Add typed Arrow execution backend boundary

tests/test_service.py

@@ -18,6 +18,7 @@ from govoplan_core.core.datasources import (
     DatasourcePublicationResult,
 )
 from govoplan_core.db.base import Base
+from govoplan_dataflow.backend.backends.duckdb import DuckDbExecutionBackend
 from govoplan_dataflow.backend.db.models import (
     DataflowPipeline,
     DataflowPipelineRevision,
@@ -320,6 +321,37 @@ class DataflowServiceTests(unittest.TestCase):
             self.session.scalar(select(func.count()).select_from(DataflowRun)),
         )
 
+    @unittest.skipUnless(
+        DuckDbExecutionBackend().available(),
+        "analytics extra is not installed",
+    )
+    def test_saved_preview_can_use_isolated_duckdb_backend(self) -> None:
+        pipeline = self._create()
+
+        response = preview_pipeline(
+            self.session,
+            tenant_id="tenant-1",
+            actor_id="user-1",
+            payload=PipelinePreviewRequest(
+                pipeline_id=pipeline.id,
+                execution_backend="duckdb",
+            ),
+            principal=principal(),
+        )
+        self.session.commit()
+
+        run = self.session.get(DataflowRun, response.run_id)
+        self.assertEqual("succeeded", response.status)
+        self.assertEqual(
+            [{"id": 2, "amount": 15}, {"id": 3, "amount": 25}],
+            response.rows,
+        )
+        self.assertEqual(2, response.total_rows)
+        self.assertFalse(response.truncated)
+        self.assertEqual(3, response.input_row_count)
+        self.assertTrue(response.executor_version.startswith("duckdb-isolated-v1"))
+        self.assertEqual(response.executor_version, run.executor_version)
+
     def test_failed_preview_keeps_upstream_lineage_and_failed_node_diagnostic(self) -> None:
         graph = sample_graph()
         graph.nodes[0].config["rows"] = [{"id": 1, "amount": "not-a-number"}]