Add exact Engine L2 reconciliation transition

infra/deploy-runner/test_engine_provider_target_host_policy.py

@@ -33,6 +33,20 @@ RUNNER = load_runner()
 
 
 class EngineProviderTargetHostPolicyTest(unittest.TestCase):
+    def require_historical_target_source(self):
+        for relative_path, expected in (
+            RUNNER.ENGINE_PROVIDER_TARGET_HOST_POLICY_TARGET_SHA256.items()
+        ):
+            path = ENGINE_ROOT / relative_path
+            if (
+                not path.is_file()
+                or hashlib.sha256(path.read_bytes()).hexdigest() != expected
+            ):
+                self.skipTest(
+                    "historical target-host policy source has advanced "
+                    "to its exact successor"
+                )
+
     def build(self, artifact_dir):
         environment = os.environ.copy()
         environment["NODEDC_ENGINE_SOURCE_ROOT"] = str(ENGINE_ROOT)
@@ -47,6 +61,7 @@ class EngineProviderTargetHostPolicyTest(unittest.TestCase):
         return json.loads(completed.stdout)
 
     def test_builder_emits_exact_deterministic_one_file_slice(self):
+        self.require_historical_target_source()
         with tempfile.TemporaryDirectory(prefix="nodedc-provider-target-host-") as directory:
             root = Path(directory)
             first = self.build(root / "first")
@@ -126,6 +141,7 @@ class EngineProviderTargetHostPolicyTest(unittest.TestCase):
         acceptance.assert_called_once_with()
 
     def test_live_acceptance_uses_exact_literal_host_contract(self):
+        self.require_historical_target_source()
         expected_live = "engine-provider-target-host-policy:exact-literal-host:v1"
         with (
             mock.patch.object(RUNNER, "component_root", return_value=ENGINE_ROOT),