feat(dashboards): build a series selection from the legend

The row action is now a labelled All/Only toggle, and clicking rows in a
narrowed legend adds to the selection instead of moving the isolation,
which leaves Add with nothing to do. Column floors grew to fit the wider
action.

Assisted-by: Claude Opus 5

frontend/src/lib/uPlotV2/components/Legend/Legend.module.scss

@@ -0,0 +1,270 @@
+@use '../../../../styles/scrollbar' as *;
+
+.container {
+	position: relative;
+	display: flex;
+	flex-direction: column;
+	height: 100%;
+	width: 100%;
+	// Let the flex children shrink below their content height so the series list
+	// scrolls within the capped legend height instead of overflowing the wrapper
+	// (the default min-height:auto would block the shrink).
+	min-height: 0;
+}
+
+/* Toolbar */
+
+.toolbar {
+	display: flex;
+	align-items: center;
+	flex-wrap: wrap;
+	gap: var(--spacing-5, 10px);
+	padding: 0 var(--spacing-4) var(--spacing-5, 10px);
+	flex-shrink: 0;
+
+	> * {
+		flex: 0 1 auto;
+	}
+}
+
+.status {
+	// Wraps rather than losing the count at its end.
+	min-width: 0;
+	font-family: var(--font-mono);
+	font-size: var(--periscope-font-size-small);
+	color: var(--l3-foreground);
+}
+
+.searchContainer {
+	flex-shrink: 0;
+	width: 100%;
+	padding-right: var(--spacing-4);
+	padding-bottom: var(--spacing-5, 10px);
+}
+
+.searchInput {
+	font-size: var(--font-size-xs);
+}
+
+.searchIcon {
+	color: var(--l3-foreground);
+}
+
+/* Series list */
+
+.scroller {
+	// flex:1 + min-height:0 pins the scroller to the space left after the
+	// toolbar instead of growing to fit every row.
+	flex: 1;
+	min-height: 0;
+	height: 100%;
+	width: 100%;
+	padding-right: var(--spacing-2);
+	overflow-x: hidden;
+	overscroll-behavior: contain;
+
+	@include custom-scrollbar;
+}
+
+.gridItem {
+	// Or the item keeps its content width and the label never ellipsizes.
+	min-width: 0;
+	max-width: 100%;
+}
+
+.gridList {
+	min-width: 0;
+	display: grid;
+	grid-auto-flow: row;
+	// min() keeps the column inside a narrow panel, where a wider one would push
+	// the row's actions out of the clipped area.
+	grid-template-columns: repeat(
+		auto-fill,
+		minmax(min(var(--legend-item-width, 240px), 100%), 1fr)
+	);
+	gap: var(--spacing-1) var(--spacing-4);
+}
+
+.container.isRight .gridList {
+	grid-template-columns: 1fr;
+}
+
+.emptyState {
+	padding: var(--spacing-16) 0;
+	font-size: var(--font-size-xs);
+	color: var(--l3-foreground);
+	text-align: center;
+}
+
+/* Row */
+
+.row {
+	// Width of the revealed actions, given up by the label on hover only.
+	--legend-actions-reserve: 78px;
+
+	position: relative;
+	display: flex;
+	align-items: center;
+	gap: var(--spacing-4);
+	height: 28px;
+	padding: 0 var(--spacing-3) 0 var(--spacing-4);
+	box-sizing: border-box;
+	width: 100%;
+	max-width: 100%;
+	min-width: 0;
+	border-radius: var(--radius);
+	cursor: pointer;
+	transition: background 160ms linear;
+
+	&:hover,
+	&:focus-visible {
+		background: var(--l3-background);
+	}
+}
+
+.isFocused {
+	background: var(--l3-background);
+}
+
+.marker {
+	// Reads as a checkbox without being one: filled when shown, hollow when
+	// hidden, deliberately not a check glyph.
+	flex: 0 0 auto;
+	box-sizing: border-box;
+	position: relative;
+	// Above the actions, so a narrow row's chip never covers the series colour.
+	z-index: 4;
+	width: 12px;
+	height: 12px;
+	padding: 0;
+	appearance: none;
+	border-width: 1.5px;
+	border-style: solid;
+	border-radius: var(--radius);
+	cursor: pointer;
+	transition:
+		transform 200ms ease,
+		box-shadow 200ms ease,
+		background-color 160ms linear,
+		opacity 160ms linear;
+
+	&:hover {
+		transform: scale(1.2);
+		box-shadow: 0 0 0 2px
+			color-mix(in srgb, var(--l1-foreground) 30%, transparent);
+	}
+
+	&:active {
+		transform: scale(0.9);
+	}
+
+	&:disabled {
+		cursor: default;
+	}
+
+	&:disabled:hover {
+		transform: none;
+		box-shadow: none;
+	}
+}
+
+// Series names run long and have no spaces to break on, so they need both a
+// cap and a break rule or the tooltip becomes one panel-wide line.
+.rowTooltip {
+	max-width: 420px;
+	white-space: normal;
+	overflow-wrap: anywhere;
+}
+
+.label {
+	flex: 1 1 auto;
+	box-sizing: border-box;
+	width: 100%;
+	min-width: 0;
+	overflow: hidden;
+	text-overflow: ellipsis;
+	white-space: nowrap;
+	font-family: var(--font-mono);
+	font-size: var(--font-size-xs);
+	letter-spacing: -0.01em;
+	color: var(--l2-foreground);
+	user-select: none;
+}
+
+.isHidden .marker {
+	opacity: 0.45;
+}
+
+.isHidden .label {
+	color: var(--l3-foreground);
+	text-decoration: line-through;
+	text-decoration-thickness: 1px;
+}
+
+/* Row actions */
+
+.actions {
+	position: absolute;
+	top: var(--spacing-2);
+	right: var(--spacing-3);
+	z-index: 3;
+	display: flex;
+	align-items: center;
+	gap: var(--spacing-2);
+	padding-left: var(--spacing-5, 10px);
+	// Sits on the row's hover background and masks the label's tail behind it.
+	background: var(--l3-background);
+	box-shadow: -8px 0 8px var(--l3-background);
+	opacity: 0;
+	transform: translateX(10px);
+	pointer-events: none;
+	transition:
+		opacity 180ms cubic-bezier(0.08, 0.52, 0.52, 1),
+		transform 180ms cubic-bezier(0.08, 0.52, 0.52, 1);
+}
+
+// :focus-visible, not :focus-within — the latter also matches the click that
+// just toggled the series, leaving the actions stuck open.
+.row:hover .actions,
+.row:focus-visible .actions,
+.row:has(:focus-visible) .actions {
+	opacity: 1;
+	transform: translateX(0);
+	pointer-events: auto;
+}
+
+// The cap spares rows sized to their actions, not their label.
+.row:hover .label,
+.row:focus-visible .label,
+.row:has(:focus-visible) .label {
+	padding-right: min(var(--legend-actions-reserve), 50%);
+}
+
+.actionTrigger {
+	display: inline-flex;
+}
+
+.actionButton {
+	--button-height: 20px;
+	--button-width: 20px;
+	--button-padding: 0;
+	--button-variant-ghost-color: var(--l3-foreground);
+	--button-variant-ghost-hover-color: var(--l1-foreground);
+
+	flex-shrink: 0;
+}
+
+.actionButton.scopeButton {
+	--button-width: auto;
+	--button-padding: 0 var(--spacing-4);
+	--button-font-size: var(--font-size-xs);
+	--button-border-radius: calc(var(--radius) * 4);
+	--button-base-border-width: 1px;
+	// --l2-border is the actions bar's own background: one step up reads.
+	--button-base-border-color: var(--l3-border);
+
+	border-style: solid;
+}
+.actionButton.scopeButton:hover {
+	border-color: var(--l2-border);
+}

frontend/src/lib/uPlotV2/components/Legend/Legend.styles.scss

@@ -1,204 +0,0 @@
-@use '../../../../styles/scrollbar' as *;
-
-.legend-search-container {
-	flex-shrink: 0;
-	width: 100%;
-	padding-right: 8px;
-
-	.legend-search-input {
-		font-size: 12px;
-	}
-}
-
-.legend-container {
-	display: flex;
-	flex-direction: column;
-	align-items: center;
-	gap: 12px;
-	height: 100%;
-	width: 100%;
-	// Allow the flex children to shrink below their content height so the
-	// virtualized grid scrolls within the capped legend height instead of
-	// overflowing the wrapper (default min-height:auto would block the shrink).
-	min-height: 0;
-
-	&:has(.legend-item-focused) .legend-item {
-		opacity: 0.3;
-	}
-
-	&:has(.legend-item-focused) .legend-item.legend-item-focused {
-		opacity: 1;
-	}
-
-	.legend-empty-state {
-		font-size: 12px;
-		color: var(--l2-foreground);
-		text-align: center;
-		padding: 12px;
-		padding: 2rem 0;
-	}
-
-	.legend-virtuoso-container {
-		// flex:1 + min-height:0 pins the scroller to the space left after the
-		// search box (RIGHT legend) and lets it scroll instead of growing to fit
-		// every row — without this the grid overflows a BOTTOM legend's fixed height.
-		flex: 1;
-		min-height: 0;
-		height: 100%;
-		width: 100%;
-
-		.virtuoso-grid-list {
-			min-width: 0;
-			display: grid;
-			grid-auto-flow: row;
-			grid-template-columns: repeat(
-				auto-fill,
-				minmax(var(--legend-average-width, 240px), 1fr)
-			);
-			column-gap: 12px;
-		}
-
-		.virtuoso-grid-item {
-			min-width: 0;
-		}
-
-		&.legend-virtuoso-container-right {
-			.virtuoso-grid-list {
-				grid-template-columns: 1fr;
-			}
-		}
-
-		&.legend-virtuoso-container-single-row {
-			.virtuoso-grid-list {
-				grid-template-columns: repeat(
-					auto-fit,
-					minmax(var(--legend-average-width, 240px), max-content)
-				);
-				justify-content: center;
-			}
-		}
-
-		@include custom-scrollbar;
-	}
-}
-
-.legend-row {
-	padding: 4px 0;
-	display: flex;
-	align-items: center;
-	flex-wrap: wrap;
-	gap: 8px 16px;
-
-	&.legend-single-row {
-		justify-content: center;
-	}
-
-	&.legend-row-right {
-		flex-direction: column;
-		align-items: flex-start;
-		justify-content: flex-start;
-	}
-	&.legend-row-bottom {
-		flex-direction: row;
-	}
-}
-
-.legend-item {
-	display: flex;
-	align-items: center;
-	gap: 6px;
-	padding: 4px 8px;
-	// Include padding within the width so a full-width row (legend-item-right) fits its
-	// column instead of overflowing by the 16px horizontal padding — there is no global
-	// border-box reset, so the default content-box would make it overflow.
-	box-sizing: border-box;
-	max-width: 100%;
-	overflow: hidden;
-	border-radius: 4px;
-	cursor: pointer;
-
-	&.legend-item-right {
-		width: 100%;
-	}
-
-	&.legend-item-off {
-		opacity: 0.3;
-		text-decoration: line-through;
-		text-decoration-thickness: 1px;
-	}
-
-	&.legend-item-focused {
-		opacity: 1;
-	}
-
-	.legend-item-label-trigger {
-		display: flex;
-		align-items: center;
-		gap: 6px;
-		flex: 1;
-		min-width: 0;
-		cursor: pointer;
-	}
-
-	.legend-marker {
-		border-width: 2px;
-		border-style: solid;
-		border-radius: 50%;
-		min-width: 11px;
-		min-height: 11px;
-		width: 11px;
-		height: 11px;
-		flex-shrink: 0;
-		cursor: pointer;
-		transition: transform 0.2s ease;
-		position: relative;
-
-		&:hover {
-			transform: scale(1.2);
-			box-shadow: 0 0 0 2px rgba(255, 255, 255, 0.3);
-		}
-
-		&:active {
-			transform: scale(0.9);
-		}
-	}
-
-	.legend-label {
-		flex: 1;
-		font-size: 12px;
-		overflow: hidden;
-		text-overflow: ellipsis;
-		white-space: nowrap;
-		min-width: 0;
-		user-select: none;
-	}
-
-	.legend-copy-button {
-		// Always laid out (space reserved) but transparent, so revealing it on
-		// hover fades the icon in without reflowing the row / shifting the label.
-		// Shrink the shared icon Button (defaults to a 2rem square) to the
-		// compact legend row via its size tokens.
-		--button-height: auto;
-		--button-width: auto;
-		--button-padding: 2px;
-
-		opacity: 0;
-		flex-shrink: 0;
-		color: var(--l2-foreground);
-		border-radius: 4px;
-		transition:
-			opacity 0.15s ease,
-			color 0.15s ease;
-
-		&:hover {
-			color: var(--l1-foreground);
-		}
-	}
-
-	&:hover {
-		background: var(--l3-background);
-		.legend-copy-button {
-			opacity: 1;
-		}
-	}
-}

frontend/src/lib/uPlotV2/components/Legend/Legend.tsx

@@ -1,139 +1,136 @@
 import { useCallback, useMemo, useRef, useState } from 'react';
 import { VirtuosoGrid } from 'react-virtuoso';
-import { Input } from 'antd';
-import { TooltipSimple } from '@signozhq/ui/tooltip';
 import cx from 'classnames';
-import { useResizeObserver } from 'hooks/useDimensions';
 import { LegendItem } from 'lib/uPlotV2/config/types';
-import CopyButton from 'periscope/components/CopyButton/CopyButton';
 
 import { LegendPosition, LegendProps } from '../types';
 
-import './Legend.styles.scss';
+import { LEGEND_ITEM_EXTRA_WIDTH, MAX_LEGEND_WIDTH } from './constants';
+import LegendRow from './LegendRow';
+import LegendToolbar from './LegendToolbar';
+import { filterLegendItems, getShownSeriesState } from './utils';
 
-export const MAX_LEGEND_WIDTH = 240;
+import styles from './Legend.module.scss';
 
 /**
- * Presentational legend. Renders the supplied `items` (markers + labels, an
- * optional copy button, and a search box for the RIGHT position) and delegates
- * all interaction to the container handlers. Source-agnostic — the uPlot
- * charts feed it via UPlotLegend; Pie feeds it directly.
+ * Presentational legend, source-agnostic: the uPlot charts feed it via
+ * UPlotLegend, Pie feeds it directly. Every state change is delegated.
  */
 export default function Legend({
 	items,
 	position,
 	averageLegendWidth = MAX_LEGEND_WIDTH,
 	focusedSeriesIndex,
-	onClick,
-	onMouseMove,
-	onMouseLeave,
+	onToggleSeries,
+	onShowOnlySeries,
+	onShowAllSeries,
+	onHoverSeries,
 	showCopy = true,
 }: LegendProps): JSX.Element {
 	const legendContainerRef = useRef<HTMLDivElement | null>(null);
-	const [legendSearchQuery, setLegendSearchQuery] = useState('');
+	const [filterQuery, setFilterQuery] = useState('');
 
-	// Search is intrinsic to the right-positioned legend.
-	const searchEnabled = position === LegendPosition.RIGHT;
-	const { width: containerWidth } = useResizeObserver(legendContainerRef);
+	const itemWidth = averageLegendWidth + LEGEND_ITEM_EXTRA_WIDTH;
+	const isRightPosition = position === LegendPosition.RIGHT;
 
-	const isSingleRow = useMemo(() => {
-		if (position !== LegendPosition.BOTTOM || containerWidth <= 0) {
-			return false;
-		}
-		const totalLegendWidth = items.length * (averageLegendWidth + 16);
-		const totalRows = Math.ceil(totalLegendWidth / containerWidth);
-		return totalRows <= 1;
-	}, [averageLegendWidth, items.length, position, containerWidth]);
-
-	const visibleLegendItems = useMemo(() => {
-		if (!searchEnabled || !legendSearchQuery.trim()) {
-			return items;
-		}
-
-		const query = legendSearchQuery.trim().toLowerCase();
-		return items.filter((item) => item.label?.toLowerCase().includes(query));
-	}, [searchEnabled, legendSearchQuery, items]);
-
-	const renderLegendItem = useCallback(
-		(item: LegendItem): JSX.Element => {
-			// `color` is uPlot's stroke union (string | fn | gradient); only a string
-			// is a usable CSS colour for the marker.
-			const markerColor = typeof item.color === 'string' ? item.color : undefined;
-			return (
-				<div
-					key={item.seriesIndex}
-					data-legend-item-id={item.seriesIndex}
-					className={cx('legend-item', `legend-item-${position.toLowerCase()}`, {
-						'legend-item-off': !item.show,
-						'legend-item-focused': focusedSeriesIndex === item.seriesIndex,
-					})}
-				>
-					<TooltipSimple title={item.label} arrow side="top" disableHoverableContent>
-						<div className="legend-item-label-trigger">
-							<div
-								className="legend-marker"
-								style={{ borderColor: markerColor }}
-								data-is-legend-marker={true}
-							/>
-							<span className="legend-label">{item.label}</span>
-						</div>
-					</TooltipSimple>
-					{showCopy && (
-						<CopyButton
-							value={item.label ?? ''}
-							size={12}
-							className="legend-copy-button"
-							ariaLabel={`Copy ${item.label}`}
-							testId="legend-copy"
-						/>
-					)}
-				</div>
-			);
-		},
-		[focusedSeriesIndex, position, showCopy],
+	const { visibleCount, soleShownSeriesIndex } = useMemo(
+		() => getShownSeriesState(items),
+		[items],
 	);
 
-	const isEmptyState = useMemo(() => {
-		if (!searchEnabled || !legendSearchQuery.trim()) {
-			return false;
-		}
-		return visibleLegendItems.length === 0;
-	}, [searchEnabled, legendSearchQuery, visibleLegendItems]);
+	// A bottom legend gets two rows; spending one on chrome costs more chart than
+	// the readout is worth.
+	const showToolbar = isRightPosition && items.length > 0;
+	const showFilter = showToolbar;
+
+	const effectiveQuery = showFilter ? filterQuery : '';
+
+	const visibleLegendItems = useMemo(
+		() => filterLegendItems(items, effectiveQuery),
+		[items, effectiveQuery],
+	);
+
+	const isEmptyState =
+		!!effectiveQuery.trim() && visibleLegendItems.length === 0;
+
+	const isAllShown = visibleCount === items.length;
+
+	/** Everything showing -> isolate, since there is nothing to exclude yet. */
+	const handleRowClick = useCallback(
+		(seriesIndex: number): void => {
+			if (isAllShown) {
+				onShowOnlySeries(seriesIndex);
+				return;
+			}
+
+			onToggleSeries(seriesIndex);
+		},
+		[isAllShown, onShowOnlySeries, onToggleSeries],
+	);
+
+	// A row that unmounts under the pointer never fires its own mouseleave.
+	const handleMouseLeave = useCallback(
+		(): void => onHoverSeries(null),
+		[onHoverSeries],
+	);
+
+	const renderLegendItem = useCallback(
+		(item: LegendItem): JSX.Element => (
+			<LegendRow
+				key={item.seriesIndex}
+				item={item}
+				isSoleShown={soleShownSeriesIndex === item.seriesIndex}
+				isAllShown={isAllShown}
+				isFocused={focusedSeriesIndex === item.seriesIndex}
+				showCopy={showCopy}
+				onRowClick={handleRowClick}
+				onToggleVisibility={onToggleSeries}
+				onShowOnly={onShowOnlySeries}
+				onShowAll={onShowAllSeries}
+				onHover={onHoverSeries}
+			/>
+		),
+		[
+			soleShownSeriesIndex,
+			isAllShown,
+			focusedSeriesIndex,
+			showCopy,
+			handleRowClick,
+			onToggleSeries,
+			onShowOnlySeries,
+			onShowAllSeries,
+			onHoverSeries,
+		],
+	);
 
 	return (
 		<div
 			ref={legendContainerRef}
-			className="legend-container"
-			onClick={onClick}
-			onMouseMove={onMouseMove}
-			onMouseLeave={onMouseLeave}
-			style={{
-				['--legend-average-width' as string]: `${averageLegendWidth + 16}px`, // 16px is the marker width
-			}}
+			className={cx(styles.container, {
+				[styles.isRight]: isRightPosition,
+			})}
+			style={{ ['--legend-item-width' as string]: `${itemWidth}px` }}
+			onMouseLeave={handleMouseLeave}
+			data-testid="legend-container"
 		>
-			{searchEnabled && (
-				<div className="legend-search-container">
-					<Input
-						allowClear
-						placeholder="Search..."
-						value={legendSearchQuery}
-						onChange={(e): void => setLegendSearchQuery(e.target.value)}
-						data-testid="legend-search-input"
-						className="legend-search-input"
-					/>
-				</div>
+			{showToolbar && (
+				<LegendToolbar
+					visibleCount={visibleCount}
+					totalCount={items.length}
+					showFilter={showFilter}
+					filterQuery={filterQuery}
+					onFilterQueryChange={setFilterQuery}
+				/>
 			)}
 			{isEmptyState ? (
-				<div className="legend-empty-state">
-					No series found matching &quot;{legendSearchQuery}&quot;
+				<div className={styles.emptyState}>
+					No series found matching &quot;{effectiveQuery}&quot;
 				</div>
 			) : (
 				<VirtuosoGrid
-					className={cx(
-						'legend-virtuoso-container',
-						`legend-virtuoso-container-${position.toLowerCase()}`,
-						{ 'legend-virtuoso-container-single-row': isSingleRow },
-					)}
+					className={styles.scroller}
+					listClassName={styles.gridList}
+					itemClassName={styles.gridItem}
 					data={visibleLegendItems}
 					itemContent={(_, item): JSX.Element => renderLegendItem(item)}
 				/>

frontend/src/lib/uPlotV2/components/Legend/LegendRow.tsx

@@ -0,0 +1,180 @@
+import { KeyboardEvent, memo, MouseEvent, useCallback } from 'react';
+import { Button } from '@signozhq/ui/button';
+import { TooltipSimple } from '@signozhq/ui/tooltip';
+import cx from 'classnames';
+import { LegendItem } from 'lib/uPlotV2/config/types';
+import CopyButton from 'periscope/components/CopyButton/CopyButton';
+
+import { LEGEND_TOOLTIP_DELAY_MS } from './constants';
+import styles from './Legend.module.scss';
+
+export interface LegendRowProps {
+	item: LegendItem;
+	/** The only series currently shown, so hiding it is refused. */
+	isSoleShown: boolean;
+	/** Nothing is hidden, so the row's action can only narrow the selection. */
+	isAllShown: boolean;
+	isFocused: boolean;
+	showCopy: boolean;
+	/** Row click, whose meaning depends on how many series are shown. */
+	onRowClick: (seriesIndex: number) => void;
+	/** Marker click: hide or show just this series. */
+	onToggleVisibility: (seriesIndex: number) => void;
+	onShowOnly: (seriesIndex: number) => void;
+	onShowAll: () => void;
+	onHover: (seriesIndex: number | null) => void;
+}
+
+/**
+ * One legend row. The marker is its own target for excluding a single series —
+ * the one thing the row click can't do while everything is showing. The actions
+ * overlay the label's tail rather than taking layout width, and their reveal is
+ * pure CSS.
+ */
+function LegendRow({
+	item,
+	isSoleShown,
+	isAllShown,
+	isFocused,
+	showCopy,
+	onRowClick,
+	onToggleVisibility,
+	onShowOnly,
+	onShowAll,
+	onHover,
+}: LegendRowProps): JSX.Element {
+	const { seriesIndex, show } = item;
+	const label = item.label ?? '';
+	const isShowAllAction = show && !isAllShown;
+	const scopeActionLabel = isShowAllAction
+		? 'Show all series'
+		: 'Show only current series';
+	// `color` is uPlot's stroke union (string | fn | gradient); only a string is
+	// a usable CSS colour for the marker.
+	const seriesColor = typeof item.color === 'string' ? item.color : undefined;
+
+	const handleRowClick = useCallback(
+		(): void => onRowClick(seriesIndex),
+		[onRowClick, seriesIndex],
+	);
+
+	const handleMarkerClick = useCallback(
+		(event: MouseEvent<HTMLButtonElement>): void => {
+			event.stopPropagation();
+			onToggleVisibility(seriesIndex);
+		},
+		[onToggleVisibility, seriesIndex],
+	);
+
+	const handleKeyDown = useCallback(
+		(event: KeyboardEvent<HTMLDivElement>): void => {
+			// Let the row actions handle their own keys.
+			if (event.target !== event.currentTarget) {
+				return;
+			}
+			if (event.key === 'Enter' || event.key === ' ') {
+				event.preventDefault();
+				onRowClick(seriesIndex);
+			}
+		},
+		[onRowClick, seriesIndex],
+	);
+
+	const handleScopeClick = useCallback(
+		(event: MouseEvent<HTMLButtonElement>): void => {
+			event.stopPropagation();
+			if (isShowAllAction) {
+				onShowAll();
+				return;
+			}
+			onShowOnly(seriesIndex);
+		},
+		[isShowAllAction, onShowAll, onShowOnly, seriesIndex],
+	);
+
+	const handleMouseEnter = useCallback(
+		(): void => onHover(seriesIndex),
+		[onHover, seriesIndex],
+	);
+
+	const handleMouseLeave = useCallback((): void => onHover(null), [onHover]);
+
+	return (
+		<div
+			className={cx(styles.row, {
+				[styles.isHidden]: !show,
+				[styles.isFocused]: isFocused,
+			})}
+			data-legend-item-id={seriesIndex}
+			data-testid={`legend-item-${seriesIndex}`}
+			role="switch"
+			tabIndex={0}
+			aria-checked={show}
+			aria-label={label}
+			onClick={handleRowClick}
+			onKeyDown={handleKeyDown}
+			onMouseEnter={handleMouseEnter}
+			onMouseLeave={handleMouseLeave}
+		>
+			<button
+				type="button"
+				className={styles.marker}
+				style={{
+					borderColor: seriesColor,
+					backgroundColor: show ? seriesColor : 'transparent',
+				}}
+				onClick={handleMarkerClick}
+				disabled={isSoleShown}
+				aria-label={`${show ? 'Hide' : 'Show'} ${label}`}
+				data-is-legend-marker={true}
+				data-testid={`legend-marker-${seriesIndex}`}
+			/>
+			<TooltipSimple
+				title={label}
+				arrow
+				side="top"
+				delayDuration={LEGEND_TOOLTIP_DELAY_MS}
+				disableHoverableContent
+				tooltipContentProps={{ className: styles.rowTooltip }}
+			>
+				<span className={styles.label}>{label}</span>
+			</TooltipSimple>
+			<div className={styles.actions}>
+				<TooltipSimple
+					title={scopeActionLabel}
+					arrow
+					side="top"
+					delayDuration={LEGEND_TOOLTIP_DELAY_MS}
+					disableHoverableContent
+					tooltipContentProps={{ className: styles.rowTooltip }}
+				>
+					{/* Radix's asChild merge strips the button's own data-testid. */}
+					<span className={styles.actionTrigger}>
+						<Button
+							variant="ghost"
+							color="secondary"
+							size="sm"
+							className={cx(styles.actionButton, styles.scopeButton)}
+							onClick={handleScopeClick}
+							aria-label={scopeActionLabel}
+							testId={`legend-scope-${seriesIndex}`}
+						>
+							{isShowAllAction ? 'All' : 'Only'}
+						</Button>
+					</span>
+				</TooltipSimple>
+				{showCopy && (
+					<CopyButton
+						value={label}
+						size={13}
+						className={styles.actionButton}
+						ariaLabel={`Copy ${label}`}
+						testId={`legend-copy-${seriesIndex}`}
+					/>
+				)}
+			</div>
+		</div>
+	);
+}
+
+export default memo(LegendRow);

frontend/src/lib/uPlotV2/components/Legend/LegendToolbar.tsx

@@ -0,0 +1,56 @@
+import { ChangeEvent, useCallback } from 'react';
+import { Input } from 'antd';
+import { Search } from '@signozhq/icons';
+
+import styles from './Legend.module.scss';
+
+export interface LegendToolbarProps {
+	visibleCount: number;
+	totalCount: number;
+	/** Search is intrinsic to the right-positioned legend. */
+	showFilter: boolean;
+	filterQuery: string;
+	onFilterQueryChange: (query: string) => void;
+}
+
+/** Legend chrome: the series search box and the "Showing N of M" readout. */
+export default function LegendToolbar({
+	visibleCount,
+	totalCount,
+	showFilter,
+	filterQuery,
+	onFilterQueryChange,
+}: LegendToolbarProps): JSX.Element {
+	const handleFilterChange = useCallback(
+		(event: ChangeEvent<HTMLInputElement>): void =>
+			onFilterQueryChange(event.target.value),
+		[onFilterQueryChange],
+	);
+
+	return (
+		<>
+			{showFilter && (
+				<div className={styles.searchContainer}>
+					<Input
+						allowClear
+						prefix={<Search size={12} className={styles.searchIcon} />}
+						placeholder="Search..."
+						value={filterQuery}
+						onChange={handleFilterChange}
+						className={styles.searchInput}
+						data-testid="legend-search-input"
+					/>
+				</div>
+			)}
+			<div className={styles.toolbar}>
+				<span
+					className={styles.status}
+					aria-live="polite"
+					data-testid="legend-status"
+				>
+					{`Showing ${visibleCount} of ${totalCount} series`}
+				</span>
+			</div>
+		</>
+	);
+}

frontend/src/lib/uPlotV2/components/Legend/UPlotLegend.tsx

@@ -8,8 +8,8 @@ import Legend from './Legend';
 
 /**
  * uPlot legend controller. Derives the legend items + focus/visibility state
- * from the chart config (useLegendsSync) and the toggle/focus interactions from
- * the plot context (useLegendActions), then renders the presentational Legend.
+ * from the chart config (useLegendsSync) and the series interactions from the
+ * plot context (useLegendActions), then renders the presentational Legend.
  * Must be rendered inside a PlotContextProvider.
  */
 export default function UPlotLegend({
@@ -17,13 +17,9 @@ export default function UPlotLegend({
 	config,
 	averageLegendWidth,
 }: UPlotLegendProps): JSX.Element {
-	const { legendItemsMap, focusedSeriesIndex, setFocusedSeriesIndex } =
-		useLegendsSync({ config });
-	const { onLegendClick, onLegendMouseMove, onLegendMouseLeave } =
-		useLegendActions({
-			setFocusedSeriesIndex,
-			focusedSeriesIndex,
-		});
+	const { legendItemsMap, focusedSeriesIndex } = useLegendsSync({ config });
+	const { onToggleSeries, onShowOnlySeries, onShowAllSeries, onHoverSeries } =
+		useLegendActions();
 
 	const items = useMemo(() => Object.values(legendItemsMap), [legendItemsMap]);
 
@@ -33,9 +29,10 @@ export default function UPlotLegend({
 			position={position}
 			averageLegendWidth={averageLegendWidth}
 			focusedSeriesIndex={focusedSeriesIndex}
-			onClick={onLegendClick}
-			onMouseMove={onLegendMouseMove}
-			onMouseLeave={onLegendMouseLeave}
+			onToggleSeries={onToggleSeries}
+			onShowOnlySeries={onShowOnlySeries}
+			onShowAllSeries={onShowAllSeries}
+			onHoverSeries={onHoverSeries}
 		/>
 	);
 }

frontend/src/lib/uPlotV2/components/Legend/__tests__/utils.test.ts

@@ -0,0 +1,45 @@
+import { LegendItem } from 'lib/uPlotV2/config/types';
+
+import { filterLegendItems, getShownSeriesState } from '../utils';
+
+const items = (shown: boolean[]): LegendItem[] =>
+	shown.map((show, index) => ({
+		seriesIndex: index + 1,
+		label: `series-${index}`,
+		color: '#000',
+		show,
+	}));
+
+describe('getShownSeriesState', () => {
+	it('counts the shown series', () => {
+		expect(getShownSeriesState(items([true, false, true]))).toStrictEqual({
+			visibleCount: 2,
+			soleShownSeriesIndex: null,
+		});
+	});
+
+	it('names the series when exactly one is shown', () => {
+		expect(getShownSeriesState(items([false, true, false]))).toStrictEqual({
+			visibleCount: 1,
+			soleShownSeriesIndex: 2,
+		});
+	});
+
+	it('reports nothing shown', () => {
+		expect(getShownSeriesState(items([false, false]))).toStrictEqual({
+			visibleCount: 0,
+			soleShownSeriesIndex: null,
+		});
+	});
+});
+
+describe('filterLegendItems', () => {
+	it('matches case-insensitively on the label', () => {
+		const filtered = filterLegendItems(items([true, true, true]), 'SERIES-1');
+		expect(filtered.map((item) => item.label)).toStrictEqual(['series-1']);
+	});
+
+	it('returns every item for a blank query', () => {
+		expect(filterLegendItems(items([true, true]), '   ')).toHaveLength(2);
+	});
+});

frontend/src/lib/uPlotV2/components/Legend/constants.ts

@@ -0,0 +1,20 @@
+/** Widest a single legend item is allowed to get when sizing the legend grid. */
+export const MAX_LEGEND_WIDTH = 240;
+
+/**
+ * Enough for a row to contain its own hover actions, which a short label would
+ * otherwise size a column too narrow for. Little room for the label is intended.
+ */
+export const MIN_LEGEND_ITEM_WIDTH = 110;
+
+/** Marker + row padding, on top of the estimated label width. */
+export const LEGEND_ITEM_EXTRA_WIDTH = 16;
+
+/** Must match `.row`'s height and the grid's row gap, or the reserved
+ * rectangle clips a row. */
+export const LEGEND_ROW_HEIGHT = 28;
+export const LEGEND_ROW_GAP = 2;
+export const LEGEND_MAX_BOTTOM_ROWS = 2;
+
+/** Hover delay before a row's full-name tooltip opens. */
+export const LEGEND_TOOLTIP_DELAY_MS = 500;

frontend/src/lib/uPlotV2/components/Legend/utils.ts

@@ -0,0 +1,34 @@
+import { LegendItem } from 'lib/uPlotV2/config/types';
+
+export interface ShownSeriesState {
+	visibleCount: number;
+	/** The series index when exactly one series is shown, else null. */
+	soleShownSeriesIndex: number | null;
+}
+
+/**
+ * Driven by what is actually shown, never a remembered isolation: hiding series
+ * one at a time down to a single one is the same state as "Only".
+ */
+export function getShownSeriesState(items: LegendItem[]): ShownSeriesState {
+	const shown = items.filter((item) => item.show);
+
+	return {
+		visibleCount: shown.length,
+		soleShownSeriesIndex: shown.length === 1 ? shown[0].seriesIndex : null,
+	};
+}
+
+export function filterLegendItems(
+	items: LegendItem[],
+	query: string,
+): LegendItem[] {
+	const normalisedQuery = query.trim().toLowerCase();
+	if (!normalisedQuery) {
+		return items;
+	}
+
+	return items.filter((item) =>
+		item.label?.toLowerCase().includes(normalisedQuery),
+	);
+}

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

@@ -12,10 +12,11 @@
 	}
 }
 
+// Matches the legend row's marker.
 .uplotTooltipItemMarker {
-	border-radius: 50%;
+	border-radius: var(--radius);
 	border-style: solid;
-	border-width: 2px;
+	border-width: 1.5px;
 	width: 12px;
 	height: 12px;
 	box-sizing: border-box;
@@ -30,11 +31,23 @@
 	justify-content: space-between;
 }
 
+// The legend's mono type; the container's Inter stays for the header.
+.uplotTooltipItemLabel,
+.uplotTooltipItemValue {
+	font-family: var(--font-mono);
+	font-size: var(--font-size-xs);
+	letter-spacing: -0.01em;
+}
+
 .uplotTooltipItemLabel {
 	white-space: normal;
 	overflow-wrap: anywhere;
 }
 
+.uplotTooltipItemValue {
+	white-space: nowrap;
+}
+
 .uplotTooltipItemContentSeparator {
 	flex: 1;
 	border-width: 0.5px;

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

@@ -25,7 +25,7 @@ export default function TooltipItem({
 		>
 			<div
 				className={Styles.uplotTooltipItemMarker}
-				style={{ borderColor: item.color }}
+				style={{ borderColor: item.color, backgroundColor: item.color }}
 				data-is-legend-marker={true}
 				data-testid={markerTestId}
 			/>
@@ -39,7 +39,7 @@ export default function TooltipItem({
 					className={Styles.uplotTooltipItemContentSeparator}
 					style={{ borderColor: item.color }}
 				/>
-				<span>{item.tooltipValue}</span>
+				<span className={Styles.uplotTooltipItemValue}>{item.tooltipValue}</span>
 			</div>
 		</div>
 	);

frontend/src/lib/uPlotV2/components/__tests__/UPlotLegend.test.tsx

@@ -61,16 +61,16 @@ describe('UPlotLegend', () => {
 		},
 	};
 
-	let onLegendClick: jest.Mock;
-	let onLegendMouseMove: jest.Mock;
-	let onLegendMouseLeave: jest.Mock;
-	let onFocusSeries: jest.Mock;
+	let onToggleSeries: jest.Mock;
+	let onShowOnlySeries: jest.Mock;
+	let onShowAllSeries: jest.Mock;
+	let onHoverSeries: jest.Mock;
 
 	beforeEach(() => {
-		onLegendClick = jest.fn();
-		onLegendMouseMove = jest.fn();
-		onLegendMouseLeave = jest.fn();
-		onFocusSeries = jest.fn();
+		onToggleSeries = jest.fn();
+		onShowOnlySeries = jest.fn();
+		onShowAllSeries = jest.fn();
+		onHoverSeries = jest.fn();
 
 		mockUseLegendsSync.mockReturnValue({
 			legendItemsMap: baseLegendItemsMap,
@@ -79,10 +79,10 @@ describe('UPlotLegend', () => {
 		});
 
 		mockUseLegendActions.mockReturnValue({
-			onLegendClick,
-			onLegendMouseMove,
-			onLegendMouseLeave,
-			onFocusSeries,
+			onToggleSeries,
+			onShowOnlySeries,
+			onShowAllSeries,
+			onHoverSeries,
 		});
 	});
 
@@ -102,28 +102,39 @@ describe('UPlotLegend', () => {
 		);
 
 	describe('layout and position', () => {
-		it('renders search input when legend position is RIGHT', () => {
+		it('renders the search input on a RIGHT legend', () => {
 			renderLegend(LegendPosition.RIGHT);
 
 			expect(screen.getByTestId('legend-search-input')).toBeInTheDocument();
 		});
 
-		it('does not render search input when legend position is BOTTOM (default)', () => {
+		it('keeps a BOTTOM legend bare — its two rows all go to series', () => {
 			renderLegend();
 
 			expect(screen.queryByTestId('legend-search-input')).not.toBeInTheDocument();
+			expect(screen.queryByTestId('legend-status')).not.toBeInTheDocument();
+			// The row interactions are the same in both placements.
+			expect(screen.getByTestId('legend-item-0')).toBeInTheDocument();
+			expect(screen.getByTestId('legend-scope-0')).toBeInTheDocument();
 		});
 
-		it('renders the marker with the correct border color', () => {
+		it('renders the marker with the series colour, filled only when shown', () => {
 			renderLegend(LegendPosition.RIGHT);
 
-			const legendMarker = document.querySelector(
-				'[data-legend-item-id="0"] [data-is-legend-marker="true"]',
-			) as HTMLElement;
-
-			expect(legendMarker).toHaveStyle({
+			expect(
+				document.querySelector(
+					'[data-legend-item-id="0"] [data-is-legend-marker="true"]',
+				),
+			).toHaveStyle({
 				'border-color': '#ff0000',
+				'background-color': '#ff0000',
 			});
+			// Hidden series read as an empty checkbox.
+			expect(
+				document.querySelector(
+					'[data-legend-item-id="1"] [data-is-legend-marker="true"]',
+				),
+			).toHaveStyle({ 'background-color': 'transparent' });
 		});
 
 		it('renders all legend items in the grid by default', () => {
@@ -136,25 +147,33 @@ describe('UPlotLegend', () => {
 		});
 	});
 
-	describe('search behavior (RIGHT position)', () => {
-		it('filters legend items based on search query (case-insensitive)', async () => {
+	describe('status readout', () => {
+		it('reports how many series are showing', () => {
+			renderLegend(LegendPosition.RIGHT);
+
+			expect(screen.getByTestId('legend-status')).toHaveTextContent(
+				'Showing 2 of 3 series',
+			);
+		});
+	});
+
+	describe('filter behavior', () => {
+		it('filters legend items based on the query (case-insensitive)', async () => {
 			const user = userEvent.setup();
 			renderLegend(LegendPosition.RIGHT);
 
-			const searchInput = screen.getByTestId('legend-search-input');
-			await user.type(searchInput, 'A');
+			await user.type(screen.getByTestId('legend-search-input'), 'a');
 
 			expect(screen.getByText('A')).toBeInTheDocument();
 			expect(screen.queryByText('B')).not.toBeInTheDocument();
 			expect(screen.queryByText('C')).not.toBeInTheDocument();
 		});
 
-		it('shows empty state when no legend items match the search query', async () => {
+		it('shows the empty state when nothing matches', async () => {
 			const user = userEvent.setup();
 			renderLegend(LegendPosition.RIGHT);
 
-			const searchInput = screen.getByTestId('legend-search-input');
-			await user.type(searchInput, 'network');
+			await user.type(screen.getByTestId('legend-search-input'), 'network');
 
 			expect(
 				screen.getByText(/No series found matching "network"/i),
@@ -162,12 +181,11 @@ describe('UPlotLegend', () => {
 			expect(screen.queryByTestId('virtuoso-grid')).not.toBeInTheDocument();
 		});
 
-		it('does not filter or show empty state when search query is empty or only whitespace', async () => {
+		it('ignores a whitespace-only query', async () => {
 			const user = userEvent.setup();
 			renderLegend(LegendPosition.RIGHT);
 
-			const searchInput = screen.getByTestId('legend-search-input');
-			await user.type(searchInput, '   ');
+			await user.type(screen.getByTestId('legend-search-input'), '   ');
 
 			expect(
 				screen.queryByText(/No series found matching/i),
@@ -178,39 +196,197 @@ describe('UPlotLegend', () => {
 		});
 	});
 
-	describe('legend actions', () => {
-		it('calls onLegendClick when a legend item is clicked', async () => {
+	describe('row interactions', () => {
+		const allShownItemsMap = {
+			0: { ...baseLegendItemsMap[0] },
+			1: { ...baseLegendItemsMap[1], show: true },
+			2: { ...baseLegendItemsMap[2] },
+		};
+
+		const mockAllShown = (): void => {
+			mockUseLegendsSync.mockReturnValue({
+				legendItemsMap: allShownItemsMap,
+				focusedSeriesIndex: null,
+				setFocusedSeriesIndex: jest.fn(),
+			});
+		};
+
+		it('isolates the series when everything is showing', async () => {
+			const user = userEvent.setup();
+			mockAllShown();
+			renderLegend(LegendPosition.RIGHT);
+
+			await user.click(screen.getByText('A'));
+
+			// Nothing the user can see is there to exclude, so the click means Only.
+			expect(onShowOnlySeries).toHaveBeenCalledWith(0);
+			expect(onToggleSeries).not.toHaveBeenCalled();
+		});
+
+		it('toggles the series once something is already hidden', async () => {
 			const user = userEvent.setup();
 			renderLegend(LegendPosition.RIGHT);
 
 			await user.click(screen.getByText('A'));
 
-			expect(onLegendClick).toHaveBeenCalledTimes(1);
+			expect(onToggleSeries).toHaveBeenCalledWith(0);
+			expect(onShowOnlySeries).not.toHaveBeenCalled();
 		});
 
-		it('calls mouseMove when the mouse moves over a legend item', async () => {
+		it('excludes just that series when its marker is clicked', async () => {
+			const user = userEvent.setup();
+			mockAllShown();
+			renderLegend(LegendPosition.RIGHT);
+
+			await user.click(screen.getByTestId('legend-marker-0'));
+
+			// The marker is the one way to exclude a single series while
+			// everything is showing — the row click isolates instead.
+			expect(onToggleSeries).toHaveBeenCalledWith(0);
+			expect(onShowOnlySeries).not.toHaveBeenCalled();
+		});
+
+		it('stops the marker offering to hide the last series showing', () => {
+			mockUseLegendsSync.mockReturnValue({
+				legendItemsMap: {
+					0: { ...baseLegendItemsMap[0] },
+					1: { ...baseLegendItemsMap[1] },
+					2: { ...baseLegendItemsMap[2], show: false },
+				},
+				focusedSeriesIndex: null,
+				setFocusedSeriesIndex: jest.fn(),
+			});
+			renderLegend(LegendPosition.RIGHT);
+
+			expect(screen.getByTestId('legend-marker-0')).toBeDisabled();
+			expect(screen.getByTestId('legend-marker-1')).toBeEnabled();
+		});
+
+		it('labels the marker with what clicking it does', () => {
+			renderLegend(LegendPosition.RIGHT);
+
+			expect(screen.getByTestId('legend-marker-0')).toHaveAttribute(
+				'aria-label',
+				'Hide A',
+			);
+			expect(screen.getByTestId('legend-marker-1')).toHaveAttribute(
+				'aria-label',
+				'Show B',
+			);
+		});
+
+		it('adds the clicked series to the selection while one is alone', async () => {
+			const user = userEvent.setup();
+			mockUseLegendsSync.mockReturnValue({
+				legendItemsMap: {
+					0: { ...baseLegendItemsMap[0] },
+					1: { ...baseLegendItemsMap[1] },
+					2: { ...baseLegendItemsMap[2], show: false },
+				},
+				focusedSeriesIndex: null,
+				setFocusedSeriesIndex: jest.fn(),
+			});
+			renderLegend(LegendPosition.RIGHT);
+
+			// Series 0 is showing alone; clicking another row builds the selection
+			// up rather than moving the isolation.
+			await user.click(screen.getByText('B'));
+
+			expect(onToggleSeries).toHaveBeenCalledWith(1);
+			expect(onShowOnlySeries).not.toHaveBeenCalled();
+		});
+
+		it('toggles the series on Enter and Space', async () => {
 			const user = userEvent.setup();
 			renderLegend(LegendPosition.RIGHT);
 
-			const legendItem = document.querySelector(
-				'[data-legend-item-id="0"]',
-			) as HTMLElement;
+			const row = screen.getByTestId('legend-item-0');
+			row.focus();
+			await user.keyboard('{Enter}');
+			await user.keyboard(' ');
 
-			await user.hover(legendItem);
-
-			expect(onLegendMouseMove).toHaveBeenCalledTimes(1);
+			expect(onToggleSeries).toHaveBeenCalledTimes(2);
+			expect(onToggleSeries).toHaveBeenCalledWith(0);
 		});
 
-		it('calls onLegendMouseLeave when the mouse leaves the legend container', async () => {
+		it('reflects visibility on the row for assistive tech', () => {
+			renderLegend(LegendPosition.RIGHT);
+
+			expect(screen.getByTestId('legend-item-0')).toHaveAttribute(
+				'aria-checked',
+				'true',
+			);
+			expect(screen.getByTestId('legend-item-1')).toHaveAttribute(
+				'aria-checked',
+				'false',
+			);
+		});
+
+		it('restores every series from All without also toggling the row', async () => {
 			const user = userEvent.setup();
 			renderLegend(LegendPosition.RIGHT);
 
-			const container = document.querySelector('.legend-container') as HTMLElement;
+			// Series 0 is shown while B is hidden, so its action is All.
+			await user.click(screen.getByTestId('legend-scope-0'));
 
-			await user.hover(container);
-			await user.unhover(container);
+			expect(onShowAllSeries).toHaveBeenCalled();
+			expect(onToggleSeries).not.toHaveBeenCalled();
+			expect(onShowOnlySeries).not.toHaveBeenCalled();
+		});
 
-			expect(onLegendMouseLeave).toHaveBeenCalledTimes(1);
+		it('isolates the series from Only on a hidden row', async () => {
+			const user = userEvent.setup();
+			renderLegend(LegendPosition.RIGHT);
+
+			await user.click(screen.getByTestId('legend-scope-1'));
+
+			expect(onShowOnlySeries).toHaveBeenCalledWith(1);
+			expect(onToggleSeries).not.toHaveBeenCalled();
+		});
+
+		it('highlights the hovered series and clears it on leave', async () => {
+			const user = userEvent.setup();
+			renderLegend(LegendPosition.RIGHT);
+
+			const row = screen.getByTestId('legend-item-0');
+			await user.hover(row);
+			expect(onHoverSeries).toHaveBeenCalledWith(0);
+
+			await user.unhover(row);
+			expect(onHoverSeries).toHaveBeenCalledWith(null);
+		});
+	});
+
+	describe('one-series state', () => {
+		const soleShownItemsMap = {
+			0: { ...baseLegendItemsMap[0] },
+			1: { ...baseLegendItemsMap[1] },
+			2: { ...baseLegendItemsMap[2], show: false },
+		};
+
+		beforeEach(() => {
+			mockUseLegendsSync.mockReturnValue({
+				legendItemsMap: soleShownItemsMap,
+				focusedSeriesIndex: null,
+				setFocusedSeriesIndex: jest.fn(),
+			});
+		});
+
+		it('offers All on the shown row and Only on the hidden ones', () => {
+			renderLegend(LegendPosition.RIGHT);
+
+			expect(screen.getByTestId('legend-scope-0')).toHaveTextContent('All');
+			expect(screen.getByTestId('legend-scope-1')).toHaveTextContent('Only');
+			expect(screen.getByTestId('legend-scope-2')).toHaveTextContent('Only');
+		});
+
+		it('restores everything from All', async () => {
+			const user = userEvent.setup();
+			renderLegend(LegendPosition.RIGHT);
+
+			await user.click(screen.getByTestId('legend-scope-0'));
+
+			expect(onShowAllSeries).toHaveBeenCalled();
 		});
 	});
 });

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

@@ -1,4 +1,4 @@
-import { MouseEventHandler, ReactNode } from 'react';
+import { ReactNode } from 'react';
 import { Timezone } from 'components/CustomTimePicker/timezoneUtils';
 import { PrecisionOption } from 'components/Graph/types';
 import uPlot from 'uplot';
@@ -118,23 +118,23 @@ export interface LegendConfig {
 /**
  * Presentational legend props. Source-agnostic: it renders whatever `items`
  * it's given and delegates interaction to the container handlers, so it serves
- * both uPlot charts (via UPlotLegend) and non-uPlot charts (Pie). The search
- * box is intrinsic to the RIGHT position (derived from `position`, not a flag).
+ * both uPlot charts (via UPlotLegend) and non-uPlot charts (Pie).
  */
 export interface LegendProps {
 	items: LegendItem[];
 	/** Legend placement; always supplied by the container. */
 	position: LegendPosition;
 	averageLegendWidth?: number;
-	/** Series index to highlight (hovered/focused). */
+	/** Series index highlighted by the chart cursor. */
 	focusedSeriesIndex: number | null;
-	/**
-	 * Container-delegated handlers. Items carry `data-legend-item-id`, so the
-	 * handler reads the target's id rather than binding per item.
-	 */
-	onClick: MouseEventHandler<HTMLDivElement>;
-	onMouseMove: MouseEventHandler<HTMLDivElement>;
-	onMouseLeave: () => void;
+	/** Row click / Space / Enter: hide or show that one series. */
+	onToggleSeries: (seriesIndex: number) => void;
+	/** "Only": show that series alone. */
+	onShowOnlySeries: (seriesIndex: number) => void;
+	/** "All": leave the narrowed selection and show every series. */
+	onShowAllSeries: () => void;
+	/** Row hover, for the chart-side highlight; null on leave. */
+	onHoverSeries: (seriesIndex: number | null) => void;
 	/** Show the per-item copy button. Default true. */
 	showCopy?: boolean;
 }

frontend/src/lib/uPlotV2/constants.ts

@@ -6,6 +6,11 @@ export const DEFAULT_HOVER_PROXIMITY_VALUE = 30; // only snap if within 30px hor
 export const DEFAULT_FOCUS_PROXIMITY_VALUE = 1e6;
 export const STEP_INTERVAL_MULTIPLIER = 3; // multiply the width computed by STEP_INTERVAL_MULTIPLIER to get the hover prox value
 
+/** Opacity applied to the series that are NOT highlighted while a legend row is hovered. */
+export const LEGEND_HIGHLIGHT_DIM_ALPHA = 0.16;
+/** Stroke-width multiplier applied to the series highlighted from the legend. */
+export const LEGEND_HIGHLIGHT_WIDTH_RATIO = 1.6;
+
 export const DEFAULT_PLOT_CONFIG: Partial<Options> = {
 	focus: {
 		alpha: 0.3,

frontend/src/lib/uPlotV2/context/PlotContext.tsx

@@ -8,6 +8,10 @@ import {
 	useMemo,
 	useRef,
 } from 'react';
+import {
+	LEGEND_HIGHLIGHT_DIM_ALPHA,
+	LEGEND_HIGHLIGHT_WIDTH_RATIO,
+} from 'lib/uPlotV2/constants';
 import type { SeriesVisibilityItem } from 'lib/visualization/panels/types';
 import { updateSeriesVisibilityToLocalStorage } from 'lib/visualization/panels/utils/legendVisibilityUtils';
 import type uPlot from 'uplot';
@@ -20,12 +24,26 @@ export interface IPlotContext {
 	setPlotContextInitialState: (state: PlotContextInitialState) => void;
 	onToggleSeriesVisibility: (seriesIndex: number) => void;
 	onToggleSeriesOnOff: (seriesIndex: number) => void;
+	/** Show this series alone. */
+	onShowOnlySeries: (seriesIndex: number) => void;
+	/** Show every series again. */
+	onShowAllSeries: () => void;
 	onFocusSeries: (seriesIndex: number | null) => void;
+	/** Lift one series above the rest (dim + thicken) without changing visibility. */
+	onHighlightSeries: (seriesIndex: number | null) => void;
 	syncSeriesVisibilityToLocalStorage: () => void;
 }
 
 export const PlotContext = createContext<IPlotContext | null>(null);
 
+/** Data series (index 0 is the x-axis) currently drawn. */
+const countShownSeries = (plot: uPlot): number =>
+	plot.series.reduce(
+		(count, series, index) =>
+			index > 0 && series.show !== false ? count + 1 : count,
+		0,
+	);
+
 export const PlotContextProvider = ({
 	children,
 }: PropsWithChildren): JSX.Element => {
@@ -33,6 +51,9 @@ export const PlotContextProvider = ({
 	const activeSeriesIndex = useRef<number | undefined>(undefined);
 	const idRef = useRef<string | undefined>(undefined);
 	const shouldSavePreferencesRef = useRef<boolean>(false);
+	/** Pre-highlight stroke widths, captured on the first highlight so it can be undone. */
+	const baseSeriesWidthsRef = useRef<Map<number, number | undefined>>(new Map());
+	const highlightedSeriesIndexRef = useRef<number | null>(null);
 
 	const setPlotContextInitialState = useCallback(
 		({
@@ -43,6 +64,8 @@ export const PlotContextProvider = ({
 			uPlotInstanceRef.current = uPlotInstance;
 			idRef.current = id;
 			activeSeriesIndex.current = undefined;
+			baseSeriesWidthsRef.current = new Map();
+			highlightedSeriesIndexRef.current = null;
 			shouldSavePreferencesRef.current = !!shouldSaveSelectionPreference;
 		},
 		[],
@@ -64,6 +87,54 @@ export const PlotContextProvider = ({
 		updateSeriesVisibilityToLocalStorage(idRef.current, seriesVisibility);
 	}, []);
 
+	const onHighlightSeries = useCallback((seriesIndex: number | null): void => {
+		const plot = uPlotInstanceRef.current;
+		if (!plot) {
+			return;
+		}
+
+		highlightedSeriesIndexRef.current = seriesIndex;
+
+		plot.series.forEach((series, index) => {
+			if (index === 0) {
+				return;
+			}
+			if (!baseSeriesWidthsRef.current.has(index)) {
+				baseSeriesWidthsRef.current.set(index, series.width);
+			}
+			const baseWidth = baseSeriesWidthsRef.current.get(index);
+			const isHighlighted = index === seriesIndex;
+
+			/* eslint-disable no-param-reassign */
+			series.alpha =
+				seriesIndex === null || isHighlighted ? 1 : LEGEND_HIGHLIGHT_DIM_ALPHA;
+			series.width =
+				isHighlighted && baseWidth !== undefined
+					? baseWidth * LEGEND_HIGHLIGHT_WIDTH_RATIO
+					: baseWidth;
+			/* eslint-enable no-param-reassign */
+		});
+
+		// Only the stroke style changed, so the cached paths stay valid.
+		plot.redraw(false);
+	}, []);
+
+	/**
+	 * Leaving the dim on a hidden series leaves every other one faded, which
+	 * reads as an isolation rather than as one series being excluded.
+	 */
+	const clearHighlightIfHidden = useCallback((): void => {
+		const plot = uPlotInstanceRef.current;
+		const highlightedIndex = highlightedSeriesIndexRef.current;
+		if (!plot || highlightedIndex === null) {
+			return;
+		}
+
+		if (plot.series[highlightedIndex]?.show === false) {
+			onHighlightSeries(null);
+		}
+	}, [onHighlightSeries]);
+
 	const onToggleSeriesVisibility = useCallback(
 		(seriesIndex: number): void => {
 			const plot = uPlotInstanceRef.current;
@@ -103,14 +174,61 @@ export const PlotContextProvider = ({
 			if (!series) {
 				return;
 			}
+
+			// An empty chart is never worth reaching.
+			const isHiding = series.show !== false;
+			if (isHiding && countShownSeries(plot) <= 1) {
+				return;
+			}
+
 			plot.setSeries(seriesIndex, { show: !series.show });
 			if (idRef.current && shouldSavePreferencesRef.current) {
 				syncSeriesVisibilityToLocalStorage();
 			}
+
+			clearHighlightIfHidden();
 		},
-		[syncSeriesVisibilityToLocalStorage],
+		[syncSeriesVisibilityToLocalStorage, clearHighlightIfHidden],
 	);
 
+	/** Applies `resolveShow` to every data series in one batch, then persists. */
+	const setSeriesVisibility = useCallback(
+		(resolveShow: (seriesIndex: number) => boolean): void => {
+			const plot = uPlotInstanceRef.current;
+			if (!plot) {
+				return;
+			}
+
+			activeSeriesIndex.current = undefined;
+
+			plot.batch(() => {
+				plot.series.forEach((_, index) => {
+					if (index === 0) {
+						return;
+					}
+					plot.setSeries(index, { show: resolveShow(index) });
+				});
+				if (idRef.current && shouldSavePreferencesRef.current) {
+					syncSeriesVisibilityToLocalStorage();
+				}
+			});
+
+			clearHighlightIfHidden();
+		},
+		[syncSeriesVisibilityToLocalStorage, clearHighlightIfHidden],
+	);
+
+	const onShowOnlySeries = useCallback(
+		(seriesIndex: number): void => {
+			setSeriesVisibility((index) => index === seriesIndex);
+		},
+		[setSeriesVisibility],
+	);
+
+	const onShowAllSeries = useCallback((): void => {
+		setSeriesVisibility(() => true);
+	}, [setSeriesVisibility]);
+
 	const onFocusSeries = useCallback((seriesIndex: number | null): void => {
 		const plot = uPlotInstanceRef.current;
 		if (!plot) {
@@ -131,14 +249,20 @@ export const PlotContextProvider = ({
 			onToggleSeriesVisibility,
 			setPlotContextInitialState,
 			onToggleSeriesOnOff,
+			onShowOnlySeries,
+			onShowAllSeries,
 			onFocusSeries,
+			onHighlightSeries,
 			syncSeriesVisibilityToLocalStorage,
 		}),
 		[
 			onToggleSeriesVisibility,
 			setPlotContextInitialState,
 			onToggleSeriesOnOff,
+			onShowOnlySeries,
+			onShowAllSeries,
 			onFocusSeries,
+			onHighlightSeries,
 			syncSeriesVisibilityToLocalStorage,
 		],
 	);

frontend/src/lib/uPlotV2/context/__tests__/PlotContext.test.tsx

@@ -26,6 +26,7 @@ const createMockPlot = (series: MockSeries[] = []): uPlot =>
 		series,
 		batch: jest.fn((fn: () => void) => fn()),
 		setSeries: jest.fn(),
+		redraw: jest.fn(),
 	}) as unknown as uPlot;
 
 interface TestComponentProps {
@@ -44,7 +45,10 @@ const TestComponent = ({
 		syncSeriesVisibilityToLocalStorage,
 		onToggleSeriesVisibility,
 		onToggleSeriesOnOff,
+		onShowOnlySeries,
+		onShowAllSeries,
 		onFocusSeries,
+		onHighlightSeries,
 	} = usePlotContext();
 	const handleInit = (): void => {
 		if (!plot || !id || typeof shouldSaveSelectionPreference !== 'boolean') {
@@ -84,6 +88,13 @@ const TestComponent = ({
 			>
 				Toggle on/off 1
 			</button>
+			<button
+				type="button"
+				data-testid="toggle-on-off-2"
+				onClick={(): void => onToggleSeriesOnOff(2)}
+			>
+				Toggle on/off 2
+			</button>
 			<button
 				type="button"
 				data-testid="toggle-on-off-5"
@@ -98,6 +109,34 @@ const TestComponent = ({
 			>
 				Focus series
 			</button>
+			<button
+				type="button"
+				data-testid="show-only-1"
+				onClick={(): void => onShowOnlySeries(1)}
+			>
+				Show only 1
+			</button>
+			<button
+				type="button"
+				data-testid="show-all"
+				onClick={(): void => onShowAllSeries()}
+			>
+				Show all
+			</button>
+			<button
+				type="button"
+				data-testid="highlight-1"
+				onClick={(): void => onHighlightSeries(1)}
+			>
+				Highlight 1
+			</button>
+			<button
+				type="button"
+				data-testid="clear-highlight"
+				onClick={(): void => onHighlightSeries(null)}
+			>
+				Clear highlight
+			</button>
 		</div>
 	);
 };
@@ -273,6 +312,7 @@ describe('PlotContext', () => {
 			const series: MockSeries[] = [
 				{ label: 'x-axis', show: true },
 				{ label: 'CPU', show: true },
+				{ label: 'Memory', show: true },
 			];
 			const plot = createMockPlot(series);
 
@@ -324,6 +364,7 @@ describe('PlotContext', () => {
 			const series: MockSeries[] = [
 				{ label: 'x-axis', show: true },
 				{ label: 'CPU', show: true },
+				{ label: 'Memory', show: true },
 			];
 			const plot = createMockPlot(series);
 
@@ -343,6 +384,48 @@ describe('PlotContext', () => {
 			expect(plot.setSeries).toHaveBeenCalledWith(1, { show: false });
 			expect(mockUpdateSeriesVisibilityToLocalStorage).not.toHaveBeenCalled();
 		});
+
+		it('refuses to hide the last series showing', async () => {
+			const user = userEvent.setup();
+			const plot = createMockPlot([
+				{ label: 'x-axis', show: true },
+				{ label: 'CPU', show: true },
+				{ label: 'Memory', show: false },
+			]);
+
+			render(
+				<PlotContextProvider>
+					<TestComponent plot={plot} id="widget-123" shouldSaveSelectionPreference />
+				</PlotContextProvider>,
+			);
+
+			await user.click(screen.getByTestId('init'));
+			await user.click(screen.getByTestId('toggle-on-off-1'));
+
+			// An empty chart is never a state worth reaching.
+			expect(plot.setSeries).not.toHaveBeenCalled();
+			expect(mockUpdateSeriesVisibilityToLocalStorage).not.toHaveBeenCalled();
+		});
+
+		it('still shows a hidden series when only one is left showing', async () => {
+			const user = userEvent.setup();
+			const plot = createMockPlot([
+				{ label: 'x-axis', show: true },
+				{ label: 'CPU', show: false },
+				{ label: 'Memory', show: true },
+			]);
+
+			render(
+				<PlotContextProvider>
+					<TestComponent plot={plot} id="widget-123" shouldSaveSelectionPreference />
+				</PlotContextProvider>,
+			);
+
+			await user.click(screen.getByTestId('init'));
+			await user.click(screen.getByTestId('toggle-on-off-1'));
+
+			expect(plot.setSeries).toHaveBeenCalledWith(1, { show: true });
+		});
 	});
 
 	describe('onFocusSeries', () => {
@@ -381,4 +464,193 @@ describe('PlotContext', () => {
 			expect(plot.setSeries).toHaveBeenCalledWith(1, { focus: true }, false);
 		});
 	});
+	describe('onShowOnlySeries', () => {
+		const renderWithSeries = (
+			series: MockSeries[],
+		): { plot: uPlot; user: ReturnType<typeof userEvent.setup> } => {
+			const user = userEvent.setup();
+			const plot = createMockPlot(series);
+
+			render(
+				<PlotContextProvider>
+					<TestComponent plot={plot} id="widget-123" shouldSaveSelectionPreference />
+				</PlotContextProvider>,
+			);
+
+			return { plot, user };
+		};
+
+		it('hides every other series, leaving the x-axis alone', async () => {
+			const { plot, user } = renderWithSeries([
+				{ label: 'x-axis', show: true },
+				{ label: 'CPU', show: true },
+				{ label: 'Memory', show: true },
+			]);
+
+			await user.click(screen.getByTestId('init'));
+			await user.click(screen.getByTestId('show-only-1'));
+
+			expect(plot.setSeries).toHaveBeenCalledWith(1, { show: true });
+			expect(plot.setSeries).toHaveBeenCalledWith(2, { show: false });
+			expect(plot.setSeries).not.toHaveBeenCalledWith(0, expect.anything());
+			expect(mockUpdateSeriesVisibilityToLocalStorage).toHaveBeenCalled();
+		});
+
+		it('keeps isolating the series that is already the only one shown', async () => {
+			const { plot, user } = renderWithSeries([
+				{ label: 'x-axis', show: true },
+				{ label: 'CPU', show: true },
+				{ label: 'Memory', show: false },
+			]);
+
+			await user.click(screen.getByTestId('init'));
+			await user.click(screen.getByTestId('show-only-1'));
+
+			expect(plot.setSeries).toHaveBeenCalledWith(1, { show: true });
+			expect(plot.setSeries).toHaveBeenCalledWith(2, { show: false });
+		});
+	});
+
+	describe('onShowAllSeries', () => {
+		it('shows every hidden series again', async () => {
+			const user = userEvent.setup();
+			const plot = createMockPlot([
+				{ label: 'x-axis', show: true },
+				{ label: 'CPU', show: true },
+				{ label: 'Memory', show: false },
+			]);
+
+			render(
+				<PlotContextProvider>
+					<TestComponent plot={plot} id="widget-123" shouldSaveSelectionPreference />
+				</PlotContextProvider>,
+			);
+
+			await user.click(screen.getByTestId('init'));
+			await user.click(screen.getByTestId('show-all'));
+
+			expect(plot.setSeries).toHaveBeenCalledWith(1, { show: true });
+			expect(plot.setSeries).toHaveBeenCalledWith(2, { show: true });
+			expect(plot.setSeries).not.toHaveBeenCalledWith(0, expect.anything());
+		});
+	});
+
+	describe('onHighlightSeries', () => {
+		const series = (): MockSeries[] => [
+			{ label: 'x-axis', show: true },
+			{ label: 'CPU', show: true, width: 2 },
+			{ label: 'Memory', show: true, width: 2 },
+		];
+
+		it('dims the other series and thickens the highlighted one', async () => {
+			const user = userEvent.setup();
+			const plot = createMockPlot(series());
+
+			render(
+				<PlotContextProvider>
+					<TestComponent plot={plot} id="widget-123" shouldSaveSelectionPreference />
+				</PlotContextProvider>,
+			);
+
+			await user.click(screen.getByTestId('init'));
+			await user.click(screen.getByTestId('highlight-1'));
+
+			expect(plot.series[1].alpha).toBe(1);
+			expect(plot.series[1].width).toBe(3.2);
+			expect(plot.series[2].alpha).toBe(0.16);
+			expect(plot.series[2].width).toBe(2);
+			// Only the stroke changed, so the cached paths are reused.
+			expect(plot.redraw).toHaveBeenCalledWith(false);
+		});
+
+		it('restores every series when the highlight is cleared', async () => {
+			const user = userEvent.setup();
+			const plot = createMockPlot(series());
+
+			render(
+				<PlotContextProvider>
+					<TestComponent plot={plot} id="widget-123" shouldSaveSelectionPreference />
+				</PlotContextProvider>,
+			);
+
+			await user.click(screen.getByTestId('init'));
+			await user.click(screen.getByTestId('highlight-1'));
+			await user.click(screen.getByTestId('clear-highlight'));
+
+			expect(plot.series[1].alpha).toBe(1);
+			expect(plot.series[1].width).toBe(2);
+			expect(plot.series[2].alpha).toBe(1);
+			expect(plot.series[2].width).toBe(2);
+		});
+
+		it('drops the dim when the highlighted series is hidden', async () => {
+			const user = userEvent.setup();
+			const plot = createMockPlot(series());
+			// The mock's setSeries doesn't mutate, so mirror what uPlot would do.
+			(plot.setSeries as jest.Mock).mockImplementation(
+				(index: number, opts: { show?: boolean }) => {
+					if (typeof opts.show === 'boolean') {
+						(plot.series[index] as MockSeries).show = opts.show;
+					}
+				},
+			);
+
+			render(
+				<PlotContextProvider>
+					<TestComponent plot={plot} id="widget-123" shouldSaveSelectionPreference />
+				</PlotContextProvider>,
+			);
+
+			await user.click(screen.getByTestId('init'));
+			await user.click(screen.getByTestId('highlight-1'));
+			await user.click(screen.getByTestId('toggle-on-off-1'));
+
+			// Otherwise every remaining series stays faded and the panel reads as
+			// an isolation instead of one series being excluded.
+			expect(plot.series[2].alpha).toBe(1);
+			expect(plot.series[2].width).toBe(2);
+		});
+
+		it('keeps the dim when a different series is hidden', async () => {
+			const user = userEvent.setup();
+			const plot = createMockPlot(series());
+			(plot.setSeries as jest.Mock).mockImplementation(
+				(index: number, opts: { show?: boolean }) => {
+					if (typeof opts.show === 'boolean') {
+						(plot.series[index] as MockSeries).show = opts.show;
+					}
+				},
+			);
+
+			render(
+				<PlotContextProvider>
+					<TestComponent plot={plot} id="widget-123" shouldSaveSelectionPreference />
+				</PlotContextProvider>,
+			);
+
+			await user.click(screen.getByTestId('init'));
+			await user.click(screen.getByTestId('highlight-1'));
+			await user.click(screen.getByTestId('toggle-on-off-2'));
+
+			expect(plot.series[1].alpha).toBe(1);
+			expect(plot.series[2].alpha).toBe(0.16);
+		});
+
+		it('leaves visibility untouched', async () => {
+			const user = userEvent.setup();
+			const plot = createMockPlot(series());
+
+			render(
+				<PlotContextProvider>
+					<TestComponent plot={plot} id="widget-123" shouldSaveSelectionPreference />
+				</PlotContextProvider>,
+			);
+
+			await user.click(screen.getByTestId('init'));
+			await user.click(screen.getByTestId('highlight-1'));
+
+			expect(plot.setSeries).not.toHaveBeenCalled();
+			expect(mockUpdateSeriesVisibilityToLocalStorage).not.toHaveBeenCalled();
+		});
+	});
 });

frontend/src/lib/uPlotV2/hooks/__tests__/useLegendActions.test.ts

@@ -11,10 +11,12 @@ const mockUsePlotContext = usePlotContext as jest.MockedFunction<
 describe('useLegendActions', () => {
 	let onToggleSeriesVisibility: jest.Mock;
 	let onToggleSeriesOnOff: jest.Mock;
-	let onFocusSeriesPlot: jest.Mock;
+	let onShowOnlySeries: jest.Mock;
+	let onShowAllSeries: jest.Mock;
+	let onFocusSeries: jest.Mock;
+	let onHighlightSeries: jest.Mock;
 	let setPlotContextInitialState: jest.Mock;
 	let syncSeriesVisibilityToLocalStorage: jest.Mock;
-	let setFocusedSeriesIndexMock: jest.Mock;
 	let cancelAnimationFrameSpy: jest.SpyInstance<void, [handle: number]>;
 
 	beforeAll(() => {
@@ -37,15 +39,20 @@ describe('useLegendActions', () => {
 	beforeEach(() => {
 		onToggleSeriesVisibility = jest.fn();
 		onToggleSeriesOnOff = jest.fn();
-		onFocusSeriesPlot = jest.fn();
+		onShowOnlySeries = jest.fn();
+		onShowAllSeries = jest.fn();
+		onFocusSeries = jest.fn();
+		onHighlightSeries = jest.fn();
 		setPlotContextInitialState = jest.fn();
 		syncSeriesVisibilityToLocalStorage = jest.fn();
-		setFocusedSeriesIndexMock = jest.fn();
 
 		mockUsePlotContext.mockReturnValue({
 			onToggleSeriesVisibility,
 			onToggleSeriesOnOff,
-			onFocusSeries: onFocusSeriesPlot,
+			onShowOnlySeries,
+			onShowAllSeries,
+			onFocusSeries,
+			onHighlightSeries,
 			setPlotContextInitialState,
 			syncSeriesVisibilityToLocalStorage,
 		});
@@ -53,149 +60,65 @@ describe('useLegendActions', () => {
 		cancelAnimationFrameSpy.mockClear();
 	});
 
-	const createMouseEvent = (options: {
-		legendItemId?: number;
-		isMarker?: boolean;
-	}): any => {
-		const { legendItemId, isMarker = false } = options;
+	describe('visibility actions', () => {
+		it('toggles a single series on row click', () => {
+			const { result } = renderHook(() => useLegendActions());
 
-		return {
-			target: {
-				dataset: {
-					...(isMarker ? { isLegendMarker: 'true' } : {}),
-				},
-				closest: jest.fn(() =>
-					legendItemId !== undefined
-						? { dataset: { legendItemId: String(legendItemId) } }
-						: null,
-				),
-			},
-		};
-	};
+			result.current.onToggleSeries(2);
 
-	describe('onLegendClick', () => {
-		it('toggles series visibility when clicking on legend label', async () => {
-			const { result } = renderHook(() =>
-				useLegendActions({
-					setFocusedSeriesIndex: setFocusedSeriesIndexMock,
-					focusedSeriesIndex: null,
-				}),
-			);
-
-			result.current.onLegendClick(createMouseEvent({ legendItemId: 0 }));
-
-			expect(onToggleSeriesVisibility).toHaveBeenCalledTimes(1);
-			expect(onToggleSeriesVisibility).toHaveBeenCalledWith(0);
-			expect(onToggleSeriesOnOff).not.toHaveBeenCalled();
-		});
-
-		it('toggles series on/off when clicking on marker', async () => {
-			const { result } = renderHook(() =>
-				useLegendActions({
-					setFocusedSeriesIndex: setFocusedSeriesIndexMock,
-					focusedSeriesIndex: null,
-				}),
-			);
-
-			result.current.onLegendClick(
-				createMouseEvent({ legendItemId: 0, isMarker: true }),
-			);
-
-			expect(onToggleSeriesOnOff).toHaveBeenCalledTimes(1);
-			expect(onToggleSeriesOnOff).toHaveBeenCalledWith(0);
+			expect(onToggleSeriesOnOff).toHaveBeenCalledWith(2);
+			// The row must never isolate — that is what "Only" is for.
 			expect(onToggleSeriesVisibility).not.toHaveBeenCalled();
 		});
 
-		it('does nothing when click target is not inside a legend item', async () => {
-			const { result } = renderHook(() =>
-				useLegendActions({
-					setFocusedSeriesIndex: setFocusedSeriesIndexMock,
-					focusedSeriesIndex: null,
-				}),
-			);
+		it('forwards the Only and All actions to the plot', () => {
+			const { result } = renderHook(() => useLegendActions());
 
-			result.current.onLegendClick(createMouseEvent({}));
+			result.current.onShowOnlySeries(1);
+			result.current.onShowAllSeries();
 
-			expect(onToggleSeriesOnOff).not.toHaveBeenCalled();
-			expect(onToggleSeriesVisibility).not.toHaveBeenCalled();
+			expect(onShowOnlySeries).toHaveBeenCalledWith(1);
+			expect(onShowAllSeries).toHaveBeenCalled();
 		});
 	});
 
-	describe('onFocusSeries', () => {
-		it('schedules focus update and calls plot focus handler via mouse move', async () => {
-			const { result } = renderHook(() =>
-				useLegendActions({
-					setFocusedSeriesIndex: setFocusedSeriesIndexMock,
-					focusedSeriesIndex: null,
-				}),
-			);
+	describe('hover highlight', () => {
+		it('highlights the hovered series', () => {
+			const { result } = renderHook(() => useLegendActions());
 
-			result.current.onLegendMouseMove(createMouseEvent({ legendItemId: 0 }));
+			result.current.onHoverSeries(2);
 
-			expect(setFocusedSeriesIndexMock).toHaveBeenCalledWith(0);
-			expect(onFocusSeriesPlot).toHaveBeenCalledWith(0);
+			expect(onHighlightSeries).toHaveBeenCalledWith(2);
 		});
 
-		it('cancels previous animation frame before scheduling new one on subsequent mouse moves', async () => {
-			const { result } = renderHook(() =>
-				useLegendActions({
-					setFocusedSeriesIndex: setFocusedSeriesIndexMock,
-					focusedSeriesIndex: null,
-				}),
-			);
+		it('clears the highlight on leave', () => {
+			const { result } = renderHook(() => useLegendActions());
 
-			result.current.onLegendMouseMove(createMouseEvent({ legendItemId: 0 }));
-			result.current.onLegendMouseMove(createMouseEvent({ legendItemId: 1 }));
+			result.current.onHoverSeries(null);
 
+			expect(onHighlightSeries).toHaveBeenCalledWith(null);
+		});
+
+		it('coalesces rapid hovers into one frame', () => {
+			const { result } = renderHook(() => useLegendActions());
+
+			result.current.onHoverSeries(1);
+			result.current.onHoverSeries(2);
+
+			// Each new hover cancels the frame the previous one queued.
 			expect(cancelAnimationFrameSpy).toHaveBeenCalled();
 		});
-	});
 
-	describe('onLegendMouseMove', () => {
-		it('focuses new series when hovering over different legend item', async () => {
-			const { result } = renderHook(() =>
-				useLegendActions({
-					setFocusedSeriesIndex: setFocusedSeriesIndexMock,
-					focusedSeriesIndex: 0,
-				}),
-			);
+		it('cancels a pending highlight frame on unmount', () => {
+			jest
+				.spyOn(global, 'requestAnimationFrame')
+				.mockImplementation((): number => 7);
 
-			result.current.onLegendMouseMove(createMouseEvent({ legendItemId: 1 }));
+			const { result, unmount } = renderHook(() => useLegendActions());
+			result.current.onHoverSeries(1);
+			unmount();
 
-			expect(setFocusedSeriesIndexMock).toHaveBeenCalledWith(1);
-			expect(onFocusSeriesPlot).toHaveBeenCalledWith(1);
-		});
-
-		it('does nothing when hovering over already focused series', async () => {
-			const { result } = renderHook(() =>
-				useLegendActions({
-					setFocusedSeriesIndex: setFocusedSeriesIndexMock,
-					focusedSeriesIndex: 1,
-				}),
-			);
-
-			result.current.onLegendMouseMove(createMouseEvent({ legendItemId: 1 }));
-
-			expect(setFocusedSeriesIndexMock).not.toHaveBeenCalled();
-			expect(onFocusSeriesPlot).not.toHaveBeenCalled();
-		});
-	});
-
-	describe('onLegendMouseLeave', () => {
-		it('cancels pending animation frame and clears focus state', async () => {
-			const { result } = renderHook(() =>
-				useLegendActions({
-					setFocusedSeriesIndex: setFocusedSeriesIndexMock,
-					focusedSeriesIndex: null,
-				}),
-			);
-
-			result.current.onLegendMouseMove(createMouseEvent({ legendItemId: 0 }));
-			result.current.onLegendMouseLeave();
-
-			expect(cancelAnimationFrameSpy).toHaveBeenCalled();
-			expect(setFocusedSeriesIndexMock).toHaveBeenCalledWith(null);
-			expect(onFocusSeriesPlot).toHaveBeenCalledWith(null);
+			expect(cancelAnimationFrameSpy).toHaveBeenCalledWith(7);
 		});
 	});
 });

frontend/src/lib/uPlotV2/hooks/useLegendActions.ts

@@ -1,117 +1,54 @@
-import {
-	Dispatch,
-	SetStateAction,
-	useCallback,
-	useEffect,
-	useRef,
-} from 'react';
+import { useCallback, useEffect, useRef } from 'react';
 import { usePlotContext } from 'lib/uPlotV2/context/PlotContext';
 
-export function useLegendActions({
-	setFocusedSeriesIndex,
-	focusedSeriesIndex,
-}: {
-	setFocusedSeriesIndex: Dispatch<SetStateAction<number | null>>;
-	focusedSeriesIndex: number | null;
-}): {
-	onLegendClick: (e: React.MouseEvent<HTMLDivElement>) => void;
-	onFocusSeries: (seriesIndex: number | null) => void;
-	onLegendMouseMove: (e: React.MouseEvent<HTMLDivElement>) => void;
-	onLegendMouseLeave: () => void;
-} {
+export interface UseLegendActionsResult {
+	onToggleSeries: (seriesIndex: number) => void;
+	/** Show this series alone. */
+	onShowOnlySeries: (seriesIndex: number) => void;
+	/** Leave the narrowed selection and show every series. */
+	onShowAllSeries: () => void;
+	/** null clears the highlight. */
+	onHoverSeries: (seriesIndex: number | null) => void;
+}
+
+/**
+ * Legend interactions, bound to the plot through PlotContext. Hover is coalesced
+ * to one chart redraw per frame.
+ */
+export function useLegendActions(): UseLegendActionsResult {
 	const {
-		onFocusSeries: onFocusSeriesPlot,
 		onToggleSeriesOnOff,
-		onToggleSeriesVisibility,
+		onShowOnlySeries,
+		onShowAllSeries,
+		onHighlightSeries,
 	} = usePlotContext();
 
-	const rafId = useRef<number | null>(null); // requestAnimationFrame id
+	const rafIdRef = useRef<number | null>(null);
 
-	const getLegendItemIdFromEvent = useCallback(
-		(e: React.MouseEvent<HTMLDivElement>): string | undefined => {
-			const target = e.target as HTMLElement | null;
-			if (!target) {
-				return undefined;
-			}
+	const cancelPendingHighlight = useCallback((): void => {
+		if (rafIdRef.current != null) {
+			cancelAnimationFrame(rafIdRef.current);
+			rafIdRef.current = null;
+		}
+	}, []);
 
-			const legendItemElement = target.closest<HTMLElement>(
-				'[data-legend-item-id]',
-			);
-
-			return legendItemElement?.dataset.legendItemId;
-		},
-		[],
-	);
-
-	const onLegendClick = useCallback(
-		(e: React.MouseEvent<HTMLDivElement>): void => {
-			const legendItemId = getLegendItemIdFromEvent(e);
-			if (!legendItemId) {
-				return;
-			}
-			const isLegendMarker = (e.target as HTMLElement).dataset.isLegendMarker;
-			const seriesIndex = Number(legendItemId);
-
-			if (isLegendMarker) {
-				onToggleSeriesOnOff(seriesIndex);
-				return;
-			}
-
-			onToggleSeriesVisibility(seriesIndex);
-		},
-		[onToggleSeriesVisibility, onToggleSeriesOnOff, getLegendItemIdFromEvent],
-	);
-
-	const onFocusSeries = useCallback(
+	const onHoverSeries = useCallback(
 		(seriesIndex: number | null): void => {
-			if (rafId.current != null) {
-				cancelAnimationFrame(rafId.current);
-			}
-			rafId.current = requestAnimationFrame(() => {
-				setFocusedSeriesIndex(seriesIndex);
-				onFocusSeriesPlot(seriesIndex);
+			cancelPendingHighlight();
+			rafIdRef.current = requestAnimationFrame(() => {
+				rafIdRef.current = null;
+				onHighlightSeries(seriesIndex);
 			});
 		},
-		// eslint-disable-next-line react-hooks/exhaustive-deps
-		[onFocusSeriesPlot],
+		[cancelPendingHighlight, onHighlightSeries],
 	);
 
-	const onLegendMouseMove = (e: React.MouseEvent<HTMLDivElement>): void => {
-		const legendItemId = getLegendItemIdFromEvent(e);
-		const seriesIndex = legendItemId ? Number(legendItemId) : null;
-		if (seriesIndex === focusedSeriesIndex) {
-			return;
-		}
-		onFocusSeries(seriesIndex);
-	};
+	useEffect(() => cancelPendingHighlight, [cancelPendingHighlight]);
 
-	const onLegendMouseLeave = useCallback(
-		(): void => {
-			// Cancel any pending RAF from handleFocusSeries to prevent race condition
-			if (rafId.current != null) {
-				cancelAnimationFrame(rafId.current);
-				rafId.current = null;
-			}
-			setFocusedSeriesIndex(null);
-			onFocusSeries(null);
-		},
-		// eslint-disable-next-line react-hooks/exhaustive-deps
-		[onFocusSeries],
-	);
-
-	// Cleanup pending animation frames on unmount
-	useEffect(
-		() => (): void => {
-			if (rafId.current != null) {
-				cancelAnimationFrame(rafId.current);
-			}
-		},
-		[],
-	);
 	return {
-		onLegendClick,
-		onFocusSeries,
-		onLegendMouseMove,
-		onLegendMouseLeave,
+		onToggleSeries: onToggleSeriesOnOff,
+		onShowOnlySeries,
+		onShowAllSeries,
+		onHoverSeries,
 	};
 }

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

@@ -45,9 +45,10 @@ export default function Pie({
 		visibleData,
 		legendItems,
 		focusedSeriesIndex,
-		onLegendClick,
-		onLegendMouseMove,
-		onLegendMouseLeave,
+		onToggleSeries,
+		onShowOnlySeries,
+		onShowAllSeries,
+		onHoverSeries,
 	} = usePieInteractions(data, id);
 
 	const {
@@ -227,9 +228,10 @@ export default function Pie({
 					position={position}
 					averageLegendWidth={averageLegendWidth}
 					focusedSeriesIndex={focusedSeriesIndex}
-					onClick={onLegendClick}
-					onMouseMove={onLegendMouseMove}
-					onMouseLeave={onLegendMouseLeave}
+					onToggleSeries={onToggleSeries}
+					onShowOnlySeries={onShowOnlySeries}
+					onShowAllSeries={onShowAllSeries}
+					onHoverSeries={onHoverSeries}
 				/>
 			</div>
 		</div>

frontend/src/lib/visualization/charts/Pie/__tests__/Pie.test.tsx

@@ -100,17 +100,29 @@ describe('Pie', () => {
 		expect(screen.getByTestId('pie')).toHaveStyle({ flexDirection: 'column' });
 	});
 
-	it('hides a slice when its legend marker is clicked', () => {
+	it('isolates a slice when its legend row is clicked with everything showing', () => {
 		renderPie();
 		const svg = screen.getByTestId('pie').querySelector('svg') as SVGElement;
 		expect(svg.querySelectorAll('path')).toHaveLength(3);
 
-		const marker = document.querySelector(
-			'[data-legend-item-id="1"] [data-is-legend-marker="true"]',
-		) as HTMLElement;
-		fireEvent.click(marker);
+		fireEvent.click(screen.getByTestId('legend-item-1'));
+
+		// Nothing visible to exclude, so the click isolates: one arc left.
+		expect(svg.querySelectorAll('path')).toHaveLength(1);
+	});
+
+	it('excludes a slice when its legend row is clicked with others already hidden', () => {
+		renderPie();
+		const svg = screen.getByTestId('pie').querySelector('svg') as SVGElement;
+
+		// Isolate, then add a second slice back, so nothing is isolated any more.
+		fireEvent.click(screen.getByTestId('legend-item-1'));
+		fireEvent.click(screen.getByTestId('legend-item-0'));
+		expect(svg.querySelectorAll('path')).toHaveLength(2);
+
+		fireEvent.click(screen.getByTestId('legend-item-0'));
 
 		// One slice hidden → one fewer arc drawn.
-		expect(svg.querySelectorAll('path')).toHaveLength(2);
+		expect(svg.querySelectorAll('path')).toHaveLength(1);
 	});
 });

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

@@ -1,6 +1,9 @@
 import { LegendPosition } from 'lib/uPlotV2/components/types';
 
-import { calculateChartDimensions } from 'lib/visualization/charts/utils';
+import {
+	calculateAverageLegendWidth,
+	calculateChartDimensions,
+} from 'lib/visualization/charts/utils';
 
 const labels = (count: number, length = 20): string[] =>
 	Array.from({ length: count }, (_, i) =>
@@ -49,63 +52,104 @@ describe('calculateChartDimensions', () => {
 		expect(dims.width).toBe(784);
 	});
 
-	it('RIGHT: never shrinks the column below the 150px floor', () => {
+	it('RIGHT: never shrinks the column below the floor that fits its chrome', () => {
 		const dims = calculateChartDimensions({
 			containerWidth: 1000,
 			containerHeight: 400,
 			legendConfig: { position: LegendPosition.RIGHT },
 			seriesLabels: labels(3, 3),
 		});
-		expect(dims.legendWidth).toBe(150);
-		expect(dims.width).toBe(850);
+		expect(dims.legendWidth).toBe(190);
+		expect(dims.width).toBe(810);
 	});
 
-	it('RIGHT: on a narrow container the legend never takes more than 40% of the width', () => {
+	it('RIGHT: on a narrow container the legend keeps its chrome, up to half the width', () => {
 		const dims = calculateChartDimensions({
 			containerWidth: 300,
 			containerHeight: 400,
 			legendConfig: { position: LegendPosition.RIGHT },
 			seriesLabels: labels(10, 40),
 		});
-		expect(dims.legendWidth).toBe(120);
-		expect(dims.width).toBe(180);
+		// 40% is 120px, too narrow for the column's own toolbar.
+		expect(dims.legendWidth).toBe(150);
+		expect(dims.width).toBe(150);
 	});
 
-	it('BOTTOM: a single row of items reserves one legend row', () => {
+	it('RIGHT: stops widening the column once the panel is narrower than its chrome', () => {
+		const dims = calculateChartDimensions({
+			containerWidth: 200,
+			containerHeight: 400,
+			legendConfig: { position: LegendPosition.RIGHT },
+			seriesLabels: labels(10, 40),
+		});
+		expect(dims.legendWidth).toBe(100);
+		expect(dims.width).toBe(100);
+	});
+
+	it('BOTTOM: items that fit one row reserve exactly one row', () => {
 		const dims = calculateChartDimensions({
 			containerWidth: 1000,
 			containerHeight: 500,
 			legendConfig: { position: LegendPosition.BOTTOM },
 			seriesLabels: labels(3),
 		});
-		// One row = line height (28) + padding (12).
+		// One 28px row + the wrapper's 12px bottom padding.
 		expect(dims.legendHeight).toBe(40);
 		expect(dims.height).toBe(460);
 		expect(dims.legendWidth).toBe(1000);
 	});
 
-	it('BOTTOM: many items cap at two rows on a tall container', () => {
+	it('BOTTOM: more items than one row reserve exactly two rows', () => {
 		const dims = calculateChartDimensions({
 			containerWidth: 1000,
 			containerHeight: 500,
 			legendConfig: { position: LegendPosition.BOTTOM },
 			seriesLabels: labels(40),
 		});
-		// Two rows = 2 * 40 - 12 (no trailing padding) = 68, under the 80px cap.
-		expect(dims.legendHeight).toBe(68);
-		expect(dims.height).toBe(432);
+		// Two 28px rows + the 2px row gap + 12px bottom padding — no room for a
+		// clipped third row, and none left over.
+		expect(dims.legendHeight).toBe(70);
+		expect(dims.height).toBe(430);
 	});
 
-	it('BOTTOM: on a short container the legend never takes more than 30% of the height', () => {
+	it('BOTTOM: items one past a row still reserve two rows', () => {
+		// 1000px wide fits 5 of these per row, so 6 items need a second row.
 		const dims = calculateChartDimensions({
 			containerWidth: 1000,
-			containerHeight: 160,
+			containerHeight: 500,
+			legendConfig: { position: LegendPosition.BOTTOM },
+			seriesLabels: labels(6),
+		});
+		expect(dims.legendHeight).toBe(70);
+	});
+
+	it('BOTTOM: drops to a single row rather than take half a short panel', () => {
+		const dims = calculateChartDimensions({
+			containerWidth: 1000,
+			containerHeight: 120,
 			legendConfig: { position: LegendPosition.BOTTOM },
 			seriesLabels: labels(40),
 		});
-		// Without the height-relative cap the legend would take 68px of a 160px
-		// panel and the chart (pie especially) collapses to a sliver.
-		expect(dims.legendHeight).toBe(48); // 30% of 160
-		expect(dims.height).toBe(112);
+		// A whole row goes rather than a clipped one being reserved.
+		expect(dims.legendHeight).toBe(40);
+		expect(dims.height).toBe(80);
+	});
+});
+
+describe('calculateAverageLegendWidth', () => {
+	it('scales with the label length', () => {
+		// 16px of chrome + 30 chars at 8px.
+		expect(calculateAverageLegendWidth(labels(4, 30))).toBe(256);
+	});
+
+	it('never drops below what a row needs to contain its hover actions', () => {
+		// Short or unnamed series would otherwise size a column the actions
+		// escape, spilling over the item beside it.
+		expect(calculateAverageLegendWidth(['cpu'])).toBe(110);
+		expect(calculateAverageLegendWidth([''])).toBe(110);
+	});
+
+	it('keeps the default estimate when there are no labels to measure', () => {
+		expect(calculateAverageLegendWidth([])).toBe(120);
 	});
 });

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

@@ -1,4 +1,10 @@
-import { MAX_LEGEND_WIDTH } from 'lib/uPlotV2/components/Legend/Legend';
+import {
+	LEGEND_MAX_BOTTOM_ROWS,
+	MIN_LEGEND_ITEM_WIDTH,
+	LEGEND_ROW_GAP,
+	LEGEND_ROW_HEIGHT,
+	MAX_LEGEND_WIDTH,
+} from 'lib/uPlotV2/components/Legend/constants';
 import { LegendConfig, LegendPosition } from 'lib/uPlotV2/components/types';
 export interface ChartDimensions {
 	width: number;
@@ -13,22 +19,31 @@ const LEGEND_WIDTH_PERCENTILE = 0.85;
 const DEFAULT_AVG_LABEL_LENGTH = 15;
 const BASE_LEGEND_WIDTH = 16;
 const LEGEND_PADDING = 12;
-const LEGEND_LINE_HEIGHT = 28;
+// Two rows are worth having, but not at the cost of half the panel.
+const MAX_SHORT_PANEL_LEGEND_RATIO = 0.5;
 
 // RIGHT legend is a vertical column with its own width budget (cap protects the donut).
 const MAX_RIGHT_LEGEND_WIDTH = 320;
 const RIGHT_LEGEND_WIDTH_RATIO = 0.4;
 // Column padding + copy button, not covered by the text-length estimate.
 const RIGHT_LEGEND_RESERVED_WIDTH = 40;
+// Fits the toolbar's "Showing N of M series" readout plus the wrapper padding.
+const MIN_RIGHT_LEGEND_WIDTH = 190;
+// Past this the split inverts and the chart becomes the smaller half.
+const RIGHT_LEGEND_FLOOR_RATIO = 0.5;
 
 /**
  * Calculates the average width of the legend items based on the labels of the series.
+ * Never returns less than a legend row needs to hold its own hover actions.
  * @param legends - The labels of the series.
  * @returns The average width of the legend items.
  */
 export function calculateAverageLegendWidth(legends: string[]): number {
 	if (legends.length === 0) {
-		return DEFAULT_AVG_LABEL_LENGTH * AVG_CHAR_WIDTH;
+		return Math.max(
+			MIN_LEGEND_ITEM_WIDTH,
+			DEFAULT_AVG_LABEL_LENGTH * AVG_CHAR_WIDTH,
+		);
 	}
 
 	const lengths = legends.map((l) => l.length).sort((a, b) => a - b);
@@ -36,7 +51,10 @@ export function calculateAverageLegendWidth(legends: string[]): number {
 	const index = Math.ceil(LEGEND_WIDTH_PERCENTILE * lengths.length) - 1;
 	const percentileLength = lengths[Math.max(0, index)];
 
-	return BASE_LEGEND_WIDTH + percentileLength * AVG_CHAR_WIDTH;
+	return Math.max(
+		MIN_LEGEND_ITEM_WIDTH,
+		BASE_LEGEND_WIDTH + percentileLength * AVG_CHAR_WIDTH,
+	);
 }
 
 /**
@@ -52,7 +70,9 @@ export function calculateAverageLegendWidth(legends: string[]): number {
  *   - Chart width is `containerWidth - legendWidth`.
  * - BOTTOM legend:
  *   - Computes how many items fit per row, then uses at most 2 rows.
- *   - `legendHeight` is derived from row count, capped by both a fixed pixel max and a % of container height.
+ *   - `legendHeight` is exactly those rows plus the wrapper's bottom padding, so
+ *     the rectangle never clips a row or reserves space for half of one. Two
+ *     rows that would take half a short panel fall back to one row.
  *   - Chart height is `containerHeight - legendHeight`, never below 0.
  * - `legendsPerSet` is the number of legend items that fit horizontally, based on the same text-width approximation.
  *
@@ -100,9 +120,14 @@ export function calculateChartDimensions({
 			MAX_RIGHT_LEGEND_WIDTH,
 			containerWidth * RIGHT_LEGEND_WIDTH_RATIO,
 		);
+		// The column's chrome outranks the 40% share on a narrow panel.
+		const floorWidth = Math.min(
+			MIN_RIGHT_LEGEND_WIDTH,
+			containerWidth * RIGHT_LEGEND_FLOOR_RATIO,
+		);
 		const rightLegendWidth = Math.min(
-			Math.max(150, desiredLegendWidth),
-			maxRightLegendWidth,
+			Math.max(MIN_RIGHT_LEGEND_WIDTH, desiredLegendWidth),
+			Math.max(floorWidth, maxRightLegendWidth),
 		);
 
 		return {
@@ -115,8 +140,6 @@ export function calculateChartDimensions({
 		};
 	}
 
-	const legendRowHeight = LEGEND_LINE_HEIGHT + LEGEND_PADDING;
-
 	const legendItemWidth = Math.ceil(
 		Math.min(approxLegendItemWidth, MAX_LEGEND_WIDTH),
 	);
@@ -125,30 +148,30 @@ export function calculateChartDimensions({
 		Math.floor((containerWidth - LEGEND_PADDING * 2) / legendItemWidth),
 	);
 
-	const legendRowCount = Math.min(
-		2,
-		Math.ceil(legendItemCount / legendItemsPerRow),
+	// The wrapper's bottom padding is inside this height (border-box).
+	const heightForRows = (rowCount: number): number =>
+		rowCount * LEGEND_ROW_HEIGHT +
+		(rowCount - 1) * LEGEND_ROW_GAP +
+		LEGEND_PADDING;
+
+	const neededRowCount = Math.max(
+		1,
+		Math.min(
+			LEGEND_MAX_BOTTOM_ROWS,
+			Math.ceil(legendItemCount / legendItemsPerRow),
+		),
 	);
 
-	const idealBottomLegendHeight =
-		legendRowCount > 1
-			? legendRowCount * legendRowHeight - LEGEND_PADDING
-			: legendRowHeight;
+	// Without this, short grid panels hand most of their area to the legend and
+	// the chart — the pie donut especially — collapses to a sliver. Dropping a
+	// whole row beats clipping one.
+	const legendRowCount =
+		neededRowCount > 1 &&
+		heightForRows(neededRowCount) > containerHeight * MAX_SHORT_PANEL_LEGEND_RATIO
+			? 1
+			: neededRowCount;
 
-	// Cap at two rows / 80px, and never more than 30% of the container height
-	// (the doc above always promised the %-cap; without it, short grid panels
-	// hand most of their area to the legend and the chart — the pie donut
-	// especially — collapses to a sliver). 30% mirrors the RIGHT-legend width cap.
-	const maxAllowedLegendHeight = Math.min(
-		2 * legendRowHeight,
-		80,
-		Math.floor(containerHeight * 0.3),
-	);
-
-	const bottomLegendHeight = Math.min(
-		idealBottomLegendHeight,
-		maxAllowedLegendHeight,
-	);
+	const bottomLegendHeight = heightForRows(legendRowCount);
 
 	return {
 		width: containerWidth,

frontend/src/lib/visualization/hooks/__tests__/usePieInteractions.test.tsx

@@ -3,7 +3,6 @@ import {
 	getStoredSeriesVisibility,
 	updateSeriesVisibilityToLocalStorage,
 } from 'lib/visualization/panels/utils/legendVisibilityUtils';
-import type { MouseEvent } from 'react';
 
 import { PieSlice } from 'lib/visualization/charts/types';
 import { usePieInteractions } from 'lib/visualization/hooks/usePieInteractions';
@@ -24,22 +23,6 @@ const DATA: PieSlice[] = [
 	{ label: 'checkout', value: 40, color: '#c' },
 ];
 
-// Builds a fake legend click/move event: `e.target.closest('[data-legend-item-id]')`
-// resolves to the item at `index`, and `e.target.dataset.isLegendMarker` flags marker clicks.
-function legendEvent(
-	index: number | null,
-	isMarker = false,
-): MouseEvent<HTMLDivElement> {
-	const itemEl =
-		index == null ? null : { dataset: { legendItemId: String(index) } };
-	return {
-		target: {
-			closest: (): unknown => itemEl,
-			dataset: { isLegendMarker: isMarker ? 'true' : undefined },
-		},
-	} as unknown as MouseEvent<HTMLDivElement>;
-}
-
 describe('usePieInteractions', () => {
 	beforeEach(() => {
 		mockGetStored.mockReturnValue(null);
@@ -59,11 +42,11 @@ describe('usePieInteractions', () => {
 		expect(result.current.active).toBeNull();
 	});
 
-	describe('marker click (toggle one)', () => {
+	describe('row toggle', () => {
 		it('hides then unhides the clicked slice', () => {
 			const { result } = renderHook(() => usePieInteractions(DATA, 'panel-1'));
 
-			act(() => result.current.onLegendClick(legendEvent(1, true)));
+			act(() => result.current.onToggleSeries(1));
 
 			expect(result.current.visibleData).toStrictEqual([DATA[0], DATA[2]]);
 			expect(result.current.legendItems[1].show).toBe(false);
@@ -73,18 +56,30 @@ describe('usePieInteractions', () => {
 				{ label: 'checkout', show: true },
 			]);
 
-			act(() => result.current.onLegendClick(legendEvent(1, true)));
+			act(() => result.current.onToggleSeries(1));
 
 			expect(result.current.visibleData).toStrictEqual(DATA);
 			expect(result.current.legendItems[1].show).toBe(true);
 		});
 	});
 
-	describe('label click (isolate / reset)', () => {
-		it('isolates the clicked slice, then resets on a second click', () => {
+	describe('the last slice showing', () => {
+		it('cannot be hidden', () => {
 			const { result } = renderHook(() => usePieInteractions(DATA));
 
-			act(() => result.current.onLegendClick(legendEvent(0, false)));
+			act(() => result.current.onShowOnlySeries(0));
+			act(() => result.current.onToggleSeries(0));
+
+			// An empty donut is never a state worth reaching.
+			expect(result.current.visibleData).toStrictEqual([DATA[0]]);
+		});
+	});
+
+	describe('Only', () => {
+		it('isolates the slice', () => {
+			const { result } = renderHook(() => usePieInteractions(DATA));
+
+			act(() => result.current.onShowOnlySeries(0));
 
 			expect(result.current.visibleData).toStrictEqual([DATA[0]]);
 			expect(result.current.legendItems.map((i) => i.show)).toStrictEqual([
@@ -92,8 +87,24 @@ describe('usePieInteractions', () => {
 				false,
 				false,
 			]);
+		});
 
-			act(() => result.current.onLegendClick(legendEvent(0, false)));
+		it('switches the isolation to another slice', () => {
+			const { result } = renderHook(() => usePieInteractions(DATA));
+
+			act(() => result.current.onShowOnlySeries(0));
+			act(() => result.current.onShowOnlySeries(2));
+
+			expect(result.current.visibleData).toStrictEqual([DATA[2]]);
+		});
+	});
+
+	describe('All', () => {
+		it('brings every hidden slice back', () => {
+			const { result } = renderHook(() => usePieInteractions(DATA));
+
+			act(() => result.current.onShowOnlySeries(0));
+			act(() => result.current.onShowAllSeries());
 
 			expect(result.current.visibleData).toStrictEqual(DATA);
 		});
@@ -103,11 +114,23 @@ describe('usePieInteractions', () => {
 		it('focuses the hovered slice and clears on leave', () => {
 			const { result } = renderHook(() => usePieInteractions(DATA));
 
-			act(() => result.current.onLegendMouseMove(legendEvent(2)));
+			act(() => result.current.onHoverSeries(2));
 			expect(result.current.active).toStrictEqual(DATA[2]);
 			expect(result.current.focusedSeriesIndex).toBe(2);
 
-			act(() => result.current.onLegendMouseLeave());
+			act(() => result.current.onHoverSeries(null));
+			expect(result.current.active).toBeNull();
+			expect(result.current.focusedSeriesIndex).toBeNull();
+		});
+
+		it('drops the focus when the focused slice is hidden', () => {
+			const { result } = renderHook(() => usePieInteractions(DATA));
+
+			act(() => result.current.onHoverSeries(1));
+			act(() => result.current.onToggleSeries(1));
+
+			// Otherwise every remaining arc stays dimmed and the donut reads as an
+			// isolation instead of one slice being excluded.
 			expect(result.current.active).toBeNull();
 			expect(result.current.focusedSeriesIndex).toBeNull();
 		});
@@ -115,8 +138,8 @@ describe('usePieInteractions', () => {
 		it('does not focus a hidden slice', () => {
 			const { result } = renderHook(() => usePieInteractions(DATA));
 
-			act(() => result.current.onLegendClick(legendEvent(1, true))); // hide cart
-			act(() => result.current.onLegendMouseMove(legendEvent(1)));
+			act(() => result.current.onToggleSeries(1));
+			act(() => result.current.onHoverSeries(1));
 
 			expect(result.current.active).toBeNull();
 		});
@@ -125,7 +148,7 @@ describe('usePieInteractions', () => {
 	describe('persistence', () => {
 		it('does not write to storage when no id is provided', () => {
 			const { result } = renderHook(() => usePieInteractions(DATA));
-			act(() => result.current.onLegendClick(legendEvent(0, true)));
+			act(() => result.current.onToggleSeries(0));
 			expect(mockUpdateStored).not.toHaveBeenCalled();
 		});
 

frontend/src/lib/visualization/hooks/usePieInteractions.ts

@@ -1,6 +1,6 @@
 import { LegendItem } from 'lib/uPlotV2/config/types';
-import type { Dispatch, MouseEvent, SetStateAction } from 'react';
-import { useCallback, useEffect, useMemo, useRef, useState } from 'react';
+import type { Dispatch, SetStateAction } from 'react';
+import { useCallback, useEffect, useMemo, useState } from 'react';
 
 import {
 	getStoredSeriesVisibility,
@@ -18,27 +18,17 @@ export interface UsePieInteractionsResult {
 	legendItems: LegendItem[];
 	/** Index of the active slice for the legend's focus highlight, or null. */
 	focusedSeriesIndex: number | null;
-	onLegendClick: (e: MouseEvent<HTMLDivElement>) => void;
-	onLegendMouseMove: (e: MouseEvent<HTMLDivElement>) => void;
-	onLegendMouseLeave: () => void;
-}
-
-// Reads the slice index off the nearest `[data-legend-item-id]` ancestor of the
-// event target (the shared Legend tags each item with its seriesIndex).
-function getLegendIndex(e: MouseEvent<HTMLDivElement>): number | null {
-	const el = (e.target as HTMLElement | null)?.closest<HTMLElement>(
-		'[data-legend-item-id]',
-	);
-	const id = el?.dataset.legendItemId;
-	return id != null ? Number(id) : null;
+	onToggleSeries: (sliceIndex: number) => void;
+	onShowOnlySeries: (sliceIndex: number) => void;
+	onShowAllSeries: () => void;
+	onHoverSeries: (sliceIndex: number | null) => void;
 }
 
 /**
- * Pie interaction + derived state: hover/focus, slice hide/unhide (mirroring the
- * uPlot legend — marker toggles one, label isolates), and persistence of the
- * hidden set to localStorage (keyed by `id`, matched by label) so it survives
- * reloads. Returns the visible slices, legend items, focus index, and the
- * legend container handlers.
+ * Pie interaction + derived state: hover/focus, slice hide/show driven by the
+ * shared legend's actions, and persistence of the hidden set to localStorage
+ * (keyed by `id`, matched by label) so it survives reloads. Returns the visible
+ * slices, legend items, focus index, and the legend handlers.
  */
 export function usePieInteractions(
 	data: PieSlice[],
@@ -48,7 +38,6 @@ export function usePieInteractions(
 	const [hiddenIndices, setHiddenIndices] = useState<Set<number>>(
 		() => new Set(),
 	);
-	const isolatedIndexRef = useRef<number | null>(null);
 
 	const legendItems = useMemo<LegendItem[]>(
 		() =>
@@ -104,65 +93,69 @@ export function usePieInteractions(
 		[id, data],
 	);
 
-	const onLegendMouseMove = useCallback(
-		(e: MouseEvent<HTMLDivElement>): void => {
-			const index = getLegendIndex(e);
+	const onHoverSeries = useCallback(
+		(sliceIndex: number | null): void => {
 			// Don't focus/dim for hidden slices — they aren't on the donut.
-			setActive(index != null && !hiddenIndices.has(index) ? data[index] : null);
+			setActive(
+				sliceIndex != null && !hiddenIndices.has(sliceIndex)
+					? data[sliceIndex]
+					: null,
+			);
 		},
 		[data, hiddenIndices],
 	);
 
-	// Marker click toggles just that slice on/off; label click isolates it
-	// (clicking the isolated one again resets to all) — mirrors the uPlot legend.
-	const onLegendClick = useCallback(
-		(e: MouseEvent<HTMLDivElement>): void => {
-			const index = getLegendIndex(e);
-			if (index == null) {
-				return;
-			}
-			const isMarker = (e.target as HTMLElement).dataset.isLegendMarker;
-
-			if (isMarker) {
-				const next = new Set(hiddenIndices);
-				if (next.has(index)) {
-					next.delete(index);
-				} else {
-					next.add(index);
+	const onToggleSeries = useCallback(
+		(sliceIndex: number): void => {
+			const next = new Set(hiddenIndices);
+			if (next.has(sliceIndex)) {
+				next.delete(sliceIndex);
+			} else {
+				// An empty donut is never worth reaching.
+				if (data.length - next.size <= 1) {
+					return;
 				}
-				applyHidden(next);
-				return;
+				next.add(sliceIndex);
 			}
+			applyHidden(next);
+		},
+		[data.length, hiddenIndices, applyHidden],
+	);
 
-			const isReset = isolatedIndexRef.current === index;
-			isolatedIndexRef.current = isReset ? null : index;
-			if (isReset) {
-				applyHidden(new Set());
-				return;
-			}
+	const onShowOnlySeries = useCallback(
+		(sliceIndex: number): void => {
 			const next = new Set<number>();
-			data.forEach((_, i) => {
-				if (i !== index) {
-					next.add(i);
+			data.forEach((_, index) => {
+				if (index !== sliceIndex) {
+					next.add(index);
 				}
 			});
 			applyHidden(next);
 		},
-		[data, hiddenIndices, applyHidden],
+		[data, applyHidden],
 	);
 
-	const onLegendMouseLeave = useCallback((): void => setActive(null), []);
+	const onShowAllSeries = useCallback(
+		(): void => applyHidden(new Set()),
+		[applyHidden],
+	);
 
-	const focusedIndex = active ? data.indexOf(active) : -1;
+	const activeIndex = active ? data.indexOf(active) : -1;
+	// Left active, a hidden slice keeps every other arc dimmed, which reads as an
+	// isolation rather than as one slice being excluded.
+	const effectiveActive =
+		activeIndex >= 0 && !hiddenIndices.has(activeIndex) ? active : null;
+	const focusedIndex = effectiveActive ? activeIndex : -1;
 
 	return {
-		active,
+		active: effectiveActive,
 		setActive,
 		visibleData,
 		legendItems,
 		focusedSeriesIndex: focusedIndex >= 0 ? focusedIndex : null,
-		onLegendClick,
-		onLegendMouseMove,
-		onLegendMouseLeave,
+		onToggleSeries,
+		onShowOnlySeries,
+		onShowAllSeries,
+		onHoverSeries,
 	};
 }

frontend/src/lib/visualization/layout/ChartLayout/ChartLayout.styles.scss

@@ -29,7 +29,6 @@
 		box-sizing: border-box;
 		min-height: 0;
 		overflow: hidden;
-		padding-left: 12px;
-		padding-bottom: 12px;
+		padding: 0 12px 12px 12px;
 	}
 }

frontend/src/lib/visualization/layout/ChartLayout/ChartLayout.tsx

@@ -1,7 +1,7 @@
 import { useMemo } from 'react';
 import cx from 'classnames';
 import { calculateChartDimensions } from 'lib/visualization/charts/utils';
-import { MAX_LEGEND_WIDTH } from 'lib/uPlotV2/components/Legend/Legend';
+import { MAX_LEGEND_WIDTH } from 'lib/uPlotV2/components/Legend/constants';
 import { LegendConfig, LegendPosition } from 'lib/uPlotV2/components/types';
 import { UPlotConfigBuilder } from 'lib/uPlotV2/config/UPlotConfigBuilder';