Apply GH-DEC-2026-020: remove companion_version from layer.yaml

A12 r2 reaches every key and value of the declaration, including the
companion's version. The standard: path in INTENT.md was already
unversioned and is unchanged. tests/test_layer_declaration.py fails if a
version key, a versioned standard path, or companion_version returns to
the INTENT.md frontmatter or layer.yaml; schema_version and comments are
not reached. One prose citation ("the v0.5 scope rule") in a rationale
value is allowlisted by exact text and reported to gate-house as open.

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_declaration.py

@@ -0,0 +1,94 @@
+"""A12 r2 (GH-DEC-2026-017 §5, GH-DEC-2026-020): the layer declaration carries
+no version of the standard or of its companion, in any key or value.
+
+The declaration is every key of the INTENT.md frontmatter and every key of the
+derived layer.yaml. Comments and `schema_version` are not reached. Stance,
+claims and classification maps are not declarations and are not checked here.
+
+Parsed as text, not YAML: pyyaml is not a dependency of this repository, and a
+skipped test would enforce nothing.
+"""
+
+import re
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[1]
+
+# A version-bearing key (any key ending in `version`, except the file's own
+# schema version) or a version in a value, including one carried in a path or
+# file name such as `security-layer-model_v0.7.md`.
+VERSION_KEY = re.compile(r"^\s*-?\s*([A-Za-z0-9_]*version)\s*:", re.IGNORECASE)
+VERSION_VALUE = re.compile(r"_v\d+(\.\d+)*|\bv\d+\.\d+")
+
+# OPEN, reported to gate-house with this repository's A12 r2 findings: a prose
+# citation of a past rule inside a rationale value ("the v0.5 scope rule") is
+# not a pin, but A12 r2's "no key or value" reads literally as reaching it.
+# Listed here, exactly, so it stays visible and nothing else slips past.
+CITATION_ALLOWLIST = {
+    "Progress events. Outside §5 by the v0.5 scope rule. Recorded, not",
+}
+
+
+def _declaration_lines(text: str) -> list[str]:
+    lines = []
+    for raw in text.splitlines():
+        line = raw.split(" #", 1)[0]
+        if line.lstrip().startswith("#") or not line.strip():
+            continue
+        lines.append(line)
+    return lines
+
+
+def _intent_frontmatter() -> str:
+    text = (ROOT / "INTENT.md").read_text()
+    match = re.match(r"^---\n(.*?)\n---\n", text, re.DOTALL)
+    assert match, "INTENT.md has no frontmatter; the declaration lives there"
+    return match.group(1)
+
+
+def _findings(name: str, text: str) -> list[str]:
+    found = []
+    for line in _declaration_lines(text):
+        key = VERSION_KEY.match(line)
+        if key and key.group(1).lower() != "schema_version":
+            found.append(f"{name}: version key: {line.strip()}")
+        elif (
+            not key
+            and VERSION_VALUE.search(line)
+            and line.strip() not in CITATION_ALLOWLIST
+        ):
+            found.append(f"{name}: versioned value: {line.strip()}")
+    return found
+
+
+def test_declaration_carries_no_version():
+    findings = _findings("INTENT.md frontmatter", _intent_frontmatter())
+    findings += _findings("layer.yaml", (ROOT / "layer.yaml").read_text())
+    assert not findings, "\n".join(findings)
+
+
+def test_companion_version_absent():
+    assert "companion_version" not in "\n".join(
+        _declaration_lines((ROOT / "layer.yaml").read_text())
+    )
+    assert "companion_version" not in "\n".join(
+        _declaration_lines(_intent_frontmatter())
+    )
+
+
+def test_standard_path_unversioned():
+    match = re.search(r"^standard:\s*(\S+)", _intent_frontmatter(), re.MULTILINE)
+    assert match, "INTENT.md frontmatter names no standard"
+    assert match.group(1) == "net-kingdom/canon/standards/security-layer-model"
+
+
+def test_detector_catches_the_forms_ruled_on():
+    # The check must see the pin under any name, not only `standard_version`.
+    assert _findings("x", 'companion_version: "0.2"\n')
+    assert _findings("x", 'standard_version: "0.7"\n')
+    assert _findings(
+        "x", "standard: net-kingdom/canon/standards/security-layer-model_v0.7.md\n"
+    )
+    assert not _findings("x", 'schema_version: "0.1"\n')
+    assert not _findings("x", "# Companion: SECURITY-COMPANION.md v0.2\n")
+    assert not _findings("x", '  statute: "§9.4"\n  "5.1": []\n')