feat(P4): regression-gate policies + docs (REQ-304..307)

regression/ policies (3): cap-013-adapter-dedup, cap-023-metrics-collector,
cap-024-deck-structure — declarative mirrors of core/regression_verify.py
over capability-inventory JSON. The imperative regression_verify.py is kept
(drives CI gate); the policies are the declarative mirror (IDEATE I1 quality
improvement).

tests: test_regression_policies.py + clean/drifted fixtures. Skip-without-kj.

docs: adapters/README.md (new kyverno-json row + PolicyEngine Protocol
section with how-to-add-OpaEngine), adapters/kyverno-json/README.md (engine,
install, policy directory layout, 4 categories, severity convention),
schemas/README.md (D-116 engine enum reuse note), modules/STANDARDS.md §10
Policy Authoring Standard, docs/METRICS.md (swappable engine narrative).

---ci---
project: acdl
phase: 4
milestone: v1.25
status: execute
phase_role: execution
requirements:
  covered: [REQ-304, REQ-305, REQ-306, REQ-307]
  partial: []
---/ci---

tests/fixtures/capability_inventory/clean.json

@@ -0,0 +1,11 @@
+{
+  "adapters": ["terraform", "checkov", "wiz", "kyverno-json"],
+  "metrics": [
+    {"name": "MTTR", "status": "grounded"},
+    {"name": "CloudSpend", "status": "derived"},
+    {"name": "TouchlessResolution", "status": "deferred"}
+  ],
+  "deck": {
+    "beats": ["Problem", "Solution", "Proof", "Roadmap+Ask"]
+  }
+}

tests/fixtures/capability_inventory/drifted.json

@@ -0,0 +1,11 @@
+{
+  "adapters": ["terraform", "checkov", "wiz", "terraform", "kyverno-json"],
+  "metrics": [
+    {"name": "MTTR", "status": "grounded"},
+    {"name": "CloudSpend", "status": "unknown"},
+    {"name": "TouchlessResolution", "status": "deferred"}
+  ],
+  "deck": {
+    "beats": ["Problem", "Solution", "Proof"]
+  }
+}

tests/test_regression_policies.py

@@ -0,0 +1,88 @@
+"""Tests for regression-gate kyverno-json policies (REQ-304, REQ-305, v1.25).
+
+Tests the 3 declarative mirrors of core/regression_verify.py:
+cap-013-adapter-dedup, cap-023-metrics-collector, cap-024-deck-structure.
+Uses clean + drifted capability-inventory fixtures. Skip-without-kj.
+"""
+
+import json
+import os
+import sys
+from pathlib import Path
+
+import pytest
+
+sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
+
+import importlib.util
+_ENGINE_PATH = Path(__file__).resolve().parent.parent / "adapters" / "kyverno-json" / "kyverno_json_engine.py"
+_spec = importlib.util.spec_from_file_location("kyverno_json_engine", _ENGINE_PATH)
+_mod = importlib.util.module_from_spec(_spec)
+_spec.loader.exec_module(_mod)
+KyvernoJsonEngine = _mod.KyvernoJsonEngine
+
+POLICY_DIR = Path(__file__).resolve().parent.parent / "adapters" / "kyverno-json" / "policies" / "regression"
+FIXTURES = Path(__file__).resolve().parent / "fixtures" / "capability_inventory"
+
+
+def _kj_installed() -> bool:
+    return _mod._which_kj() is not None
+
+
+@pytest.fixture(autouse=True)
+def _require_kj():
+    if not _kj_installed():
+        pytest.skip("kj not installed (scripts/install-kyverno-json.sh)")
+
+
+def _load(name):
+    with open(FIXTURES / name, "r", encoding="utf-8") as fh:
+        return json.load(fh)
+
+
+class TestCleanInventory:
+    def test_clean_inventory_no_fails(self):
+        eng = KyvernoJsonEngine()
+        out = eng.evaluate(_load("clean.json"), POLICY_DIR, "cid-clean")
+        fails = [p for p in out if p["result"] == "fail"]
+        assert fails == [], f"expected no fails on clean inventory, got: {fails}"
+
+
+class TestDriftedInventory:
+    def test_drifted_inventory_has_fails(self):
+        eng = KyvernoJsonEngine()
+        out = eng.evaluate(_load("drifted.json"), POLICY_DIR, "cid-drift")
+        fails = [p for p in out if p["result"] == "fail"]
+        assert len(fails) >= 1, "expected at least one fail on the drifted inventory"
+
+
+class TestPolicyFilesExist:
+    def test_three_regression_policies_present(self):
+        files = sorted(os.listdir(POLICY_DIR))
+        assert "cap-013-adapter-dedup.json" in files
+        assert "cap-023-metrics-collector.json" in files
+        assert "cap-024-deck-structure.json" in files
+
+    def test_policies_are_valid_json(self):
+        for f in os.listdir(POLICY_DIR):
+            if f.endswith(".json"):
+                with open(POLICY_DIR / f, "r", encoding="utf-8") as fh:
+                    data = json.load(fh)
+                assert data["apiVersion"] == "json.kyverno.io/v1alpha1"
+                assert data["kind"] == "ValidatingPolicy"
+                assert "nova.cloudinit.dev/severity" in data["metadata"]["annotations"]
+
+
+class TestFixturesExist:
+    def test_clean_and_drifted_fixtures_present(self):
+        assert (FIXTURES / "clean.json").is_file()
+        assert (FIXTURES / "drifted.json").is_file()
+
+    def test_drifted_fixture_has_duplicate_adapter(self):
+        data = _load("drifted.json")
+        # The drifted fixture has 'terraform' twice (adapter dedup violation).
+        assert data["adapters"].count("terraform") == 2
+
+    def test_drifted_fixture_has_missing_roadmap_beat(self):
+        data = _load("drifted.json")
+        assert "Roadmap+Ask" not in data["deck"]["beats"]