fix(scada): preserve observation fields in chart evidence

tests/unit/test_mcp_query.py

@@ -1116,6 +1116,31 @@ def test_time_series_sql_is_bounded_and_field_names_cannot_inject_sql():
     asyncio.run(check())
 
 
+@pytest.mark.parametrize("field", ["monitored_value", "cleaned_value"])
+def test_scada_detail_preserves_the_requested_field_with_its_value_alias(monkeypatch, field):
+    at = datetime.now(timezone.utc)
+    monkeypatch.setattr(query_service, "permissions_for_context", lambda ctx: PERMISSIONS)
+    monkeypatch.setattr(query_service.reads, "series_rows", AsyncMock(return_value=[{
+        "device_id": "D1", "time": at, "value": 32.0,
+    }]))
+    monkeypatch.setattr(query_service.reads, "scada_devices", AsyncMock(return_value=[{
+        "device_id": "D1", "measurement_unit": "m",
+    }]))
+
+    class Scope:
+        project = object()
+        connection = Connection()
+
+        @asynccontextmanager
+        async def timescale(self):
+            yield self.connection
+
+    args = ScadaInput(context_handle="a" * 43, device_ids=["D1"], field=field,
+                      start=at - timedelta(hours=3), end=at)
+    result = asyncio.run(query_service.execute_query(Scope(), binding(), TOOLS["query_scada_readings"], args))
+    assert result.data[0][field] == result.data[0]["value"] == 32.0
+
+
 def test_analysis_preserves_run_units_and_reports_inference(monkeypatch):
     from app.mcp.models import AnalysisValuesInput
     from unittest.mock import AsyncMock