fix(race-story): sync chapter highlight and empty-state E2E (#68)

Clamp active-chapter detection to the same scrub bounds as chapter clicks,
keep an explicit selection on click for out-of-window timestamps, point E2E
at the empty-state card, and move Race Story empty-state styles out of app.css.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/components/ChapterStrip.tsx

@@ -1,3 +1,5 @@
+import { useEffect, useRef } from 'react'
+import { BookOpen } from 'lucide-react'
 import type { Chapter } from '../types'
 import {
   activeChapterIndex,
@@ -5,6 +7,7 @@ import {
   chapterLapRange,
   chapterStartScrub,
 } from '../lib/chapters'
+import { EmptyStateCard } from './EmptyStateCard'
 import '../styles/chapters.css'
 
 interface Props {
@@ -14,6 +17,8 @@ interface Props {
   tRange: number
   tourActive: boolean
   tourChapterIndex: number | null
+  /** Explicit selection from a chapter click; wins over scrub-derived active. */
+  selectedChapterIndex?: number | null
   onChapterClick: (index: number, scrub: number) => void
   onTourToggle: () => void
 }
@@ -25,19 +30,38 @@ export function ChapterStrip({
   tRange,
   tourActive,
   tourChapterIndex,
+  selectedChapterIndex = null,
   onChapterClick,
   onTourToggle,
 }: Props) {
+  const scrollRef = useRef<HTMLDivElement>(null)
+  const activeIndex = activeChapterIndex(chapters, scrubTime, tMin, tRange)
+  const highlightedIndex = tourActive
+    ? tourChapterIndex
+    : (selectedChapterIndex ?? activeIndex)
+
+  useEffect(() => {
+    if (highlightedIndex === null || !scrollRef.current) return
+    const card = scrollRef.current.querySelector<HTMLElement>(
+      `[data-testid="chapter-card-${highlightedIndex}"]`,
+    )
+    card?.scrollIntoView?.({ behavior: 'smooth', inline: 'center', block: 'nearest' })
+  }, [highlightedIndex])
+
   if (chapters.length === 0) {
     return (
       <div className="chapter-strip" data-testid="chapter-strip">
-        <p className="chapter-strip-empty">No story chapters for this session.</p>
+        <EmptyStateCard
+          icon={BookOpen}
+          title="No story chapters"
+          hint="This session does not have enough race-control or position data to build narrative chapters."
+          testId="chapter-strip-empty"
+          className="chapter-strip-empty-card"
+        />
       </div>
     )
   }
 
-  const activeIndex = activeChapterIndex(chapters, scrubTime, tMin, tRange)
-
   return (
     <div className="chapter-strip" data-testid="chapter-strip">
       <div className="chapter-strip-header">
@@ -53,34 +77,39 @@ export function ChapterStrip({
           </button>
         </div>
       </div>
-      <div className="chapter-strip-scroll" role="list" aria-label="Race story chapters">
-        {chapters.map((chapter, index) => {
-          const scrub = chapterStartScrub(chapter, tMin, tRange) ?? index / Math.max(chapters.length - 1, 1)
-          const isActive = tourActive
-            ? tourChapterIndex === index
-            : activeIndex === index
-          const headline = chapter.headline || chapter.title
+      <div className="chapter-strip-scroll-wrap">
+        <div
+          ref={scrollRef}
+          className="chapter-strip-scroll"
+          role="list"
+          aria-label="Race story chapters"
+        >
+          {chapters.map((chapter, index) => {
+            const scrub = chapterStartScrub(chapter, tMin, tRange) ?? index / Math.max(chapters.length - 1, 1)
+            const isActive = highlightedIndex === index
+            const headline = chapter.headline || chapter.title
 
-          return (
-            <button
-              key={`${chapter.kind}-${chapter.start_lap}-${index}`}
-              type="button"
-              role="listitem"
-              className={`chapter-card ${isActive ? (tourActive ? 'tour-active' : 'active') : ''}`}
-              onClick={() => onChapterClick(index, scrub)}
-              aria-current={isActive ? 'true' : undefined}
-              data-testid={`chapter-card-${index}`}
-            >
-              <div className="chapter-card-top">
-                <span className={`chapter-kind chapter-kind--${chapter.kind}`}>
-                  {chapterKindLabel(chapter.kind)}
-                </span>
-                <span className="chapter-lap-range">{chapterLapRange(chapter)}</span>
-              </div>
-              <span className="chapter-headline">{headline}</span>
-            </button>
-          )
-        })}
+            return (
+              <button
+                key={`${chapter.kind}-${chapter.start_lap}-${index}`}
+                type="button"
+                role="listitem"
+                className={`chapter-card ${isActive ? (tourActive ? 'tour-active' : 'active') : ''}`}
+                onClick={() => onChapterClick(index, scrub)}
+                aria-current={isActive ? 'true' : undefined}
+                data-testid={`chapter-card-${index}`}
+              >
+                <div className="chapter-card-top">
+                  <span className={`chapter-kind chapter-kind--${chapter.kind}`}>
+                    {chapterKindLabel(chapter.kind)}
+                  </span>
+                  <span className="chapter-lap-range">{chapterLapRange(chapter)}</span>
+                </div>
+                <span className="chapter-headline">{headline}</span>
+              </button>
+            )
+          })}
+        </div>
       </div>
     </div>
   )

frontend/src/components/EmptyStateCard.tsx

@@ -0,0 +1,20 @@
+import type { LucideIcon } from 'lucide-react'
+import type { ReactNode } from 'react'
+
+interface Props {
+  icon: LucideIcon
+  title: string
+  hint: ReactNode
+  testId?: string
+  className?: string
+}
+
+export function EmptyStateCard({ icon: Icon, title, hint, testId, className = '' }: Props) {
+  return (
+    <div className={`empty-state ui-card ${className}`.trim()} data-testid={testId}>
+      <Icon size={32} className="empty-state-icon" aria-hidden />
+      <div className="empty-state-title">{title}</div>
+      <div className="empty-state-desc">{hint}</div>
+    </div>
+  )
+}

frontend/src/components/RaceStoryCanvas.tsx

@@ -1,13 +1,30 @@
 import { useEffect, useMemo, useRef, useState } from 'react'
 import { useQuery } from '@tanstack/react-query'
+import { LineChart } from 'lucide-react'
 import type { Driver, EnrichedResult, EnrichedGrid, PositionSample, Lap, Meeting, Session, Chapter } from '../types'
 import { fetchReplayFrames, fetchTrackOutline } from '../api'
 import { ReplayTrackMap } from './ReplayTrackMap'
 import { ChapterStrip } from './ChapterStrip'
+import { EmptyStateCard } from './EmptyStateCard'
 import { gridDelta, gridDeltaClass, formatDuration, formatGap } from '../utils'
-import { chapterEndScrub, chapterStartScrub, chapterTourDurations } from '../lib/chapters'
+import {
+  chapterBandFill,
+  chapterEndScrub,
+  chapterStartScrub,
+  chapterTourDurations,
+  deCollideYPositions,
+  decimatedPositionLabels,
+} from '../lib/chapters'
+import { isReplayMapAvailable } from '../lib/replayMap'
+import '../styles/race-story.css'
 
 const CHAPTER_TOUR_MS = 90_000
+const CHART_W = 640
+const CHART_H = 180
+const CHART_PL = 40
+const CHART_PR = 48
+const CHART_PT = 8
+const CHART_PB = 20
 
 interface Props {
   data: {
@@ -48,10 +65,10 @@ export function RaceStoryCanvas({ data }: Props) {
   const [playbackSpeed, setPlaybackSpeed] = useState(10)
   const [chapterTourActive, setChapterTourActive] = useState(false)
   const [tourChapterIndex, setTourChapterIndex] = useState<number | null>(null)
+  const [selectedChapterIndex, setSelectedChapterIndex] = useState<number | null>(null)
   const svgRef = useRef<SVGSVGElement>(null)
   const tourRef = useRef({ chapterIndex: 0, startedAt: 0, durationMs: 0, startScrub: 0, endScrub: 0 })
 
-  // Position Evolution Chart Logic
   const allTimes = useMemo(() => [...new Set(positions.map((p) => p.date))].sort(), [positions])
   const hasChartData = hasPositions && allTimes.length > 0
   const chartTiming = useMemo(() => {
@@ -62,18 +79,38 @@ export function RaceStoryCanvas({ data }: Props) {
   }, [allTimes, hasChartData])
   const circuitKey = session?.circuit_key ?? meeting?.circuit_key ?? 0
   const outlineYear = meeting?.year ?? (session?.date_start ? new Date(session.date_start).getFullYear() : 0)
+  const canProbeMap = Boolean(session?.session_key) && circuitKey > 0 && outlineYear > 0
 
   const replayQuery = useQuery({
     queryKey: ['replay-frames', session?.session_key, 5000],
     queryFn: () => fetchReplayFrames(session!.session_key, 5000),
-    enabled: mapOpen && Boolean(session?.session_key),
+    enabled: canProbeMap,
   })
   const outlineQuery = useQuery({
     queryKey: ['track-outline', circuitKey, outlineYear],
     queryFn: () => fetchTrackOutline(circuitKey, outlineYear),
-    enabled: mapOpen && circuitKey > 0 && outlineYear > 0,
+    enabled: canProbeMap,
   })
 
+  const mapProbeSettled = !canProbeMap || (!replayQuery.isLoading && !outlineQuery.isLoading)
+  const mapAvailable = useMemo(
+    () =>
+      canProbeMap &&
+      isReplayMapAvailable(
+        replayQuery.data,
+        outlineQuery.data,
+        replayQuery.isError || outlineQuery.isError,
+      ),
+    [canProbeMap, outlineQuery.data, outlineQuery.isError, replayQuery.data, replayQuery.isError],
+  )
+  const showMapPanel = mapOpen && mapAvailable
+
+  useEffect(() => {
+    if (!mapAvailable && mapOpen) {
+      setMapOpen(false)
+    }
+  }, [mapAvailable, mapOpen])
+
   useEffect(() => {
     if (!isPlaying || !chartTiming) return
 
@@ -104,9 +141,14 @@ export function RaceStoryCanvas({ data }: Props) {
   const jumpToChapter = (index: number, scrub: number) => {
     setIsPlaying(false)
     stopChapterTour()
+    setSelectedChapterIndex(index)
     setScrubTime(scrub)
   }
 
+  const clearChapterSelection = () => {
+    setSelectedChapterIndex(null)
+  }
+
   const toggleChapterTour = () => {
     if (chapterTourActive) {
       stopChapterTour()
@@ -114,6 +156,7 @@ export function RaceStoryCanvas({ data }: Props) {
     }
     if (!chartTiming || chapters.length === 0) return
     setIsPlaying(false)
+    setSelectedChapterIndex(null)
     setChapterTourActive(true)
     setTourChapterIndex(0)
     const startScrub = chapterStartScrub(chapters[0], chartTiming.tMin, chartTiming.tRange) ?? 0
@@ -203,7 +246,7 @@ export function RaceStoryCanvas({ data }: Props) {
         pos: p.position,
       })
     }
-    const dnfSet = new Set(results.filter(r => r.dnf || r.dns || r.dsq).map(r => r.driver_number))
+    const dnfSet = new Set(results.filter((r) => r.dnf || r.dns || r.dsq).map((r) => r.driver_number))
     for (const [dNum, samples] of byDriver.entries()) {
       samples.sort((a, b) => a.t - b.t)
       if (samples.length > 0 && !dnfSet.has(dNum)) {
@@ -211,16 +254,16 @@ export function RaceStoryCanvas({ data }: Props) {
       }
     }
 
-    const getInterpPos = (samples: {t: number, pos: number}[], t: number) => {
+    const getInterpPos = (samples: { t: number; pos: number }[], t: number) => {
       if (!samples || samples.length === 0) return null
       if (t <= samples[0].t) return samples[0].pos
       if (t >= samples[samples.length - 1].t) return samples[samples.length - 1].pos
       for (let i = 0; i < samples.length - 1; i++) {
-        if (samples[i].t <= t && samples[i+1].t >= t) {
-          const dt = samples[i+1].t - samples[i].t
+        if (samples[i].t <= t && samples[i + 1].t >= t) {
+          const dt = samples[i + 1].t - samples[i].t
           if (dt === 0) return samples[i].pos
           const frac = (t - samples[i].t) / dt
-          return samples[i].pos + (samples[i+1].pos - samples[i].pos) * frac
+          return samples[i].pos + (samples[i + 1].pos - samples[i].pos) * frac
         }
       }
       return null
@@ -244,22 +287,23 @@ export function RaceStoryCanvas({ data }: Props) {
     const maxPos = Math.max(...positions.map((p) => p.position), results.length, 2)
     const colorByDriver = new Map(results.map((r) => [r.driver_number, r.team_colour]))
     const acronymByDriver = new Map(results.map((r) => [r.driver_number, r.name_acronym]))
+    const positionLabels = decimatedPositionLabels(maxPos)
 
-    const W = 640
-    const H = 180
-    const PL = 40
-    const PR = 48
-    const PT = 8
-    const PB = 20
+    const W = CHART_W
+    const H = CHART_H
+    const PL = CHART_PL
+    const PR = CHART_PR
+    const PT = CHART_PT
+    const PB = CHART_PB
     const plotW = W - PL - PR
     const plotH = H - PT - PB
 
     const toX = (t: number) => PL + t * plotW
     const toY = (pos: number) => PT + ((pos - 1) / Math.max(maxPos - 1, 1)) * plotH
 
-    const winner = results.find(r => r.position === 1)
-    const winnerLaps = winner ? laps.filter(l => l.driver_number === winner.driver_number) : []
-    const lapTicks: { lap: number, t: number }[] = []
+    const winner = results.find((r) => r.position === 1)
+    const winnerLaps = winner ? laps.filter((l) => l.driver_number === winner.driver_number) : []
+    const lapTicks: { lap: number; t: number }[] = []
     const lapInterval = winnerLaps.length < 30 ? 5 : 10
 
     for (const lap of winnerLaps) {
@@ -271,7 +315,6 @@ export function RaceStoryCanvas({ data }: Props) {
       }
     }
 
-    // Safety Car / VSC periods
     const scPeriods: { start: number; end: number | null; type: 'SC' | 'VSC' }[] = []
     let activeSC: { start: number; type: 'SC' | 'VSC' } | null = null
     const rc = [...race_control].sort((a, b) => new Date(a.date).getTime() - new Date(b.date).getTime())
@@ -296,9 +339,34 @@ export function RaceStoryCanvas({ data }: Props) {
       scPeriods.push({ start: activeSC.start, end: null, type: activeSC.type })
     }
 
+    const chapterBands = chapters
+      .map((chapter, index) => {
+        const startT = chapterStartScrub(chapter, tMin, tRange)
+        const endT = chapterEndScrub(chapter, tMin, tRange)
+        if (startT === null) return null
+        const end = endT ?? startT
+        return {
+          key: `${chapter.kind}-${index}`,
+          start: Math.min(startT, end),
+          end: Math.max(startT, end),
+          fill: chapterBandFill(chapter.kind),
+        }
+      })
+      .filter((band): band is NonNullable<typeof band> => band !== null)
+
+    const labelCandidates = Array.from(byDriver.entries())
+      .map(([dNum, samples]) => {
+        const last = samples[samples.length - 1]
+        if (!last) return null
+        return { key: dNum, y: toY(last.pos) }
+      })
+      .filter((item): item is { key: number; y: number } => item !== null)
+    const labelYByDriver = deCollideYPositions(labelCandidates, 12)
+
     const handlePointerMove = (e: React.PointerEvent<SVGRectElement>) => {
       setIsPlaying(false)
       stopChapterTour()
+      clearChapterSelection()
       if (!svgRef.current) return
       const rect = svgRef.current.getBoundingClientRect()
       const x = e.clientX - rect.left
@@ -307,14 +375,34 @@ export function RaceStoryCanvas({ data }: Props) {
     }
 
     chartContent = (
-      <div className="rs-chart-container scroll-x" data-testid="position-chart">
+      <div
+        className={`rs-chart-container scroll-x${showMapPanel ? '' : ' rs-chart-container--full'}`}
+        data-testid="position-chart"
+      >
         <svg
           ref={svgRef}
+          className="rs-position-chart-svg"
           viewBox={`0 0 ${W} ${H}`}
-          style={{ width: '100%', minWidth: 280, maxWidth: W, display: 'block' }}
           role="img"
           aria-label="Position evolution chart"
         >
+          {chapterBands.map((band) => {
+            const x1 = toX(Math.max(0, band.start))
+            const x2 = toX(Math.min(1, band.end))
+            if (x2 <= PL || x1 >= W - PR) return null
+            return (
+              <rect
+                key={band.key}
+                x={x1}
+                y={PT}
+                width={Math.max(0, x2 - x1)}
+                height={plotH}
+                fill={band.fill}
+                data-testid="chapter-band"
+              />
+            )
+          })}
+
           {scPeriods.map((sc, i) => {
             const startT = (sc.start - tMin) / tRange
             const endT = sc.end ? (sc.end - tMin) / tRange : 1
@@ -333,33 +421,41 @@ export function RaceStoryCanvas({ data }: Props) {
             )
           })}
 
-          {Array.from({ length: maxPos }, (_, i) => i + 1).map((pos) => (
+          {positionLabels.map((pos) => (
             <g key={pos}>
               <line
                 x1={PL}
                 x2={W - PR}
                 y1={toY(pos)}
                 y2={toY(pos)}
-                stroke="var(--border)"
-                strokeWidth={0.5}
+                className="rs-chart-grid-line"
               />
               <text
                 x={PL - 4}
                 y={toY(pos) + 4}
                 textAnchor="end"
-                fill="var(--text-3)"
-                fontSize={8}
-                fontFamily="var(--f-mono)"
+                className="rs-chart-axis-label"
               >
                 P{pos}
               </text>
             </g>
           ))}
 
-          {lapTicks.map(tick => (
+          {lapTicks.map((tick) => (
             <g key={`lap-${tick.lap}`}>
-              <line x1={toX(tick.t)} x2={toX(tick.t)} y1={H - PB} y2={H - PB + 4} stroke="var(--border)" strokeWidth={1} />
-              <text x={toX(tick.t)} y={H - PB + 14} textAnchor="middle" fill="var(--text-3)" fontSize={9} fontFamily="var(--f-mono)">
+              <line
+                x1={toX(tick.t)}
+                x2={toX(tick.t)}
+                y1={H - PB}
+                y2={H - PB + 4}
+                className="rs-chart-lap-tick"
+              />
+              <text
+                x={toX(tick.t)}
+                y={H - PB + 14}
+                textAnchor="middle"
+                className="rs-chart-axis-label"
+              >
                 L{tick.lap}
               </text>
             </g>
@@ -372,8 +468,9 @@ export function RaceStoryCanvas({ data }: Props) {
             const last = samples[samples.length - 1]
             const isHovered = hoverDriver === dNum
             const isFaded = hoverDriver !== null && !isHovered
+            const labelY = last ? (labelYByDriver.get(dNum) ?? toY(last.pos)) : 0
 
-            const driverPits = pit_stops.filter(p => p.driver_number === dNum)
+            const driverPits = pit_stops.filter((p) => p.driver_number === dNum)
 
             return (
               <g
@@ -415,7 +512,7 @@ export function RaceStoryCanvas({ data }: Props) {
                 {last && (
                   <text
                     x={toX(last.t) + 6}
-                    y={toY(last.pos) + 4}
+                    y={labelY + 4}
                     fill={color}
                     fontSize={isHovered ? 11 : 9}
                     fontFamily="var(--f-mono)"
@@ -451,42 +548,54 @@ export function RaceStoryCanvas({ data }: Props) {
             fill="transparent"
             onPointerMove={handlePointerMove}
             onPointerLeave={() => {
-              if (!isPlaying) setScrubTime(null)
+              if (!isPlaying) {
+                clearChapterSelection()
+                setScrubTime(null)
+              }
             }}
             style={{ cursor: 'crosshair', touchAction: 'none' }}
           />
         </svg>
-        <div className="rs-replay-tools" aria-label="Race replay controls">
+        <div className="rs-segmented-control" aria-label="Race replay controls" data-testid="replay-controls">
           <button
             type="button"
-            className={`rs-tool-btn ${isPlaying ? 'active' : ''}`}
+            className={`rs-segment ${isPlaying ? 'active' : ''}`}
             onClick={() => {
               setScrubTime((current) => current ?? 0)
               stopChapterTour()
+              clearChapterSelection()
               setIsPlaying((current) => !current)
             }}
+            aria-pressed={isPlaying}
           >
             {isPlaying ? 'Pause' : 'Play'}
           </button>
-          <div className="rs-speed-group" aria-label="Playback speed">
-            {[1, 10, 30].map((speed) => (
+          <span className="rs-segment-divider" aria-hidden />
+          {[1, 10, 30].map((speed) => (
+            <button
+              key={speed}
+              type="button"
+              className={`rs-segment ${playbackSpeed === speed ? 'active' : ''}`}
+              onClick={() => setPlaybackSpeed(speed)}
+              aria-pressed={playbackSpeed === speed}
+            >
+              {speed}x
+            </button>
+          ))}
+          {mapProbeSettled && mapAvailable && (
+            <>
+              <span className="rs-segment-divider" aria-hidden />
               <button
-                key={speed}
                 type="button"
-                className={`rs-speed-btn ${playbackSpeed === speed ? 'active' : ''}`}
-                onClick={() => setPlaybackSpeed(speed)}
+                className={`rs-segment ${mapOpen ? 'active' : ''}`}
+                onClick={() => setMapOpen((current) => !current)}
+                aria-pressed={mapOpen}
+                data-testid="replay-map-toggle"
               >
-                {speed}x
+                Map
               </button>
-            ))}
-          </div>
-          <button
-            type="button"
-            className={`rs-tool-btn ${mapOpen ? 'active' : ''}`}
-            onClick={() => setMapOpen((current) => !current)}
-          >
-            Map
-          </button>
+            </>
+          )}
         </div>
       </div>
     )
@@ -502,36 +611,41 @@ export function RaceStoryCanvas({ data }: Props) {
           tRange={chartTiming.tRange}
           tourActive={chapterTourActive}
           tourChapterIndex={tourChapterIndex}
+          selectedChapterIndex={selectedChapterIndex}
           onChapterClick={jumpToChapter}
           onTourToggle={toggleChapterTour}
         />
       )}
-      <div className="rs-replay-shell">
+      <div className={`rs-replay-shell${showMapPanel ? ' rs-replay-shell--split' : ''}`}>
         <div className="rs-replay-main">
           {hasChartData ? (
             chartContent
           ) : (
-            <div className="analysis-notice">
-              <strong>Lap-by-lap positions not available.</strong> This session does not
-              have ingested position samples in <code>/api/v1/race-hub</code>.
-            </div>
+            <EmptyStateCard
+              icon={LineChart}
+              title="Lap-by-lap positions not available"
+              hint={
+                <>
+                  This session does not have ingested position samples in{' '}
+                  <code>/api/v1/race-hub</code>.
+                </>
+              }
+              testId="race-story-no-positions"
+              className="race-story-empty-card"
+            />
           )}
         </div>
-        {mapOpen && (
-          <div className="rs-replay-map-slot">
-            {circuitKey > 0 && outlineYear > 0 ? (
-              <ReplayTrackMap
-                outline={outlineQuery.data}
-                replay={replayQuery.data}
-                tMs={replayTMs}
-                drivers={drivers}
-                results={results}
-                loading={outlineQuery.isLoading || replayQuery.isLoading}
-                error={outlineQuery.isError || replayQuery.isError}
-              />
-            ) : (
-              <div className="rs-replay-map-placeholder">track identity unavailable for replay map</div>
-            )}
+        {showMapPanel && (
+          <div className="rs-replay-map-slot" data-testid="replay-map-slot">
+            <ReplayTrackMap
+              outline={outlineQuery.data}
+              replay={replayQuery.data}
+              tMs={replayTMs}
+              drivers={drivers}
+              results={results}
+              loading={outlineQuery.isLoading || replayQuery.isLoading}
+              error={outlineQuery.isError || replayQuery.isError}
+            />
           </div>
         )}
       </div>
@@ -542,7 +656,8 @@ export function RaceStoryCanvas({ data }: Props) {
             const gridPos = grid.find((g) => g.driver_number === r.driver_number)?.position ?? 0
             const currentPos = scrubTime !== null ? i + 1 : r.position
             const isWinner = i === 0 && r.position === 1
-            const pClass = currentPos === 1 ? 'rs-pos-p1' : currentPos === 2 ? 'rs-pos-p2' : currentPos === 3 ? 'rs-pos-p3' : ''
+            const pClass =
+              currentPos === 1 ? 'rs-pos-p1' : currentPos === 2 ? 'rs-pos-p2' : currentPos === 3 ? 'rs-pos-p3' : ''
 
             let currentPoints: number | string = r.points
             if (scrubTime !== null) {
@@ -559,9 +674,7 @@ export function RaceStoryCanvas({ data }: Props) {
                 onMouseLeave={() => setHoverDriver(null)}
               >
                 <div className="rs-driver-left">
-                  <div className={`rs-pos-col ${pClass}`}>
-                    {currentPos}
-                  </div>
+                  <div className={`rs-pos-col ${pClass}`}>{currentPos}</div>
                   <div className="rs-driver-cell">
                     <div
                       className="rs-driver-color"

frontend/src/components/ReplayTrackMap.tsx

@@ -1,7 +1,9 @@
 import { useMemo, useState } from 'react'
+import { Loader2, MapPin, Satellite } from 'lucide-react'
 import type { Driver, EnrichedResult, ReplayFramesResponse, TrackOutline } from '../types'
 import { buildOutlinePath } from '../lib/trackmap'
 import { interpolateReplayCars, replayCarToSvg } from '../lib/replay'
+import { EmptyStateCard } from './EmptyStateCard'
 import '../styles/replay-map.css'
 
 interface Props {
@@ -60,7 +62,13 @@ export function ReplayTrackMap({
   if (loading) {
     return (
       <section className="replay-map-panel" data-testid="replay-track-map">
-        <div className="replay-map-empty">loading replay GPS...</div>
+        <EmptyStateCard
+          icon={Loader2}
+          title="Loading replay map"
+          hint="Fetching track outline and historical GPS frames."
+          testId="replay-map-loading"
+          className="replay-map-empty-card"
+        />
       </section>
     )
   }
@@ -68,7 +76,13 @@ export function ReplayTrackMap({
   if (error) {
     return (
       <section className="replay-map-panel" data-testid="replay-track-map">
-        <div className="replay-map-empty">replay GPS unavailable for this session</div>
+        <EmptyStateCard
+          icon={Satellite}
+          title="Replay GPS unavailable"
+          hint="This session does not have ingested location samples for the replay map."
+          testId="replay-map-error"
+          className="replay-map-empty-card"
+        />
       </section>
     )
   }
@@ -76,7 +90,13 @@ export function ReplayTrackMap({
   if (!outline || !outlinePath) {
     return (
       <section className="replay-map-panel" data-testid="replay-track-map">
-        <div className="replay-map-empty">track outline unavailable for this session</div>
+        <EmptyStateCard
+          icon={MapPin}
+          title="Track outline unavailable"
+          hint="Circuit GPS outline data is missing for this session."
+          testId="replay-map-no-outline"
+          className="replay-map-empty-card"
+        />
       </section>
     )
   }
@@ -84,7 +104,13 @@ export function ReplayTrackMap({
   if (!replay?.frames?.length || cars.length === 0) {
     return (
       <section className="replay-map-panel" data-testid="replay-track-map">
-        <div className="replay-map-empty">historical GPS unavailable for this session</div>
+        <EmptyStateCard
+          icon={Satellite}
+          title="Historical GPS unavailable"
+          hint="Fewer than two replay frames were returned for this session."
+          testId="replay-map-no-frames"
+          className="replay-map-empty-card"
+        />
       </section>
     )
   }

frontend/src/components/RivalryCompare.tsx

@@ -0,0 +1,271 @@
+import { useMemo, useState } from 'react'
+import type { ChampHubDriver, ChampionshipHub } from '../types'
+import { teamColor } from '../utils'
+import { gapSeries, h2hTally, lastRounds } from '../lib/rivalry'
+import '../styles/rivalry.css'
+
+const PAD_L = 48
+const PAD_T = 16
+const PLOT_W = 882
+const PLOT_H = 316
+const GAP_PLOT_H = 200
+
+function fmtPts(n: number): string {
+  return Number.isInteger(n) ? String(n) : n.toFixed(1)
+}
+
+/** Up to ~7 evenly spaced round labels, always including the last round. */
+function xTicks(n: number, labels: string[], x: (i: number) => number): { x: number; label: string }[] {
+  const step = Math.max(1, Math.ceil(n / 7))
+  const ticks: { x: number; label: string }[] = []
+  for (let i = 0; i < n; i += step) {
+    ticks.push({ x: x(i), label: labels[i] ?? `R${i + 1}` })
+  }
+  const last = labels[n - 1] ?? `R${n}`
+  if (ticks[ticks.length - 1]?.label !== last) {
+    ticks.push({ x: x(n - 1), label: last })
+  }
+  return ticks
+}
+
+function polyline(values: number[], x: (i: number) => number, y: (v: number) => number): string {
+  return values.map((v, i) => `${x(i).toFixed(1)},${y(v).toFixed(1)}`).join(' ')
+}
+
+interface PickerProps {
+  id: 'a' | 'b'
+  label: string
+  drivers: ChampHubDriver[]
+  value: number
+  color: string
+  onChange: (driverNumber: number) => void
+}
+
+function DriverPicker({ id, label, drivers, value, color, onChange }: PickerProps) {
+  return (
+    <label className="rivalry-picker">
+      <span className="rivalry-picker-label">{label}</span>
+      <select
+        className="rivalry-picker-select"
+        style={{ borderLeft: `3px solid ${color}` }}
+        value={value}
+        data-testid={`rivalry-pick-${id}`}
+        onChange={(e) => onChange(Number(e.target.value))}
+      >
+        {drivers.map((d) => (
+          <option key={d.driver_number} value={d.driver_number}>
+            {d.name_acronym} · {d.full_name}
+          </option>
+        ))}
+      </select>
+    </label>
+  )
+}
+
+export function RivalryCompare({ hub }: { hub: ChampionshipHub }) {
+  const { drivers } = hub
+  const [pickA, setPickA] = useState<number | null>(null)
+  const [pickB, setPickB] = useState<number | null>(null)
+
+  // Default to the top two in the standings; fall back there if a picked
+  // driver disappears (e.g. season switch re-fetches the hub).
+  const a = drivers.find((d) => d.driver_number === pickA) ?? drivers[0]
+  const b = drivers.find((d) => d.driver_number === pickB) ?? drivers[1]
+
+  const tally = useMemo(
+    () => (a && b ? h2hTally(a.round_positions ?? [], b.round_positions ?? [], hub.round_labels) : null),
+    [a, b, hub.round_labels],
+  )
+
+  if (drivers.length < 2) {
+    return (
+      <div className="champ-chart-empty" data-testid="champ-view-rivalry">
+        Need at least two drivers in the standings to compare a rivalry.
+      </div>
+    )
+  }
+
+  const colorA = teamColor(a.team_colour)
+  const colorB = teamColor(b.team_colour)
+  const sameTeam = a.team_name === b.team_name
+
+  const cumA = a.cumulative ?? []
+  const cumB = b.cumulative ?? []
+  const rounds = Math.min(cumA.length, cumB.length)
+  const gaps = gapSeries(cumA, cumB)
+  const lastGap = gaps[gaps.length - 1] ?? 0
+  const strip = tally ? lastRounds(tally, 5) : []
+
+  const pickers = (
+    <div className="rivalry-pickers">
+      <DriverPicker id="a" label="Driver A" drivers={drivers} value={a.driver_number} color={colorA} onChange={setPickA} />
+      <span className="rivalry-vs mono">vs</span>
+      <DriverPicker id="b" label="Driver B" drivers={drivers} value={b.driver_number} color={colorB} onChange={setPickB} />
+    </div>
+  )
+
+  if (rounds === 0) {
+    return (
+      <div className="rivalry" data-testid="champ-view-rivalry">
+        {pickers}
+        <div className="champ-chart-empty">
+          No completed rounds yet — the rivalry will appear after the first race.
+        </div>
+      </div>
+    )
+  }
+
+  // Points race scales.
+  const peak = Math.max(...cumA.slice(0, rounds), ...cumB.slice(0, rounds), 1)
+  const maxY = Math.max(50, Math.ceil(peak / 50) * 50)
+  const px = (i: number) => (rounds <= 1 ? PAD_L : PAD_L + (i * PLOT_W) / (rounds - 1))
+  const py = (v: number) => PAD_T + PLOT_H - (v / maxY) * PLOT_H
+  const pyGrid = [0, 0.25, 0.5, 0.75, 1].map((f) => ({ y: py(maxY * f), label: Math.round(maxY * f) }))
+  const pxGrid = xTicks(rounds, hub.round_labels, px)
+
+  // Gap scales: symmetric around zero.
+  const maxAbs = Math.max(10, Math.ceil(Math.max(...gaps.map(Math.abs), 1) / 10) * 10)
+  const gy = (v: number) => PAD_T + GAP_PLOT_H / 2 - (v / maxAbs) * (GAP_PLOT_H / 2)
+  const gyGrid = [maxAbs, 0, -maxAbs].map((v) => ({ y: gy(v), label: v > 0 ? `+${v}` : String(v) }))
+  const gxGrid = xTicks(rounds, hub.round_labels, px)
+
+  const gapLeader = lastGap === 0 ? null : lastGap > 0 ? a : b
+  const gapCaption = gapLeader
+    ? `${gapLeader.name_acronym} leads by ${fmtPts(Math.abs(lastGap))} pts after ${hub.round_labels[rounds - 1] ?? `R${rounds}`}.`
+    : 'Dead level on points.'
+
+  return (
+    <div className="rivalry" data-testid="champ-view-rivalry">
+      {pickers}
+
+      <div className="rivalry-h2h" data-testid="rivalry-h2h">
+        <div className="rivalry-h2h-score">
+          <span className="rivalry-h2h-code mono" style={{ color: colorA }}>
+            {a.name_acronym}
+          </span>
+          <span className="rivalry-h2h-num mono" data-testid="rivalry-h2h-num">
+            {tally ? `${tally.a}–${tally.b}` : '—'}
+          </span>
+          <span className="rivalry-h2h-code mono" style={{ color: colorB }}>
+            {b.name_acronym}
+          </span>
+        </div>
+        <span className="rivalry-h2h-meta">
+          Race head-to-head · {tally?.rounds.length ?? 0} round{(tally?.rounds.length ?? 0) === 1 ? '' : 's'} counted
+          {tally && tally.skipped > 0 ? ` · ${tally.skipped} skipped` : ''}
+        </span>
+        {strip.length > 0 && (
+          <div className="rivalry-strip" data-testid="rivalry-strip">
+            <span className="rivalry-strip-label">Last {strip.length}</span>
+            {strip.map((r) => (
+              <span className="rivalry-chip" key={r.round} title={`${r.label}: ${a.name_acronym} P${r.posA} · ${b.name_acronym} P${r.posB}`}>
+                <span className="rivalry-chip-round mono">{r.label}</span>
+                <span className="rivalry-chip-winner mono" style={{ color: r.winner === 'a' ? colorA : colorB }}>
+                  {r.winner === 'a' ? a.name_acronym : b.name_acronym}
+                </span>
+              </span>
+            ))}
+          </div>
+        )}
+      </div>
+
+      <section className="rivalry-section" data-testid="rivalry-points-race">
+        <div className="champ-chart-head">
+          <span className="champ-chart-title mono">
+            Points race — {a.name_acronym} vs {b.name_acronym}
+          </span>
+          <span className="champ-chart-meta">
+            Rounds 1–{rounds} · {hub.season}
+          </span>
+        </div>
+        <div className="champ-chart">
+          <svg viewBox="0 0 1000 380" className="champ-chart-svg" preserveAspectRatio="none">
+            {pyGrid.map((g) => (
+              <g key={g.label}>
+                <line x1={PAD_L} y1={g.y} x2={930} y2={g.y} stroke="var(--border)" strokeWidth="1" />
+                <text x={40} y={g.y + 4} textAnchor="end" className="champ-chart-axis">
+                  {g.label}
+                </text>
+              </g>
+            ))}
+            {pxGrid.map((g, i) => (
+              <text key={i} x={g.x} y={372} textAnchor="middle" className="champ-chart-axis">
+                {g.label}
+              </text>
+            ))}
+            {[
+              { slot: 'a', d: a, color: colorA, dash: '0', values: cumA.slice(0, rounds) },
+              { slot: 'b', d: b, color: colorB, dash: sameTeam ? '5 4' : '0', values: cumB.slice(0, rounds) },
+            ].map((s) => (
+              <g key={s.slot}>
+                <polyline
+                  points={polyline(s.values, px, py)}
+                  fill="none"
+                  stroke={s.color}
+                  strokeWidth="2.4"
+                  strokeDasharray={s.dash}
+                  strokeLinejoin="round"
+                  strokeLinecap="round"
+                />
+                <circle cx={px(s.values.length - 1)} cy={py(s.values[s.values.length - 1])} r="3" fill={s.color} />
+                <text
+                  x={px(s.values.length - 1) + 8}
+                  y={py(s.values[s.values.length - 1]) + 4}
+                  fill={s.color}
+                  className="champ-chart-label"
+                >
+                  {s.d.name_acronym}
+                </text>
+              </g>
+            ))}
+          </svg>
+        </div>
+      </section>
+
+      <section className="rivalry-section" data-testid="rivalry-gap">
+        <div className="champ-chart-head">
+          <span className="champ-chart-title mono">
+            Gap over season — {a.name_acronym} − {b.name_acronym}
+          </span>
+          <span className="champ-chart-meta">{gapCaption}</span>
+        </div>
+        <div className="champ-chart">
+          <svg viewBox="0 0 1000 250" className="champ-chart-svg" preserveAspectRatio="none">
+            {gyGrid.map((g) => (
+              <g key={g.label}>
+                <line
+                  x1={PAD_L}
+                  y1={g.y}
+                  x2={930}
+                  y2={g.y}
+                  stroke={g.label === '0' ? 'var(--border-2)' : 'var(--border)'}
+                  strokeWidth={g.label === '0' ? 1.5 : 1}
+                />
+                <text x={40} y={g.y + 4} textAnchor="end" className="champ-chart-axis">
+                  {g.label}
+                </text>
+              </g>
+            ))}
+            {gxGrid.map((g, i) => (
+              <text key={i} x={g.x} y={242} textAnchor="middle" className="champ-chart-axis">
+                {g.label}
+              </text>
+            ))}
+            <polyline
+              points={polyline(gaps, px, gy)}
+              fill="none"
+              stroke={colorA}
+              strokeWidth="2.4"
+              strokeLinejoin="round"
+              strokeLinecap="round"
+            />
+            <circle cx={px(gaps.length - 1)} cy={gy(lastGap)} r="3" fill={colorA} />
+          </svg>
+        </div>
+        <p className="rivalry-caption">
+          Above the zero line: {a.name_acronym} ahead. Below: {b.name_acronym} ahead.
+        </p>
+      </section>
+    </div>
+  )
+}

frontend/src/lib/chapters.ts

@@ -53,7 +53,10 @@ export function chapterEndScrub(
   return Math.max(0, Math.min(1, (ms - tMin) / tRange))
 }
 
-/** Index of the chapter containing the current scrub position, if any. */
+/** Index of the chapter containing the current scrub position, if any.
+ * Uses the same 0–1 clamped bounds as chapterStartScrub/chapterEndScrub so
+ * chapters whose timestamps fall outside the position-sample window still
+ * activate when the scrubber is parked at the clamped edge. */
 export function activeChapterIndex(
   chapters: Chapter[],
   scrubTime: number | null,
@@ -61,15 +64,13 @@ export function activeChapterIndex(
   tRange: number,
 ): number | null {
   if (scrubTime === null || chapters.length === 0 || tRange <= 0) return null
-  const chartMs = tMin + scrubTime * tRange
   for (let i = 0; i < chapters.length; i++) {
-    const ch = chapters[i]
-    const startMs = ch.start_time ? new Date(ch.start_time).getTime() : NaN
-    const endRaw = ch.end_time ?? ch.start_time
-    const endMs = endRaw ? new Date(endRaw).getTime() : NaN
-    if (!Number.isNaN(startMs) && !Number.isNaN(endMs) && chartMs >= startMs && chartMs <= endMs) {
-      return i
-    }
+    const start = chapterStartScrub(chapters[i], tMin, tRange)
+    const end = chapterEndScrub(chapters[i], tMin, tRange)
+    if (start === null || end === null) continue
+    const lo = Math.min(start, end)
+    const hi = Math.max(start, end)
+    if (scrubTime >= lo && scrubTime <= hi) return i
   }
   return null
 }
@@ -80,3 +81,52 @@ export function chapterTourDurations(chapters: Chapter[], totalMs = 90_000): num
   const perChapter = totalMs / chapters.length
   return chapters.map(() => perChapter)
 }
+
+/** Decimated position axis labels, e.g. P1, P5, P10, P15, P20. */
+export function decimatedPositionLabels(maxPos: number): number[] {
+  if (maxPos <= 1) return [1]
+  const labels = new Set<number>([1])
+  for (let pos = 5; pos < maxPos; pos += 5) {
+    labels.add(pos)
+  }
+  labels.add(maxPos)
+  return [...labels].sort((a, b) => a - b)
+}
+
+/** Subtle background fill for chapter time-bands on the position graph. */
+export function chapterBandFill(kind: string): string {
+  switch (kind) {
+    case 'safety_car':
+      return 'rgba(255, 153, 0, 0.14)'
+    case 'virtual_safety_car':
+      return 'rgba(255, 204, 0, 0.12)'
+    case 'red_flag':
+      return 'rgba(230, 36, 41, 0.12)'
+    case 'pit_phase':
+      return 'rgba(96, 165, 250, 0.08)'
+    case 'decisive_swing':
+      return 'rgba(34, 197, 94, 0.08)'
+    case 'finish':
+      return 'rgba(255, 204, 0, 0.06)'
+    default:
+      return 'rgba(255, 255, 255, 0.03)'
+  }
+}
+
+/** Minimum vertical spacing between colliding labels (SVG units). */
+export function deCollideYPositions(
+  items: ReadonlyArray<{ key: string | number; y: number }>,
+  minGap = 12,
+): Map<string | number, number> {
+  if (items.length === 0) return new Map()
+  const sorted = [...items].sort((a, b) => a.y - b.y)
+  const adjusted = sorted.map((item) => ({ ...item }))
+  for (let i = 1; i < adjusted.length; i++) {
+    const prev = adjusted[i - 1]
+    const curr = adjusted[i]
+    if (curr.y - prev.y < minGap) {
+      curr.y = prev.y + minGap
+    }
+  }
+  return new Map(adjusted.map((item) => [item.key, item.y]))
+}

frontend/src/lib/replayMap.ts

@@ -0,0 +1,14 @@
+import type { ReplayFramesResponse, TrackOutline } from '../types'
+
+/** Whether replay map can render (probe uses existing frames + outline queries). */
+export function isReplayMapAvailable(
+  replay: ReplayFramesResponse | null | undefined,
+  outline: TrackOutline | null | undefined,
+  hasError: boolean,
+): boolean {
+  if (hasError) return false
+  const frames = replay?.frames ?? []
+  if (frames.length < 2) return false
+  if (!outline?.points?.length) return false
+  return true
+}

frontend/src/lib/rivalry.ts

@@ -0,0 +1,61 @@
+// Pure helpers for the championship rivalry compare view.
+
+/** One round that counted toward the head-to-head tally. */
+export interface H2HRound {
+  round: number // 1-based season round
+  label: string
+  posA: number
+  posB: number
+  winner: 'a' | 'b'
+}
+
+export interface H2HTally {
+  a: number
+  b: number
+  /** Rounds counted in the tally, in season order. */
+  rounds: H2HRound[]
+  /** Rounds skipped because either driver had no finishing position. */
+  skipped: number
+}
+
+/**
+ * Per-round points gap (a − b) across the rounds both cumulative series
+ * cover. Positive values mean driver A is ahead.
+ */
+export function gapSeries(a: number[], b: number[]): number[] {
+  const n = Math.min(a.length, b.length)
+  const out: number[] = []
+  for (let i = 0; i < n; i++) out.push(a[i] - b[i])
+  return out
+}
+
+/**
+ * Race head-to-head: per round, the lower finishing position wins. Rounds
+ * where either driver has no position (0 / missing) are skipped from the
+ * tally, as are equal positions (defensive — races can't tie).
+ */
+export function h2hTally(posA: number[], posB: number[], labels: string[]): H2HTally {
+  const n = Math.max(posA.length, posB.length)
+  const rounds: H2HRound[] = []
+  let a = 0
+  let b = 0
+  let skipped = 0
+  for (let i = 0; i < n; i++) {
+    const pa = posA[i] ?? 0
+    const pb = posB[i] ?? 0
+    if (pa <= 0 || pb <= 0 || pa === pb) {
+      skipped++
+      continue
+    }
+    const winner = pa < pb ? 'a' : 'b'
+    if (winner === 'a') a++
+    else b++
+    rounds.push({ round: i + 1, label: labels[i] ?? `R${i + 1}`, posA: pa, posB: pb, winner })
+  }
+  return { a, b, rounds, skipped }
+}
+
+/** Last n counted rounds of a tally, for the mini strip. */
+export function lastRounds(tally: H2HTally, n: number): H2HRound[] {
+  return tally.rounds.slice(-n)
+}

frontend/src/pages/ChampionshipPage.tsx

@@ -5,12 +5,13 @@ import { fetchChampionshipHub, fetchSeasons } from '../api'
 import { teamColor } from '../utils'
 import type { ChampHubDriver, ChampionshipHub } from '../types'
 import { ChampionshipSimulator } from '../components/ChampionshipSimulator'
+import { RivalryCompare } from '../components/RivalryCompare'
 import { Meaning } from '../components/Meaning'
 import { TeammateH2H } from '../components/TeammateH2H'
 import { teammatePairs } from '../lib/h2h'
 import { pointsGapMeaning } from '../lib/meaning'
 
-type View = 'drivers' | 'constructors' | 'progression' | 'simulator'
+type View = 'drivers' | 'constructors' | 'progression' | 'rivalry' | 'simulator'
 
 const GOLD = '#ffd700'
 const SILVER = '#c0c0c0'
@@ -216,6 +217,14 @@ function ChampionshipBody({ hub, view, setView }: BodyProps) {
           >
             Progression
           </button>
+          <button
+            type="button"
+            className={`champ-tab${view === 'rivalry' ? ' is-active' : ''}`}
+            onClick={() => setView('rivalry')}
+            data-testid="champ-tab-rivalry"
+          >
+            Rivalry
+          </button>
           <button
             type="button"
             className={`champ-tab${view === 'simulator' ? ' is-active' : ''}`}
@@ -251,6 +260,7 @@ function ChampionshipBody({ hub, view, setView }: BodyProps) {
       )}
       {view === 'constructors' && <ConstructorsView hub={hub} />}
       {view === 'progression' && <ProgressionView hub={hub} />}
+      {view === 'rivalry' && <RivalryCompare hub={hub} />}
       {view === 'simulator' && <ChampionshipSimulator hub={hub} />}
     </div>
   )

frontend/src/styles/chapters.css

@@ -9,6 +9,7 @@
   align-items: center;
   justify-content: space-between;
   gap: var(--s4);
+  flex-wrap: wrap;
 }
 
 .chapter-strip-title {
@@ -44,6 +45,31 @@
   color: var(--text);
 }
 
+.chapter-strip-scroll-wrap {
+  position: relative;
+}
+
+.chapter-strip-scroll-wrap::before,
+.chapter-strip-scroll-wrap::after {
+  content: '';
+  position: absolute;
+  top: 0;
+  bottom: var(--s2);
+  width: 28px;
+  pointer-events: none;
+  z-index: 1;
+}
+
+.chapter-strip-scroll-wrap::before {
+  left: 0;
+  background: linear-gradient(to right, var(--bg), transparent);
+}
+
+.chapter-strip-scroll-wrap::after {
+  right: 0;
+  background: linear-gradient(to left, var(--bg), transparent);
+}
+
 .chapter-strip-scroll {
   display: flex;
   gap: var(--s3);
@@ -51,10 +77,26 @@
   padding-bottom: var(--s2);
   scroll-snap-type: x mandatory;
   -webkit-overflow-scrolling: touch;
+  scrollbar-width: thin;
+  scrollbar-color: var(--border-2) transparent;
+}
+
+.chapter-strip-scroll::-webkit-scrollbar {
+  height: 4px;
+}
+
+.chapter-strip-scroll::-webkit-scrollbar-track {
+  background: transparent;
+}
+
+.chapter-strip-scroll::-webkit-scrollbar-thumb {
+  background: var(--border-2);
+  border-radius: 999px;
 }
 
 .chapter-card {
   flex: 0 0 min(240px, 72vw);
+  min-height: 88px;
   display: flex;
   flex-direction: column;
   gap: var(--s2);
@@ -64,7 +106,7 @@
   background: var(--surface);
   text-align: left;
   cursor: pointer;
-  scroll-snap-align: start;
+  scroll-snap-align: center;
   transition: border-color 0.15s, background 0.15s, box-shadow 0.15s;
 }
 
@@ -145,10 +187,22 @@
   -webkit-line-clamp: 2;
   -webkit-box-orient: vertical;
   overflow: hidden;
+  flex: 1;
 }
 
-.chapter-strip-empty {
-  font-size: 12px;
-  color: var(--text-3);
-  padding: var(--s3) 0;
+.chapter-strip-empty-card {
+  padding: var(--s6) var(--s5);
+  margin: 0;
+}
+
+.chapter-strip-empty-card .empty-state-icon {
+  display: block;
+  margin: 0 auto var(--s3);
+  color: var(--text-3);
+}
+
+@media (max-width: 900px) {
+  .chapter-strip-header {
+    align-items: flex-start;
+  }
 }

frontend/src/styles/race-story.css

@@ -0,0 +1,157 @@
+.race-story-empty-card {
+  padding: var(--s6) var(--s5);
+  margin: 0;
+}
+
+.race-story-empty-card .empty-state-icon {
+  display: block;
+  margin: 0 auto var(--s3);
+  color: var(--text-3);
+}
+
+.rs-replay-shell {
+  display: grid;
+  grid-template-columns: 1fr;
+  gap: var(--s5);
+  align-items: stretch;
+}
+
+.rs-replay-shell--split {
+  grid-template-columns: minmax(0, 1.4fr) minmax(260px, 0.8fr);
+}
+
+.rs-replay-main {
+  min-width: 0;
+}
+
+.rs-chart-container {
+  --rs-chart-max-width: 100%;
+}
+
+.rs-chart-container--full {
+  --rs-chart-max-width: 100%;
+}
+
+.rs-segmented-control {
+  display: inline-flex;
+  align-items: stretch;
+  flex-wrap: wrap;
+  gap: 0;
+  margin-top: var(--s3);
+  border: 1px solid var(--border-2);
+  border-radius: var(--s1);
+  background: var(--surface);
+  overflow: hidden;
+}
+
+.rs-segment {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  min-height: 30px;
+  padding: 0 var(--s4);
+  font-family: var(--f-mono);
+  font-size: 10px;
+  font-weight: 700;
+  letter-spacing: 0.04em;
+  color: var(--text-3);
+  background: transparent;
+  border: none;
+  border-right: 1px solid var(--border);
+  cursor: pointer;
+  transition: background 0.12s, color 0.12s;
+}
+
+.rs-segment:last-child {
+  border-right: none;
+}
+
+.rs-segment:hover:not(:disabled) {
+  color: var(--text);
+  background: var(--surface-h);
+}
+
+.rs-segment:focus-visible {
+  outline: 2px solid var(--red);
+  outline-offset: -2px;
+  z-index: 1;
+}
+
+.rs-segment.active {
+  color: var(--text);
+  background: rgba(230, 36, 41, 0.12);
+  box-shadow: inset 0 -2px 0 var(--red);
+}
+
+.rs-segment:disabled {
+  opacity: 0.45;
+  cursor: not-allowed;
+}
+
+.rs-segment-divider {
+  width: 1px;
+  align-self: stretch;
+  background: var(--border);
+  flex-shrink: 0;
+}
+
+.rs-replay-map-slot {
+  min-width: 0;
+}
+
+.rs-position-chart-svg {
+  width: 100%;
+  min-width: 280px;
+  max-width: var(--rs-chart-max-width, 640px);
+  display: block;
+}
+
+.rs-chart-axis-label {
+  fill: var(--text-3);
+  font-family: var(--f-mono);
+  font-size: 9px;
+}
+
+.rs-chart-grid-line {
+  stroke: var(--border);
+  stroke-width: 0.5;
+}
+
+.rs-chart-lap-tick {
+  stroke: var(--border);
+  stroke-width: 1;
+}
+
+@media (max-width: 900px) {
+  .rs-replay-shell--split {
+    grid-template-columns: 1fr;
+  }
+
+  .rs-segmented-control {
+    width: 100%;
+  }
+
+  .rs-segment {
+    flex: 1 1 auto;
+  }
+}
+
+@media (max-width: 560px) {
+  .rs-segmented-control {
+    flex-direction: column;
+    align-items: stretch;
+  }
+
+  .rs-segment {
+    border-right: none;
+    border-bottom: 1px solid var(--border);
+  }
+
+  .rs-segment:last-child {
+    border-bottom: none;
+  }
+
+  .rs-segment-divider {
+    display: none;
+  }
+}

frontend/src/styles/replay-map.css

@@ -1,76 +1,9 @@
-.rs-replay-shell {
-  display: grid;
-  grid-template-columns: minmax(0, 1.4fr) minmax(260px, 0.8fr);
-  gap: var(--s5);
-  align-items: stretch;
-}
-
-.rs-replay-main {
-  min-width: 0;
-}
-
-.rs-replay-tools {
-  display: flex;
-  align-items: center;
-  flex-wrap: wrap;
-  gap: var(--s3);
-  margin-top: var(--s3);
-}
-
-.rs-tool-btn,
-.rs-speed-btn {
-  height: 28px;
-  padding: 0 var(--s4);
-  font-family: var(--f-mono);
-  font-size: 10px;
-  font-weight: 700;
-  color: var(--text-2);
-  background: var(--surface);
-  border: 1px solid var(--border-2);
-  border-radius: 2px;
-  cursor: pointer;
-}
-
-.rs-tool-btn:hover,
-.rs-speed-btn:hover {
-  color: var(--text);
-  border-color: var(--text-3);
-}
-
-.rs-tool-btn.active,
-.rs-speed-btn.active {
-  color: var(--text);
-  border-color: var(--red);
-  background: rgba(230, 36, 41, 0.12);
-}
-
-.rs-speed-group {
-  display: inline-flex;
-  gap: 2px;
-}
-
-.rs-replay-map-slot {
-  min-width: 0;
-}
-
-.rs-replay-map-placeholder {
-  min-height: 244px;
-  display: grid;
-  place-items: center;
-  padding: var(--s5);
-  color: var(--text-3);
-  font-family: var(--f-mono);
-  font-size: 11px;
-  text-align: center;
-  border: 1px dashed var(--border-2);
-  background: var(--surface);
-}
-
 .replay-map-panel {
   min-height: 244px;
   height: 100%;
   border: 1px solid var(--border);
   background: var(--surface);
+  border-radius: var(--s2);
 }
 
 .replay-map-stage {
@@ -143,19 +76,16 @@
   stroke-width: 1.2;
 }
 
-.replay-map-empty {
+.replay-map-empty-card {
   min-height: 244px;
   display: grid;
-  place-items: center;
-  padding: var(--s5);
-  color: var(--text-3);
-  font-family: var(--f-mono);
-  font-size: 11px;
-  text-align: center;
+  place-content: center;
+  padding: var(--s6);
+  margin: 0;
 }
 
-@media (max-width: 860px) {
-  .rs-replay-shell {
-    grid-template-columns: 1fr;
-  }
+.replay-map-empty-card .empty-state-icon {
+  display: block;
+  margin: 0 auto var(--s3);
+  color: var(--text-3);
 }

frontend/src/styles/rivalry.css

@@ -0,0 +1,134 @@
+.rivalry {
+  display: flex;
+  flex-direction: column;
+  gap: var(--s5);
+}
+
+.rivalry-pickers {
+  display: flex;
+  flex-wrap: wrap;
+  gap: var(--s4);
+  align-items: flex-end;
+}
+
+.rivalry-vs {
+  font-size: 11px;
+  letter-spacing: 0.06em;
+  text-transform: uppercase;
+  color: var(--text-3);
+  padding-bottom: var(--s3);
+}
+
+.rivalry-picker {
+  display: flex;
+  flex-direction: column;
+  gap: var(--s2);
+  min-width: 200px;
+}
+
+.rivalry-picker-label {
+  font-family: var(--f-mono);
+  font-size: 11px;
+  letter-spacing: 0.06em;
+  text-transform: uppercase;
+  color: var(--text-3);
+}
+
+.rivalry-picker-select {
+  font-family: var(--f-mono);
+  font-size: 13px;
+  padding: var(--s2) var(--s3);
+  border: 1px solid var(--border);
+  border-radius: 4px;
+  background: var(--surface-2);
+  color: var(--text);
+}
+
+.rivalry-picker-select:focus {
+  outline: 2px solid var(--red);
+  outline-offset: 1px;
+}
+
+.rivalry-h2h {
+  display: flex;
+  flex-wrap: wrap;
+  align-items: center;
+  gap: var(--s4) var(--s5);
+  padding: var(--s4) var(--s5);
+  border: 1px solid var(--border);
+  border-radius: 4px;
+  background: var(--surface-2);
+}
+
+.rivalry-h2h-score {
+  display: flex;
+  align-items: baseline;
+  gap: var(--s3);
+}
+
+.rivalry-h2h-code {
+  font-size: 14px;
+  font-weight: 700;
+}
+
+.rivalry-h2h-num {
+  font-size: 24px;
+  font-weight: 700;
+  color: var(--text);
+}
+
+.rivalry-h2h-meta {
+  font-family: var(--f-mono);
+  font-size: 11px;
+  color: var(--text-3);
+}
+
+.rivalry-strip {
+  display: flex;
+  align-items: center;
+  gap: var(--s2);
+  margin-left: auto;
+}
+
+.rivalry-strip-label {
+  font-family: var(--f-mono);
+  font-size: 10px;
+  letter-spacing: 0.06em;
+  text-transform: uppercase;
+  color: var(--text-3);
+  margin-right: var(--s2);
+}
+
+.rivalry-chip {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: 1px;
+  padding: var(--s1) var(--s3);
+  border: 1px solid var(--border);
+  border-radius: 4px;
+  background: var(--surface);
+}
+
+.rivalry-chip-round {
+  font-size: 9px;
+  color: var(--text-3);
+}
+
+.rivalry-chip-winner {
+  font-size: 11px;
+  font-weight: 700;
+}
+
+.rivalry-section {
+  display: flex;
+  flex-direction: column;
+  gap: var(--s3);
+}
+
+.rivalry-caption {
+  font-family: var(--f-mono);
+  font-size: 11px;
+  color: var(--text-3);
+  margin: 0;
+}

frontend/src/test/BriefingPage.test.tsx

@@ -73,6 +73,7 @@ const drivers: ChampHubDriver[] = [
     cumulative: [25, 43, 68, 100],
     teammate_wins: 4,
     teammate_losses: 1,
+    round_positions: [],
   },
   {
     driver_number: 4,
@@ -89,6 +90,7 @@ const drivers: ChampHubDriver[] = [
     cumulative: [18, 36, 54, 80],
     teammate_wins: 3,
     teammate_losses: 2,
+    round_positions: [],
   },
 ]
 

frontend/src/test/ChampionshipPage.test.tsx

@@ -29,6 +29,7 @@ function driver(over: Partial<ChampHubDriver>): ChampHubDriver {
     poles: 4,
     form: [25, 18, 25, 15, 25],
     cumulative: [25, 43, 68, 83, 108, 200],
+    round_positions: [1, 2, 1, 3, 1, 1],
     teammate_wins: 9,
     teammate_losses: 1,
     ...over,
@@ -47,6 +48,7 @@ const drivers: ChampHubDriver[] = [
     position: 2,
     wins: 3,
     cumulative: [18, 36, 54, 80, 120, 160],
+    round_positions: [2, 1, 2, 2, 2, 2],
   }),
   driver({
     driver_number: 16,
@@ -58,6 +60,7 @@ const drivers: ChampHubDriver[] = [
     position: 3,
     wins: 1,
     cumulative: [15, 28, 40, 60, 90, 120],
+    round_positions: [3, 3, 3, 0, 3, 3],
   }),
 ]
 
@@ -129,6 +132,22 @@ describe('ChampionshipPage', () => {
     expect(screen.getByText('Cumulative points', { exact: false })).toBeInTheDocument()
   })
 
+  it('switches to the rivalry view with the top two drivers preselected', async () => {
+    renderPage()
+
+    await waitFor(() => expect(screen.getByTestId('championship')).toBeInTheDocument())
+
+    fireEvent.click(screen.getByTestId('champ-tab-rivalry'))
+    expect(screen.getByTestId('champ-view-rivalry')).toBeInTheDocument()
+    // Default pair is the top two in the standings: VER vs NOR.
+    expect(screen.getByTestId('rivalry-pick-a')).toHaveValue('1')
+    expect(screen.getByTestId('rivalry-pick-b')).toHaveValue('4')
+    // VER beats NOR in rounds 1, 3, 5, 6 → 4–2.
+    expect(screen.getByTestId('rivalry-h2h-num')).toHaveTextContent('4–2')
+    expect(screen.getByTestId('rivalry-points-race')).toBeInTheDocument()
+    expect(screen.getByTestId('rivalry-gap')).toBeInTheDocument()
+  })
+
   it('switches to the simulator view and projects standings', async () => {
     renderPage()
 

frontend/src/test/ChampionshipSimulator.test.tsx

@@ -17,6 +17,7 @@ function driver(over: Partial<ChampHubDriver>): ChampHubDriver {
     poles: 0,
     form: [],
     cumulative: [],
+    round_positions: [],
     teammate_wins: 0,
     teammate_losses: 0,
     ...over,

frontend/src/test/ChapterStrip.test.tsx

@@ -68,6 +68,25 @@ describe('ChapterStrip', () => {
     expect(screen.getByText('L12–L15')).toBeInTheDocument()
   })
 
+  it('renders an empty-state card when there are no chapters', () => {
+    const queryClient = new QueryClient({ defaultOptions: { queries: { retry: false } } })
+    render(
+      <QueryClientProvider client={queryClient}>
+        <ChapterStrip
+          chapters={[]}
+          scrubTime={null}
+          tMin={tMin}
+          tRange={tRange}
+          tourActive={false}
+          tourChapterIndex={null}
+          onChapterClick={vi.fn()}
+          onTourToggle={vi.fn()}
+        />
+      </QueryClientProvider>,
+    )
+    expect(screen.getByTestId('chapter-strip-empty')).toBeInTheDocument()
+  })
+
   it('highlights the active chapter from scrub time', () => {
     const scrub = (new Date('2025-05-25T13:13:00Z').getTime() - tMin) / tRange
     renderStrip({ scrubTime: scrub })
@@ -84,4 +103,26 @@ describe('ChapterStrip', () => {
     expect(index).toBe(1)
     expect(scrub).toBeCloseTo(0.6, 2)
   })
+
+  it('highlights an explicitly selected chapter even when scrub is outside its raw window', () => {
+    // Scrub parked at chart start; chapter 1's raw times are mid-race, but selection wins.
+    const queryClient = new QueryClient({ defaultOptions: { queries: { retry: false } } })
+    render(
+      <QueryClientProvider client={queryClient}>
+        <ChapterStrip
+          chapters={chapters}
+          scrubTime={0}
+          tMin={tMin}
+          tRange={tRange}
+          tourActive={false}
+          tourChapterIndex={null}
+          selectedChapterIndex={1}
+          onChapterClick={vi.fn()}
+          onTourToggle={vi.fn()}
+        />
+      </QueryClientProvider>,
+    )
+    expect(screen.getByTestId('chapter-card-1')).toHaveClass('active')
+    expect(screen.getByTestId('chapter-card-0')).not.toHaveClass('active')
+  })
 })

frontend/src/test/RacePreviewPage.test.tsx

@@ -109,6 +109,7 @@ const hubDriver = (over: Partial<ChampHubDriver>): ChampHubDriver => ({
   poles: 4,
   form: [25],
   cumulative: [200],
+  round_positions: [1],
   teammate_wins: 9,
   teammate_losses: 1,
   ...over,

frontend/src/test/RaceStoryCanvas.test.tsx

@@ -2,7 +2,7 @@ import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
 import { fireEvent, render, screen, waitFor } from '@testing-library/react'
 import { beforeEach, describe, expect, it, vi } from 'vitest'
 import { RaceStoryCanvas } from '../components/RaceStoryCanvas'
-import type { RaceHub, ReplayFramesResponse, TrackOutline } from '../types'
+import type { Chapter, RaceHub, ReplayFramesResponse, TrackOutline } from '../types'
 
 vi.mock('../api', () => ({
   fetchReplayFrames: vi.fn(),
@@ -28,9 +28,35 @@ const replay: ReplayFramesResponse = {
   session_key: 99,
   interval_ms: 5000,
   start_time: '2025-05-25T13:00:00Z',
-  frames: [{ t: 0, cars: { '1': { x: 10, y: 20 } } }],
+  frames: [
+    { t: 0, cars: { '1': { x: 10, y: 20 } } },
+    { t: 5000, cars: { '1': { x: 50, y: 50 } } },
+  ],
 }
 
+const chapters: Chapter[] = [
+  {
+    kind: 'start',
+    title: 'Start',
+    headline: 'Lights out',
+    start_lap: 1,
+    end_lap: 1,
+    start_time: '2025-05-25T13:00:00Z',
+    end_time: '2025-05-25T13:01:00Z',
+    driver_numbers: [],
+  },
+  {
+    kind: 'safety_car',
+    title: 'Safety Car',
+    headline: 'Incident brings out the Safety Car',
+    start_lap: 2,
+    end_lap: 2,
+    start_time: '2025-05-25T13:05:00Z',
+    end_time: '2025-05-25T13:05:00Z',
+    driver_numbers: [],
+  },
+]
+
 const raceHub: RaceHub = {
   source: 'local',
   session_key: 99,
@@ -103,14 +129,14 @@ const raceHub: RaceHub = {
   race_control: [],
   weather: [],
   laps: [],
-  chapters: [],
+  chapters,
 }
 
-function renderCanvas() {
+function renderCanvas(overrides: Partial<RaceHub> = {}) {
   const queryClient = new QueryClient({ defaultOptions: { queries: { retry: false } } })
   return render(
     <QueryClientProvider client={queryClient}>
-      <RaceStoryCanvas data={raceHub} />
+      <RaceStoryCanvas data={{ ...raceHub, ...overrides }} />
     </QueryClientProvider>,
   )
 }
@@ -122,14 +148,93 @@ describe('RaceStoryCanvas replay map', () => {
     mockFetchTrackOutline.mockResolvedValue(outline)
   })
 
-  it('fetches replay frames lazily when the map panel opens', async () => {
+  it('probes replay frames on mount and opens the map when data is available', async () => {
     renderCanvas()
 
-    expect(mockFetchReplayFrames).not.toHaveBeenCalled()
-    fireEvent.click(screen.getByRole('button', { name: 'Map' }))
-
     await waitFor(() => expect(mockFetchReplayFrames).toHaveBeenCalledWith(99, 5000))
     expect(mockFetchTrackOutline).toHaveBeenCalledWith(1, 2025)
+
+    const mapToggle = await screen.findByTestId('replay-map-toggle')
+    fireEvent.click(mapToggle)
+
     expect(await screen.findByTestId('replay-track-map')).toBeInTheDocument()
+    expect(screen.getByTestId('replay-map-slot')).toBeInTheDocument()
+  })
+
+  it('hides the map toggle when replay frames are unavailable', async () => {
+    mockFetchReplayFrames.mockResolvedValue({ ...replay, frames: [] })
+    renderCanvas()
+
+    await waitFor(() => expect(mockFetchReplayFrames).toHaveBeenCalled())
+    await waitFor(() => expect(screen.queryByTestId('replay-map-toggle')).not.toBeInTheDocument())
+  })
+
+  it('uses full-width chart layout when the map is closed', async () => {
+    renderCanvas()
+
+    await waitFor(() => expect(mockFetchReplayFrames).toHaveBeenCalled())
+    const chart = screen.getByTestId('position-chart')
+    expect(chart).toHaveClass('rs-chart-container--full')
+    expect(screen.queryByTestId('replay-map-slot')).not.toBeInTheDocument()
+    expect(document.querySelector('.rs-replay-shell--split')).not.toBeInTheDocument()
+  })
+
+  it('syncs active chapter highlight when a chapter card is clicked', async () => {
+    renderCanvas()
+
+    fireEvent.click(screen.getByTestId('chapter-card-1'))
+    await waitFor(() => expect(screen.getByTestId('chapter-card-1')).toHaveClass('active'))
+    expect(screen.getByTestId('chapter-card-0')).not.toHaveClass('active')
+  })
+
+  it('highlights out-of-window chapters after click (clamped scrub + selection)', async () => {
+    // Position samples start at 13:05; start chapter ends at 13:01 — outside the window.
+    renderCanvas({
+      positions: [
+        { session_key: 99, driver_number: 1, meeting_key: 1, date: '2025-05-25T13:05:00Z', position: 1 },
+        { session_key: 99, driver_number: 1, meeting_key: 1, date: '2025-05-25T13:10:00Z', position: 1 },
+      ],
+      chapters: [
+        {
+          kind: 'start',
+          title: 'Start',
+          headline: 'Lights out before samples',
+          start_lap: 1,
+          end_lap: 1,
+          start_time: '2025-05-25T13:00:00Z',
+          end_time: '2025-05-25T13:01:00Z',
+          driver_numbers: [],
+        },
+        {
+          kind: 'finish',
+          title: 'Finish',
+          headline: 'Flag after samples',
+          start_lap: 78,
+          end_lap: 78,
+          start_time: '2025-05-25T13:20:00Z',
+          end_time: '2025-05-25T13:21:00Z',
+          driver_numbers: [],
+        },
+      ],
+    })
+
+    fireEvent.click(screen.getByTestId('chapter-card-0'))
+    await waitFor(() => expect(screen.getByTestId('chapter-card-0')).toHaveClass('active'))
+    expect(screen.getByTestId('chapter-card-1')).not.toHaveClass('active')
+
+    fireEvent.click(screen.getByTestId('chapter-card-1'))
+    await waitFor(() => expect(screen.getByTestId('chapter-card-1')).toHaveClass('active'))
+    expect(screen.getByTestId('chapter-card-0')).not.toHaveClass('active')
+  })
+
+  it('renders the empty-state card when positions are unavailable', () => {
+    renderCanvas({
+      datasets: { positions: { status: 'missing', source: 'local', count: 0 } },
+      positions: [],
+      chapters: [],
+    })
+
+    expect(screen.getByTestId('race-story-no-positions')).toBeInTheDocument()
+    expect(screen.getByText('Lap-by-lap positions not available')).toBeInTheDocument()
   })
 })

frontend/src/test/ReplayTrackMap.test.tsx

@@ -44,9 +44,10 @@ const results: EnrichedResult[] = [
 ]
 
 describe('ReplayTrackMap', () => {
-  it('renders an empty state when replay frames are missing', () => {
+  it('renders an empty-state card when replay frames are missing', () => {
     render(<ReplayTrackMap outline={outline} replay={{ ...replay, frames: [] }} tMs={0} drivers={[]} results={results} />)
-    expect(screen.getByTestId('replay-track-map')).toHaveTextContent(/historical GPS unavailable/i)
+    expect(screen.getByTestId('replay-map-no-frames')).toBeInTheDocument()
+    expect(screen.getByText('Historical GPS unavailable')).toBeInTheDocument()
   })
 
   it('renders car labels from result metadata', () => {

frontend/src/test/RivalryCompare.test.tsx

@@ -0,0 +1,114 @@
+import { describe, it, expect } from 'vitest'
+import { render, screen, fireEvent } from '@testing-library/react'
+import { RivalryCompare } from '../components/RivalryCompare'
+import type { ChampHubDriver, ChampionshipHub } from '../types'
+
+function driver(over: Partial<ChampHubDriver>): ChampHubDriver {
+  return {
+    driver_number: 1,
+    name_acronym: 'VER',
+    full_name: 'Max Verstappen',
+    team_name: 'Red Bull',
+    team_colour: '3671c6',
+    points: 100,
+    position: 1,
+    wins: 2,
+    podiums: 3,
+    poles: 1,
+    form: [25, 18, 25],
+    cumulative: [25, 43, 68],
+    round_positions: [1, 2, 1],
+    teammate_wins: 3,
+    teammate_losses: 0,
+    ...over,
+  }
+}
+
+function makeHub(drivers: ChampHubDriver[]): ChampionshipHub {
+  return {
+    season: 2025,
+    round: 3,
+    total_rounds: 10,
+    rounds_left: 7,
+    last_race: 'Japan GP',
+    round_labels: ['R1', 'R2', 'R3'],
+    drivers,
+    teams: [],
+  }
+}
+
+const hub = makeHub([
+  driver({}),
+  driver({
+    driver_number: 4,
+    name_acronym: 'NOR',
+    full_name: 'Lando Norris',
+    team_name: 'McLaren',
+    team_colour: 'ff8000',
+    points: 90,
+    position: 2,
+    cumulative: [18, 43, 61],
+    round_positions: [2, 1, 2],
+  }),
+  driver({
+    driver_number: 16,
+    name_acronym: 'LEC',
+    full_name: 'Charles Leclerc',
+    team_name: 'Ferrari',
+    team_colour: 'e8002d',
+    points: 50,
+    position: 3,
+    cumulative: [15, 28, 40],
+    round_positions: [3, 0, 3],
+  }),
+])
+
+describe('RivalryCompare', () => {
+  it('defaults to the top two drivers and shows the H2H score', () => {
+    render(<RivalryCompare hub={hub} />)
+
+    expect(screen.getByTestId('champ-view-rivalry')).toBeInTheDocument()
+    expect(screen.getByTestId('rivalry-pick-a')).toHaveValue('1')
+    expect(screen.getByTestId('rivalry-pick-b')).toHaveValue('4')
+    // VER wins R1 and R3, NOR wins R2.
+    expect(screen.getByTestId('rivalry-h2h-num')).toHaveTextContent('2–1')
+    expect(screen.getByText('3 rounds counted', { exact: false })).toBeInTheDocument()
+    expect(screen.getByTestId('rivalry-points-race')).toBeInTheDocument()
+    expect(screen.getByTestId('rivalry-gap')).toBeInTheDocument()
+    // Last gap: 68 − 61 = +7 → VER ahead.
+    expect(screen.getByText('VER leads by 7 pts', { exact: false })).toBeInTheDocument()
+  })
+
+  it('recomputes when a different driver is picked and skips missing rounds', () => {
+    render(<RivalryCompare hub={hub} />)
+
+    fireEvent.change(screen.getByTestId('rivalry-pick-b'), { target: { value: '16' } })
+
+    // VER vs LEC: R2 skipped (LEC has no position), VER wins R1 and R3.
+    expect(screen.getByTestId('rivalry-h2h-num')).toHaveTextContent('2–0')
+    expect(screen.getByText('2 rounds counted · 1 skipped', { exact: false })).toBeInTheDocument()
+  })
+
+  it('shows an empty state with fewer than two drivers', () => {
+    render(<RivalryCompare hub={makeHub([driver({})])} />)
+    expect(screen.getByTestId('champ-view-rivalry')).toHaveTextContent('at least two drivers')
+  })
+
+  it('shows an empty message when no rounds are completed', () => {
+    const empty = makeHub([
+      driver({ cumulative: [], round_positions: [], form: [] }),
+      driver({
+        driver_number: 4,
+        name_acronym: 'NOR',
+        cumulative: [],
+        round_positions: [],
+        form: [],
+      }),
+    ])
+    empty.round = 0
+    empty.round_labels = []
+
+    render(<RivalryCompare hub={empty} />)
+    expect(screen.getByTestId('champ-view-rivalry')).toHaveTextContent('No completed rounds yet')
+  })
+})

frontend/src/test/chapters.test.ts

@@ -1,10 +1,13 @@
 import { describe, expect, it } from 'vitest'
 import {
   activeChapterIndex,
+  chapterBandFill,
   chapterKindLabel,
   chapterLapRange,
   chapterStartScrub,
   chapterTourDurations,
+  deCollideYPositions,
+  decimatedPositionLabels,
 } from '../lib/chapters'
 import type { Chapter } from '../types'
 
@@ -57,7 +60,65 @@ describe('chapters lib', () => {
     expect(activeChapterIndex(sampleChapters, scrub, tMin, tRange)).toBe(1)
   })
 
+  it('activates chapters whose timestamps clamp outside the position window', () => {
+    // Position samples only cover 13:05–13:10; chapters sit before/after that window.
+    const tMin = new Date('2025-05-25T13:05:00Z').getTime()
+    const tMax = new Date('2025-05-25T13:10:00Z').getTime()
+    const tRange = tMax - tMin
+    const outOfWindow: Chapter[] = [
+      {
+        kind: 'start',
+        title: 'Start',
+        headline: 'Lights out',
+        start_lap: 1,
+        end_lap: 1,
+        start_time: '2025-05-25T13:00:00Z',
+        end_time: '2025-05-25T13:01:00Z',
+        driver_numbers: [],
+      },
+      {
+        kind: 'finish',
+        title: 'Finish',
+        headline: 'Chequered flag',
+        start_lap: 78,
+        end_lap: 78,
+        start_time: '2025-05-25T13:20:00Z',
+        end_time: '2025-05-25T13:21:00Z',
+        driver_numbers: [],
+      },
+    ]
+
+    expect(chapterStartScrub(outOfWindow[0], tMin, tRange)).toBe(0)
+    expect(chapterStartScrub(outOfWindow[1], tMin, tRange)).toBe(1)
+    expect(activeChapterIndex(outOfWindow, 0, tMin, tRange)).toBe(0)
+    expect(activeChapterIndex(outOfWindow, 1, tMin, tRange)).toBe(1)
+    expect(activeChapterIndex(outOfWindow, 0.5, tMin, tRange)).toBeNull()
+  })
+
   it('splits 90s evenly across chapters', () => {
     expect(chapterTourDurations(sampleChapters)).toEqual([45_000, 45_000])
   })
+
+  it('decimates position axis labels', () => {
+    expect(decimatedPositionLabels(22)).toEqual([1, 5, 10, 15, 20, 22])
+  })
+
+  it('returns chapter band fills by kind', () => {
+    expect(chapterBandFill('safety_car')).toContain('rgba')
+    expect(chapterBandFill('virtual_safety_car')).toContain('rgba')
+  })
+
+  it('de-collides overlapping label y positions', () => {
+    const adjusted = deCollideYPositions(
+      [
+        { key: 'a', y: 10 },
+        { key: 'b', y: 12 },
+        { key: 'c', y: 30 },
+      ],
+      12,
+    )
+    expect(adjusted.get('a')).toBe(10)
+    expect(adjusted.get('b')).toBe(22)
+    expect(adjusted.get('c')).toBe(34)
+  })
 })

frontend/src/test/digest.test.ts

@@ -51,6 +51,7 @@ const driver = (over: Partial<ChampHubDriver>): ChampHubDriver => ({
   cumulative: [25, 43, 68, 100],
   teammate_wins: 4,
   teammate_losses: 1,
+  round_positions: [],
   ...over,
 })
 

frontend/src/test/h2h.test.ts

@@ -18,6 +18,7 @@ function driver(over: Partial<ChampHubDriver>): ChampHubDriver {
     cumulative: [],
     teammate_wins: 9,
     teammate_losses: 1,
+    round_positions: [],
     ...over,
   }
 }

frontend/src/test/preview.test.ts

@@ -54,6 +54,7 @@ const hubDriver = (over: Partial<ChampHubDriver>): ChampHubDriver => ({
   poles: 4,
   form: [25],
   cumulative: [200],
+  round_positions: [1],
   teammate_wins: 9,
   teammate_losses: 1,
   ...over,

frontend/src/test/replayMap.test.ts

@@ -0,0 +1,33 @@
+import { describe, expect, it } from 'vitest'
+import { isReplayMapAvailable } from '../lib/replayMap'
+import type { ReplayFramesResponse, TrackOutline } from '../types'
+
+const outline: TrackOutline = {
+  circuit_key: 1,
+  bounds: { minX: 0, maxX: 100, minY: 0, maxY: 100 },
+  points: [{ x: 0, y: 0 }],
+}
+
+const replay: ReplayFramesResponse = {
+  session_key: 1,
+  interval_ms: 5000,
+  start_time: '2025-05-25T13:00:00Z',
+  frames: [
+    { t: 0, cars: {} },
+    { t: 5000, cars: {} },
+  ],
+}
+
+describe('isReplayMapAvailable', () => {
+  it('returns true when frames and outline are present', () => {
+    expect(isReplayMapAvailable(replay, outline, false)).toBe(true)
+  })
+
+  it('returns false when frames are sparse', () => {
+    expect(isReplayMapAvailable({ ...replay, frames: [{ t: 0, cars: {} }] }, outline, false)).toBe(false)
+  })
+
+  it('returns false on query error', () => {
+    expect(isReplayMapAvailable(replay, outline, true)).toBe(false)
+  })
+})

frontend/src/test/rivalry.test.ts

@@ -0,0 +1,71 @@
+import { describe, it, expect } from 'vitest'
+import { gapSeries, h2hTally, lastRounds } from '../lib/rivalry'
+
+describe('gapSeries', () => {
+  it('computes per-round a − b', () => {
+    expect(gapSeries([25, 43, 68], [18, 36, 54])).toEqual([7, 7, 14])
+  })
+
+  it('handles negative gaps (b ahead)', () => {
+    expect(gapSeries([10, 20], [18, 36])).toEqual([-8, -16])
+  })
+
+  it('truncates to the shorter series', () => {
+    expect(gapSeries([25, 43, 68], [18])).toEqual([7])
+    expect(gapSeries([], [18, 36])).toEqual([])
+  })
+})
+
+describe('h2hTally', () => {
+  it('tallies lower-position wins per round', () => {
+    const t = h2hTally([1, 2, 1], [2, 1, 3], ['R1', 'R2', 'R3'])
+    expect(t.a).toBe(2)
+    expect(t.b).toBe(1)
+    expect(t.skipped).toBe(0)
+    expect(t.rounds.map((r) => r.winner)).toEqual(['a', 'b', 'a'])
+    expect(t.rounds[0]).toEqual({ round: 1, label: 'R1', posA: 1, posB: 2, winner: 'a' })
+  })
+
+  it('skips rounds where either driver has no position', () => {
+    // R2: a missing (0). R3: b missing (0). Only R1 and R4 count.
+    const t = h2hTally([1, 0, 5, 3], [4, 2, 0, 1], ['R1', 'R2', 'R3', 'R4'])
+    expect(t.a).toBe(1)
+    expect(t.b).toBe(1)
+    expect(t.skipped).toBe(2)
+    expect(t.rounds.map((r) => r.round)).toEqual([1, 4])
+  })
+
+  it('handles arrays of different lengths (missing tail = skipped)', () => {
+    const t = h2hTally([1, 2, 3], [2], ['R1', 'R2', 'R3'])
+    expect(t.a).toBe(1)
+    expect(t.b).toBe(0)
+    expect(t.skipped).toBe(2)
+  })
+
+  it('skips equal positions defensively and falls back on labels', () => {
+    const t = h2hTally([2, 1], [2, 3], ['R1'])
+    expect(t.a).toBe(1)
+    expect(t.b).toBe(0)
+    expect(t.skipped).toBe(1)
+    expect(t.rounds[0].label).toBe('R2')
+  })
+
+  it('returns an empty tally for empty inputs', () => {
+    const t = h2hTally([], [], [])
+    expect(t).toEqual({ a: 0, b: 0, rounds: [], skipped: 0 })
+  })
+})
+
+describe('lastRounds', () => {
+  it('returns the last n counted rounds in order', () => {
+    const t = h2hTally([1, 1, 1, 2, 1, 1, 2], [2, 2, 2, 1, 2, 2, 1], [])
+    const last = lastRounds(t, 5)
+    expect(last).toHaveLength(5)
+    expect(last.map((r) => r.round)).toEqual([3, 4, 5, 6, 7])
+  })
+
+  it('returns fewer when the tally has fewer counted rounds', () => {
+    const t = h2hTally([1, 0], [2, 0], [])
+    expect(lastRounds(t, 5)).toHaveLength(1)
+  })
+})

frontend/src/test/simulator.test.ts

@@ -29,6 +29,7 @@ function driver(over: Partial<ChampHubDriver>): ChampHubDriver {
     poles: 0,
     form: [],
     cumulative: [],
+    round_positions: [],
     teammate_wins: 0,
     teammate_losses: 0,
     ...over,

frontend/src/types.ts

@@ -391,6 +391,7 @@ export interface ChampHubDriver {
   poles: number
   form: number[]
   cumulative: number[]
+  round_positions: number[]
   teammate_wins: number
   teammate_losses: number
 }

internal/web/api.go

@@ -614,8 +614,9 @@ type champHubDriver struct {
 	Wins           int       `json:"wins"`
 	Podiums        int       `json:"podiums"`
 	Poles          int       `json:"poles"`
-	Form           []float64 `json:"form"`       // last 5 races' points
-	Cumulative     []float64 `json:"cumulative"` // running total per completed round
+	Form           []float64 `json:"form"`            // last 5 races' points
+	Cumulative     []float64 `json:"cumulative"`      // running total per completed round
+	RoundPositions []int     `json:"round_positions"` // finishing position per completed round (0 = no result)
 	TeammateWins   int       `json:"teammate_wins"`
 	TeammateLosses int       `json:"teammate_losses"`
 }
@@ -995,6 +996,10 @@ func aggregateChampionshipHub(
 		if len(form) > 5 {
 			form = form[len(form)-5:]
 		}
+		roundPositions := make([]int, completed)
+		for round := 1; round <= completed; round++ {
+			roundPositions[round-1] = a.finishByRound[round]
+		}
 		info := driverInfo[c.DriverNumber]
 		drivers = append(drivers, champHubDriver{
 			DriverNumber:   c.DriverNumber,
@@ -1009,6 +1014,7 @@ func aggregateChampionshipHub(
 			Poles:          a.poles,
 			Form:           form,
 			Cumulative:     cumulative[c.DriverNumber],
+			RoundPositions: roundPositions,
 			TeammateWins:   twins[c.DriverNumber],
 			TeammateLosses: tloss[c.DriverNumber],
 		})

internal/web/championship_hub_test.go

@@ -17,20 +17,22 @@ func TestAggregateChampionshipHub(t *testing.T) {
 		1: {DriverNumber: 1, NameAcronym: "VER", FullName: "Max Verstappen", TeamName: "Red Bull", TeamColour: "3671c6"},
 		2: {DriverNumber: 2, NameAcronym: "PER", FullName: "Sergio Perez", TeamName: "Red Bull", TeamColour: "3671c6"},
 		3: {DriverNumber: 3, NameAcronym: "HAM", FullName: "Lewis Hamilton", TeamName: "Mercedes", TeamColour: "27f4d2"},
+		4: {DriverNumber: 4, NameAcronym: "NOR", FullName: "Lando Norris", TeamName: "McLaren", TeamColour: "ff8000"},
 	}
 
 	champ := []models.ChampionshipDriver{
 		{DriverNumber: 1, PointsCurrent: 50, PositionCurrent: 1, SessionKey: 99},
 		{DriverNumber: 3, PointsCurrent: 33, PositionCurrent: 2, SessionKey: 99},
 		{DriverNumber: 2, PointsCurrent: 30, PositionCurrent: 3, SessionKey: 99},
+		{DriverNumber: 4, PointsCurrent: 12, PositionCurrent: 4, SessionKey: 99},
 	}
 	teams := []models.ChampionshipTeam{
 		{TeamName: "Red Bull", PointsCurrent: 80, PositionCurrent: 1},
 		{TeamName: "Mercedes", PointsCurrent: 33, PositionCurrent: 2},
 	}
 
-	// Round 1: VER P1(25), HAM P2(18), PER P3(15). Pole: VER.
-	// Round 2: VER P1(25), PER P2(18), HAM P3(15). Pole: HAM.
+	// Round 1: VER P1(25), HAM P2(18), PER P3(15). Pole: VER. NOR absent.
+	// Round 2: VER P1(25), PER P2(18), HAM P3(15), NOR P4(12). Pole: HAM.
 	races := []meetingRace{
 		{
 			Meeting: models.Meeting{MeetingName: "Bahrain GP"},
@@ -39,7 +41,7 @@ func TestAggregateChampionshipHub(t *testing.T) {
 		},
 		{
 			Meeting: models.Meeting{MeetingName: "Saudi GP"},
-			Results: []models.SessionResult{raceResult(1, 1, 25), raceResult(2, 2, 18), raceResult(3, 3, 15)},
+			Results: []models.SessionResult{raceResult(1, 1, 25), raceResult(2, 2, 18), raceResult(3, 3, 15), raceResult(4, 4, 12)},
 			Grid:    []models.StartingGrid{{DriverNumber: 3, Position: 1}},
 		},
 		// Round 3: not yet run (no results) — should not count as completed.
@@ -67,9 +69,9 @@ func TestAggregateChampionshipHub(t *testing.T) {
 		t.Errorf("round labels = %v, want [R1 R2]", resp.RoundLabels)
 	}
 
-	// Drivers are sorted by official position: VER, HAM, PER.
-	if len(resp.Drivers) != 3 {
-		t.Fatalf("drivers = %d, want 3", len(resp.Drivers))
+	// Drivers are sorted by official position: VER, HAM, PER, NOR.
+	if len(resp.Drivers) != 4 {
+		t.Fatalf("drivers = %d, want 4", len(resp.Drivers))
 	}
 	ver := resp.Drivers[0]
 	if ver.NameAcronym != "VER" || ver.Position != 1 {
@@ -91,6 +93,9 @@ func TestAggregateChampionshipHub(t *testing.T) {
 	if len(ver.Cumulative) != 2 || ver.Cumulative[0] != 25 || ver.Cumulative[1] != 50 {
 		t.Errorf("VER cumulative = %v, want [25 50]", ver.Cumulative)
 	}
+	if len(ver.RoundPositions) != 2 || ver.RoundPositions[0] != 1 || ver.RoundPositions[1] != 1 {
+		t.Errorf("VER round positions = %v, want [1 1]", ver.RoundPositions)
+	}
 	// VER beat teammate PER in both rounds.
 	if ver.TeammateWins != 2 || ver.TeammateLosses != 0 {
 		t.Errorf("VER h2h = %d-%d, want 2-0", ver.TeammateWins, ver.TeammateLosses)
@@ -109,6 +114,9 @@ func TestAggregateChampionshipHub(t *testing.T) {
 	if per.Poles != 0 {
 		t.Errorf("PER poles = %d, want 0", per.Poles)
 	}
+	if len(per.RoundPositions) != 2 || per.RoundPositions[0] != 3 || per.RoundPositions[1] != 2 {
+		t.Errorf("PER round positions = %v, want [3 2]", per.RoundPositions)
+	}
 
 	// HAM has no teammate in the data — no h2h recorded.
 	var ham champHubDriver
@@ -124,6 +132,17 @@ func TestAggregateChampionshipHub(t *testing.T) {
 		t.Errorf("HAM poles = %d, want 1", ham.Poles)
 	}
 
+	// NOR missed round 1 — position 0 marks the absent round.
+	var nor champHubDriver
+	for _, d := range resp.Drivers {
+		if d.NameAcronym == "NOR" {
+			nor = d
+		}
+	}
+	if len(nor.RoundPositions) != 2 || nor.RoundPositions[0] != 0 || nor.RoundPositions[1] != 4 {
+		t.Errorf("NOR round positions = %v, want [0 4]", nor.RoundPositions)
+	}
+
 	// Teams sorted by position; Red Bull wins = VER(2) + PER(0) = 2.
 	if len(resp.Teams) != 2 {
 		t.Fatalf("teams = %d, want 2", len(resp.Teams))

tests/race-hub.spec.ts

@@ -39,7 +39,17 @@ test.describe('Race Hub Weekend Workspace', () => {
     await expect(
       page.getByRole('img', { name: 'Position evolution chart' }),
     ).toBeVisible()
-    await expect(page.getByText('Lap-by-lap positions not available.')).not.toBeVisible()
+    await expect(page.getByTestId('race-story-no-positions')).not.toBeVisible()
+  })
+
+  test('Race Story highlights a chapter card when clicked', async ({ page }) => {
+    await page.goto(`/race-hub?session_key=${FULL_SESSION}`)
+    await page.getByRole('tab', { name: 'Race Story' }).click()
+
+    const firstCard = page.getByTestId('chapter-card-0')
+    await expect(firstCard).toBeVisible()
+    await firstCard.click()
+    await expect(firstCard).toHaveClass(/active/)
   })
 
   test('strategy tab renders stint chart when stints are available', async ({ page }) => {
@@ -58,13 +68,15 @@ test.describe('Race Hub Weekend Workspace', () => {
     await expect(page.locator('[data-testid="strategy-chart"]')).not.toBeVisible()
   })
 
-  test('Race Story shows missing notice when positions are unavailable', async ({
+  test('Race Story shows empty-state card when positions are unavailable', async ({
     page,
   }) => {
     await page.goto(`/race-hub?session_key=${CORE_ONLY_SESSION}`)
     await page.getByRole('tab', { name: 'Race Story' }).click()
 
-    await expect(page.getByText('Lap-by-lap positions not available.')).toBeVisible()
+    const empty = page.getByTestId('race-story-no-positions')
+    await expect(empty).toBeVisible()
+    await expect(empty.getByText('Lap-by-lap positions not available')).toBeVisible()
     await expect(page.locator('[data-testid="position-chart"]')).not.toBeVisible()
   })
 

tests/visual/helpers.ts

@@ -36,6 +36,14 @@ export async function gotoRaceHubReady(page: Page, sessionKey = FULL_SESSION): P
   await waitForScreenshotReady(page)
 }
 
+export async function gotoRaceStoryReady(page: Page, sessionKey = FULL_SESSION): Promise<void> {
+  await page.goto(`/race-hub?session_key=${sessionKey}`)
+  await expect(page.getByTestId('race-hub')).toBeVisible()
+  await page.getByRole('tab', { name: 'Race Story' }).click()
+  await expect(page.getByTestId('position-chart')).toBeVisible()
+  await waitForScreenshotReady(page)
+}
+
 export async function gotoDataLibraryReady(page: Page): Promise<void> {
   await page.goto('/admin')
   await expect(page.getByTestId('data-library')).toBeVisible()

tests/visual/race-story.spec.ts

@@ -0,0 +1,9 @@
+import { test } from '@playwright/test'
+import { gotoRaceStoryReady, screenshotPage } from './helpers'
+
+test.describe('Race Story visual regression', () => {
+  test('race-story', async ({ page }) => {
+    await gotoRaceStoryReady(page)
+    await screenshotPage(page, 'race-story')
+  })
+})