Verify exact-run CSV publication

docs/USER_GUIDE.md

@@ -31,7 +31,10 @@ does not publish a result.
 A report configured against an exact published Dataflow run reads that run's
 immutable Datasource materialization. It does not rerun the flow with current
 inputs. The evidence identifies the Dataflow run and materialization, and access
-to both is checked again when the report runs.
+to both is checked again when the report runs. CSV export therefore provides an
+Excel-readable publication of the exact authorized Dataflow result, with
+spreadsheet formula markers escaped and the run lineage retained on the
+Reporting execution.
 
 The **Effective access** explanation states when dimensions, measures, source
 rows, or actions were removed by Policy. A result with no hidden elements says

tests/test_reporting_service.py

@@ -384,7 +384,7 @@ class ReportingServiceTests(unittest.TestCase):
             )
         self.assertTrue(raised.exception.execution_id)
 
-    def test_dataflow_dataset_can_pin_an_exact_published_run(self) -> None:
+    def test_dataflow_run_can_be_exported_as_formula_safe_csv(self) -> None:
         payload = dataset_payload()
         rows = list(payload.pop("static_rows"))
         payload.update(
@@ -410,7 +410,7 @@ class ReportingServiceTests(unittest.TestCase):
             report_id="report-1",
             report_revision=1,
             parameters={},
-            query=None,
+            query=ReportQuery(mode="detail", dimensions=["note"]),
             idempotency_key="published-dataflow-run",
         )
 
@@ -421,6 +421,15 @@ class ReportingServiceTests(unittest.TestCase):
             provider.last_request.run_ref,
         )
         self.assertTrue(result["provenance"]["source"]["immutable_run"])
+        content, content_type, filename = export_execution(
+            self.session,
+            self.principal,
+            execution_id=str(result["execution_id"]),
+            format="csv",
+        )
+        self.assertEqual("text/csv; charset=utf-8", content_type)
+        self.assertTrue(filename.endswith(".csv"))
+        self.assertIn("'=cmd", content.decode("utf-8-sig"))
 
     def test_restricted_access_and_service_scope_guards(self) -> None:
         self._create_report_graph(