chore: scatter plot base work

frontend/__mocks__/uplotMock.ts

@@ -48,6 +48,7 @@ const mockPaths = {
 const mockTzDate = jest.fn(
 	(date: Date, _timezone: string) => new Date(date.getTime()),
 );
+const mockOrient = jest.fn();
 
 // Mock uPlot constructor - this needs to be a proper constructor function
 function MockUPlot(
@@ -61,6 +62,9 @@ function MockUPlot(
 // Add static methods to the constructor
 MockUPlot.tzDate = mockTzDate;
 MockUPlot.paths = mockPaths;
+MockUPlot.orient = mockOrient;
+// Pinned so canvas-space maths in path builders is deterministic under jsdom.
+MockUPlot.pxRatio = 1;
 
 // Export the constructor as default
 export default MockUPlot;

frontend/src/lib/uPlotV2/components/Tooltip/ScatterTooltip.module.scss

@@ -0,0 +1,100 @@
+// Surface matches the shared Tooltip: same tokens, same radius, no shadow.
+// Padding lives on the sections so a footer can reach the container edges.
+.container {
+	font-family: 'Inter';
+	font-size: 12px;
+	background: var(--l2-background);
+	-webkit-font-smoothing: antialiased;
+	color: var(--l2-foreground);
+	border-radius: 6px;
+	border: 1px solid var(--l2-border);
+	display: flex;
+	flex-direction: column;
+	min-width: 200px;
+
+	&.pinned {
+		border-color: var(--ring);
+	}
+}
+
+.divider {
+	display: block;
+	width: 100%;
+	height: 1px;
+	background-color: var(--l2-border);
+}
+
+.header {
+	display: flex;
+	align-items: center;
+	gap: var(--spacing-2);
+	padding: var(--spacing-3) var(--spacing-4);
+}
+
+// Matches the legend row's marker.
+.marker {
+	width: 10px;
+	height: 10px;
+	border-radius: var(--radius);
+	flex-shrink: 0;
+}
+
+.title {
+	flex: 1;
+	min-width: 0;
+	font-family: var(--font-mono);
+	font-size: var(--font-size-xs);
+	font-weight: 600;
+	color: var(--text-vanilla-100);
+	overflow: hidden;
+	text-overflow: ellipsis;
+	white-space: nowrap;
+}
+
+.status {
+	display: flex;
+	align-items: center;
+	gap: var(--spacing-1);
+	font-size: 11px;
+	color: var(--text-vanilla-400);
+	flex-shrink: 0;
+}
+
+.rows {
+	display: flex;
+	flex-direction: column;
+	gap: var(--spacing-1);
+	padding: var(--spacing-3) var(--spacing-4);
+}
+
+.row {
+	display: flex;
+	align-items: baseline;
+	justify-content: space-between;
+	gap: var(--spacing-4);
+	font-family: var(--font-mono);
+	font-size: var(--font-size-xs);
+	font-variant-numeric: tabular-nums;
+	color: var(--text-vanilla-100);
+}
+
+// The group values name the point; the channels are what it says.
+.rowMuted {
+	color: var(--text-vanilla-400);
+}
+
+.rowLabel {
+	flex: 1;
+	min-width: 0;
+	overflow: hidden;
+	text-overflow: ellipsis;
+	white-space: nowrap;
+}
+
+.rowValue {
+	flex: 0 0 auto;
+	max-width: 60%;
+	overflow: hidden;
+	text-overflow: ellipsis;
+	white-space: nowrap;
+}

frontend/src/lib/uPlotV2/components/Tooltip/ScatterTooltip.tsx

@@ -0,0 +1,111 @@
+import { useMemo } from 'react';
+import cx from 'classnames';
+import { Pin } from '@signozhq/icons';
+
+import { ScatterTooltipProps } from '../types';
+import { buildChannelRows, resolveHoveredPoint } from './scatterTooltipContent';
+
+import Styles from './ScatterTooltip.module.scss';
+
+/**
+ * One point, its channels, then the group values that name it. Purpose-built
+ * rather than composed from the shared `Tooltip`, whose list is one row per
+ * series at a shared x; a scatter point has no such neighbours.
+ */
+export default function ScatterTooltip({
+	uPlotInstance,
+	dataIndexes,
+	seriesIndex,
+	channels,
+	resolvePointLabels,
+	decimalPrecision,
+	isPinned,
+	dismiss,
+	renderTooltipFooter,
+}: ScatterTooltipProps): JSX.Element | null {
+	const point = useMemo(
+		() => resolveHoveredPoint(uPlotInstance, seriesIndex, dataIndexes),
+		[uPlotInstance, seriesIndex, dataIndexes],
+	);
+
+	const rows = useMemo(
+		() => (point ? buildChannelRows(point, channels, decimalPrecision) : []),
+		[point, channels, decimalPrecision],
+	);
+
+	const labels = useMemo(
+		() =>
+			point
+				? (resolvePointLabels?.(point.seriesIndex, point.dataIndex) ?? [])
+				: [],
+		[point, resolvePointLabels],
+	);
+
+	if (!point) {
+		return null;
+	}
+
+	return (
+		<div
+			className={cx(Styles.container, { [Styles.pinned]: isPinned })}
+			data-pinned={isPinned}
+			data-testid="scatter-tooltip"
+		>
+			<div className={Styles.header}>
+				<span className={Styles.marker} style={{ backgroundColor: point.color }} />
+				<span
+					className={Styles.title}
+					title={point.label}
+					data-testid="scatter-tooltip-title"
+				>
+					{point.label}
+				</span>
+				{isPinned && (
+					<span className={Styles.status} data-testid="scatter-tooltip-status">
+						<Pin size={12} />
+						<span>Pinned</span>
+					</span>
+				)}
+			</div>
+
+			<span className={Styles.divider} />
+
+			<div className={Styles.rows}>
+				{rows.map((row) => (
+					<div
+						key={row.label}
+						className={Styles.row}
+						data-testid="scatter-tooltip-row"
+					>
+						<span className={Styles.rowLabel}>{row.label}</span>
+						<span className={Styles.rowValue}>{row.value}</span>
+					</div>
+				))}
+			</div>
+
+			{labels.length > 0 && (
+				<>
+					<span className={Styles.divider} />
+					<div className={Styles.rows}>
+						{labels.map((label) => (
+							<div
+								key={label.key}
+								className={cx(Styles.row, Styles.rowMuted)}
+								data-testid="scatter-tooltip-label"
+							>
+								<span className={Styles.rowLabel} title={label.key}>
+									{label.key}
+								</span>
+								<span className={Styles.rowValue} title={label.value}>
+									{label.value}
+								</span>
+							</div>
+						))}
+					</div>
+				</>
+			)}
+
+			{renderTooltipFooter?.({ isPinned, dismiss })}
+		</div>
+	);
+}

frontend/src/lib/uPlotV2/components/Tooltip/__tests__/scatterTooltipContent.test.ts

@@ -0,0 +1,94 @@
+import type uPlot from 'uplot';
+
+import {
+	buildChannelRows,
+	resolveHoveredPoint,
+	ScatterHoveredPoint,
+} from '../scatterTooltipContent';
+
+jest.mock('components/Graph/yAxisConfig', () => ({
+	getToolTipValue: jest.fn((value: number | string, unit?: string) =>
+		`${value} ${unit ?? ''}`.trim(),
+	),
+}));
+
+const plot = {
+	data: [
+		null,
+		[
+			[10, 20],
+			[100, 200],
+			[5, null],
+		],
+		[[30], [300]],
+	],
+	series: [
+		{},
+		{ label: 'cart', stroke: '#ff0000' },
+		{ label: 'checkout', stroke: (): string => '#00ff00' },
+	],
+} as unknown as uPlot;
+
+describe('resolveHoveredPoint', () => {
+	it('reads the focused series at its own data index', () => {
+		expect(resolveHoveredPoint(plot, 1, [null, 1, null])).toStrictEqual({
+			seriesIndex: 1,
+			dataIndex: 1,
+			label: 'cart',
+			color: '#ff0000',
+			x: 20,
+			y: 200,
+			size: null,
+		});
+	});
+
+	it('carries the size column when present and resolves function strokes', () => {
+		expect(resolveHoveredPoint(plot, 1, [null, 0, null])?.size).toBe(5);
+		expect(resolveHoveredPoint(plot, 2, [null, null, 0])).toMatchObject({
+			label: 'checkout',
+			color: '#00ff00',
+			size: null,
+		});
+	});
+
+	it('is null without a focused series or an index for it', () => {
+		expect(resolveHoveredPoint(plot, null, [null, 0, null])).toBeNull();
+		expect(resolveHoveredPoint(plot, 0, [0, 0, null])).toBeNull();
+		expect(resolveHoveredPoint(plot, 1, [null, null, null])).toBeNull();
+	});
+});
+
+describe('buildChannelRows', () => {
+	const point: ScatterHoveredPoint = {
+		seriesIndex: 1,
+		dataIndex: 0,
+		label: 'cart',
+		color: '#f00',
+		x: 12,
+		y: 340,
+		size: 7,
+	};
+
+	it('formats x and y with their own units', () => {
+		const rows = buildChannelRows(point, {
+			x: { label: 'Throughput', unit: 'reqps' },
+			y: { label: 'p99', unit: 'ms' },
+		});
+
+		expect(rows).toStrictEqual([
+			{ label: 'Throughput', value: '12 reqps' },
+			{ label: 'p99', value: '340 ms' },
+		]);
+	});
+
+	it('adds the size row only when the channel is mapped and the point has one', () => {
+		const channels = {
+			x: { label: 'x' },
+			y: { label: 'y' },
+			size: { label: 'Errors' },
+		};
+
+		expect(buildChannelRows(point, channels)).toHaveLength(3);
+		expect(buildChannelRows({ ...point, size: null }, channels)).toHaveLength(2);
+	});
+});

frontend/src/lib/uPlotV2/components/Tooltip/scatterTooltipContent.ts

@@ -0,0 +1,90 @@
+import { PrecisionOption } from 'components/Graph/types';
+import { getToolTipValue } from 'components/Graph/yAxisConfig';
+import type uPlot from 'uplot';
+
+import type {
+	ScatterChannel,
+	ScatterChannels,
+	ScatterSeriesData,
+} from '../../plugins/ScatterPlugin/types';
+import { resolveSeriesColor } from './utils';
+
+export interface ScatterHoveredPoint {
+	seriesIndex: number;
+	dataIndex: number;
+	label: string;
+	color: string;
+	x: number;
+	y: number;
+	size: number | null;
+}
+
+export interface ScatterTooltipRow {
+	label: string;
+	value: string;
+}
+
+/** The point the cursor resolved to: the focused series' own index into its columns. */
+export function resolveHoveredPoint(
+	u: uPlot,
+	seriesIndex: number | null,
+	dataIndexes: Array<number | null>,
+): ScatterHoveredPoint | null {
+	if (seriesIndex == null || seriesIndex < 1) {
+		return null;
+	}
+	const dataIndex = dataIndexes[seriesIndex];
+	const series = u.series[seriesIndex];
+	const columns = u.data[seriesIndex] as unknown as
+		| ScatterSeriesData
+		| undefined;
+	if (dataIndex == null || !series || !columns) {
+		return null;
+	}
+	const x = columns[0][dataIndex];
+	const y = columns[1][dataIndex];
+	if (x == null || y == null) {
+		return null;
+	}
+	return {
+		seriesIndex,
+		dataIndex,
+		label: String(series.label ?? ''),
+		color: resolveSeriesColor(series.stroke, u, seriesIndex),
+		x,
+		y,
+		size: columns[2]?.[dataIndex] ?? null,
+	};
+}
+
+function formatChannel(
+	value: number,
+	channel: ScatterChannel,
+	decimalPrecision?: PrecisionOption,
+): string {
+	return getToolTipValue(value, channel.unit, decimalPrecision);
+}
+
+export function buildChannelRows(
+	point: ScatterHoveredPoint,
+	channels: ScatterChannels,
+	decimalPrecision?: PrecisionOption,
+): ScatterTooltipRow[] {
+	const rows: ScatterTooltipRow[] = [
+		{
+			label: channels.x.label,
+			value: formatChannel(point.x, channels.x, decimalPrecision),
+		},
+		{
+			label: channels.y.label,
+			value: formatChannel(point.y, channels.y, decimalPrecision),
+		},
+	];
+	if (channels.size && point.size != null) {
+		rows.push({
+			label: channels.size.label,
+			value: formatChannel(point.size, channels.size, decimalPrecision),
+		});
+	}
+	return rows;
+}

frontend/src/lib/uPlotV2/components/types.ts

@@ -5,6 +5,10 @@ import uPlot from 'uplot';
 
 import { UPlotConfigBuilder } from '../config/UPlotConfigBuilder';
 import { LegendItem } from '../config/types';
+import type {
+	ScatterChannels,
+	ScatterPointLabel,
+} from '../plugins/ScatterPlugin/types';
 import { SyncTooltipFilterMode } from '../plugins/TooltipPlugin/types';
 
 /**
@@ -103,6 +107,17 @@ export interface BarTooltipProps extends BaseTooltipProps, TooltipRenderArgs {
 export interface HistogramTooltipProps
 	extends BaseTooltipProps, TooltipRenderArgs {}
 
+/** Not part of `TooltipProps`: it describes one point's channels, not a series list. */
+export interface ScatterTooltipProps
+	extends BaseTooltipProps, TooltipRenderArgs {
+	channels: ScatterChannels;
+	/** The group values behind a point, e.g. `service.name` → `cart`. */
+	resolvePointLabels?: (
+		seriesIndex: number,
+		dataIndex: number,
+	) => ScatterPointLabel[];
+}
+
 export type TooltipProps =
 	| TimeSeriesTooltipProps
 	| BarTooltipProps

frontend/src/lib/uPlotV2/config/UPlotAxisBuilder.ts

@@ -58,32 +58,49 @@ export class UPlotAxisBuilder extends ConfigBuilder<AxisProps, Axis> {
 	}
 
 	/**
-	 * Build values formatter for X-axis (time)
+	 * Build values formatter for X-axis: time, or a value axis when a unit or
+	 * precision is given (scatter). Neither leaves uPlot's numeric default.
 	 */
 	private buildXAxisValuesFormatter(): uPlot.Axis.Values | undefined {
-		const { isTimeAxis } = this.props;
+		const { isTimeAxis, yAxisUnit, decimalPrecision } = this.props;
 
 		if (isTimeAxis) {
 			return uPlotXAxisValuesFormat as uPlot.Axis.Values;
 		}
 
+		if (yAxisUnit !== undefined || decimalPrecision !== undefined) {
+			return this.buildValueAxisFormatter();
+		}
+
 		return undefined;
 	}
 
 	/**
-	 * Build values formatter for Y-axis (values with units)
+	 * Build values formatter for a value axis (values with units). A split outside
+	 * the scale's range gets no label: uPlot's arcsinh splits always include
+	 * ±threshold, and it would draw that label past the plot's edge.
 	 */
-	private buildYAxisValuesFormatter(): uPlot.Axis.Values {
-		const { yAxisUnit, decimalPrecision } = this.props;
+	private buildValueAxisFormatter(): uPlot.Axis.Values {
+		const { yAxisUnit, decimalPrecision, scaleKey } = this.props;
 
-		return (_, t): string[] =>
-			t.map((v) => {
-				if (v === null || v === undefined || Number.isNaN(v)) {
+		return (u, t): string[] => {
+			const scale = u?.scales?.[scaleKey];
+			const min = scale?.min ?? -Infinity;
+			const max = scale?.max ?? Infinity;
+			return t.map((v) => {
+				if (
+					v === null ||
+					v === undefined ||
+					Number.isNaN(v) ||
+					v < min ||
+					v > max
+				) {
 					return '';
 				}
 				const value = getToolTipValue(v.toString(), yAxisUnit, decimalPrecision);
 				return `${value}`;
 			});
+		};
 	}
 
 	/**
@@ -101,7 +118,7 @@ export class UPlotAxisBuilder extends ConfigBuilder<AxisProps, Axis> {
 		return scaleKey === 'x'
 			? this.buildXAxisValuesFormatter()
 			: scaleKey === 'y'
-				? this.buildYAxisValuesFormatter()
+				? this.buildValueAxisFormatter()
 				: undefined;
 	}
 

frontend/src/lib/uPlotV2/config/UPlotConfigBuilder.ts

@@ -19,6 +19,7 @@ import {
 	ConfigBuilder,
 	ConfigBuilderProps,
 	LegendItem,
+	PlotMode,
 	SelectionPreferencesSource,
 	StackMode,
 } from './types';
@@ -65,6 +66,8 @@ export class UPlotConfigBuilder extends ConfigBuilder<
 
 	private stackMode: StackMode = StackMode.None;
 
+	private mode: PlotMode = PlotMode.Aligned;
+
 	private cursor: Cursor | undefined;
 
 	private hooks: Hooks.Arrays = {};
@@ -160,6 +163,15 @@ export class UPlotConfigBuilder extends ConfigBuilder<
 		return this.stackMode;
 	}
 
+	/** Faceted series carry their own x column each; see `SeriesProps.facets`. */
+	setMode(mode: PlotMode): void {
+		this.mode = mode;
+	}
+
+	getMode(): PlotMode {
+		return this.mode;
+	}
+
 	/**
 	 * Add or merge a scale configuration
 	 */
@@ -512,6 +524,10 @@ export class UPlotConfigBuilder extends ConfigBuilder<
 			{} as Record<string, uPlot.Scale>,
 		);
 
+		if (this.mode === PlotMode.Faceted) {
+			config.mode = this.mode as number as uPlot.Mode;
+		}
+
 		config.hooks = this.hooks;
 		config.select = this.select;
 

frontend/src/lib/uPlotV2/config/UPlotScaleBuilder.ts

@@ -93,6 +93,7 @@ export class UPlotScaleBuilder extends ConfigBuilder<
 			time,
 			distr,
 			logBase,
+			asinhThreshold: this.props.asinhThreshold,
 		});
 
 		const { rangeConfig, hardMinOnly, hardMaxOnly, hasFixedRange } =

frontend/src/lib/uPlotV2/config/UPlotSeriesBuilder.ts

@@ -87,6 +87,8 @@ export class UPlotSeriesBuilder extends ConfigBuilder<
 			lineConfig.fill = finalFillColor;
 		} else if (this.props.drawStyle === DrawStyle.Histogram) {
 			lineConfig.fill = `${finalFillColor}40`;
+		} else if (this.props.drawStyle === DrawStyle.Scatter) {
+			lineConfig.fill = `${finalFillColor}${toAlphaHex(resolveFillOpacity(fillOpacity))}`;
 		} else if (fillMode && fillMode !== FillMode.None) {
 			const resolvedOpacity = resolveFillOpacity(fillOpacity);
 			if (fillMode === FillMode.Solid) {
@@ -122,7 +124,8 @@ export class UPlotSeriesBuilder extends ConfigBuilder<
 			return { paths: pathBuilder };
 		}
 
-		if (drawStyle === DrawStyle.Points) {
+		// Scatter without a `pathBuilder` has nothing to draw its discs with.
+		if (drawStyle === DrawStyle.Points || drawStyle === DrawStyle.Scatter) {
 			return { paths: (): null => null };
 		}
 
@@ -194,6 +197,10 @@ export class UPlotSeriesBuilder extends ConfigBuilder<
 		if (drawStyle === DrawStyle.Points) {
 			return true;
 		}
+		// The discs are the series path; uPlot's own points would double-draw them.
+		if (drawStyle === DrawStyle.Scatter) {
+			return false;
+		}
 		return !!showPoints;
 	}
 
@@ -218,7 +225,7 @@ export class UPlotSeriesBuilder extends ConfigBuilder<
 	}
 
 	getConfig(): ExtendedSeries {
-		const { scaleKey, label, spanGaps, show = true, metric } = this.props;
+		const { scaleKey, label, spanGaps, show = true, metric, facets } = this.props;
 
 		const resolvedLineColor = this.getLineColor();
 
@@ -246,6 +253,7 @@ export class UPlotSeriesBuilder extends ConfigBuilder<
 			...pathConfig,
 			points: Object.keys(pointsConfig).length > 0 ? pointsConfig : undefined,
 			metric,
+			...(facets && { facets }),
 		};
 	}
 }

frontend/src/lib/uPlotV2/config/__tests__/UPlotAxisBuilder.test.ts

@@ -376,3 +376,51 @@ describe('UPlotAxisBuilder', () => {
 		expect(config.values).toBeDefined();
 	});
 });
+
+describe('UPlotAxisBuilder value x axis', () => {
+	it('formats a non-time x axis with its unit', () => {
+		(getToolTipValue as jest.Mock).mockReturnValue('1.2K req/s');
+		const config = new UPlotAxisBuilder(
+			createAxisProps({ scaleKey: 'x', isTimeAxis: false, yAxisUnit: 'reqps' }),
+		).getConfig();
+
+		const values = (config.values as uPlot.Axis.DynamicValues)(
+			{} as uPlot,
+			[1200],
+			0,
+			0,
+			0,
+		);
+
+		expect(values).toStrictEqual(['1.2K req/s']);
+		expect(getToolTipValue).toHaveBeenCalledWith('1200', 'reqps', undefined);
+	});
+
+	it('leaves a non-time x axis to uPlot when nothing says how to format it', () => {
+		const config = new UPlotAxisBuilder(
+			createAxisProps({ scaleKey: 'x', isTimeAxis: false }),
+		).getConfig();
+
+		expect(config.values).toBeUndefined();
+	});
+});
+
+describe('UPlotAxisBuilder out-of-range splits', () => {
+	it('leaves a split the scale cannot place unlabelled', () => {
+		(getToolTipValue as jest.Mock).mockImplementation((v: string) => `${v} ms`);
+		const config = new UPlotAxisBuilder(
+			createAxisProps({ scaleKey: 'y', yAxisUnit: 'ms' }),
+		).getConfig();
+		const u = { scales: { y: { min: 0, max: 1000 } } } as unknown as uPlot;
+
+		const values = (config.values as uPlot.Axis.DynamicValues)(
+			u,
+			[-10, 0, 500, 5000],
+			0,
+			0,
+			0,
+		);
+
+		expect(values).toStrictEqual(['', '0 ms', '500 ms', '']);
+	});
+});

frontend/src/lib/uPlotV2/config/__tests__/UPlotConfigBuilder.test.ts

@@ -5,7 +5,12 @@ import {
 	STEP_INTERVAL_MULTIPLIER,
 } from '../../constants';
 import type { SeriesProps } from '../types';
-import { DrawStyle, SelectionPreferencesSource, StackMode } from '../types';
+import {
+	DrawStyle,
+	PlotMode,
+	SelectionPreferencesSource,
+	StackMode,
+} from '../types';
 import { UPlotConfigBuilder } from '../UPlotConfigBuilder';
 
 // Mock only the real boundary that hits localStorage
@@ -651,3 +656,15 @@ describe('UPlotConfigBuilder stacking', () => {
 		expect(builder.getConfig().bands).toStrictEqual([{ series: [1, 3] }]);
 	});
 });
+
+describe('UPlotConfigBuilder plot mode', () => {
+	it('leaves mode unset for aligned data and emits 2 when faceted', () => {
+		const aligned = new UPlotConfigBuilder({ id: 'aligned' });
+		expect(aligned.getConfig().mode).toBeUndefined();
+
+		const faceted = new UPlotConfigBuilder({ id: 'faceted' });
+		faceted.setMode(PlotMode.Faceted);
+		expect(faceted.getMode()).toBe(PlotMode.Faceted);
+		expect(faceted.getConfig().mode).toBe(2);
+	});
+});

frontend/src/lib/uPlotV2/config/__tests__/UPlotSeriesBuilder.test.ts

@@ -399,3 +399,39 @@ describe('UPlotSeriesBuilder', () => {
 		expect(builder.getConfig().fill).toBeUndefined();
 	});
 });
+
+describe('UPlotSeriesBuilder scatter', () => {
+	it('draws through the given path builder and hides uPlot points', () => {
+		const pathBuilder = jest.fn();
+		const config = new UPlotSeriesBuilder(
+			createBaseProps({
+				drawStyle: DrawStyle.Scatter,
+				pathBuilder,
+				facets: [{ scale: 'x' }, { scale: 'y' }],
+				lineColor: '#ff0000',
+				fillOpacity: 0.5,
+				lineWidth: 1,
+				pointSize: 8,
+			}),
+		).getConfig();
+
+		expect(config.paths).toBe(pathBuilder);
+		expect(config.facets).toStrictEqual([{ scale: 'x' }, { scale: 'y' }]);
+		expect(config.points?.show).toBe(false);
+		expect(config.points?.size).toBe(8);
+		expect(config.stroke).toBe('#ff0000');
+		expect(config.width).toBe(1);
+		expect(config.fill).toBe('#ff000080');
+	});
+
+	it('draws nothing without a path builder', () => {
+		const config = new UPlotSeriesBuilder(
+			createBaseProps({ drawStyle: DrawStyle.Scatter }),
+		).getConfig();
+
+		expect(
+			(config.paths as uPlot.Series.PathBuilder)({} as uPlot, 1, 0, 0),
+		).toBeNull();
+		expect(config.facets).toBeUndefined();
+	});
+});

frontend/src/lib/uPlotV2/config/types.ts

@@ -88,7 +88,8 @@ export interface AxisProps {
 	isDarkMode?: boolean;
 	/** Axis is on a log scale — thins the grid lines to keep dense decades readable. */
 	isLogScale?: boolean;
-	/** Unit the y axis ticks are formatted in (`spec.formatting.unit`). */
+	/** Unit the value ticks are formatted in (`spec.formatting.unit`). Named for the
+	 *  y axis, the only value axis until scatter; a non-time x axis reads it too. */
 	yAxisUnit?: string;
 	/**
 	 * X axis carries timestamps, so its ticks format as dates/times. Declared by the caller
@@ -107,6 +108,15 @@ export interface AxisProps {
 export enum DistributionType {
 	Linear = 'linear',
 	Logarithmic = 'logarithmic',
+	/** arcsinh: linear within ±`asinhThreshold`, logarithmic beyond. Takes zero and
+	 *  negatives, which a plain log cannot place. */
+	SymmetricLog = 'symlog',
+}
+
+/** uPlot's data layout: one shared x per chart, or per-series x/y columns. */
+export enum PlotMode {
+	Aligned = 1,
+	Faceted = 2,
 }
 
 export interface ScaleProps {
@@ -123,6 +133,8 @@ export interface ScaleProps {
 	auto?: boolean;
 	logBase?: uPlot.Scale.LogBase;
 	distribution?: DistributionType;
+	/** Half-width of a `SymmetricLog` scale's linear band around zero. Default 1. */
+	asinhThreshold?: number;
 }
 
 export enum DisconnectedValuesMode {
@@ -144,6 +156,8 @@ export enum DrawStyle {
 	Points = 'points',
 	Bar = 'bar',
 	Histogram = 'histogram',
+	/** Faceted (mode 2) discs at per-series x/y, drawn by the caller's `pathBuilder`. */
+	Scatter = 'scatter',
 }
 
 export enum LineInterpolation {
@@ -227,6 +241,8 @@ export interface SeriesProps extends LineConfig, PointsConfig, BarConfig {
 	isDarkMode?: boolean;
 	stepInterval?: number;
 	metric?: { [key: string]: string };
+	/** Mode 2 only: the scales the series' own x and y columns are read against. */
+	facets?: Series.Facet[];
 }
 
 export interface LegendItem {

frontend/src/lib/uPlotV2/plugins/ScatterPlugin/__tests__/geometry.test.ts

@@ -0,0 +1,114 @@
+import type uPlot from 'uplot';
+
+import { Quadtree } from '../../../utils/quadtree';
+import {
+	resolveHit,
+	resolvePointDiameter,
+	resolveSizeDomain,
+} from '../geometry';
+import { ScatterHit, ScatterPointSize } from '../types';
+
+const POINT_SIZE: ScatterPointSize = { fixed: 6, min: 4, max: 20 };
+
+const asData = (columns: unknown[]): uPlot.AlignedData =>
+	columns as unknown as uPlot.AlignedData;
+
+describe('resolveSizeDomain', () => {
+	it('spans the size columns of every series, skipping nulls', () => {
+		const data = asData([
+			null,
+			[
+				[1, 2],
+				[1, 2],
+				[10, null],
+			],
+			[[3], [3], [40]],
+		]);
+
+		expect(resolveSizeDomain(data)).toStrictEqual({ min: 10, max: 40 });
+	});
+
+	it('is null when no series carries sizes', () => {
+		expect(resolveSizeDomain(asData([null, [[1], [1]]]))).toBeNull();
+		expect(resolveSizeDomain(asData([null, [[1], [1], [null]]]))).toBeNull();
+	});
+});
+
+describe('resolvePointDiameter', () => {
+	it('uses the fixed diameter without a size or a domain', () => {
+		expect(resolvePointDiameter(null, { min: 0, max: 10 }, POINT_SIZE)).toBe(6);
+		expect(resolvePointDiameter(5, null, POINT_SIZE)).toBe(6);
+	});
+
+	it('maps the domain ends to min and max', () => {
+		const domain = { min: 0, max: 100 };
+		expect(resolvePointDiameter(0, domain, POINT_SIZE)).toBe(4);
+		expect(resolvePointDiameter(100, domain, POINT_SIZE)).toBe(20);
+	});
+
+	it('scales by area, not diameter', () => {
+		const midArea = (4 ** 2 + 20 ** 2) / 2;
+		expect(
+			resolvePointDiameter(50, { min: 0, max: 100 }, POINT_SIZE),
+		).toBeCloseTo(Math.sqrt(midArea));
+	});
+
+	it('clamps values outside the domain', () => {
+		const domain = { min: 10, max: 20 };
+		expect(resolvePointDiameter(-5, domain, POINT_SIZE)).toBe(4);
+		expect(resolvePointDiameter(500, domain, POINT_SIZE)).toBe(20);
+	});
+
+	it('uses the midpoint when every size is the same', () => {
+		expect(resolvePointDiameter(7, { min: 7, max: 7 }, POINT_SIZE)).toBe(12);
+	});
+});
+
+describe('resolveHit', () => {
+	const hit = (
+		seriesIndex: number,
+		dataIndex: number,
+		x: number,
+		y: number,
+		d: number,
+	): ScatterHit => ({ seriesIndex, dataIndex, x, y, w: d, h: d });
+
+	it('returns the disc under the cursor', () => {
+		const tree = new Quadtree<ScatterHit>(0, 0, 100, 100);
+		tree.add(hit(1, 0, 10, 10, 6));
+		tree.add(hit(2, 3, 50, 50, 6));
+
+		expect(resolveHit(tree, 13, 13, 0)).toMatchObject({
+			seriesIndex: 1,
+			dataIndex: 0,
+		});
+		expect(resolveHit(tree, 52, 52, 0)).toMatchObject({
+			seriesIndex: 2,
+			dataIndex: 3,
+		});
+	});
+
+	it('is null when the cursor is off every disc', () => {
+		const tree = new Quadtree<ScatterHit>(0, 0, 100, 100);
+		tree.add(hit(1, 0, 10, 10, 6));
+
+		expect(resolveHit(tree, 30, 30, 0)).toBeNull();
+	});
+
+	it('tolerance widens each disc', () => {
+		const tree = new Quadtree<ScatterHit>(0, 0, 100, 100);
+		tree.add(hit(1, 0, 10, 10, 6));
+
+		expect(resolveHit(tree, 18, 13, 0)).toBeNull();
+		expect(resolveHit(tree, 18, 13, 3)).not.toBeNull();
+	});
+
+	it('prefers the disc whose centre is nearest when they overlap', () => {
+		const tree = new Quadtree<ScatterHit>(0, 0, 100, 100);
+		tree.add(hit(1, 0, 10, 10, 10));
+		tree.add(hit(1, 1, 14, 10, 10));
+
+		expect(resolveHit(tree, 13, 15, 0)?.dataIndex).toBe(0);
+		expect(resolveHit(tree, 21, 15, 0)?.dataIndex).toBe(1);
+	});
+});

frontend/src/lib/uPlotV2/plugins/ScatterPlugin/__tests__/scatterPlugin.test.ts

@@ -0,0 +1,248 @@
+import uPlot from 'uplot';
+
+import { PlotMode } from '../../../config/types';
+import { UPlotConfigBuilder } from '../../../config/UPlotConfigBuilder';
+import {
+	applyScatterPlugin,
+	createScatterPlugin,
+	SCATTER_FACETS,
+} from '../scatterPlugin';
+
+jest.mock('lib/visualization/panels/utils/legendVisibilityUtils', () => ({
+	getStoredSeriesVisibility: jest.fn(),
+}));
+
+/** jsdom has no Path2D; the builder only needs something that takes the calls. */
+class FakePath2D {
+	moveTo = jest.fn();
+	arc = jest.fn();
+}
+
+type OrientCallback = Parameters<typeof uPlot.orient>[2];
+
+interface FakePlotArgs {
+	series: Array<{ xs: number[]; ys: number[]; sizes?: Array<number | null> }>;
+	cursor?: { left: number; top: number };
+	scaleX?: { min: number; max: number };
+	scaleY?: { min: number; max: number };
+}
+
+/**
+ * A 100×100 plot at the canvas origin with identity scales: value 10 draws at
+ * pixel 10 on x, and at 100 − 10 on y (uPlot's y grows downward).
+ */
+function createFakePlot({
+	series,
+	cursor = { left: -1, top: -1 },
+	scaleX = { min: 0, max: 100 },
+	scaleY = { min: 0, max: 100 },
+}: FakePlotArgs): uPlot {
+	const data = [
+		null,
+		...series.map((entry) =>
+			entry.sizes ? [entry.xs, entry.ys, entry.sizes] : [entry.xs, entry.ys],
+		),
+	];
+	return {
+		data,
+		series: [{}, ...series.map((_, index) => ({ label: `s${index + 1}` }))],
+		bbox: { left: 0, top: 0, width: 100, height: 100 },
+		cursor,
+		scales: { x: scaleX, y: scaleY },
+	} as unknown as uPlot;
+}
+
+/** Stands in for `uPlot.orient`: identity x, flipped y, an `arc` that records. */
+function orientWithIdentityScales(
+	u: uPlot,
+	seriesIdx: number,
+	cb: OrientCallback,
+): void {
+	const columns = (u.data as unknown as Array<number[][] | null>)[seriesIdx];
+	if (!columns) {
+		return;
+	}
+	const scaleX = (u.scales as unknown as Record<string, uPlot.Scale>).x;
+	const scaleY = (u.scales as unknown as Record<string, uPlot.Scale>).y;
+	const valToPosX = (value: number): number => value;
+	const valToPosY = (value: number): number => 100 - value;
+	// Real uPlot's `arc` helper forwards to the path; the test counts those calls.
+	const arc = (path: FakePath2D, ...args: number[]): void => {
+		path.arc(...args);
+	};
+	cb(
+		u.series[seriesIdx],
+		columns[0],
+		columns[1],
+		scaleX,
+		scaleY,
+		valToPosX as unknown as uPlot.ValToPos,
+		valToPosY as unknown as uPlot.ValToPos,
+		0,
+		0,
+		100,
+		100,
+		jest.fn() as never,
+		jest.fn() as never,
+		jest.fn() as never,
+		arc as never,
+		jest.fn() as never,
+	);
+}
+
+describe('createScatterPlugin', () => {
+	beforeAll(() => {
+		(globalThis as { Path2D?: unknown }).Path2D = FakePath2D;
+	});
+
+	beforeEach(() => {
+		(uPlot.orient as jest.Mock).mockImplementation(orientWithIdentityScales);
+	});
+
+	afterEach(() => {
+		(uPlot.orient as jest.Mock).mockReset();
+	});
+
+	function drawAll(
+		u: uPlot,
+		plugin: ReturnType<typeof createScatterPlugin>,
+	): void {
+		plugin.hooks.drawClear(u);
+		for (let seriesIdx = 1; seriesIdx < u.series.length; seriesIdx++) {
+			const columns = (u.data as unknown as number[][][])[seriesIdx];
+			plugin.pathBuilder(u, seriesIdx, 0, columns[0].length - 1);
+		}
+	}
+
+	/** Runs the cursor scan the way uPlot does: every data series, in order. */
+	function scan(
+		u: uPlot,
+		plugin: ReturnType<typeof createScatterPlugin>,
+	): Array<number | null> {
+		const dataIdx = plugin.cursor.dataIdx as NonNullable<uPlot.Cursor['dataIdx']>;
+		const indexes: Array<number | null> = [null];
+		for (let seriesIdx = 1; seriesIdx < u.series.length; seriesIdx++) {
+			indexes.push(dataIdx(u, seriesIdx, 0, 0));
+		}
+		return indexes;
+	}
+
+	it('returns one path that strokes and fills the same discs', () => {
+		const plugin = createScatterPlugin();
+		const u = createFakePlot({ series: [{ xs: [10, 20], ys: [10, 20] }] });
+		plugin.hooks.drawClear(u);
+
+		const paths = plugin.pathBuilder(u, 1, 0, 1) as uPlot.Series.Paths;
+
+		expect(paths.stroke).toBeInstanceOf(FakePath2D);
+		expect(paths.fill).toBe(paths.stroke);
+		expect((paths.fill as unknown as FakePath2D).arc).toHaveBeenCalledTimes(2);
+	});
+
+	it('resolves the hovered point to its own series and index', () => {
+		const plugin = createScatterPlugin({
+			pointSize: { fixed: 6, min: 4, max: 20 },
+		});
+		const u = createFakePlot({
+			series: [
+				{ xs: [10, 50], ys: [10, 50] },
+				{ xs: [80], ys: [80] },
+			],
+			// Over the second series' only point: x 80, y drawn at 100 − 80.
+			cursor: { left: 80, top: 20 },
+		});
+		drawAll(u, plugin);
+
+		expect(scan(u, plugin)).toStrictEqual([null, null, 0]);
+		expect(plugin.getHit()).toMatchObject({ seriesIndex: 2, dataIndex: 0 });
+	});
+
+	it('returns null for every series when the cursor is off the plot or off any disc', () => {
+		const plugin = createScatterPlugin();
+		const u = createFakePlot({
+			series: [{ xs: [10], ys: [10] }],
+			cursor: { left: -1, top: -1 },
+		});
+		drawAll(u, plugin);
+
+		expect(scan(u, plugin)).toStrictEqual([null, null]);
+
+		(u.cursor as { left: number; top: number }).left = 50;
+		(u.cursor as { left: number; top: number }).top = 50;
+		expect(scan(u, plugin)).toStrictEqual([null, null]);
+	});
+
+	it('skips points outside the visible scale range', () => {
+		const plugin = createScatterPlugin();
+		const u = createFakePlot({
+			series: [{ xs: [10, 500], ys: [10, 10] }],
+			cursor: { left: 10, top: 90 },
+		});
+		drawAll(u, plugin);
+
+		const paths = plugin.pathBuilder(u, 1, 0, 1) as uPlot.Series.Paths;
+		expect((paths.fill as unknown as FakePath2D).arc).toHaveBeenCalledTimes(1);
+		expect(scan(u, plugin)).toStrictEqual([null, 0]);
+	});
+
+	it('sizes the hover marker from the hit disc, in CSS pixels', () => {
+		const plugin = createScatterPlugin({
+			pointSize: { fixed: 8, min: 4, max: 20 },
+		});
+		const u = createFakePlot({
+			series: [{ xs: [10], ys: [10] }],
+			cursor: { left: 10, top: 90 },
+		});
+		drawAll(u, plugin);
+		scan(u, plugin);
+
+		const bbox = plugin.cursor.points?.bbox;
+		expect(bbox?.(u, 1)).toStrictEqual({ left: 6, top: 86, width: 8, height: 8 });
+		expect(bbox?.(u, 2)).toMatchObject({ width: 0, height: 0 });
+	});
+
+	it('drawClear drops cached paths on data series only', () => {
+		const plugin = createScatterPlugin();
+		const u = createFakePlot({ series: [{ xs: [1], ys: [1] }] });
+		const [xSeries, dataSeries] = u.series as Array<{ _paths?: unknown }>;
+		xSeries._paths = 'x';
+		dataSeries._paths = 'cached';
+
+		plugin.hooks.drawClear(u);
+
+		expect(xSeries._paths).toBe('x');
+		expect(dataSeries._paths).toBeNull();
+	});
+
+	it('focus distance is zero, so the hit series wins focus', () => {
+		const plugin = createScatterPlugin();
+		expect(plugin.cursor.focus?.dist?.({} as uPlot, 1, 0, 0, 0)).toBe(0);
+	});
+});
+
+describe('applyScatterPlugin', () => {
+	it('switches the builder to faceted mode and disables drag selection', () => {
+		const builder = new UPlotConfigBuilder({ id: 'scatter' });
+		const plugin = createScatterPlugin();
+
+		applyScatterPlugin(builder, plugin);
+		const config = builder.getConfig();
+
+		expect(builder.getMode()).toBe(PlotMode.Faceted);
+		expect(config.mode).toBe(2);
+		expect(config.cursor?.drag).toMatchObject({
+			x: false,
+			y: false,
+			setScale: false,
+		});
+		expect(config.hooks?.drawClear).toHaveLength(1);
+		expect(config.hooks?.destroy).toHaveLength(1);
+	});
+
+	it('facets read x and y against the shared scales', () => {
+		expect(SCATTER_FACETS).toStrictEqual([
+			{ scale: 'x', auto: true },
+			{ scale: 'y', auto: true },
+		]);
+	});
+});

frontend/src/lib/uPlotV2/plugins/ScatterPlugin/geometry.ts

@@ -0,0 +1,96 @@
+import type uPlot from 'uplot';
+
+import type { Quadtree } from '../../utils/quadtree';
+import type { ScatterHit, ScatterPointSize, ScatterSeriesData } from './types';
+
+export interface SizeDomain {
+	min: number;
+	max: number;
+}
+
+/**
+ * Extent of the size column across every series, so equal values draw equal
+ * discs whichever group they belong to. `null` when nothing carries a size.
+ */
+export function resolveSizeDomain(data: uPlot.AlignedData): SizeDomain | null {
+	let min = Infinity;
+	let max = -Infinity;
+	for (let seriesIndex = 1; seriesIndex < data.length; seriesIndex++) {
+		const sizes = (data[seriesIndex] as unknown as ScatterSeriesData)[2];
+		if (!sizes) {
+			continue;
+		}
+		for (const size of sizes) {
+			if (size == null || !Number.isFinite(size)) {
+				continue;
+			}
+			min = Math.min(min, size);
+			max = Math.max(max, size);
+		}
+	}
+	return min <= max ? { min, max } : null;
+}
+
+/**
+ * Disc diameter for a size value. Area, not diameter, follows the value: a
+ * point worth twice as much should look twice as big.
+ */
+export function resolvePointDiameter(
+	size: number | null | undefined,
+	domain: SizeDomain | null,
+	pointSize: ScatterPointSize,
+): number {
+	if (size == null || domain == null || !Number.isFinite(size)) {
+		return pointSize.fixed;
+	}
+	if (domain.max === domain.min) {
+		return (pointSize.min + pointSize.max) / 2;
+	}
+	const t = Math.min(
+		1,
+		Math.max(0, (size - domain.min) / (domain.max - domain.min)),
+	);
+	const minArea = pointSize.min ** 2;
+	const maxArea = pointSize.max ** 2;
+	return Math.sqrt(minArea + (maxArea - minArea) * t);
+}
+
+/**
+ * Nearest disc under the cursor, or `null`. Overlapping discs resolve to the one
+ * whose centre is closest; `tolerance` widens every disc so thin points stay
+ * hoverable.
+ */
+export function resolveHit(
+	tree: Quadtree<ScatterHit>,
+	cx: number,
+	cy: number,
+	tolerance: number,
+): ScatterHit | null {
+	let best: ScatterHit | null = null;
+	let bestDistance = Infinity;
+
+	tree.get(
+		cx - tolerance,
+		cy - tolerance,
+		tolerance * 2,
+		tolerance * 2,
+		(hit) => {
+			const left = hit.x - tolerance;
+			const top = hit.y - tolerance;
+			const right = hit.x + hit.w + tolerance;
+			const bottom = hit.y + hit.h + tolerance;
+			if (cx < left || cx > right || cy < top || cy > bottom) {
+				return;
+			}
+			const dx = cx - (hit.x + hit.w / 2);
+			const dy = cy - (hit.y + hit.h / 2);
+			const distance = dx * dx + dy * dy;
+			if (distance < bestDistance) {
+				best = hit;
+				bestDistance = distance;
+			}
+		},
+	);
+
+	return best;
+}

frontend/src/lib/uPlotV2/plugins/ScatterPlugin/scatterPlugin.ts

@@ -0,0 +1,206 @@
+import uPlot, { Series } from 'uplot';
+
+import { DEFAULT_FOCUS_PROXIMITY_VALUE } from '../../constants';
+import { PlotMode } from '../../config/types';
+import type { UPlotConfigBuilder } from '../../config/UPlotConfigBuilder';
+import { Quadtree } from '../../utils/quadtree';
+import {
+	resolveHit,
+	resolvePointDiameter,
+	resolveSizeDomain,
+	SizeDomain,
+} from './geometry';
+import {
+	DEFAULT_HOVER_TOLERANCE_PX,
+	DEFAULT_SCATTER_POINT_SIZE,
+	ScatterHit,
+	ScatterPluginOptions,
+	ScatterSeriesData,
+} from './types';
+
+/** Every scatter series reads its own x and y columns against the shared scales. */
+export const SCATTER_FACETS: Series.Facet[] = [
+	{ scale: 'x', auto: true },
+	{ scale: 'y', auto: true },
+];
+
+const HIDDEN_BBOX: uPlot.BBox = { left: -10, top: -10, width: 0, height: 0 };
+
+const TWO_PI = 2 * Math.PI;
+
+/** uPlot caches built paths on the series; the field is internal to it. */
+type SeriesWithPaths = Series & { _paths?: Series.Paths | null };
+
+export interface ScatterPlugin {
+	/** Draws every point of a series as one path and indexes the discs for hover. */
+	pathBuilder: Series.PathBuilder;
+	/** Hover by disc rather than by nearest x: mode 2 has no shared x to scan. */
+	cursor: uPlot.Cursor;
+	hooks: {
+		drawClear: (u: uPlot) => void;
+		destroy: (u: uPlot) => void;
+	};
+	getHit: () => ScatterHit | null;
+}
+
+export function createScatterPlugin({
+	pointSize = DEFAULT_SCATTER_POINT_SIZE,
+	hoverTolerance = DEFAULT_HOVER_TOLERANCE_PX,
+}: ScatterPluginOptions = {}): ScatterPlugin {
+	let tree: Quadtree<ScatterHit> | null = null;
+	let hit: ScatterHit | null = null;
+
+	// The domain spans every series, so it is resolved once per dataset rather than
+	// once per series path.
+	let cachedData: uPlot.AlignedData | null = null;
+	let cachedDomain: SizeDomain | null = null;
+
+	function getSizeDomain(u: uPlot): SizeDomain | null {
+		if (cachedData !== u.data) {
+			cachedDomain = resolveSizeDomain(u.data);
+			cachedData = u.data;
+		}
+		return cachedDomain;
+	}
+
+	const pathBuilder: Series.PathBuilder = (u, seriesIdx, idx0, idx1) => {
+		const path = new Path2D();
+		const sizes = (u.data[seriesIdx] as unknown as ScatterSeriesData)[2];
+		const domain = getSizeDomain(u);
+		const { pxRatio } = uPlot;
+
+		uPlot.orient(
+			u,
+			seriesIdx,
+			(
+				_series,
+				dataX,
+				dataY,
+				scaleX,
+				scaleY,
+				valToPosX,
+				valToPosY,
+				xOff,
+				yOff,
+				xDim,
+				yDim,
+				_moveTo,
+				_lineTo,
+				_rect,
+				arc,
+			) => {
+				const xMin = scaleX.min ?? -Infinity;
+				const xMax = scaleX.max ?? Infinity;
+				const yMin = scaleY.min ?? -Infinity;
+				const yMax = scaleY.max ?? Infinity;
+
+				for (let i = idx0; i <= idx1; i++) {
+					const x = dataX[i];
+					const y = dataY[i];
+					if (
+						x == null ||
+						y == null ||
+						x < xMin ||
+						x > xMax ||
+						y < yMin ||
+						y > yMax
+					) {
+						continue;
+					}
+
+					const diameter =
+						resolvePointDiameter(sizes?.[i], domain, pointSize) * pxRatio;
+					const radius = diameter / 2;
+					const cx = valToPosX(x, scaleX, xDim, xOff);
+					const cy = valToPosY(y, scaleY, yDim, yOff);
+
+					path.moveTo(cx + radius, cy);
+					arc(path, cx, cy, radius, 0, TWO_PI);
+
+					tree?.add({
+						x: cx - radius - u.bbox.left,
+						y: cy - radius - u.bbox.top,
+						w: diameter,
+						h: diameter,
+						seriesIndex: seriesIdx,
+						dataIndex: i,
+					});
+				}
+			},
+		);
+
+		return { stroke: path, fill: path, clip: null };
+	};
+
+	const cursor: uPlot.Cursor = {
+		// Selection would set the dashboard time range; neither axis is time here.
+		drag: { x: false, y: false, setScale: false },
+		dataIdx: (u, seriesIdx): number | null => {
+			// uPlot asks series 1..n in order on every cursor move; resolve once.
+			if (seriesIdx === 1) {
+				const { left = -1, top = -1 } = u.cursor;
+				const { pxRatio } = uPlot;
+				hit =
+					tree && left >= 0 && top >= 0
+						? resolveHit(
+								tree,
+								left * pxRatio,
+								top * pxRatio,
+								hoverTolerance * pxRatio,
+							)
+						: null;
+			}
+			return hit?.seriesIndex === seriesIdx ? hit.dataIndex : null;
+		},
+		points: {
+			bbox: (_u, seriesIdx): uPlot.BBox => {
+				if (hit?.seriesIndex !== seriesIdx) {
+					return HIDDEN_BBOX;
+				}
+				const { pxRatio } = uPlot;
+				return {
+					left: hit.x / pxRatio,
+					top: hit.y / pxRatio,
+					width: hit.w / pxRatio,
+					height: hit.h / pxRatio,
+				};
+			},
+		},
+		// uPlot only measures series that returned a data index, i.e. the hit one.
+		focus: { prox: DEFAULT_FOCUS_PROXIMITY_VALUE, dist: (): number => 0 },
+	};
+
+	return {
+		pathBuilder,
+		cursor,
+		hooks: {
+			drawClear: (u: uPlot): void => {
+				tree = new Quadtree<ScatterHit>(0, 0, u.bbox.width, u.bbox.height);
+				// The tree only knows what the path builder last drew, so cached paths
+				// must be rebuilt alongside it.
+				u.series.forEach((series, index) => {
+					if (index > 0) {
+						(series as SeriesWithPaths)._paths = null;
+					}
+				});
+			},
+			destroy: (): void => {
+				tree = null;
+				hit = null;
+				cachedData = null;
+				cachedDomain = null;
+			},
+		},
+		getHit: (): ScatterHit | null => hit,
+	};
+}
+
+export function applyScatterPlugin(
+	builder: UPlotConfigBuilder,
+	plugin: ScatterPlugin,
+): void {
+	builder.setMode(PlotMode.Faceted);
+	builder.setCursor(plugin.cursor);
+	builder.addHook('drawClear', plugin.hooks.drawClear);
+	builder.addHook('destroy', plugin.hooks.destroy);
+}

frontend/src/lib/uPlotV2/plugins/ScatterPlugin/types.ts

@@ -0,0 +1,58 @@
+import type { QuadtreeRect } from '../../utils/quadtree';
+
+/** Diameters in CSS pixels. `min`/`max` bound the area scale when a size column is mapped. */
+export interface ScatterPointSize {
+	fixed: number;
+	min: number;
+	max: number;
+}
+
+export const DEFAULT_SCATTER_POINT_SIZE: ScatterPointSize = {
+	fixed: 6,
+	min: 4,
+	max: 24,
+};
+
+/** CSS pixels around a point's disc that still register as a hover. */
+export const DEFAULT_HOVER_TOLERANCE_PX = 3;
+
+export interface ScatterPluginOptions {
+	pointSize?: ScatterPointSize;
+	hoverTolerance?: number;
+}
+
+/**
+ * One faceted series: parallel columns, one point per index. Sizes are in the
+ * caller's units and mapped to `pointSize` at draw time; `null` draws at `fixed`.
+ */
+export type ScatterSeriesData = [
+	xs: number[],
+	ys: number[],
+	sizes?: Array<number | null>,
+];
+
+/** Mode-2 data: series 0 is uPlot's x placeholder and carries nothing. */
+export type ScatterChartData = [null, ...ScatterSeriesData[]];
+
+/** A drawn point's disc, in canvas pixels relative to the plot area. */
+export interface ScatterHit extends QuadtreeRect {
+	seriesIndex: number;
+	dataIndex: number;
+}
+
+export interface ScatterChannel {
+	label: string;
+	unit?: string;
+}
+
+/** What each visual channel plots, for the tooltip and axes. */
+export interface ScatterChannels {
+	x: ScatterChannel;
+	y: ScatterChannel;
+	size?: ScatterChannel;
+}
+
+export interface ScatterPointLabel {
+	key: string;
+	value: string;
+}

frontend/src/lib/uPlotV2/utils/__tests__/quadtree.test.ts

@@ -0,0 +1,70 @@
+import { Quadtree, QuadtreeRect } from '../quadtree';
+
+interface Item extends QuadtreeRect {
+	id: number;
+}
+
+function collect(
+	tree: Quadtree<Item>,
+	x: number,
+	y: number,
+	w: number,
+	h: number,
+): Set<number> {
+	const ids = new Set<number>();
+	tree.get(x, y, w, h, (item) => ids.add(item.id));
+	return ids;
+}
+
+describe('Quadtree', () => {
+	it('returns items in the queried region and not those far from it', () => {
+		const tree = new Quadtree<Item>(0, 0, 100, 100);
+		tree.add({ id: 1, x: 10, y: 10, w: 5, h: 5 });
+		tree.add({ id: 2, x: 80, y: 80, w: 5, h: 5 });
+
+		// Below the split threshold every item is visited; callers refine the hit.
+		expect(collect(tree, 9, 9, 8, 8)).toStrictEqual(new Set([1, 2]));
+	});
+
+	it('splits past the object limit and still finds every item', () => {
+		const tree = new Quadtree<Item>(0, 0, 100, 100);
+		const total = 50;
+		for (let id = 0; id < total; id++) {
+			tree.add({ id, x: (id % 10) * 10, y: Math.floor(id / 10) * 10, w: 4, h: 4 });
+		}
+
+		expect(collect(tree, 0, 0, 100, 100).size).toBe(total);
+	});
+
+	it('after a split, a query in one quadrant skips items confined to another', () => {
+		const tree = new Quadtree<Item>(0, 0, 100, 100);
+		for (let id = 0; id < 20; id++) {
+			// All in the north-west quadrant.
+			tree.add({ id, x: 1 + id, y: 1, w: 2, h: 2 });
+		}
+		tree.add({ id: 99, x: 90, y: 90, w: 2, h: 2 });
+
+		const northWest = collect(tree, 0, 0, 10, 10);
+		expect(northWest.has(99)).toBe(false);
+		expect(collect(tree, 85, 85, 10, 10).has(99)).toBe(true);
+	});
+
+	it('reports an item straddling the midline from either side', () => {
+		const tree = new Quadtree<Item>(0, 0, 100, 100);
+		for (let id = 0; id < 20; id++) {
+			tree.add({ id, x: 1, y: 1 + id, w: 2, h: 2 });
+		}
+		tree.add({ id: 99, x: 48, y: 48, w: 4, h: 4 });
+
+		expect(collect(tree, 40, 40, 5, 5).has(99)).toBe(true);
+		expect(collect(tree, 55, 55, 5, 5).has(99)).toBe(true);
+	});
+
+	it('clear empties the tree', () => {
+		const tree = new Quadtree<Item>(0, 0, 100, 100);
+		tree.add({ id: 1, x: 10, y: 10, w: 5, h: 5 });
+		tree.clear();
+
+		expect(collect(tree, 0, 0, 100, 100).size).toBe(0);
+	});
+});

frontend/src/lib/uPlotV2/utils/__tests__/scale.test.ts

@@ -195,3 +195,40 @@ describe('scale utils', () => {
 		});
 	});
 });
+
+describe('symmetric log scale', () => {
+	it('maps to uPlot arcsinh with the given linear threshold', () => {
+		expect(
+			scaleUtils.getDistributionConfig({
+				time: false,
+				distr: DistributionType.SymmetricLog,
+				asinhThreshold: 0.01,
+			}),
+		).toStrictEqual({ distr: 4, log: 10, asinh: 0.01 });
+
+		expect(
+			scaleUtils.getDistributionConfig({
+				time: false,
+				distr: DistributionType.SymmetricLog,
+			}).asinh,
+		).toBe(scaleUtils.DEFAULT_ASINH_THRESHOLD);
+	});
+
+	it('ranges a distr 4 scale through uPlot.rangeAsinh', () => {
+		const rangeAsinh = jest.fn(() => [-10, 1000] as uPlot.Range.MinMax);
+		Object.assign(uPlot, { rangeAsinh });
+
+		const rangeFn = scaleUtils.createRangeFunction({
+			rangeConfig: {} as uPlot.Range.Config,
+			hardMinOnly: false,
+			hardMaxOnly: false,
+			hasFixedRange: false,
+			min: null,
+			max: null,
+		});
+		const u = { scales: { y: { distr: 4, log: 10 } } } as unknown as uPlot;
+
+		expect(rangeFn(u, -3, 700, 'y')).toStrictEqual([-10, 1000]);
+		expect(rangeAsinh).toHaveBeenCalledWith(-3, 700, 10, true);
+	});
+});

frontend/src/lib/uPlotV2/utils/quadtree.ts

@@ -0,0 +1,110 @@
+export interface QuadtreeRect {
+	x: number;
+	y: number;
+	w: number;
+	h: number;
+}
+
+const MAX_OBJECTS = 10;
+const MAX_LEVELS = 4;
+
+/**
+ * Spatial index over axis-aligned rectangles, for answering "what is under the
+ * cursor" on charts whose marks have no shared x order to binary-search. An item
+ * straddling a quadrant boundary lives in every quadrant it touches, so `get` can
+ * report it more than once.
+ */
+export class Quadtree<T extends QuadtreeRect = QuadtreeRect> {
+	private items: T[] = [];
+	private quadrants: Quadtree<T>[] | null = null;
+
+	constructor(
+		private readonly x: number,
+		private readonly y: number,
+		private readonly w: number,
+		private readonly h: number,
+		private readonly level = 0,
+	) {}
+
+	add(item: T): void {
+		if (this.quadrants) {
+			this.forEachQuadrant(item, (quadrant) => quadrant.add(item));
+			return;
+		}
+
+		this.items.push(item);
+
+		if (this.items.length > MAX_OBJECTS && this.level < MAX_LEVELS) {
+			this.split();
+			const items = this.items;
+			this.items = [];
+			for (const existing of items) {
+				this.forEachQuadrant(existing, (quadrant) => quadrant.add(existing));
+			}
+		}
+	}
+
+	/** Visits every item whose quadrant overlaps the rectangle; callers refine the test. */
+	get(
+		x: number,
+		y: number,
+		w: number,
+		h: number,
+		visit: (item: T) => void,
+	): void {
+		for (const item of this.items) {
+			visit(item);
+		}
+		if (this.quadrants) {
+			this.forEachQuadrant({ x, y, w, h }, (quadrant) =>
+				quadrant.get(x, y, w, h, visit),
+			);
+		}
+	}
+
+	clear(): void {
+		this.items = [];
+		this.quadrants = null;
+	}
+
+	private split(): void {
+		const w = this.w / 2;
+		const h = this.h / 2;
+		const level = this.level + 1;
+		// North-east, north-west, south-west, south-east.
+		this.quadrants = [
+			new Quadtree<T>(this.x + w, this.y, w, h, level),
+			new Quadtree<T>(this.x, this.y, w, h, level),
+			new Quadtree<T>(this.x, this.y + h, w, h, level),
+			new Quadtree<T>(this.x + w, this.y + h, w, h, level),
+		];
+	}
+
+	private forEachQuadrant(
+		rect: QuadtreeRect,
+		visit: (quadrant: Quadtree<T>) => void,
+	): void {
+		if (!this.quadrants) {
+			return;
+		}
+		const midX = this.x + this.w / 2;
+		const midY = this.y + this.h / 2;
+		const startsNorth = rect.y < midY;
+		const startsWest = rect.x < midX;
+		const endsEast = rect.x + rect.w > midX;
+		const endsSouth = rect.y + rect.h > midY;
+
+		if (startsNorth && endsEast) {
+			visit(this.quadrants[0]);
+		}
+		if (startsWest && startsNorth) {
+			visit(this.quadrants[1]);
+		}
+		if (startsWest && endsSouth) {
+			visit(this.quadrants[2]);
+		}
+		if (endsEast && endsSouth) {
+			visit(this.quadrants[3]);
+		}
+	}
+}

frontend/src/lib/uPlotV2/utils/scale.ts

@@ -58,18 +58,23 @@ function normalizeLogLimit(
 	return logBase ** exp;
 }
 
+export const DEFAULT_ASINH_THRESHOLD = 1;
+
 /**
- * Returns uPlot scale distribution options for the Y axis.
- * Time (X) scale gets no distr/log; Y scale gets distr 1 (linear) or 3 (log) and log base 2 or 10.
+ * Returns uPlot scale distribution options for a value axis.
+ * Time scales get no distr/log; value scales get distr 1 (linear), 3 (log) or
+ * 4 (arcsinh, uPlot's symmetric log) and log base 2 or 10.
  */
 export function getDistributionConfig({
 	time,
 	distr,
 	logBase,
+	asinhThreshold,
 }: {
 	time: ScaleProps['time'];
 	distr?: DistributionType;
 	logBase?: number;
+	asinhThreshold?: number;
 }): Partial<Scale> {
 	if (time) {
 		return {};
@@ -77,6 +82,14 @@ export function getDistributionConfig({
 
 	const resolvedLogBase = (logBase ?? 10) === 2 ? 2 : 10;
 
+	if (distr === DistributionType.SymmetricLog) {
+		return {
+			distr: 4,
+			log: resolvedLogBase,
+			asinh: asinhThreshold ?? DEFAULT_ASINH_THRESHOLD,
+		};
+	}
+
 	return {
 		distr: distr === DistributionType.Logarithmic ? 3 : 1,
 		log: resolvedLogBase,
@@ -197,6 +210,33 @@ function getLogScaleRange(
 	);
 }
 
+/**
+ * Computes the arcsinh-scale range using uPlot.rangeAsinh, which pads to whole
+ * magnitudes on either side of zero and pins an edge that sits exactly on zero.
+ */
+function getAsinhScaleRange(
+	minMax: Range.MinMax,
+	params: RangeFunctionParams,
+	dataMin: number | null,
+	dataMax: number | null,
+	logBase?: uPlot.Scale['log'],
+): Range.MinMax {
+	const { min, max } = params;
+	const resolvedMin = min ?? dataMin;
+	const resolvedMax = max ?? dataMax;
+
+	if (resolvedMin == null || resolvedMax == null) {
+		return minMax;
+	}
+
+	return uPlot.rangeAsinh(
+		resolvedMin,
+		resolvedMax,
+		(logBase ?? 10) as 2 | 10,
+		true,
+	);
+}
+
 /**
  * Snaps log-scale [min, max] to exact powers of logBase (nearest magnitude below/above).
  * If min and max would be equal after snapping, max is increased by one magnitude so the range is valid.
@@ -299,6 +339,8 @@ export function createRangeFunction(
 			minMax = getLogScaleRange(minMax, params, dataMin, dataMax, logBase);
 			const logFn = scale.log === 2 ? Math.log2 : Math.log10;
 			minMax = adjustLogRange(minMax, (logBase ?? 10) as number, logFn);
+		} else if (scale.distr === 4) {
+			minMax = getAsinhScaleRange(minMax, params, dataMin, dataMax, logBase);
 		}
 
 		minMax = applyHardLimits(minMax, params, scale.distr ?? 1);

frontend/src/lib/visualization/charts/Scatter/Scatter.stories.tsx

@@ -0,0 +1,253 @@
+import { useMemo, useState } from 'react';
+import type { Meta, StoryObj } from '@storybook/react-vite';
+import { useIsDarkMode } from 'hooks/useDarkMode';
+import { LegendPosition } from 'lib/uPlotV2/components/types';
+import type { Threshold } from 'lib/uPlotV2/hooks/types';
+import type { ScatterPointLabel } from 'lib/uPlotV2/plugins/ScatterPlugin/types';
+
+import Scatter from './Scatter';
+import {
+	buildScatterConfig,
+	prepareScatterChartData,
+	ScatterSeries,
+} from './utils';
+
+const SERVICES = [
+	'frontend',
+	'cart',
+	'checkout',
+	'payment',
+	'shipping',
+	'currency',
+	'email',
+	'recommendation',
+	'ads',
+	'product-catalog',
+];
+
+type Shape = 'spread' | 'single' | 'sameX';
+
+interface ScatterStoryProps {
+	groups: number;
+	pointsPerGroup: number;
+	/** Adds an error-count size column. */
+	sized: boolean;
+	xLog: boolean;
+	yLog: boolean;
+	/** Zeroes a share of y values, which forces the symmetric log. */
+	withZeros: boolean;
+	shape: Shape;
+	thresholds: boolean;
+	pointSize: number;
+	/** 0–1. */
+	fillOpacity: number;
+	width: number;
+	height: number;
+}
+
+/** Deterministic, so a story renders the same points on every run. */
+function createRng(seed: number): () => number {
+	let state = seed >>> 0;
+	return (): number => {
+		state = (state * 1664525 + 1013904223) >>> 0;
+		return state / 2 ** 32;
+	};
+}
+
+function buildSeries({
+	groups,
+	pointsPerGroup,
+	sized,
+	withZeros,
+	shape,
+}: ScatterStoryProps): ScatterSeries[] {
+	const rng = createRng(42);
+	return Array.from({ length: groups }, (_, groupIndex) => {
+		const label = SERVICES[groupIndex % SERVICES.length];
+		// Each service sits in its own throughput/latency band, so groups are telling
+		// apart rather than one cloud.
+		const baseThroughput = 20 * 2 ** (groupIndex % 5);
+		const baseLatency = 40 + 60 * (groupIndex % 4);
+
+		const count = shape === 'single' ? 1 : pointsPerGroup;
+		const xs: number[] = [];
+		const ys: number[] = [];
+		const sizes: Array<number | null> = [];
+
+		for (let i = 0; i < count; i++) {
+			const throughput =
+				shape === 'sameX' ? baseThroughput : baseThroughput * (0.5 + rng() * 1.5);
+			// Latency grows with load, plus noise; the odd outlier keeps the axis honest.
+			const outlier = rng() < 0.03 ? 4 + rng() * 6 : 1;
+			let latency =
+				baseLatency *
+				(0.8 + (throughput / baseThroughput) * 0.4 + rng() * 0.3) *
+				outlier;
+			if (withZeros && rng() < 0.2) {
+				latency = 0;
+			}
+			xs.push(Number(throughput.toFixed(2)));
+			ys.push(Number(latency.toFixed(2)));
+			sizes.push(rng() < 0.1 ? null : Math.round(rng() * rng() * 500));
+		}
+
+		return sized ? { label, xs, ys, sizes } : { label, xs, ys };
+	});
+}
+
+const THRESHOLDS: Threshold[] = [
+	{
+		thresholdValue: 300,
+		thresholdUnit: 'ms',
+		thresholdColor: '#E5484D',
+		thresholdLabel: 'p99 SLO',
+	},
+];
+
+function ScatterStory(props: ScatterStoryProps): JSX.Element {
+	const {
+		xLog,
+		yLog,
+		sized,
+		thresholds,
+		pointSize,
+		fillOpacity,
+		width,
+		height,
+	} = props;
+	const isDarkMode = useIsDarkMode();
+	const [drawMs, setDrawMs] = useState<number | null>(null);
+
+	const series = useMemo(() => buildSeries(props), [props]);
+	const pointCount = series.reduce((sum, entry) => sum + entry.xs.length, 0);
+	const drawLabel = drawMs === null ? '—' : `${drawMs.toFixed(1)} ms`;
+
+	const config = useMemo(() => {
+		const builder = buildScatterConfig({
+			id: 'scatter-story',
+			series,
+			isDarkMode,
+			x: { unit: 'reqps', isLogScale: xLog },
+			y: { unit: 'ms', isLogScale: yLog },
+			pointSize: { fixed: pointSize, min: 4, max: pointSize * 4 },
+			fillOpacity,
+			thresholds: thresholds ? THRESHOLDS : undefined,
+		});
+		let started = 0;
+		builder.addHook('drawClear', (): void => {
+			started = performance.now();
+		});
+		builder.addHook('draw', (): void => {
+			setDrawMs(performance.now() - started);
+		});
+		return builder;
+	}, [series, isDarkMode, xLog, yLog, pointSize, fillOpacity, thresholds]);
+
+	const data = useMemo(() => prepareScatterChartData(series), [series]);
+
+	const resolvePointLabels = (
+		seriesIndex: number,
+		dataIndex: number,
+	): ScatterPointLabel[] => [
+		{ key: 'service.name', value: series[seriesIndex - 1]?.label ?? '' },
+		{
+			key: 'k8s.pod.name',
+			value: `pod-${dataIndex.toString().padStart(3, '0')}`,
+		},
+	];
+
+	return (
+		<div style={{ width, padding: 16 }}>
+			<Scatter
+				config={config}
+				data={data}
+				width={width}
+				height={height}
+				legendConfig={{ position: LegendPosition.BOTTOM }}
+				channels={{
+					x: { label: 'Throughput', unit: 'reqps' },
+					y: { label: 'p99 latency', unit: 'ms' },
+					...(sized && { size: { label: 'Errors', unit: 'short' } }),
+				}}
+				resolvePointLabels={resolvePointLabels}
+				canPinTooltip
+			/>
+			<p style={{ fontFamily: 'var(--font-mono)', fontSize: 12, opacity: 0.7 }}>
+				{`${pointCount.toLocaleString()} points · last draw ${drawLabel}`}
+			</p>
+		</div>
+	);
+}
+
+const meta = {
+	title: 'Charts/Scatter',
+	component: ScatterStory,
+	parameters: { layout: 'padded' },
+	args: {
+		groups: 1,
+		pointsPerGroup: 10,
+		sized: false,
+		xLog: false,
+		yLog: false,
+		withZeros: false,
+		shape: 'spread',
+		thresholds: false,
+		pointSize: 6,
+		fillOpacity: 0.7,
+		width: 800,
+		height: 420,
+	},
+	argTypes: {
+		shape: { control: 'radio', options: ['spread', 'single', 'sameX'] },
+		fillOpacity: { control: { type: 'range', min: 0, max: 1, step: 0.05 } },
+		pointSize: { control: { type: 'range', min: 2, max: 16, step: 1 } },
+	},
+} satisfies Meta<ScatterStoryProps>;
+
+export default meta;
+
+type Story = StoryObj<ScatterStoryProps>;
+
+/** One service, ten points: axes formatted with units, hover picks the right point. */
+export const Basic: Story = {};
+
+/** Five services, one legend entry each; toggling a row hides its points. */
+export const Grouped: Story = {
+	args: { groups: 5, pointsPerGroup: 40 },
+};
+
+/** Error count as disc area, between the configured min and max diameters. */
+export const Sized: Story = {
+	args: { groups: 5, pointsPerGroup: 40, sized: true, pointSize: 5 },
+};
+
+/** Log x; a fifth of the latencies are 0, so y falls back to the symmetric log. */
+export const LogAxes: Story = {
+	args: {
+		groups: 5,
+		pointsPerGroup: 60,
+		xLog: true,
+		yLog: true,
+		withZeros: true,
+	},
+};
+
+/** A single point still gets a padded range rather than an empty plot. */
+export const SinglePoint: Story = {
+	args: { shape: 'single' },
+};
+
+/** Fifty points sharing one x collide on nothing: no shared x array to align. */
+export const SameX: Story = {
+	args: { groups: 3, pointsPerGroup: 50, shape: 'sameX' },
+};
+
+/** Horizontal line with label on the y axis; the scale stretches to include it. */
+export const Thresholds: Story = {
+	args: { groups: 3, pointsPerGroup: 40, thresholds: true },
+};
+
+/** Perf harness: raise `pointsPerGroup` and read the draw time under the chart. */
+export const Dense: Story = {
+	args: { groups: 5, pointsPerGroup: 1000, pointSize: 4, fillOpacity: 0.5 },
+};

frontend/src/lib/visualization/charts/Scatter/Scatter.tsx

@@ -0,0 +1,65 @@
+import { useCallback } from 'react';
+import ChartWrapper from 'lib/visualization/charts/ChartWrapper/ChartWrapper';
+import ScatterTooltip from 'lib/uPlotV2/components/Tooltip/ScatterTooltip';
+import {
+	ScatterTooltipProps,
+	TooltipRenderArgs,
+} from 'lib/uPlotV2/components/types';
+import uPlot from 'uplot';
+
+import { ScatterChartProps } from 'lib/visualization/charts/types';
+
+// Faceted uPlot reads series 1's facets at init, so a chart with no series cannot
+// mount; empty aligned data makes the shell show its no-data state instead.
+const EMPTY_ALIGNED_DATA: uPlot.AlignedData = [[]];
+
+export default function Scatter(props: ScatterChartProps): JSX.Element {
+	const {
+		children,
+		customTooltip,
+		channels,
+		resolvePointLabels,
+		pinnedTooltipElement,
+		...rest
+	} = props;
+
+	const renderTooltip = useCallback(
+		(args: TooltipRenderArgs): React.ReactNode => {
+			if (customTooltip) {
+				return customTooltip(args);
+			}
+			const tooltipProps: ScatterTooltipProps = {
+				...args,
+				id: rest.config.getId(),
+				channels,
+				resolvePointLabels,
+				decimalPrecision: rest.decimalPrecision,
+				canPinTooltip: rest.canPinTooltip,
+				renderTooltipFooter: rest.renderTooltipFooter,
+			};
+			return <ScatterTooltip {...tooltipProps} />;
+		},
+		[
+			customTooltip,
+			channels,
+			resolvePointLabels,
+			rest.config,
+			rest.decimalPrecision,
+			rest.canPinTooltip,
+			rest.renderTooltipFooter,
+		],
+	);
+
+	const hasSeries = rest.data.length > 1;
+
+	return (
+		<ChartWrapper
+			{...rest}
+			data={hasSeries ? rest.data : EMPTY_ALIGNED_DATA}
+			customTooltip={renderTooltip}
+			pinnedTooltipElement={pinnedTooltipElement}
+		>
+			{children}
+		</ChartWrapper>
+	);
+}

frontend/src/lib/visualization/charts/Scatter/__tests__/utils.test.ts

@@ -0,0 +1,118 @@
+import { DistributionType } from 'lib/uPlotV2/config/types';
+
+import {
+	buildScatterConfig,
+	prepareScatterChartData,
+	resolveAxisDistribution,
+	ScatterSeries,
+} from '../utils';
+
+jest.mock('lib/visualization/panels/utils/legendVisibilityUtils', () => ({
+	getStoredSeriesVisibility: jest.fn(),
+}));
+
+const SERIES: ScatterSeries[] = [
+	{ label: 'cart', xs: [10, 20], ys: [100, 200], sizes: [1, null] },
+	{ label: 'checkout', xs: [30], ys: [0] },
+];
+
+describe('prepareScatterChartData', () => {
+	it('lays series out as facets behind an empty x slot', () => {
+		expect(prepareScatterChartData(SERIES)).toStrictEqual([
+			null,
+			[
+				[10, 20],
+				[100, 200],
+				[1, null],
+			],
+			[[30], [0]],
+		]);
+	});
+});
+
+describe('resolveAxisDistribution', () => {
+	it('is linear unless log is asked for', () => {
+		expect(resolveAxisDistribution([0, 1], false)).toStrictEqual({
+			distribution: DistributionType.Linear,
+		});
+	});
+
+	it('is a plain log when every value is positive', () => {
+		expect(resolveAxisDistribution([1, 100], true)).toStrictEqual({
+			distribution: DistributionType.Logarithmic,
+		});
+	});
+
+	it('falls back to a symmetric log around the smallest magnitude when zero is present', () => {
+		expect(resolveAxisDistribution([0, 0.05, 300], true)).toStrictEqual({
+			distribution: DistributionType.SymmetricLog,
+			asinhThreshold: 0.01,
+		});
+	});
+
+	it('uses a unit threshold when nothing is positive', () => {
+		expect(resolveAxisDistribution([0, -5], true)).toStrictEqual({
+			distribution: DistributionType.SymmetricLog,
+			asinhThreshold: 1,
+		});
+	});
+});
+
+describe('buildScatterConfig', () => {
+	const build = (
+		overrides: Partial<Parameters<typeof buildScatterConfig>[0]> = {},
+	): ReturnType<typeof buildScatterConfig> =>
+		buildScatterConfig({
+			id: 'scatter',
+			series: SERIES,
+			isDarkMode: true,
+			x: { unit: 'reqps' },
+			y: { unit: 'ms', isLogScale: true },
+			...overrides,
+		});
+
+	it('emits a faceted plot with two value scales', () => {
+		const config = build().getConfig();
+
+		expect(config.mode).toBe(2);
+		expect(config.scales?.x).toMatchObject({ time: false, distr: 1 });
+		// The y column has a 0, so log becomes the symmetric variant.
+		expect(config.scales?.y).toMatchObject({ time: false, distr: 4 });
+	});
+
+	it('draws one faceted series per group with the plugin path builder', () => {
+		const config = build().getConfig();
+		const [, cart, checkout] = config.series ?? [];
+
+		expect(config.series).toHaveLength(3);
+		expect(cart).toMatchObject({
+			label: 'cart',
+			facets: [
+				{ scale: 'x', auto: true },
+				{ scale: 'y', auto: true },
+			],
+		});
+		expect(typeof cart?.paths).toBe('function');
+		expect(cart?.paths).toBe(checkout?.paths);
+		expect(cart?.points?.show).toBe(false);
+	});
+
+	it('formats both axes with their units', () => {
+		const config = build().getConfig();
+		const [xAxis, yAxis] = config.axes ?? [];
+
+		expect(xAxis).toMatchObject({ scale: 'x', side: 2, space: 90 });
+		expect(yAxis).toMatchObject({ scale: 'y', side: 3 });
+		expect(typeof xAxis?.values).toBe('function');
+		expect(typeof yAxis?.values).toBe('function');
+	});
+
+	it('registers a y threshold draw hook when thresholds are given', () => {
+		const config = build({
+			thresholds: [{ thresholdValue: 300, thresholdUnit: 'ms' }],
+		}).getConfig();
+
+		expect(config.hooks?.draw).toHaveLength(1);
+		expect(build().getConfig().hooks?.draw).toBeUndefined();
+	});
+});

frontend/src/lib/visualization/charts/Scatter/utils.ts

@@ -0,0 +1,209 @@
+import { PrecisionOption } from 'components/Graph/types';
+import {
+	DistributionType,
+	DrawStyle,
+	SelectionPreferencesSource,
+} from 'lib/uPlotV2/config/types';
+import { UPlotConfigBuilder } from 'lib/uPlotV2/config/UPlotConfigBuilder';
+import { Threshold } from 'lib/uPlotV2/hooks/types';
+import {
+	applyScatterPlugin,
+	createScatterPlugin,
+	SCATTER_FACETS,
+} from 'lib/uPlotV2/plugins/ScatterPlugin/scatterPlugin';
+import {
+	DEFAULT_SCATTER_POINT_SIZE,
+	ScatterChartData,
+	ScatterPointSize,
+	ScatterSeriesData,
+} from 'lib/uPlotV2/plugins/ScatterPlugin/types';
+import uPlot from 'uplot';
+
+/** Circle outline; the fill carries the colour. */
+const POINT_STROKE_WIDTH = 1;
+
+/** Unit-suffixed x labels are wider than uPlot's 50px default assumes. */
+const X_AXIS_TICK_SPACE_PX = 90;
+const X_AXIS_END_LABEL_PADDING_PX = 40;
+
+export interface ScatterSeries {
+	/** Group label, as the legend names it. */
+	label: string;
+	xs: number[];
+	ys: number[];
+	/** Optional third channel, in the caller's units. */
+	sizes?: Array<number | null>;
+}
+
+export interface ScatterAxisOptions {
+	unit?: string;
+	softMin?: number | null;
+	softMax?: number | null;
+	isLogScale?: boolean;
+}
+
+export interface BuildScatterConfigArgs {
+	id: string;
+	series: ScatterSeries[];
+	isDarkMode: boolean;
+	x: ScatterAxisOptions;
+	y: ScatterAxisOptions;
+	pointSize?: ScatterPointSize;
+	/** 0–1. */
+	fillOpacity?: number;
+	colorMapping?: Record<string, string>;
+	/** Drawn on the y axis. */
+	thresholds?: Threshold[];
+	decimalPrecision?: PrecisionOption;
+	selectionPreferencesSource?: SelectionPreferencesSource;
+	shouldSaveSelectionPreference?: boolean;
+}
+
+/** `[null, [xs, ys, sizes?], …]`: uPlot's faceted layout, series 0 empty. */
+export function prepareScatterChartData(
+	series: ScatterSeries[],
+): uPlot.AlignedData {
+	const data: ScatterChartData = [
+		null,
+		...series.map(
+			(entry): ScatterSeriesData =>
+				entry.sizes ? [entry.xs, entry.ys, entry.sizes] : [entry.xs, entry.ys],
+		),
+	];
+	return data as unknown as uPlot.AlignedData;
+}
+
+export interface AxisDistribution {
+	distribution: DistributionType;
+	asinhThreshold?: number;
+}
+
+/**
+ * A log axis needs every value above zero; a rate that is sometimes 0 would drop
+ * those points. Zero or negatives switch to a symmetric log whose linear band
+ * ends at the smallest non-zero magnitude, so nothing is lost and the small
+ * values still spread out.
+ */
+export function resolveAxisDistribution(
+	values: number[],
+	isLogScale?: boolean,
+): AxisDistribution {
+	if (!isLogScale) {
+		return { distribution: DistributionType.Linear };
+	}
+	let minPositive = Infinity;
+	let needsSymmetric = false;
+	for (const value of values) {
+		if (!Number.isFinite(value)) {
+			continue;
+		}
+		if (value <= 0) {
+			needsSymmetric = true;
+		} else {
+			minPositive = Math.min(minPositive, value);
+		}
+	}
+	if (!needsSymmetric) {
+		return { distribution: DistributionType.Logarithmic };
+	}
+	const asinhThreshold = Number.isFinite(minPositive)
+		? 10 ** Math.floor(Math.log10(minPositive))
+		: 1;
+	return { distribution: DistributionType.SymmetricLog, asinhThreshold };
+}
+
+export function buildScatterConfig({
+	id,
+	series,
+	isDarkMode,
+	x,
+	y,
+	pointSize = DEFAULT_SCATTER_POINT_SIZE,
+	fillOpacity,
+	colorMapping = {},
+	thresholds,
+	decimalPrecision,
+	selectionPreferencesSource,
+	shouldSaveSelectionPreference,
+}: BuildScatterConfigArgs): UPlotConfigBuilder {
+	const builder = new UPlotConfigBuilder({
+		id,
+		selectionPreferencesSource,
+		shouldSaveSelectionPreference,
+	});
+
+	const plugin = createScatterPlugin({ pointSize });
+	applyScatterPlugin(builder, plugin);
+	// The last x label is centred on the plot's right edge; room for its unit.
+	builder.setPadding([16, X_AXIS_END_LABEL_PADDING_PX, 8, 8]);
+
+	const xDistribution = resolveAxisDistribution(
+		series.flatMap((entry) => entry.xs),
+		x.isLogScale,
+	);
+	const yDistribution = resolveAxisDistribution(
+		series.flatMap((entry) => entry.ys),
+		y.isLogScale,
+	);
+
+	const yThresholds =
+		thresholds && thresholds.length > 0
+			? { scaleKey: 'y', thresholds, yAxisUnit: y.unit }
+			: undefined;
+
+	builder.addScale({
+		scaleKey: 'x',
+		time: false,
+		softMin: x.softMin ?? undefined,
+		softMax: x.softMax ?? undefined,
+		...xDistribution,
+	});
+	builder.addScale({
+		scaleKey: 'y',
+		time: false,
+		softMin: y.softMin ?? undefined,
+		softMax: y.softMax ?? undefined,
+		thresholds: yThresholds,
+		...yDistribution,
+	});
+
+	builder.addAxis({
+		scaleKey: 'x',
+		side: 2,
+		isDarkMode,
+		isTimeAxis: false,
+		yAxisUnit: x.unit ?? '',
+		decimalPrecision,
+		isLogScale: xDistribution.distribution !== DistributionType.Linear,
+		space: X_AXIS_TICK_SPACE_PX,
+	});
+	builder.addAxis({
+		scaleKey: 'y',
+		side: 3,
+		isDarkMode,
+		yAxisUnit: y.unit ?? '',
+		decimalPrecision,
+		isLogScale: yDistribution.distribution !== DistributionType.Linear,
+	});
+
+	series.forEach((entry) => {
+		builder.addSeries({
+			scaleKey: 'y',
+			label: entry.label,
+			colorMapping,
+			drawStyle: DrawStyle.Scatter,
+			pathBuilder: plugin.pathBuilder,
+			facets: SCATTER_FACETS,
+			lineWidth: POINT_STROKE_WIDTH,
+			pointSize: pointSize.fixed,
+			fillOpacity,
+			isDarkMode,
+		});
+	});
+
+	if (yThresholds) {
+		builder.addThresholds(yThresholds);
+	}
+
+	return builder;
+}

frontend/src/lib/visualization/charts/types.ts

@@ -9,6 +9,10 @@ import {
 	TooltipRenderArgs,
 } from 'lib/uPlotV2/components/types';
 import { UPlotConfigBuilder } from 'lib/uPlotV2/config/UPlotConfigBuilder';
+import type {
+	ScatterChannels,
+	ScatterPointLabel,
+} from 'lib/uPlotV2/plugins/ScatterPlugin/types';
 import {
 	DashboardCursorSync,
 	SyncTooltipFilterMode,
@@ -74,6 +78,15 @@ export interface HistogramChartProps extends ChartWrapperProps {
 	isQueriesMerged?: boolean;
 }
 
+/** `data` is mode-2 (`prepareScatterChartData`); `config` comes from `buildScatterConfig`. */
+export interface ScatterChartProps extends ChartWrapperProps {
+	channels: ScatterChannels;
+	resolvePointLabels?: (
+		seriesIndex: number,
+		dataIndex: number,
+	) => ScatterPointLabel[];
+}
+
 /**
  * One resolved pie/donut slice: a display label, its (already parsed) positive
  * numeric value, and the colour used for the arc + legend swatch.