fix: set PlotOptionsFlags on flags data series (#9097)

## Summary

- When the chart-level type differs from `flags` (e.g. `column`), a
`DataSeries` containing `FlagItem` objects would not render as flags
because it lacked `PlotOptionsFlags`
- Adds `applyFlagsPlotOptions()` to `ChartRenderer` that auto-detects
flag series by their data items and sets `PlotOptionsFlags` when
missing, while preserving any pre-configured plot options

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: tomivirkki

vaadin-ai-components-flow-parent/vaadin-ai-components-flow/src/main/java/com/vaadin/flow/component/ai/chart/ChartRenderer.java

@@ -31,7 +31,9 @@
 import com.vaadin.flow.component.charts.model.Configuration;
 import com.vaadin.flow.component.charts.model.DataSeries;
 import com.vaadin.flow.component.charts.model.DataSeriesItem;
+import com.vaadin.flow.component.charts.model.FlagItem;
 import com.vaadin.flow.component.charts.model.GanttSeries;
+import com.vaadin.flow.component.charts.model.PlotOptionsFlags;
 import com.vaadin.flow.component.charts.model.Series;
 
 /**
@@ -94,6 +96,7 @@ public static void renderChart(Chart chart,
         nameUnnamedSeries(config, allSeries);
 
         applySeriesConfig(allSeries, seriesConfig);
+        applyFlagsPlotOptions(allSeries);
 
         // Apply axis defaults from series data after LLM config,
         // so that data-driven axis type detection (e.g. datetime)
@@ -222,6 +225,27 @@ private static void nameUnnamedSeries(Configuration config,
         }
     }
 
+    /**
+     * Ensures any DataSeries containing FlagItem objects has PlotOptionsFlags
+     * set, so flags render correctly even when the chart-level type is
+     * different (e.g. column).
+     */
+    private static void applyFlagsPlotOptions(List<Series> allSeries) {
+        for (var series : allSeries) {
+            if (!(series instanceof DataSeries ds)) {
+                continue;
+            }
+            if (ds.getPlotOptions() instanceof PlotOptionsFlags) {
+                continue;
+            }
+            boolean hasFlags = ds.getData().stream()
+                    .anyMatch(FlagItem.class::isInstance);
+            if (hasFlags) {
+                ds.setPlotOptions(new PlotOptionsFlags());
+            }
+        }
+    }
+
     /**
      * Extracts per-series configuration (plot options, y-axis) from the
      * configuration's current series, keyed by series name. These are

vaadin-ai-components-flow-parent/vaadin-ai-components-flow/src/test/java/com/vaadin/flow/component/ai/chart/ChartRenderingTest.java

@@ -35,6 +35,7 @@
 import com.vaadin.flow.component.charts.model.DataSeries;
 import com.vaadin.flow.component.charts.model.DataSeriesItem;
 import com.vaadin.flow.component.charts.model.OhlcItem;
+import com.vaadin.flow.component.charts.model.PlotOptionsFlags;
 import com.vaadin.flow.component.charts.util.ChartSerialization;
 import com.vaadin.tests.MockUIExtension;
 
@@ -1046,6 +1047,54 @@ void waterfallWithSumItemsCategoriesIncludeSumNames() {
 
     // --- Helpers ---
 
+    @Nested
+    class FlagsChart {
+
+        @Test
+        void flagsSeriesRendersAsFlagsOnColumnChart() {
+            databaseProvider.results = List
+                    .of(row("_title", "Launch", "_text", "Product launch"));
+
+            updateConfiguration("{\"chart\":{\"type\":\"column\"}}");
+            updateData("SELECT title AS _title, text AS _text FROM flags");
+            controller.onRequestCompleted();
+
+            var series = chart.getConfiguration().getSeries();
+            Assertions.assertEquals(1, series.size());
+
+            var flagsSeries = (DataSeries) series.getFirst();
+            Assertions.assertInstanceOf(PlotOptionsFlags.class,
+                    flagsSeries.getPlotOptions(),
+                    "Flags series should have PlotOptionsFlags "
+                            + "regardless of chart-level type");
+        }
+
+        @Test
+        void flagsSeriesPreservesExistingPlotOptionsFlags() {
+            databaseProvider.results = List
+                    .of(row("_title", "Launch", "_text", "Product launch"));
+
+            updateConfiguration("{\"chart\":{\"type\":\"line\"},"
+                    + "\"title\":{\"text\":\"Events\"},"
+                    + "\"series\":[{\"name\":\"Events\","
+                    + "\"type\":\"flags\","
+                    + "\"plotOptions\":{\"onSeries\":\"price\"}}]}");
+            updateData("SELECT title AS _title, text AS _text FROM flags");
+            controller.onRequestCompleted();
+
+            var series = chart.getConfiguration().getSeries();
+            Assertions.assertEquals(1, series.size());
+
+            var flagsSeries = (DataSeries) series.getFirst();
+            var plotOptions = flagsSeries.getPlotOptions();
+            Assertions.assertInstanceOf(PlotOptionsFlags.class, plotOptions,
+                    "Flags series should have PlotOptionsFlags");
+            Assertions.assertEquals("price",
+                    ((PlotOptionsFlags) plotOptions).getOnSeries(),
+                    "Pre-configured onSeries should be preserved");
+        }
+    }
+
     private static Map<String, Object> row(Object... kvPairs) {
         Map<String, Object> map = new LinkedHashMap<>();
         for (int i = 0; i < kvPairs.length; i += 2) {