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

@@ -17,6 +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
 }
@@ -28,12 +30,15 @@ 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 : activeIndex
+  const highlightedIndex = tourActive
+    ? tourChapterIndex
+    : (selectedChapterIndex ?? activeIndex)
 
   useEffect(() => {
     if (highlightedIndex === null || !scrollRef.current) return
@@ -81,9 +86,7 @@ export function ChapterStrip({
         >
           {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 isActive = highlightedIndex === index
             const headline = chapter.headline || chapter.title
 
             return (

frontend/src/components/RaceStoryCanvas.tsx

@@ -65,6 +65,7 @@ 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 })
 
@@ -140,9 +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()
@@ -150,6 +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
@@ -359,6 +366,7 @@ export function RaceStoryCanvas({ data }: Props) {
     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
@@ -540,7 +548,10 @@ export function RaceStoryCanvas({ data }: Props) {
             fill="transparent"
             onPointerMove={handlePointerMove}
             onPointerLeave={() => {
-              if (!isPlaying) setScrubTime(null)
+              if (!isPlaying) {
+                clearChapterSelection()
+                setScrubTime(null)
+              }
             }}
             style={{ cursor: 'crosshair', touchAction: 'none' }}
           />
@@ -552,6 +563,7 @@ export function RaceStoryCanvas({ data }: Props) {
             onClick={() => {
               setScrubTime((current) => current ?? 0)
               stopChapterTour()
+              clearChapterSelection()
               setIsPlaying((current) => !current)
             }}
             aria-pressed={isPlaying}
@@ -599,6 +611,7 @@ export function RaceStoryCanvas({ data }: Props) {
           tRange={chartTiming.tRange}
           tourActive={chapterTourActive}
           tourChapterIndex={tourChapterIndex}
+          selectedChapterIndex={selectedChapterIndex}
           onChapterClick={jumpToChapter}
           onTourToggle={toggleChapterTour}
         />