Add deterministic reproducibility test for layered admissibility artifact

tests/test_artifact_reproducibility.py

@@ -0,0 +1,46 @@
+from __future__ import annotations
+
+import json
+from collections.abc import Callable
+from dataclasses import dataclass
+from pathlib import Path
+
+from scripts.generate_layered_admissibility_artifact import (
+    generate_layered_admissibility_artifact,
+)
+
+
+@dataclass(frozen=True)
+class DeterministicArtifactSpec:
+    """Configuration for a reproducible committed artifact check."""
+
+    name: str
+    committed_path: Path
+    regenerate: Callable[[Path], Path]
+
+
+ARTIFACT_SPECS: tuple[DeterministicArtifactSpec, ...] = (
+    DeterministicArtifactSpec(
+        name="layered_admissibility_results",
+        committed_path=Path("artifacts/layered_admissibility_results.json"),
+        regenerate=generate_layered_admissibility_artifact,
+    ),
+)
+
+
+def _load_json(path: Path) -> object:
+    return json.loads(path.read_text(encoding="utf-8"))
+
+
+def test_committed_deterministic_artifacts_are_reproducible(tmp_path: Path) -> None:
+    for spec in ARTIFACT_SPECS:
+        regenerated_path = tmp_path / spec.committed_path.name
+        spec.regenerate(regenerated_path)
+
+        regenerated_payload = _load_json(regenerated_path)
+        committed_payload = _load_json(spec.committed_path)
+
+        assert regenerated_payload == committed_payload, (
+            f"Deterministic artifact drift detected for '{spec.name}'. "
+            f"Regenerate with: python scripts/generate_layered_admissibility_artifact.py"
+        )