keep hidden events hidden across date-range changes

Clicking a legend item on the events chart toggled hidden via
chart.current.getDatasetMeta(idx).hidden, which lives on Chart.js's
per-dataset meta object. Each time chartData changed (date-range
switch, refetch, focusLabel update) the second useEffect in Chart.tsx
replaces datasets wholesale, Chart.js regenerates the meta, and the
hidden flags vanish, so previously-toggled-off events came back on
their own.

Lift the hidden state into React. EventsChart owns a Set<string> of
hidden labels and passes it down via a new optional hiddenLabels prop
on Chart, plus an onLegendClick callback for controlled toggling.
Chart re-applies hidden after the existing focusLabel pass so the set
survives every data refresh, and falls back to the original
meta-based behaviour when no callback is provided so other charts
(website overview, revenue) keep their existing semantics.

Verified with the seeded Demo SaaS data: hide signup_started in the
Last 24 hours view, switch to Last 7 days then Last 30 days, the
label stays greyed in the legend and absent from the bars; clicking
again restores it. State is component-scoped, so it intentionally
resets on reload or navigation away from the events page.

src/components/charts/Chart.tsx

@@ -18,6 +18,8 @@ export interface ChartProps extends BoxProps {
   updateMode?: UpdateMode;
   animationDuration?: number;
   onTooltip?: (model: any) => void;
+  hiddenLabels?: Set<string>;
+  onLegendClick?: (label: string, willBeHidden: boolean) => void;
 }
 
 export function Chart({
@@ -27,6 +29,8 @@ export function Chart({
   updateMode,
   onTooltip,
   chartOptions,
+  hiddenLabels,
+  onLegendClick,
   ...props
 }: ChartProps) {
   const canvas = useRef(null);
@@ -61,6 +65,15 @@ export function Chart({
   }, [chartOptions]);
 
   const handleLegendClick = (item: LegendItem) => {
+    if (onLegendClick && type === 'bar') {
+      // Controlled mode: caller owns the hidden state. We report the click
+      // and let the parent push a new hiddenLabels set on the next render.
+      const { datasetIndex } = item;
+      const ds = chart.current.data.datasets[datasetIndex];
+      onLegendClick(ds.label, !ds.hidden);
+      return;
+    }
+
     if (type === 'bar') {
       const { datasetIndex } = item;
       const meta = chart.current.getDatasetMeta(datasetIndex);
@@ -111,13 +124,24 @@ export function Chart({
         });
       }
 
+      // Re-apply caller-driven hidden flags after focusLabel handling so a
+      // dataset stays hidden across data changes (e.g. date-range switches)
+      // even though Chart.js regenerates dataset meta on every replace.
+      if (hiddenLabels) {
+        chart.current.data.datasets.forEach((ds: { hidden: boolean; label: any }) => {
+          if (hiddenLabels.has(ds.label)) {
+            ds.hidden = true;
+          }
+        });
+      }
+
       chart.current.options = options;
 
       chart.current.update(updateMode);
 
       setLegendItems(chart.current.legend.legendItems);
     }
-  }, [chartData, options, updateMode]);
+  }, [chartData, options, updateMode, hiddenLabels]);
 
   return (
     <Column gap="6">

src/components/metrics/EventsChart.tsx

@@ -26,6 +26,16 @@ export function EventsChart({ websiteId, focusLabel, limit }: EventsChartProps)
   const { locale, dateLocale } = useLocale();
   const { data, isLoading, error } = useWebsiteEventsSeriesQuery(websiteId, { limit });
   const [label, setLabel] = useState<string>(focusLabel);
+  const [hiddenLabels, setHiddenLabels] = useState<Set<string>>(() => new Set());
+
+  const handleLegendClick = useCallback((legendLabel: string, willBeHidden: boolean) => {
+    setHiddenLabels(prev => {
+      const next = new Set(prev);
+      if (willBeHidden) next.add(legendLabel);
+      else next.delete(legendLabel);
+      return next;
+    });
+  }, []);
 
   const chartData: any = useMemo(() => {
     if (!data) return;
@@ -87,6 +97,8 @@ export function EventsChart({ websiteId, focusLabel, limit }: EventsChartProps)
           stacked={true}
           renderXLabel={renderXLabel}
           height="400px"
+          hiddenLabels={hiddenLabels}
+          onLegendClick={handleLegendClick}
         />
       )}
     </LoadingPanel>