feat: complete fabric authority cutover contract

Assistant: codex
Assistant-Model: gpt-5.6-sol
Assistant-Session: 01a053ff-1d6f-7fe2-ac1c-a6eb40a42a0c

tests/test_fabric_cutover.py

@@ -0,0 +1,69 @@
+from __future__ import annotations
+
+from copy import deepcopy
+
+from fin_hub.fabric_cutover import evaluate_fabric_cutover, fabric_content_hash
+
+
+def _authority() -> dict:
+    return {
+        "apiVersion": "railiance.fabric/v1alpha2",
+        "kind": "FabricGraphExport",
+        "schema_version": "financial-fabric-v1",
+        "generated_at": "2026-08-31T12:00:00Z",
+        "source": {
+            "producer": "railiance-fabric",
+            "commit": "snapshot-set:sha256:abc",
+            "path": "registry://accepted-snapshots",
+        },
+        "actors": [{"id": "actor.king"}],
+        "fabrics": [{"id": "fabric.main"}],
+        "nodes": [{"id": "service.one"}],
+        "edges": [],
+        "unresolved": [],
+    }
+
+
+def _projection(authority: dict) -> dict:
+    return {
+        "schema_version": authority["schema_version"],
+        "node_count": 1,
+        "edge_count": 0,
+        "actor_count": 1,
+        "fabric_count": 1,
+        "unresolved_count": 0,
+        "latest_import": {
+            "api_version": authority["apiVersion"],
+            "schema_version": authority["schema_version"],
+            "export_kind": authority["kind"],
+            "content_hash": fabric_content_hash(authority),
+            "source_commit": authority["source"]["commit"],
+            "source_path": authority["source"]["path"],
+            "exported_at": authority["generated_at"],
+        },
+    }
+
+
+def test_cutover_gate_accepts_exact_counts_hash_and_provenance() -> None:
+    authority = _authority()
+    report = evaluate_fabric_cutover(authority, _projection(authority))
+    assert report["ready"] is True
+    assert report["failures"] == []
+
+
+def test_cutover_gate_rejects_count_or_hash_drift() -> None:
+    authority = _authority()
+    projection = _projection(authority)
+    projection["node_count"] = 2
+    projection["latest_import"]["content_hash"] = "stale"
+    report = evaluate_fabric_cutover(authority, projection)
+    assert report["ready"] is False
+    assert {"node_count", "content_hash"}.issubset(report["failures"])
+
+
+def test_cutover_gate_rejects_unversioned_authority_provenance() -> None:
+    authority = deepcopy(_authority())
+    authority["source"]["commit"] = "working-tree"
+    report = evaluate_fabric_cutover(authority, _projection(authority))
+    assert report["ready"] is False
+    assert "authority:source.commit must identify an immutable authority revision" in report["failures"]