Apply GH-DEC-2026-017: INTENT.md governs, the sidecar is derived, no version

- Remove standard_version from layer.yaml and INTENT.md frontmatter (§5, A12).
- Mark layer.yaml derived: true, derived_from: INTENT.md (§1, A11).
- Checker and tests change in the same commit: standard_version is no longer
  a required key (it is now rejected in either form), the derived marking is
  required, both layer values are checked against the closed four-token
  vocabulary, and the two forms are compared after an ASCII case fold (A9).
  A disagreement surviving the fold is reported as a finding.
- Nothing re-spelled: INTENT.md keeps "Engine", layer.yaml keeps "engine".

Scope check (§9.5 / GH-DEC-2026-017 §4): maturity-engine does not score
layer declarations anywhere. scoring.py grades gap-register conformance
states, and seed gaps concern capabilities, not §11 declarations, so no
non-§4 repository is graded. No scoring change required.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Assistant: claude-code
Assistant-Model: opus
Assistant-Process: 63291@bnt-lap001
Assistant-Session: 8bd77868-ca68-4f49-bb1e-d539ecc0d703

tests/test_layer_conformance.py

@@ -15,6 +15,16 @@ DECL = ROOT / "layer.yaml"
 INTENT = ROOT / "INTENT.md"
 
 
+def _fold(value: object) -> str:
+    return str(value).strip().encode("ascii", "ignore").decode().lower()
+
+
+def _intent_frontmatter() -> dict:
+    match = re.match(r"^---\n(.*?)\n---\n", INTENT.read_text(), re.DOTALL)
+    assert match
+    return yaml.safe_load(match.group(1))
+
+
 def _run(*args: str) -> subprocess.CompletedProcess[str]:
     return subprocess.run(
         [sys.executable, str(SCRIPT), *args],
@@ -27,21 +37,42 @@ def test_declaration_exists_and_declares_engine_pip():
     assert DECL.exists()
     data = yaml.safe_load(DECL.read_text())
     assert data["repository"] == "maturity-engine"
-    assert data["layer"] == "engine"
-    assert data["role"] == "pip"
+    assert _fold(data["layer"]) == "engine"
+    assert _fold(data["role"]) == "pip"
     assert data["framework"] == "netkingdom-security-layer-model"
-    assert data["standard_version"] == "0.7"
     assert "pep_stance" not in data or not data.get("pep_stance")
 
 
-def test_frontmatter_agrees_with_layer_yaml():
-    text = INTENT.read_text()
-    match = re.match(r"^---\n(.*?)\n---\n", text, re.DOTALL)
-    assert match
-    meta = yaml.safe_load(match.group(1))
+def test_intent_md_carries_the_governing_layer_key():
+    """GH-DEC-2026-017 §1: the INTENT.md frontmatter key is the declaration."""
+    assert _fold(_intent_frontmatter()["layer"]) == "engine"
+
+
+def test_sidecar_is_marked_derived_and_names_its_source():
     data = yaml.safe_load(DECL.read_text())
-    assert str(meta["layer"]).lower() == str(data["layer"]).lower()
-    assert str(meta["role"]).lower() == str(data["role"]).lower()
+    assert data["derived"] is True
+    assert data["derived_from"] == "INTENT.md"
+
+
+def test_frontmatter_agrees_with_layer_yaml_once_case_is_folded():
+    """A11 agreement, A9 fold. Deliberately a fold, not an equality: an
+    equality would silently demand the re-spelling the ruling declined."""
+    meta = _intent_frontmatter()
+    data = yaml.safe_load(DECL.read_text())
+    assert _fold(meta["layer"]) == _fold(data["layer"])
+    assert _fold(meta["role"]) == _fold(data["role"])
+
+
+def test_both_layer_values_are_in_the_closed_vocabulary():
+    vocabulary = {"taxonomy", "tooling", "engine", "staff"}
+    assert _fold(_intent_frontmatter()["layer"]) in vocabulary
+    assert _fold(yaml.safe_load(DECL.read_text())["layer"]) in vocabulary
+
+
+def test_no_declaration_carries_a_standard_version():
+    """GH-DEC-2026-017 §5 / A12."""
+    assert "standard_version" not in yaml.safe_load(DECL.read_text())
+    assert "standard_version" not in _intent_frontmatter()
 
 
 def test_no_tooling_contacts_or_pep():