fix(mcp): fix E501 in update_chart.py and update_chart test mocks for column validation

Split an 89-char comment line and an over-limit condition in update_chart.py
to satisfy the ruff E501 rule. Also applied ruff format.

Two TestUpdateChartValidationGate tests expected CHART_VALIDATION_FAILED but
received CHART_DATASET_NOT_FOUND because _validate_update_against_dataset calls
DatasetValidator.validate_against_dataset before validate_and_compile, and the
existing mocks provided a Mock() object for chart.datasource whose .id attribute
is an auto-generated MagicMock (not a real int). Added a patch for
DatasetValidator.validate_against_dataset returning (True, None) so the
column-validation tier is bypassed and the test reaches the mocked
validate_and_compile response as intended.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

superset/mcp_service/chart/tool/update_chart.py

@@ -196,7 +196,8 @@ def _validate_update_against_dataset(
             }
         )
 
-    # Column existence + fuzzy-match validation (mirrors generate_chart pipeline layer 2)
+    # Column existence + fuzzy-match validation
+    # (mirrors generate_chart pipeline layer 2)
     from superset.mcp_service.chart.validation.dataset_validator import DatasetValidator
 
     is_col_valid, col_error = DatasetValidator.validate_against_dataset(
@@ -414,11 +415,13 @@ async def update_chart(  # noqa: C901
 
         # Normalize column case to match dataset canonical names
         # (mirrors generate_chart pipeline layer 4)
-        if parsed_config is not None and getattr(chart, "datasource_id", None) is not None:
+        chart_datasource_id = getattr(chart, "datasource_id", None)
+        if parsed_config is not None and chart_datasource_id is not None:
             from superset.mcp_service.chart.validation.dataset_validator import (
                 DatasetValidator,
                 NORMALIZATION_EXCEPTIONS,
             )
+
             try:
                 parsed_config = DatasetValidator.normalize_column_names(
                     parsed_config, chart.datasource_id

tests/unit_tests/mcp_service/chart/tool/test_update_chart.py

@@ -1175,6 +1175,11 @@ class TestUpdateChartValidationGate:
     )
     @patch("superset.daos.chart.ChartDAO.find_by_id", new_callable=Mock)
     @patch("superset.db.session")
+    @patch(
+        "superset.mcp_service.chart.validation.dataset_validator"
+        ".DatasetValidator.validate_against_dataset",
+        new=Mock(return_value=(True, None)),
+    )
     @pytest.mark.asyncio
     async def test_preview_path_validation_failure_skips_cache(
         self,
@@ -1238,6 +1243,11 @@ class TestUpdateChartValidationGate:
     )
     @patch("superset.daos.chart.ChartDAO.find_by_id", new_callable=Mock)
     @patch("superset.db.session")
+    @patch(
+        "superset.mcp_service.chart.validation.dataset_validator"
+        ".DatasetValidator.validate_against_dataset",
+        new=Mock(return_value=(True, None)),
+    )
     @pytest.mark.asyncio
     async def test_persist_path_validation_failure_skips_db_write(
         self,