Squash chart bars/legend into top-N + Other for many-series panels

PanelChart's BarChart and PieChart rendered one bar/slice and legend
row per PromqlSeries with no bound, so panels with many series wrapped
the 8-color palette (repeating colors) and produced unreadable,
unbounded legends. Add squashRows(), which sorts by value descending
and collapses series beyond COLORS.length - 1 into a single "Other"
bucket (sum of the rest), applied to both bar and pie chart data before
render. Panels at or below the threshold are unaffected.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XFUNZwCvz3kcod3352ZR2o

webapp/src/components/PanelChart.tsx

@@ -25,6 +25,22 @@ export function seriesLabel(labels: Record<string, string>): string {
 // Fixed, small categorical palette to avoid a colour-scale dependency; cycles if there are more series than colours.
 const COLORS = ['#38bdf8', '#f472b6', '#a78bfa', '#4ade80', '#fbbf24', '#fb7185', '#2dd4bf', '#f97316']
 
+// One less than the palette size: above this many series, keep the top MAX_KEPT_SERIES (by value) and squash the
+// rest into a single "Other" bucket, so the squashed range never exceeds COLORS.length and never repeats a colour.
+const MAX_KEPT_SERIES = COLORS.length - 1
+
+// Sorts rows by value descending and, if there are more than MAX_KEPT_SERIES, keeps the top MAX_KEPT_SERIES and
+// collapses the remainder into a single "Other" row summing their values. Below the threshold, rows are returned
+// unchanged so panels with few series keep their existing bar/slice order and colour assignment.
+function squashRows(rows: { name: string; value: number }[]): { name: string; value: number }[] {
+  if (rows.length <= MAX_KEPT_SERIES) return rows
+  const sorted = [...rows].sort((a, b) => b.value - a.value)
+  const kept = sorted.slice(0, MAX_KEPT_SERIES)
+  const rest = sorted.slice(MAX_KEPT_SERIES)
+  const otherValue = rest.reduce((sum, r) => sum + r.value, 0)
+  return [...kept, { name: `Other (${rest.length})`, value: otherValue }]
+}
+
 // Merges series into one row-per-timestamp dataset (recharts wants a single array keyed by series name); a timestamp missing from a series is left undefined there, which recharts skips when drawing that line.
 function toLineData(series: PromqlSeries[]): { rows: Record<string, number | string>[]; keys: string[] } {
   const keys = series.map((s) => seriesLabel(s.labels))
@@ -101,7 +117,7 @@ export function PanelChart({ series, chartType }: { series: PromqlSeries[]; char
   }
 
   if (chartType === 'bar') {
-    const rows = series.map((s) => ({ name: seriesLabel(s.labels), value: latestValue(s) }))
+    const rows = squashRows(series.map((s) => ({ name: seriesLabel(s.labels), value: latestValue(s) })))
     return (
       <ResponsiveContainer width="100%" height={220}>
         <BarChart data={rows} margin={{ top: 8, right: 16, left: 0, bottom: 0 }}>
@@ -119,7 +135,7 @@ export function PanelChart({ series, chartType }: { series: PromqlSeries[]; char
     )
   }
 
-  const rows = series.map((s) => ({ name: seriesLabel(s.labels), value: sumValue(s) }))
+  const rows = squashRows(series.map((s) => ({ name: seriesLabel(s.labels), value: sumValue(s) })))
   const total = rows.reduce((sum, r) => sum + r.value, 0)
   if (total === 0) {
     return <div className="flex h-48 items-center justify-center text-xs text-text-faint">No non-zero values in range.</div>