):
+    result = {}
+    for key_node, value_node in node.value:
+        key = loader.construct_object(key_node, deep=deep)
+        if not isinstance(key, str) or key in result:
+            raise PlanError("plan mappings require unique string keys")
+        result[key] = loader.construct_object(value_node, deep=deep)
+    return result
+
+
+_PlanLoader.add_constructor(yaml.resolver.BaseResolver.DEFAULT_MAPPING_TAG, _unique_mapping)
+
+
 @dataclass
 class ConstructionPlan:
     id: str
@@ -29,15 +46,26 @@ class ConstructionPlan:
     consumer_repo: str
     credential_type: str
     path: Path
+    build_spec: dict[str, Any] | None = None
+    approved_spec_sha256: str | None = None
 
     @classmethod
     def load(cls, path: str | Path) -> ConstructionPlan:
         path = Path(path)
         text = path.read_text()
-        parts = text.split("---", 2)
-        if len(parts) < 3 or not text.startswith("---"):
+        lines = text.splitlines()
+        if not lines or lines[0] != "---":
             raise PlanError(f"{path}: missing YAML frontmatter")
-        data: dict[str, Any] = yaml.safe_load(parts[1]) or {}
+        try:
+            end = lines.index("---", 1)
+        except ValueError:
+            raise PlanError(f"{path}: missing YAML frontmatter delimiter") from None
+        try:
+            data = yaml.load("\n".join(lines[1:end]), Loader=_PlanLoader)
+        except yaml.YAMLError as exc:
+            raise PlanError(f"{path}: invalid YAML frontmatter") from exc
+        if not isinstance(data, dict):
+            raise PlanError(f"{path}: frontmatter must be a mapping")
         missing = {"id", "status"} - set(data)
         if missing:
             raise PlanError(f"{path}: frontmatter missing field(s): {', '.join(sorted(missing))}")
@@ -50,7 +78,12 @@ class ConstructionPlan:
             consumer_repo=data.get("consumer_repo", ""),
             credential_type=data.get("credential_type", ""),
             path=path,
+            build_spec=data.get("build_spec"),
+            approved_spec_sha256=data.get("approved_spec_sha256"),
         )
 
     def is_approved(self) -> bool:
-        return self.status == "approved" and bool(self.approved_by) and bool(self.approved_at)
+        return self.status == "approved" and all(
+            isinstance(value, str) and bool(value.strip())
+            for value in (self.approved_by, self.approved_at)
+        )
diff --git a/tests/test_executor.py b/tests/test_executor.py
index 8cd09d5..92a3a91 100644
--- a/tests/test_executor.py
+++ b/tests/test_executor.py
@@ -1,4 +1,10 @@
+import hashlib
 import json
+import os
+import stat
+import subprocess
+
+import yaml
 from unittest.mock import MagicMock, patch
 
 import pytest
@@ -9,6 +15,8 @@ from ops_mason.executor import (
     BuildRefused,
     KubernetesKVSpec,
     _policy_hcl,
+    build_spec_document,
+    build_spec_digest,
     build_approle_kv_lane,
     build_kubernetes_kv_lane,
 )
@@ -23,18 +31,18 @@ def test_policy_hcl_uses_kv_v2_data_and_metadata_paths() -> None:
 from ops_mason.plan import ConstructionPlan
 
 
-def _plan(tmp_path, *, status="approved", approved_by="bernd", approved_at="2026-07-27"):
-    text = (
-        "---\n"
-        "id: test-lane\n"
-        f"status: {status}\n"
-        + (f'approved_by: "{approved_by}"\n' if approved_by else "approved_by: null\n")
-        + (f'approved_at: "{approved_at}"\n' if approved_at else "approved_at: null\n")
-        + "---\n# Plan\n"
-    )
+POLICY = 'path "reins/data/test/openrouter" { capabilities = ["read"] }\n'
+POLICY_HASH = hashlib.sha256(POLICY.encode()).hexdigest()
+
+
+def _plan(tmp_path, *, status="approved", approved_by="bernd", approved_at="2026-07-27", spec=None):
+    document = build_spec_document(spec or _spec(tmp_path))
+    fields = dict(id="test-lane", status=status, approved_by=approved_by,
+                  approved_at=approved_at, credential_type=document["engine"],
+                  build_spec=document, approved_spec_sha256=build_spec_digest(document))
     p = tmp_path / "plan.md"
-    p.write_text(text)
-    return ConstructionPlan.load(str(p))
+    p.write_text("---\n" + yaml.safe_dump(fields) + "---\n# Plan\n")
+    return ConstructionPlan.load(p)
 
 
 def _spec(tmp_path) -> AppRoleKVSpec:
@@ -81,7 +89,9 @@ def test_build_writes_policy_approle_and_delivers_credentials(tmp_path) -> None:
 
     def fake_run(cmd, input=None, capture_output=True, text=True, timeout=30):
         result = MagicMock(returncode=0, stderr="")
-        if cmd[1:3] == ["read", "-field=role_id"]:
+        if cmd[1:3] == ["policy", "read"]:
+            result.stdout = POLICY
+        elif cmd[1:3] == ["read", "-field=role_id"]:
             result.stdout = "role-id-value\n"
         elif "-field=secret_id" in cmd:
             result.stdout = "secret-id-value\n"
@@ -121,10 +131,14 @@ def test_reuse_policy_does_not_rewrite_existing_policy(tmp_path) -> None:
     plan = _plan(tmp_path)
     spec = _spec(tmp_path)
     spec.reuse_policy = True
+    spec.reuse_policy_sha256 = POLICY_HASH
+    plan = _plan(tmp_path, spec=spec)
 
     def fake_run(cmd, input=None, capture_output=True, text=True, timeout=30):
         result = MagicMock(returncode=0, stderr="")
-        if cmd[1:3] == ["read", "-field=role_id"]:
+        if cmd[1:3] == ["policy", "read"]:
+            result.stdout = POLICY
+        elif cmd[1:3] == ["read", "-field=role_id"]:
             result.stdout = "role-id-value\n"
         elif "-field=secret_id" in cmd:
             result.stdout = "secret-id-value\n"
@@ -136,7 +150,7 @@ def test_reuse_policy_does_not_rewrite_existing_policy(tmp_path) -> None:
         build_approle_kv_lane(plan, spec)
 
     bao_cmds = [c.args[0] for c in run.call_args_list]
-    assert not any(cmd[:2] == ["bao", "policy"] for cmd in bao_cmds)
+    assert not any(cmd[:3] == ["bao", "policy", "write"] for cmd in bao_cmds)
     assert any(cmd[1:3] == ["write", "auth/approle/role/test-lane"] for cmd in bao_cmds)
 
 
@@ -169,7 +183,7 @@ def test_bao_failure_raises_build_error(tmp_path) -> None:
 
     fake_result = MagicMock(returncode=1, stderr="permission denied", stdout="")
     with patch("ops_mason.executor.subprocess.run", return_value=fake_result):
-        with pytest.raises(BuildError, match="permission denied"):
+        with pytest.raises(BuildError, match="output suppressed"):
             build_approle_kv_lane(plan, spec)
 
 
@@ -177,6 +191,7 @@ def _kubernetes_spec(tmp_path) -> KubernetesKVSpec:
     return KubernetesKVSpec(
         policy_name="workload-kv-read-binky-qonto-api",
         role_name="external-secrets-rapp-qonto",
+        policy_sha256=POLICY_HASH,
         service_account_names=("external-secrets",),
         service_account_namespaces=("external-secrets",),
         audit_log_path=tmp_path / "audit.jsonl",
@@ -194,7 +209,8 @@ def test_kubernetes_lane_refusal_never_calls_bao(tmp_path) -> None:
 def test_kubernetes_lane_builds_exact_service_account_binding(tmp_path) -> None:
     plan = _plan(tmp_path)
     spec = _kubernetes_spec(tmp_path)
-    result = MagicMock(returncode=0, stderr="", stdout="")
+    plan = _plan(tmp_path, spec=spec)
+    result = MagicMock(returncode=0, stderr="", stdout=POLICY)
     with (
         patch("ops_mason.executor.subprocess.run", return_value=result) as run,
         patch("ops_mason.executor.record_build") as audit,
@@ -220,6 +236,7 @@ def test_kubernetes_lane_requires_nonempty_bindings(tmp_path) -> None:
     spec = KubernetesKVSpec(
         policy_name="policy",
         role_name="role",
+        policy_sha256=POLICY_HASH,
         service_account_names=(),
         service_account_namespaces=("external-secrets",),
     )
@@ -227,3 +244,176 @@ def test_kubernetes_lane_requires_nonempty_bindings(tmp_path) -> None:
         with pytest.raises(BuildRefused, match="explicit service account"):
             build_kubernetes_kv_lane(plan, spec)
     run.assert_not_called()
+
+
+def _edit_plan(plan, edit):
+    text = plan.path.read_text().split("---", 2)
+    data = yaml.safe_load(text[1])
+    edit(data)
+    plan.path.write_text("---\n" + yaml.safe_dump(data) + "---" + text[2])
+
+
+@pytest.mark.parametrize("field,value", [
+    ("kv_path", "reins/another/openrouter"), ("policy_name", "other-policy"),
+    ("approle_name", "other-role"), ("token_num_uses", 0),
+    ("token_ttl", "10m"), ("token_max_ttl", "1h"), ("secret_id_ttl", "15m"),
+    ("bao_bin", "another-bao"),
+])
+def test_changed_build_scope_refused_before_bao(tmp_path, field, value):
+    spec = _spec(tmp_path)
+    plan = _plan(tmp_path, spec=spec)
+    setattr(spec, field, value)
+    with patch("ops_mason.executor.subprocess.run") as run:
+        with pytest.raises(BuildRefused, match="approved specification"):
+            build_approle_kv_lane(plan, spec)
+    run.assert_not_called()
+    assert not spec.delivery_dir.exists()
+
+
+def test_destination_is_part_of_approval(tmp_path):
+    plan = _plan(tmp_path)
+    spec = _spec(tmp_path)
+    spec.delivery_dir = tmp_path / "elsewhere"
+    with patch("ops_mason.executor.subprocess.run") as run:
+        with pytest.raises(BuildRefused, match="approved specification"):
+            build_approle_kv_lane(plan, spec)
+    run.assert_not_called()
+
+
+@pytest.mark.parametrize("edit", [
+    lambda d: d.update(status="reviewed"),
+    lambda d: d.update(approved_spec_sha256="0" * 64),
+    lambda d: d.pop("build_spec"),
+    lambda d: d.update(credential_type="openbao-kubernetes-kv"),
+    lambda d: d["build_spec"].update(token_num_uses=0),
+])
+def test_changed_or_legacy_plan_refused_even_with_previously_loaded_approval(tmp_path, edit):
+    plan = _plan(tmp_path)
+    _edit_plan(plan, edit)
+    with patch("ops_mason.executor.subprocess.run") as run:
+        with pytest.raises(BuildRefused):
+            build_approle_kv_lane(plan, _spec(tmp_path))
+    run.assert_not_called()
+
+
+@pytest.mark.parametrize("field,value", [
+    ("kv_path", "reins/test/*"), ("kv_path", "reins/test/+"),
+    ("kv_path", "reins/test/"), ("kv_path", "reins/../test"),
+    ("kv_path", 'reins/test/" { capabilities = ["sudo"] }'),
+    ("kv_path", "reins//test"), ("kv_path", "reins"),
+    ("policy_name", "a,b"), ("approle_name", "../other"),
+    ("kv_capabilities", ("read", "sudo")), ("kv_capabilities", ("create", "read")),
+    ("token_num_uses", True), ("token_num_uses", -1),
+    ("token_ttl", "0"), ("token_max_ttl", "1s"),
+    ("delivery_dir", None), ("reuse_policy", "false"),
+])
+def test_unsafe_spec_is_rejected_before_any_command(tmp_path, field, value):
+    plan = _plan(tmp_path)
+    spec = _spec(tmp_path)
+    setattr(spec, field, value)
+    with patch("ops_mason.executor.subprocess.run") as run:
+        with pytest.raises(BuildRefused):
+            build_approle_kv_lane(plan, spec)
+    run.assert_not_called()
+
+
+@pytest.mark.parametrize("bindings", [("*",), ("a,b",), ("../a",), ("valid", "valid")])
+def test_kubernetes_wildcard_or_ambiguous_bindings_refused(tmp_path, bindings):
+    spec = _kubernetes_spec(tmp_path)
+    plan = _plan(tmp_path, spec=spec)
+    spec.service_account_names = bindings
+    with patch("ops_mason.executor.subprocess.run") as run:
+        with pytest.raises(BuildRefused):
+            build_kubernetes_kv_lane(plan, spec)
+    run.assert_not_called()
+
+
+def test_kubernetes_valid_but_unapproved_binding_refused(tmp_path):
+    spec = _kubernetes_spec(tmp_path)
+    plan = _plan(tmp_path, spec=spec)
+    spec.service_account_namespaces = ("other",)
+    with patch("ops_mason.executor.subprocess.run") as run:
+        with pytest.raises(BuildRefused, match="approved specification"):
+            build_kubernetes_kv_lane(plan, spec)
+    run.assert_not_called()
+
+
+@pytest.mark.parametrize("engine", ["approle", "kubernetes"])
+def test_changed_reused_policy_refuses_before_mutation(tmp_path, engine):
+    if engine == "approle":
+        spec = _spec(tmp_path)
+        spec.reuse_policy, spec.reuse_policy_sha256 = True, POLICY_HASH
+        build = build_approle_kv_lane
+    else:
+        spec = _kubernetes_spec(tmp_path)
+        build = build_kubernetes_kv_lane
+    plan = _plan(tmp_path, spec=spec)
+    with patch("ops_mason.executor.subprocess.run", return_value=MagicMock(returncode=0, stdout=POLICY + "# changed")) as run:
+        with pytest.raises(BuildRefused, match="content pin"):
+            build(plan, spec)
+    assert len(run.call_args_list) == 1
+    assert run.call_args.args[0][1:3] == ["policy", "read"]
+
+
+def test_credentials_are_private_before_first_bao_call_even_with_open_umask(tmp_path):
+    plan, spec = _plan(tmp_path), _spec(tmp_path)
+    def fake_run(*args, **kwargs):
+        assert stat.S_IMODE(spec.delivery_dir.stat().st_mode) == 0o700
+        for name in ("role_id", "secret_id"):
+            assert stat.S_IMODE((spec.delivery_dir / name).stat().st_mode) == 0o600
+        return MagicMock(returncode=0, stdout="synthetic-credential\n", stderr="")
+    previous = os.umask(0)
+    try:
+        with patch("ops_mason.executor.subprocess.run", side_effect=fake_run):
+            build_approle_kv_lane(plan, spec)
+    finally:
+        os.umask(previous)
+    assert "synthetic-credential" not in spec.audit_log_path.read_text()
+
+
+@pytest.mark.parametrize("case", ["existing", "symlink-file", "symlink-directory", "symlink-parent", "public-directory", "hardlink"])
+def test_unsafe_delivery_refuses_without_mutation_or_overwrite(tmp_path, case):
+    spec = _spec(tmp_path)
+    victim = tmp_path / "victim"
+    victim.write_text("leave untouched")
+    if case == "symlink-directory":
+        target = tmp_path / "target"
+        target.mkdir(mode=0o700)
+        spec.delivery_dir.symlink_to(target, target_is_directory=True)
+    elif case == "symlink-parent":
+        parent = tmp_path / "parent"
+        parent.symlink_to(tmp_path, target_is_directory=True)
+        spec.delivery_dir = parent / "delivery"
+    else:
+        spec.delivery_dir.mkdir(mode=0o700)
+        if case == "public-directory":
+            spec.delivery_dir.chmod(0o755)
+        elif case == "existing":
+            (spec.delivery_dir / "secret_id").write_text("existing-credential")
+        elif case == "hardlink":
+            os.link(victim, spec.delivery_dir / "secret_id")
+        else:
+            (spec.delivery_dir / "secret_id").symlink_to(victim)
+    plan = _plan(tmp_path, spec=spec)
+    with patch("ops_mason.executor.subprocess.run") as run:
+        with pytest.raises(BuildRefused):
+            build_approle_kv_lane(plan, spec)
+    run.assert_not_called()
+    assert victim.read_text() == "leave untouched"
+    if case == "existing":
+        assert (spec.delivery_dir / "secret_id").read_text() == "existing-credential"
+
+
+@pytest.mark.parametrize("failure", ["exit", "timeout"])
+def test_command_errors_never_echo_credentials(tmp_path, failure):
+    plan, spec = _plan(tmp_path), _spec(tmp_path)
+    marker = "synthetic-sensitive-output"
+    kwargs = ({"return_value": MagicMock(returncode=1, stdout=marker, stderr=marker)}
+              if failure == "exit" else
+              {"side_effect": subprocess.TimeoutExpired(["bao"], 30, output=marker, stderr=marker)})
+    with patch("ops_mason.executor.subprocess.run", **kwargs):
+        with pytest.raises(BuildError) as error:
+            build_approle_kv_lane(plan, spec)
+    assert marker not in str(error.value)
+    assert not spec.audit_log_path.exists()
+    assert stat.S_IMODE((spec.delivery_dir / "secret_id").stat().st_mode) == 0o600
diff --git a/tests/test_plan.py b/tests/test_plan.py
index 35a9e4b..ec7cc11 100644
--- a/tests/test_plan.py
+++ b/tests/test_plan.py
@@ -49,3 +49,24 @@ def test_missing_required_field_raises(tmp_path) -> None:
     path = _write(tmp_path, "id: p\n# status omitted")
     with pytest.raises(PlanError, match="missing field"):
         ConstructionPlan.load(path)
+
+
+@pytest.mark.parametrize("frontmatter", [
+    "id: p\nstatus: reviewed\nstatus: approved",
+    "id: p\nstatus: approved\nbuild_spec:\n  token_num_uses: 8\n  token_num_uses: 0",
+    "- not-a-mapping",
+])
+def test_ambiguous_or_malformed_approval_document_refused(tmp_path, frontmatter):
+    with pytest.raises(PlanError):
+        ConstructionPlan.load(_write(tmp_path, frontmatter))
+
+
+@pytest.mark.parametrize("approver", ['" "', "true", "[bernd]"])
+def test_non_string_or_blank_approval_marker_is_not_approval(tmp_path, approver):
+    path = _write(tmp_path, f'id: p\nstatus: approved\napproved_by: {approver}\napproved_at: "2026-09-28"')
+    assert not ConstructionPlan.load(path).is_approved()
+
+
+def test_triple_dash_inside_specification_is_not_frontmatter_delimiter(tmp_path):
+    path = _write(tmp_path, 'id: p\nstatus: draft\nbuild_spec:\n  policy_name: "lane---example"')
+    assert ConstructionPlan.load(path).build_spec["policy_name"] == "lane---example"
diff --git a/workplans/MASON-WP-0001-foundation.md b/workplans/MASON-WP-0001-foundation.md
index e6919b6..a0ab789 100644
--- a/workplans/MASON-WP-0001-foundation.md
+++ b/workplans/MASON-WP-0001-foundation.md
@@ -130,6 +130,18 @@ approved (`test_refusal_never_calls_bao`); role_id/secret_id land as
 `0600` files and never appear in a log line or exception message; the
 policy HCL goes over stdin, never argv.
 
+**Hardening follow-up (2026-09-28).** The existing build executor now binds
+execution to a reviewed `build_spec` plus `approved_spec_sha256`, reloads the
+approval before use, validates literal scope/token/binding inputs, and pins
+existing policy contents. Credential files are exclusively created as 0600
+inside caller-owned 0700 directories before issuance, with symlinks and
+existing destinations refused. Command errors suppress sensitive output.
+Historical build approvals were not rewritten and no live lane was changed.
+The suite passes 108 tests, including refusal-before-mutation, policy drift,
+permissive-umask, symlink/hardlink/overwrite and error-output regressions.
+The source contract and recovery limitations are documented in
+`docs/construction-plan-format.md`. This is maintenance of T04, not a new task.
+
 ```task
 id: MASON-WP-0001-T04
 status: done