feat(mcp): add series_limit to generate_chart XY config

Add series_limit parameter to XYChartConfig so callers can control
how many distinct series (group_by values) the chart renders.  When
set, the value is forwarded as form_data["series_limit"], which
Superset's echarts timeseries plugins interpret to cap the number of
rendered series lines/bars.

superset/mcp_service/chart/chart_utils.py

@@ -648,7 +648,7 @@ def _resolve_default_x_axis(
     return config.model_copy(update={"x": ColumnRef(name=dataset.main_dttm_col)})
 
 
-def map_xy_config(
+def map_xy_config(  # noqa: C901
     config: XYChartConfig, dataset_id: int | str | None = None
 ) -> Dict[str, Any]:
     """Map XY chart config to form_data with defensive validation."""
@@ -714,6 +714,9 @@ def map_xy_config(
 
     form_data["row_limit"] = config.row_limit
 
+    if config.series_limit is not None:
+        form_data["series_limit"] = config.series_limit
+
     # Add stacking configuration
     if getattr(config, "stacked", False):
         form_data["stack"] = "Stack"

superset/mcp_service/chart/schemas.py

@@ -1304,6 +1304,16 @@ class XYChartConfig(UnknownFieldCheckMixin):
         "Do NOT use adhoc_filters or raw SQL expressions.",
     )
     row_limit: int = Field(10000, description="Max data points", ge=1, le=50000)
+    series_limit: int | None = Field(
+        None,
+        description=(
+            "Max number of series to show when group_by is set. "
+            "Limits the distinct values rendered as separate lines/bars. "
+            "Only applies when group_by is specified."
+        ),
+        ge=1,
+        le=10000,
+    )
 
     @field_validator("group_by", mode="before")
     @classmethod

tests/unit_tests/mcp_service/chart/test_chart_schemas.py

@@ -452,6 +452,43 @@ class TestRowLimit:
                 row_limit=100000,
             )
 
+    def test_xy_chart_series_limit_default_none(self) -> None:
+        """Test that XYChartConfig series_limit defaults to None."""
+        config = XYChartConfig(
+            chart_type="xy",
+            x=ColumnRef(name="date"),
+            y=[ColumnRef(name="revenue", aggregate="SUM")],
+        )
+        assert config.series_limit is None
+
+    def test_xy_chart_series_limit_custom(self) -> None:
+        """Test that XYChartConfig accepts a custom series_limit."""
+        config = XYChartConfig(
+            chart_type="xy",
+            x=ColumnRef(name="date"),
+            y=[ColumnRef(name="revenue", aggregate="SUM")],
+            group_by=[ColumnRef(name="region")],
+            series_limit=5,
+        )
+        assert config.series_limit == 5
+
+    def test_xy_chart_series_limit_validation(self) -> None:
+        """Test that XYChartConfig rejects invalid series_limit values."""
+        with pytest.raises(ValidationError):
+            XYChartConfig(
+                chart_type="xy",
+                x=ColumnRef(name="date"),
+                y=[ColumnRef(name="revenue", aggregate="SUM")],
+                series_limit=0,
+            )
+        with pytest.raises(ValidationError):
+            XYChartConfig(
+                chart_type="xy",
+                x=ColumnRef(name="date"),
+                y=[ColumnRef(name="revenue", aggregate="SUM")],
+                series_limit=10001,
+            )
+
     def test_table_chart_default_row_limit(self) -> None:
         """Test that TableChartConfig has default row_limit of 1000."""
         config = TableChartConfig(

tests/unit_tests/mcp_service/chart/test_chart_utils.py

@@ -804,6 +804,38 @@ class TestMapXYConfig:
 
         assert result["row_limit"] == 10000
 
+    @patch("superset.mcp_service.chart.chart_utils.is_column_truly_temporal")
+    def test_map_xy_config_series_limit(self, mock_is_temporal) -> None:
+        """Test that series_limit is mapped to form_data when set."""
+        mock_is_temporal.return_value = True
+        config = XYChartConfig(
+            chart_type="xy",
+            x=ColumnRef(name="date"),
+            y=[ColumnRef(name="revenue", aggregate="SUM")],
+            kind="line",
+            group_by=[ColumnRef(name="region")],
+            series_limit=10,
+        )
+
+        result = map_xy_config(config)
+
+        assert result["series_limit"] == 10
+
+    @patch("superset.mcp_service.chart.chart_utils.is_column_truly_temporal")
+    def test_map_xy_config_no_series_limit_by_default(self, mock_is_temporal) -> None:
+        """Test that series_limit is omitted from form_data when not set."""
+        mock_is_temporal.return_value = True
+        config = XYChartConfig(
+            chart_type="xy",
+            x=ColumnRef(name="date"),
+            y=[ColumnRef(name="revenue", aggregate="SUM")],
+            kind="line",
+        )
+
+        result = map_xy_config(config)
+
+        assert "series_limit" not in result
+
     @patch("superset.mcp_service.chart.chart_utils.is_column_truly_temporal")
     def test_map_xy_config_saved_metric(self, mock_is_temporal: Any) -> None:
         """Test XY config with saved metric emits string in metrics list"""