feat: add replay track map scrubber

Spike: replay location fan-out is bounded with a semaphore at 4 concurrent GetLocation calls, covered by TestAssembleReplayFramesBoundsLocationFanOut. Adds /api/v1/replay/frames with 5s interval floor, 3000-frame cap, nearest-sample snapping, and empty-driver omission. Wires RaceStoryCanvas to lazy-load replay frames plus cached track outlines when the map panel opens, sharing the existing scrubber/playback state across chart and map. Tests: HOME=/private/tmp/box-box-home GOCACHE=/private/tmp/box-box-go-cache GOMODCACHE=/Users/aman/go/pkg/mod go test ./internal/web; go build ./... (same env, passed with read-only module stat-cache warning); npm run test; npx tsc --noEmit. Full go test ./... is blocked in this sandbox by existing network/listener-dependent internal/api and internal/news tests.
Merge pull request #60 from AmanTahiliani/feat/issue-19-auto-chapter-detection-rc-position-swing
2026-08-08 12:07:23 -04:00 · 2026-07-11 18:17:15 -04:00 · 2026-07-11 18:06:33 -04:00 · 2026-07-11 18:04:44 -04:00 · 2026-07-11 17:59:51 -04:00 · 2026-07-11 17:59:00 -04:00
26 changed files with 3571 additions and 16 deletions
--- a/frontend/src/api.ts
+++ b/frontend/src/api.ts
@@ -2,12 +2,15 @@ import type {
  ArticleContent,
  CarDataSample,
  ChampionshipHub,
+  EnrichedGrid,
+  EnrichedResult,
  LapsComparisonResponse,
  LiveStateResponse,
  LiveSessionMeta,
  Meeting,
  NewsItem,
  RaceHub,
+  ReplayFramesResponse,
  Session,
  TrackOutline,
  Weekend,
@@ -40,7 +43,11 @@ export async function fetchLocalMeetings(year: number): Promise<Meeting[]> {
 }

 export async function fetchSeasonMeetings(year: number): Promise<Meeting[]> {
-  const res = await fetch(`/api/v1/meetings?year=${year}&source=openf1`)
+  return fetchMeetings(year, 'openf1')
+}
+
+export async function fetchMeetings(year: number, source = 'auto'): Promise<Meeting[]> {
+  const res = await fetch(`/api/v1/meetings?year=${year}&source=${source}`)
  if (!res.ok) {
    throw new Error(`API ${res.status}: ${res.statusText}`)
  }
@@ -48,6 +55,47 @@ export async function fetchSeasonMeetings(year: number): Promise<Meeting[]> {
  return Array.isArray(meetings) ? meetings : []
 }

+export async function fetchResults(sessionKey: number, source = 'auto'): Promise<EnrichedResult[]> {
+  const res = await fetch(`/api/v1/results?session_key=${sessionKey}&source=${source}`)
+  if (!res.ok) {
+    throw new Error(`API ${res.status}: ${res.statusText}`)
+  }
+  const results = await res.json()
+  return Array.isArray(results) ? results : []
+}
+
+export async function fetchStartingGrid(sessionKey: number, source = 'auto'): Promise<EnrichedGrid[]> {
+  const res = await fetch(`/api/v1/grid?session_key=${sessionKey}&source=${source}`)
+  if (!res.ok) {
+    throw new Error(`API ${res.status}: ${res.statusText}`)
+  }
+  const grid = await res.json()
+  return Array.isArray(grid) ? grid : []
+}
+
+export async function fetchTrackOutline(circuitKey: number, year: number): Promise<TrackOutline | null> {
+  const res = await fetch(`/api/v1/track-outline?circuit_key=${circuitKey}&year=${year}`)
+  if (!res.ok) return null
+  const data = await res.json()
+  if (data?.error || !Array.isArray(data?.points) || data.points.length < 2) return null
+  return data as TrackOutline
+}
+
+export async function fetchReplayFrames(
+  sessionKey: number,
+  intervalMs = 5000,
+): Promise<ReplayFramesResponse> {
+  const params = new URLSearchParams({
+    session_key: String(sessionKey),
+    interval_ms: String(intervalMs),
+  })
+  const res = await fetch(`/api/v1/replay/frames?${params}`)
+  if (!res.ok) {
+    throw new Error(`API ${res.status}: ${res.statusText}`)
+  }
+  return res.json()
+}
+
 export async function fetchSessions(meetingKey: number, source = 'openf1'): Promise<Session[]> {
  const res = await fetch(`/api/v1/sessions?meeting_key=${meetingKey}&source=${source}`)
  if (!res.ok) {
--- a/frontend/src/components/Nav.tsx
+++ b/frontend/src/components/Nav.tsx
@@ -16,6 +16,9 @@ export function Nav() {
        <Link to="/race-hub" search={{}} activeProps={{ className: 'active' }}>
          Race Hub
        </Link>
+        <Link to="/preview" activeProps={{ className: 'active' }}>
+          Preview
+        </Link>
        <Link to="/championship" activeProps={{ className: 'active' }}>
          Championship
        </Link>
--- a/frontend/src/components/RaceStoryCanvas.tsx
+++ b/frontend/src/components/RaceStoryCanvas.tsx
@@ -1,5 +1,8 @@
-import { useState, useMemo, useRef, useCallback } from 'react'
-import type { EnrichedResult, EnrichedGrid, PositionSample, Lap, Session } from '../types'
+import { useEffect, useMemo, useRef, useState } from 'react'
+import { useQuery } from '@tanstack/react-query'
+import type { Driver, EnrichedResult, EnrichedGrid, PositionSample, Lap, Meeting, Session } from '../types'
+import { fetchReplayFrames, fetchTrackOutline } from '../api'
+import { ReplayTrackMap } from './ReplayTrackMap'
 import { gridDelta, gridDeltaClass, formatDuration, formatGap } from '../utils'

 interface Props {
@@ -12,28 +15,97 @@ interface Props {
    race_control?: any[]
    pit_stops?: any[]
    session?: Session
+    meeting?: Meeting
+    drivers?: Driver[]
  }
 }

 export function RaceStoryCanvas({ data }: Props) {
-  const { results, starting_grid: grid, positions, datasets, race_control = [], pit_stops = [], laps = [] } = data
+  const {
+    results,
+    starting_grid: grid,
+    positions,
+    datasets,
+    race_control = [],
+    pit_stops = [],
+    laps = [],
+    session,
+    meeting,
+    drivers = [],
+  } = data
  const hasPositions = datasets['positions']?.status === 'available'

  const [scrubTime, setScrubTime] = useState<number | null>(null)
  const [hoverDriver, setHoverDriver] = useState<number | null>(null)
+  const [mapOpen, setMapOpen] = useState(false)
+  const [isPlaying, setIsPlaying] = useState(false)
+  const [playbackSpeed, setPlaybackSpeed] = useState(10)
  const svgRef = useRef<SVGSVGElement>(null)

  // 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(() => {
+    if (!hasChartData) return null
+    const tMin = new Date(allTimes[0]).getTime()
+    const tMax = new Date(allTimes[allTimes.length - 1]).getTime()
+    return { tMin, tMax, tRange: Math.max(tMax - tMin, 1) }
+  }, [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 replayQuery = useQuery({
+    queryKey: ['replay-frames', session?.session_key, 5000],
+    queryFn: () => fetchReplayFrames(session!.session_key, 5000),
+    enabled: mapOpen && Boolean(session?.session_key),
+  })
+  const outlineQuery = useQuery({
+    queryKey: ['track-outline', circuitKey, outlineYear],
+    queryFn: () => fetchTrackOutline(circuitKey, outlineYear),
+    enabled: mapOpen && circuitKey > 0 && outlineYear > 0,
+  })
+
+  useEffect(() => {
+    if (!isPlaying || !chartTiming) return
+
+    let frame = 0
+    let last = performance.now()
+    const tick = (now: number) => {
+      const delta = now - last
+      last = now
+      setScrubTime((current) => {
+        const next = Math.min(1, (current ?? 0) + (delta * playbackSpeed) / chartTiming.tRange)
+        if (next >= 1) {
+          setIsPlaying(false)
+        }
+        return next
+      })
+      frame = requestAnimationFrame(tick)
+    }
+
+    frame = requestAnimationFrame(tick)
+    return () => cancelAnimationFrame(frame)
+  }, [chartTiming, isPlaying, playbackSpeed])
+
+  const replayTMs = useMemo(() => {
+    const replay = replayQuery.data
+    const frames = replay?.frames ?? []
+    if (frames.length === 0) return 0
+    const lastFrameT = frames[frames.length - 1].t
+    const progress = scrubTime ?? 0
+    if (!chartTiming || !replay?.start_time) {
+      return Math.max(0, Math.min(lastFrameT, Math.round(progress * lastFrameT)))
+    }
+    const replayStart = new Date(replay.start_time).getTime()
+    const chartTime = chartTiming.tMin + progress * chartTiming.tRange
+    return Math.max(0, Math.min(lastFrameT, Math.round(chartTime - replayStart)))
+  }, [chartTiming, replayQuery.data, scrubTime])

  let chartContent = null
  let displayResults = results

-  if (hasChartData) {
-    const tMin = new Date(allTimes[0]).getTime()
-    const tMax = new Date(allTimes[allTimes.length - 1]).getTime()
-    const tRange = Math.max(tMax - tMin, 1)
+  if (hasChartData && chartTiming) {
+    const { tMin, tRange } = chartTiming

    const byDriver = new Map<number, Array<{ t: number; pos: number }>>()
    for (const p of positions) {
@@ -137,6 +209,7 @@ export function RaceStoryCanvas({ data }: Props) {
    }

    const handlePointerMove = (e: React.PointerEvent<SVGRectElement>) => {
+      setIsPlaying(false)
      if (!svgRef.current) return
      const rect = svgRef.current.getBoundingClientRect()
      const x = e.clientX - rect.left
@@ -288,16 +361,51 @@ export function RaceStoryCanvas({ data }: Props) {
            height={plotH}
            fill="transparent"
            onPointerMove={handlePointerMove}
-            onPointerLeave={() => setScrubTime(null)}
+            onPointerLeave={() => {
+              if (!isPlaying) setScrubTime(null)
+            }}
            style={{ cursor: 'crosshair', touchAction: 'none' }}
          />
        </svg>
+        <div className="rs-replay-tools" aria-label="Race replay controls">
+          <button
+            type="button"
+            className={`rs-tool-btn ${isPlaying ? 'active' : ''}`}
+            onClick={() => {
+              setScrubTime((current) => current ?? 0)
+              setIsPlaying((current) => !current)
+            }}
+          >
+            {isPlaying ? 'Pause' : 'Play'}
+          </button>
+          <div className="rs-speed-group" aria-label="Playback speed">
+            {[1, 10, 30].map((speed) => (
+              <button
+                key={speed}
+                type="button"
+                className={`rs-speed-btn ${playbackSpeed === speed ? 'active' : ''}`}
+                onClick={() => setPlaybackSpeed(speed)}
+              >
+                {speed}x
+              </button>
+            ))}
+          </div>
+          <button
+            type="button"
+            className={`rs-tool-btn ${mapOpen ? 'active' : ''}`}
+            onClick={() => setMapOpen((current) => !current)}
+          >
+            Map
+          </button>
+        </div>
      </div>
    )
  }

  return (
    <div className="race-story-canvas">
+      <div className="rs-replay-shell">
+        <div className="rs-replay-main">
          {hasChartData ? (
            chartContent
          ) : (
@@ -306,6 +414,25 @@ export function RaceStoryCanvas({ data }: Props) {
              have ingested position samples in <code>/api/v1/race-hub</code>.
            </div>
          )}
+        </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>
+            )}
+          </div>
+        )}
+      </div>

      {displayResults.length > 0 && (
        <div className="rs-field-list">
--- a/frontend/src/components/ReplayTrackMap.tsx
+++ b/frontend/src/components/ReplayTrackMap.tsx
@@ -0,0 +1,133 @@
+import { useMemo, useState } from 'react'
+import type { Driver, EnrichedResult, ReplayFramesResponse, TrackOutline } from '../types'
+import { buildOutlinePath } from '../lib/trackmap'
+import { interpolateReplayCars, replayCarToSvg } from '../lib/replay'
+import '../styles/replay-map.css'
+
+interface Props {
+  outline?: TrackOutline | null
+  replay?: ReplayFramesResponse | null
+  tMs: number
+  drivers: Driver[]
+  results: EnrichedResult[]
+  loading?: boolean
+  error?: boolean
+}
+
+export function ReplayTrackMap({
+  outline,
+  replay,
+  tMs,
+  drivers,
+  results,
+  loading = false,
+  error = false,
+}: Props) {
+  const [pinned, setPinned] = useState<string | null>(null)
+  const outlinePath = useMemo(() => buildOutlinePath(outline?.points ?? []), [outline])
+  const driverInfo = useMemo(() => {
+    const info = new Map<string, { label: string; color: string }>()
+    for (const driver of drivers) {
+      info.set(String(driver.driver_number), {
+        label: driver.name_acronym || String(driver.driver_number),
+        color: normalizeColor(driver.team_colour),
+      })
+    }
+    for (const result of results) {
+      const key = String(result.driver_number)
+      if (!info.has(key)) {
+        info.set(key, {
+          label: result.name_acronym || key,
+          color: normalizeColor(result.team_colour),
+        })
+      }
+    }
+    return info
+  }, [drivers, results])
+
+  const cars = useMemo(() => {
+    if (!outline?.bounds || !replay?.frames?.length) return []
+    const positions = interpolateReplayCars(replay.frames, tMs)
+    return Object.entries(positions)
+      .map(([number, car]) => ({
+        number,
+        svg: replayCarToSvg(car, outline.bounds),
+        info: driverInfo.get(number),
+      }))
+      .sort((a, b) => Number(a.number) - Number(b.number))
+  }, [driverInfo, outline?.bounds, replay?.frames, tMs])
+
+  if (loading) {
+    return (
+      <section className="replay-map-panel" data-testid="replay-track-map">
+        <div className="replay-map-empty">loading replay GPS...</div>
+      </section>
+    )
+  }
+
+  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>
+      </section>
+    )
+  }
+
+  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>
+      </section>
+    )
+  }
+
+  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>
+      </section>
+    )
+  }
+
+  return (
+    <section className="replay-map-panel" data-testid="replay-track-map">
+      <div className="replay-map-stage">
+        <svg className="replay-map-svg" viewBox="0 0 100 100" role="img" aria-label="Replay track map">
+          <path className="replay-map-outline-shadow" d={outlinePath} />
+          <path className="replay-map-outline" d={outlinePath} />
+          {cars.map((car) => {
+            const label = car.info?.label ?? car.number
+            const selected = pinned === car.number
+            return (
+              <g
+                key={car.number}
+                role="button"
+                tabIndex={0}
+                aria-label={`${label} replay position`}
+                className={`replay-car ${selected ? 'replay-car-pinned' : ''}`}
+                transform={`translate(${car.svg.x.toFixed(2)} ${car.svg.y.toFixed(2)})`}
+                onClick={() => setPinned(selected ? null : car.number)}
+                onKeyDown={(event) => {
+                  if (event.key === 'Enter' || event.key === ' ') {
+                    event.preventDefault()
+                    setPinned(selected ? null : car.number)
+                  }
+                }}
+              >
+                <title>{label}</title>
+                <circle r="2.7" fill={car.info?.color ?? '#777777'} />
+                <text y="0.85">{label}</text>
+              </g>
+            )
+          })}
+        </svg>
+      </div>
+    </section>
+  )
+}
+
+function normalizeColor(color: string | undefined): string {
+  const raw = color?.trim()
+  if (!raw) return '#777777'
+  return raw.startsWith('#') ? raw : `#${raw}`
+}
--- a/frontend/src/lib/preview.ts
+++ b/frontend/src/lib/preview.ts
@@ -0,0 +1,123 @@
+import type { ChampionshipHub, EnrichedGrid, EnrichedResult, Meeting, Session } from '../types'
+import {
+  currentAndNextSession,
+  nextUpcomingMeeting,
+  sessionStartTime,
+  sortSessionsByStart,
+} from './schedule'
+
+export const RACE_WIN_POINTS = 25
+export const SPRINT_WIN_POINTS = 8
+export const SPRINT_WEEKEND_MAX_POINTS = RACE_WIN_POINTS + SPRINT_WIN_POINTS
+
+export function pickPreviewMeeting(meetings: Meeting[], now: Date): Meeting | null {
+  const active = meetings.filter((m) => !m.is_cancelled)
+  return nextUpcomingMeeting(active, now)
+}
+
+export function findPriorYearMeetingByCircuit(
+  priorYearMeetings: Meeting[],
+  circuitKey: number | undefined,
+): Meeting | null {
+  if (!circuitKey) return null
+  return priorYearMeetings.find((m) => m.circuit_key === circuitKey && !m.is_cancelled) ?? null
+}
+
+export function findRaceSession(sessions: Session[]): Session | null {
+  const sorted = sortSessionsByStart(sessions)
+  return (
+    sorted.find((s) => {
+      const type = s.session_type?.toLowerCase() ?? ''
+      return type.includes('race') && !type.includes('sprint')
+    }) ?? null
+  )
+}
+
+export function isSprintWeekend(sessions: Session[]): boolean {
+  return sessions.some((s) => {
+    const label = `${s.session_type} ${s.session_name}`.toLowerCase()
+    return /\bsprint\b/.test(label) && !label.includes('sprint qualifying') && !label.includes('sprint shootout')
+  })
+}
+
+export interface PodiumPlace {
+  position: number
+  name_acronym: string
+  full_name: string
+  team_name: string
+  team_colour: string
+}
+
+export interface PolePosition {
+  name_acronym: string
+  full_name: string
+  team_name: string
+  team_colour: string
+}
+
+export function extractPodium(results: EnrichedResult[]): PodiumPlace[] {
+  return results
+    .filter((r) => r.position >= 1 && r.position <= 3 && !r.dns && !r.dsq)
+    .sort((a, b) => a.position - b.position)
+    .map((r) => ({
+      position: r.position,
+      name_acronym: r.name_acronym,
+      full_name: r.full_name,
+      team_name: r.team_name,
+      team_colour: r.team_colour,
+    }))
+}
+
+export function extractPole(grid: EnrichedGrid[]): PolePosition | null {
+  const pole = grid.find((g) => g.position === 1)
+  if (!pole) return null
+  return {
+    name_acronym: pole.name_acronym,
+    full_name: pole.full_name,
+    team_name: pole.team_name,
+    team_colour: pole.team_colour,
+  }
+}
+
+export interface TitleFightDriver {
+  name_acronym: string
+  full_name: string
+  team_colour: string
+  points: number
+  position: number
+  gapToLeader: number
+  gapAfterRaceWin: number
+  gapAfterSprintWeekendMax: number
+}
+
+export function buildTitleFightContext(hub: ChampionshipHub): TitleFightDriver[] {
+  if (hub.drivers.length === 0) return []
+  const leader = hub.drivers[0]
+  return hub.drivers.slice(0, 3).map((d) => ({
+    name_acronym: d.name_acronym,
+    full_name: d.full_name,
+    team_colour: d.team_colour,
+    points: d.points,
+    position: d.position,
+    gapToLeader: leader.points - d.points,
+    gapAfterRaceWin: leader.points - (d.points + RACE_WIN_POINTS),
+    gapAfterSprintWeekendMax: leader.points - (d.points + SPRINT_WEEKEND_MAX_POINTS),
+  }))
+}
+
+export function countdownTargetSession(sessions: Session[], now: Date): Session | null {
+  const sorted = sortSessionsByStart(sessions)
+  const { next } = currentAndNextSession(sorted, now)
+  if (next) return next
+  for (const session of sorted) {
+    const start = sessionStartTime(session)
+    if (start && start > now) return session
+  }
+  return null
+}
+
+export function formatPointsGap(gap: number): string {
+  if (gap === 0) return 'LEADER'
+  const sign = gap > 0 ? '+' : ''
+  return `${sign}${Number.isInteger(gap) ? gap : gap.toFixed(1)}`
+}
--- a/frontend/src/lib/replay.ts
+++ b/frontend/src/lib/replay.ts
@@ -0,0 +1,75 @@
+import type { ReplayCarPosition, ReplayFrame, TrackBounds } from '../types'
+import { canvasToSvg, normalizeRawPoint } from './trackmap'
+
+export interface ReplayFramePair {
+  previous: ReplayFrame | null
+  next: ReplayFrame | null
+}
+
+export function lookupReplayFramePair(
+  frames: ReadonlyArray<ReplayFrame>,
+  tMs: number,
+): ReplayFramePair {
+  if (frames.length === 0) return { previous: null, next: null }
+  if (tMs <= frames[0].t) return { previous: frames[0], next: frames[0] }
+  const last = frames[frames.length - 1]
+  if (tMs >= last.t) return { previous: last, next: last }
+
+  let lo = 0
+  let hi = frames.length - 1
+  while (lo <= hi) {
+    const mid = Math.floor((lo + hi) / 2)
+    const frame = frames[mid]
+    if (frame.t === tMs) return { previous: frame, next: frame }
+    if (frame.t < tMs) {
+      lo = mid + 1
+    } else {
+      hi = mid - 1
+    }
+  }
+
+  return { previous: frames[Math.max(0, hi)], next: frames[Math.min(frames.length - 1, lo)] }
+}
+
+export function interpolateReplayCars(
+  frames: ReadonlyArray<ReplayFrame>,
+  tMs: number,
+): Record<string, ReplayCarPosition> {
+  const { previous, next } = lookupReplayFramePair(frames, tMs)
+  if (!previous && !next) return {}
+  if (!previous) return next?.cars ?? {}
+  if (!next || previous.t === next.t) return previous.cars
+
+  const span = next.t - previous.t
+  const fraction = span <= 0 ? 0 : clamp01((tMs - previous.t) / span)
+  const cars: Record<string, ReplayCarPosition> = {}
+  const numbers = new Set([...Object.keys(previous.cars), ...Object.keys(next.cars)])
+
+  for (const number of numbers) {
+    const before = previous.cars[number]
+    const after = next.cars[number]
+    if (before && after) {
+      cars[number] = {
+        x: before.x + (after.x - before.x) * fraction,
+        y: before.y + (after.y - before.y) * fraction,
+      }
+    } else if (before) {
+      cars[number] = before
+    } else if (after) {
+      cars[number] = after
+    }
+  }
+  return cars
+}
+
+export function replayCarToSvg(
+  car: ReplayCarPosition,
+  bounds: TrackBounds,
+): ReplayCarPosition {
+  return canvasToSvg(normalizeRawPoint({ x: car.x, y: car.y }, bounds))
+}
+
+function clamp01(value: number): number {
+  if (!Number.isFinite(value)) return 0
+  return Math.min(1, Math.max(0, value))
+}
--- a/frontend/src/pages/RacePreviewPage.tsx
+++ b/frontend/src/pages/RacePreviewPage.tsx
@@ -0,0 +1,442 @@
+import { useEffect, useMemo, useState, type ReactNode } from 'react'
+import { useQuery } from '@tanstack/react-query'
+import {
+  fetchChampionshipHub,
+  fetchMeetings,
+  fetchResults,
+  fetchSeasons,
+  fetchSessions,
+  fetchStartingGrid,
+  fetchTrackOutline,
+} from '../api'
+import { countryAccent, countryFlag, formatGpDateRange } from '../lib/gpIdentity'
+import {
+  buildTitleFightContext,
+  countdownTargetSession,
+  extractPodium,
+  extractPole,
+  findPriorYearMeetingByCircuit,
+  findRaceSession,
+  formatPointsGap,
+  isSprintWeekend,
+  pickPreviewMeeting,
+  RACE_WIN_POINTS,
+  SPRINT_WEEKEND_MAX_POINTS,
+} from '../lib/preview'
+import { formatCountdown, formatSessionScheduleTime, sessionStartTime, sortSessionsByStart } from '../lib/schedule'
+import { buildOutlinePath } from '../lib/trackmap'
+import { teamColor } from '../utils'
+import type { Meeting, Session, TrackOutline } from '../types'
+import '../styles/preview.css'
+
+function SectionState({
+  loading,
+  error,
+  empty,
+  emptyMessage,
+  children,
+}: {
+  loading?: boolean
+  error?: Error | null
+  empty?: boolean
+  emptyMessage?: string
+  children: ReactNode
+}) {
+  if (loading) {
+    return <div className="preview-section-state">Loading…</div>
+  }
+  if (error) {
+    return (
+      <div className="preview-section-state error">
+        {error instanceof Error ? error.message : 'Failed to load'}
+      </div>
+    )
+  }
+  if (empty) {
+    return <div className="preview-section-state">{emptyMessage ?? 'No data available'}</div>
+  }
+  return <>{children}</>
+}
+
+function TrackOutlineCard({
+  outline,
+  loading,
+  error,
+  accent,
+}: {
+  outline: TrackOutline | null | undefined
+  loading: boolean
+  error: Error | null
+  accent: string
+}) {
+  const outlinePath = useMemo(() => buildOutlinePath(outline?.points ?? []), [outline])
+
+  return (
+    <section className="preview-card" data-testid="preview-track-card">
+      <h2 className="preview-card-title">Circuit</h2>
+      <SectionState
+        loading={loading}
+        error={error}
+        empty={!outline || !outlinePath}
+        emptyMessage="Track outline unavailable for this circuit"
+      >
+        <div className="preview-track-stage" style={{ ['--preview-accent' as string]: accent }}>
+          <svg className="preview-track-svg" viewBox="0 0 100 100" role="img" aria-label="Circuit outline">
+            <path className="preview-track-shadow" d={outlinePath} />
+            <path className="preview-track-outline" d={outlinePath} />
+          </svg>
+        </div>
+      </SectionState>
+    </section>
+  )
+}
+
+function LastYearCard({
+  year,
+  loading,
+  error,
+  podium,
+  pole,
+  isFirstTime,
+}: {
+  year: number | null
+  loading: boolean
+  error: Error | null
+  podium: ReturnType<typeof extractPodium>
+  pole: ReturnType<typeof extractPole>
+  isFirstTime: boolean
+}) {
+  return (
+    <section className="preview-card" data-testid="preview-last-year-card">
+      <h2 className="preview-card-title">Last year here</h2>
+      {year != null && !isFirstTime && <p className="preview-card-sub">{year} race weekend</p>}
+      <SectionState
+        loading={loading}
+        error={error}
+        empty={isFirstTime || podium.length === 0}
+        emptyMessage={
+          isFirstTime
+            ? 'First time on the calendar — no prior race at this circuit'
+            : 'No race results available for the previous visit'
+        }
+      >
+        <div className="preview-podium">
+          {podium.map((place) => (
+            <div key={place.position} className="preview-podium-row">
+              <span className="preview-podium-pos">P{place.position}</span>
+              <span className="preview-podium-code" style={{ color: teamColor(place.team_colour) }}>
+                {place.name_acronym}
+              </span>
+              <span className="preview-podium-team">{place.team_name}</span>
+            </div>
+          ))}
+        </div>
+        {pole && (
+          <p className="preview-pole">
+            Pole: <strong style={{ color: teamColor(pole.team_colour) }}>{pole.name_acronym}</strong>{' '}
+            ({pole.team_name})
+          </p>
+        )}
+      </SectionState>
+    </section>
+  )
+}
+
+function TitleFightCard({
+  loading,
+  error,
+  drivers,
+  sprintWeekend,
+  season,
+}: {
+  loading: boolean
+  error: Error | null
+  drivers: ReturnType<typeof buildTitleFightContext>
+  sprintWeekend: boolean
+  season: number | null
+}) {
+  return (
+    <section className="preview-card preview-card--wide" data-testid="preview-title-fight-card">
+      <h2 className="preview-card-title">Title fight context</h2>
+      {season != null && <p className="preview-card-sub">{season} drivers&apos; championship · top 3</p>}
+      <SectionState
+        loading={loading}
+        error={error}
+        empty={drivers.length === 0}
+        emptyMessage="Championship standings not available"
+      >
+        <table className="preview-title-table">
+          <thead>
+            <tr>
+              <th>Driver</th>
+              <th>Pts</th>
+              <th>Gap</th>
+              <th>If win (+{RACE_WIN_POINTS})</th>
+            </tr>
+          </thead>
+          <tbody>
+            {drivers.map((d) => (
+              <tr key={d.name_acronym}>
+                <td>
+                  <span style={{ color: teamColor(d.team_colour), fontWeight: 600 }}>{d.name_acronym}</span>
+                </td>
+                <td className="mono">{d.points}</td>
+                <td className="mono">{formatPointsGap(d.gapToLeader)}</td>
+                <td className="mono">
+                  {d.position === 1 ? 'LEADER' : formatPointsGap(d.gapAfterRaceWin)}
+                </td>
+              </tr>
+            ))}
+          </tbody>
+        </table>
+        {sprintWeekend && (
+          <p className="preview-sprint-note" data-testid="preview-sprint-note">
+            Sprint weekend: up to {SPRINT_WEEKEND_MAX_POINTS} pts available (race win {RACE_WIN_POINTS} + sprint win
+            8). Max gain would reduce gaps by {SPRINT_WEEKEND_MAX_POINTS} vs a standard race win.
+          </p>
+        )}
+      </SectionState>
+    </section>
+  )
+}
+
+function PreviewHeader({
+  meeting,
+  sessions,
+  countdownSession,
+  now,
+  accent,
+}: {
+  meeting: Meeting
+  sessions: Session[]
+  countdownSession: Session | null
+  now: Date
+  accent: string
+}) {
+  const countdownTarget = countdownSession ? sessionStartTime(countdownSession) : null
+
+  return (
+    <header
+      className="preview-header"
+      data-testid="preview-header"
+      style={{ ['--preview-accent' as string]: accent }}
+    >
+      <div className="preview-header-accent" />
+      <div className="preview-header-body">
+        <div className="preview-header-top">
+          <div>
+            <h1 className="preview-gp-name">
+              {countryFlag(meeting) && <span className="preview-gp-flag">{countryFlag(meeting)}</span>}
+              {meeting.meeting_name}
+            </h1>
+            <p className="preview-circuit">
+              {meeting.circuit_short_name}
+              {meeting.location ? ` · ${meeting.location}` : ''}
+              {formatGpDateRange(meeting) ? ` · ${formatGpDateRange(meeting)}` : ''}
+            </p>
+          </div>
+          {countdownTarget && (
+            <div className="preview-countdown" data-testid="preview-countdown">
+              <span className="preview-countdown-label">
+                {countdownSession?.session_name ?? 'Next session'}
+              </span>
+              <span className="preview-countdown-value">{formatCountdown(countdownTarget, now)}</span>
+            </div>
+          )}
+        </div>
+        {sessions.length > 0 && (
+          <div className="preview-schedule" data-testid="preview-schedule">
+            {sessions.map((session) => (
+              <div key={session.session_key} className="preview-schedule-item">
+                <span className="preview-schedule-name">{session.session_name}</span>
+                <span className="preview-schedule-time">{formatSessionScheduleTime(session.date_start)}</span>
+              </div>
+            ))}
+          </div>
+        )}
+      </div>
+    </header>
+  )
+}
+
+export function RacePreviewPage() {
+  const [now, setNow] = useState(() => Date.now())
+
+  useEffect(() => {
+    const timer = window.setInterval(() => setNow(Date.now()), 1000)
+    return () => window.clearInterval(timer)
+  }, [])
+
+  const nowDate = useMemo(() => new Date(now), [now])
+
+  const seasonsQuery = useQuery({
+    queryKey: ['seasons'],
+    queryFn: fetchSeasons,
+  })
+
+  const latestSeason = seasonsQuery.data?.[0] ?? null
+
+  const meetingsQuery = useQuery({
+    queryKey: ['meetings', latestSeason, 'auto'],
+    queryFn: () => fetchMeetings(latestSeason!, 'auto'),
+    enabled: latestSeason != null,
+  })
+
+  const previewMeeting = useMemo(
+    () => pickPreviewMeeting(meetingsQuery.data ?? [], nowDate),
+    [meetingsQuery.data, nowDate],
+  )
+
+  const sessionsQuery = useQuery({
+    queryKey: ['sessions', previewMeeting?.meeting_key, 'auto'],
+    queryFn: () => fetchSessions(previewMeeting!.meeting_key, 'auto'),
+    enabled: previewMeeting != null,
+  })
+
+  const sessions = useMemo(
+    () => sortSessionsByStart(sessionsQuery.data ?? []),
+    [sessionsQuery.data],
+  )
+
+  const countdownSession = useMemo(() => countdownTargetSession(sessions, nowDate), [sessions, nowDate])
+  const sprintWeekend = useMemo(() => isSprintWeekend(sessions), [sessions])
+
+  const priorYear = previewMeeting ? previewMeeting.year - 1 : null
+
+  const priorMeetingsQuery = useQuery({
+    queryKey: ['meetings', priorYear, 'auto'],
+    queryFn: () => fetchMeetings(priorYear!, 'auto'),
+    enabled: priorYear != null && previewMeeting != null,
+  })
+
+  const priorMeeting = useMemo(
+    () => findPriorYearMeetingByCircuit(priorMeetingsQuery.data ?? [], previewMeeting?.circuit_key),
+    [priorMeetingsQuery.data, previewMeeting?.circuit_key],
+  )
+
+  const priorSessionsQuery = useQuery({
+    queryKey: ['sessions', priorMeeting?.meeting_key, 'auto'],
+    queryFn: () => fetchSessions(priorMeeting!.meeting_key, 'auto'),
+    enabled: priorMeeting != null,
+  })
+
+  const priorRaceSession = useMemo(
+    () => findRaceSession(priorSessionsQuery.data ?? []),
+    [priorSessionsQuery.data],
+  )
+
+  const priorResultsQuery = useQuery({
+    queryKey: ['results', priorRaceSession?.session_key, 'auto'],
+    queryFn: () => fetchResults(priorRaceSession!.session_key, 'auto'),
+    enabled: priorRaceSession != null,
+  })
+
+  const priorGridQuery = useQuery({
+    queryKey: ['grid', priorRaceSession?.session_key, 'auto'],
+    queryFn: () => fetchStartingGrid(priorRaceSession!.session_key, 'auto'),
+    enabled: priorRaceSession != null,
+  })
+
+  const trackOutlineQuery = useQuery({
+    queryKey: ['track-outline', previewMeeting?.circuit_key, previewMeeting?.year],
+    queryFn: () => fetchTrackOutline(previewMeeting!.circuit_key!, previewMeeting!.year),
+    enabled: previewMeeting?.circuit_key != null && previewMeeting.circuit_key > 0,
+  })
+
+  const championshipQuery = useQuery({
+    queryKey: ['championship-hub', latestSeason],
+    queryFn: () => fetchChampionshipHub(latestSeason!),
+    enabled: latestSeason != null,
+  })
+
+  const podium = useMemo(() => extractPodium(priorResultsQuery.data ?? []), [priorResultsQuery.data])
+  const pole = useMemo(() => extractPole(priorGridQuery.data ?? []), [priorGridQuery.data])
+  const titleFight = useMemo(
+    () => (championshipQuery.data ? buildTitleFightContext(championshipQuery.data) : []),
+    [championshipQuery.data],
+  )
+
+  const accent = countryAccent(previewMeeting)
+  const isFirstTimeCircuit = priorMeeting == null && priorYear != null && !priorMeetingsQuery.isLoading
+
+  if (seasonsQuery.isLoading || meetingsQuery.isLoading) {
+    return <div className="page loading-state" data-testid="preview-loading">loading preview…</div>
+  }
+
+  if (seasonsQuery.isError || meetingsQuery.isError) {
+    const err = seasonsQuery.error ?? meetingsQuery.error
+    return (
+      <div className="page error-box" data-testid="preview-error">
+        {err instanceof Error ? err.message : 'Failed to load preview'}
+      </div>
+    )
+  }
+
+  if (!previewMeeting) {
+    return (
+      <div className="preview-page" data-testid="preview-season-over">
+        <div className="preview-empty">
+          <span className="preview-empty-eyebrow mono">box-box · race preview</span>
+          <h1 className="preview-empty-title">Season complete</h1>
+          <p className="preview-empty-sub">
+            No upcoming races on the {latestSeason ?? 'current'} calendar. Check back when the next season schedule is
+            published.
+          </p>
+        </div>
+        {titleFight.length > 0 && (
+          <TitleFightCard
+            loading={championshipQuery.isLoading}
+            error={championshipQuery.isError ? (championshipQuery.error as Error) : null}
+            drivers={titleFight}
+            sprintWeekend={false}
+            season={latestSeason}
+          />
+        )}
+      </div>
+    )
+  }
+
+  return (
+    <div className="preview-page" data-testid="preview-page">
+      <PreviewHeader
+        meeting={previewMeeting}
+        sessions={sessions}
+        countdownSession={countdownSession}
+        now={nowDate}
+        accent={accent}
+      />
+
+      <div className="preview-grid">
+        <TrackOutlineCard
+          outline={trackOutlineQuery.data}
+          loading={trackOutlineQuery.isLoading}
+          error={trackOutlineQuery.isError ? (trackOutlineQuery.error as Error) : null}
+          accent={accent}
+        />
+
+        <LastYearCard
+          year={priorMeeting?.year ?? priorYear}
+          loading={priorMeetingsQuery.isLoading || priorSessionsQuery.isLoading || priorResultsQuery.isLoading}
+          error={
+            priorMeetingsQuery.isError
+              ? (priorMeetingsQuery.error as Error)
+              : priorResultsQuery.isError
+                ? (priorResultsQuery.error as Error)
+                : null
+          }
+          podium={podium}
+          pole={pole}
+          isFirstTime={isFirstTimeCircuit}
+        />
+      </div>
+
+      <TitleFightCard
+        loading={championshipQuery.isLoading}
+        error={championshipQuery.isError ? (championshipQuery.error as Error) : null}
+        drivers={titleFight}
+        sprintWeekend={sprintWeekend}
+        season={latestSeason}
+      />
+    </div>
+  )
+}
--- a/frontend/src/router.tsx
+++ b/frontend/src/router.tsx
@@ -6,6 +6,7 @@ import { DataLibraryPage } from './pages/DataLibraryPage'
 import { LiveTimingPage } from './pages/LiveTimingPage'
 import { BriefingPage } from './pages/BriefingPage'
 import { ChampionshipPage } from './pages/ChampionshipPage'
+import { RacePreviewPage } from './pages/RacePreviewPage'

 type RaceHubSearch = {
  session_key?: number
@@ -70,6 +71,12 @@ export const briefingRoute = createRoute({
  component: BriefingPage,
 })

+export const previewRoute = createRoute({
+  getParentRoute: () => rootRoute,
+  path: '/preview',
+  component: RacePreviewPage,
+})
+
 const routeTree = rootRoute.addChildren([
  commandCenterRoute,
  raceHubRoute,
@@ -78,6 +85,7 @@ const routeTree = rootRoute.addChildren([
  liveTimingRoute,
  championshipRoute,
  briefingRoute,
+  previewRoute,
 ])

 export const router = createRouter({ routeTree })
--- a/frontend/src/styles/preview.css
+++ b/frontend/src/styles/preview.css
@@ -0,0 +1,309 @@
+.preview-page {
+  display: flex;
+  flex-direction: column;
+  gap: var(--s6);
+  padding: var(--s6);
+  max-width: 1200px;
+  margin: 0 auto;
+}
+
+.preview-empty {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  gap: var(--s4);
+  min-height: 320px;
+  text-align: center;
+  padding: var(--s8);
+  background: var(--surface);
+  border: 1px solid rgba(255, 255, 255, 0.08);
+  border-radius: 8px;
+}
+
+.preview-empty-eyebrow {
+  font-size: 0.7rem;
+  letter-spacing: 0.12em;
+  text-transform: uppercase;
+  color: var(--text-3);
+}
+
+.preview-empty-title {
+  font-size: 1.5rem;
+  font-weight: 600;
+  margin: 0;
+}
+
+.preview-empty-sub {
+  color: var(--text-2);
+  max-width: 36rem;
+  margin: 0;
+}
+
+.preview-header {
+  display: flex;
+  background: var(--surface);
+  border: 1px solid rgba(255, 255, 255, 0.08);
+  border-radius: 8px;
+  overflow: hidden;
+  min-height: 140px;
+}
+
+.preview-header-accent {
+  width: 4px;
+  flex-shrink: 0;
+  background: var(--preview-accent, var(--gp-accent));
+  box-shadow: 0 0 12px var(--preview-accent, var(--gp-accent));
+}
+
+.preview-header-body {
+  flex: 1;
+  padding: var(--s5);
+  display: flex;
+  flex-direction: column;
+  gap: var(--s4);
+  min-width: 0;
+}
+
+.preview-header-top {
+  display: flex;
+  flex-wrap: wrap;
+  align-items: flex-start;
+  justify-content: space-between;
+  gap: var(--s4);
+}
+
+.preview-gp-name {
+  font-size: 1.4rem;
+  font-weight: 600;
+  margin: 0;
+  display: flex;
+  align-items: center;
+  gap: var(--s3);
+}
+
+.preview-gp-flag {
+  font-size: 1.5rem;
+  line-height: 1;
+}
+
+.preview-circuit {
+  color: var(--text-2);
+  font-size: 0.9rem;
+  margin: 0;
+}
+
+.preview-countdown {
+  text-align: right;
+}
+
+.preview-countdown-label {
+  display: block;
+  font-size: 0.7rem;
+  letter-spacing: 0.08em;
+  text-transform: uppercase;
+  color: var(--text-3);
+  margin-bottom: var(--s1);
+}
+
+.preview-countdown-value {
+  font-family: var(--mono);
+  font-size: 1.1rem;
+  font-variant-numeric: tabular-nums;
+  color: var(--text-1);
+}
+
+.preview-schedule {
+  display: grid;
+  grid-template-columns: repeat(auto-fill, minmax(160px, 1fr));
+  gap: var(--s2);
+}
+
+.preview-schedule-item {
+  display: flex;
+  flex-direction: column;
+  gap: 2px;
+  padding: var(--s2) var(--s3);
+  background: rgba(255, 255, 255, 0.03);
+  border-radius: 4px;
+  font-size: 0.8rem;
+}
+
+.preview-schedule-name {
+  font-weight: 600;
+  color: var(--text-1);
+}
+
+.preview-schedule-time {
+  font-family: var(--mono);
+  font-size: 0.75rem;
+  color: var(--text-2);
+}
+
+.preview-grid {
+  display: grid;
+  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
+  gap: var(--s5);
+}
+
+.preview-card {
+  background: var(--surface);
+  border: 1px solid rgba(255, 255, 255, 0.08);
+  border-radius: 8px;
+  padding: var(--s5);
+  display: flex;
+  flex-direction: column;
+  gap: var(--s4);
+  min-height: 200px;
+}
+
+.preview-card-title {
+  font-size: 0.75rem;
+  letter-spacing: 0.1em;
+  text-transform: uppercase;
+  color: var(--text-3);
+  margin: 0;
+}
+
+.preview-card-sub {
+  font-size: 0.85rem;
+  color: var(--text-2);
+  margin: calc(-1 * var(--s2)) 0 0;
+}
+
+.preview-track-stage {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  flex: 1;
+  min-height: 180px;
+  padding: var(--s4);
+}
+
+.preview-track-svg {
+  width: 100%;
+  max-width: 280px;
+  height: auto;
+}
+
+.preview-track-outline {
+  fill: none;
+  stroke: var(--preview-accent, var(--gp-accent));
+  stroke-width: 1.8;
+  stroke-linecap: round;
+  stroke-linejoin: round;
+  opacity: 0.9;
+}
+
+.preview-track-shadow {
+  fill: none;
+  stroke: rgba(0, 0, 0, 0.5);
+  stroke-width: 3;
+  stroke-linecap: round;
+  stroke-linejoin: round;
+}
+
+.preview-podium {
+  display: flex;
+  flex-direction: column;
+  gap: var(--s3);
+}
+
+.preview-podium-row {
+  display: flex;
+  align-items: center;
+  gap: var(--s3);
+  font-size: 0.9rem;
+}
+
+.preview-podium-pos {
+  width: 1.5rem;
+  font-family: var(--mono);
+  font-weight: 600;
+  color: var(--text-3);
+}
+
+.preview-podium-code {
+  font-weight: 600;
+  min-width: 2.5rem;
+}
+
+.preview-podium-team {
+  color: var(--text-2);
+  font-size: 0.8rem;
+}
+
+.preview-pole {
+  padding-top: var(--s3);
+  border-top: 1px solid rgba(255, 255, 255, 0.06);
+  font-size: 0.85rem;
+  color: var(--text-2);
+}
+
+.preview-pole strong {
+  color: var(--text-1);
+}
+
+.preview-title-table {
+  width: 100%;
+  border-collapse: collapse;
+  font-size: 0.85rem;
+}
+
+.preview-title-table th,
+.preview-title-table td {
+  padding: var(--s2) var(--s3);
+  text-align: left;
+  border-bottom: 1px solid rgba(255, 255, 255, 0.05);
+}
+
+.preview-title-table th {
+  font-size: 0.7rem;
+  letter-spacing: 0.06em;
+  text-transform: uppercase;
+  color: var(--text-3);
+  font-weight: 500;
+}
+
+.preview-title-table td.mono {
+  font-family: var(--mono);
+  font-variant-numeric: tabular-nums;
+}
+
+.preview-sprint-note {
+  font-size: 0.8rem;
+  color: var(--text-2);
+  margin: 0;
+  padding: var(--s3);
+  background: rgba(255, 255, 255, 0.03);
+  border-radius: 4px;
+}
+
+.preview-section-state {
+  flex: 1;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  color: var(--text-3);
+  font-size: 0.85rem;
+  text-align: center;
+  padding: var(--s5);
+}
+
+.preview-section-state.error {
+  color: var(--red, #e74c3c);
+}
+
+@media (max-width: 640px) {
+  .preview-page {
+    padding: var(--s4);
+  }
+
+  .preview-header-top {
+    flex-direction: column;
+  }
+
+  .preview-countdown {
+    text-align: left;
+  }
+}
--- a/frontend/src/styles/replay-map.css
+++ b/frontend/src/styles/replay-map.css
@@ -0,0 +1,161 @@
+.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);
+}
+
+.replay-map-stage {
+  position: relative;
+  min-height: 244px;
+  height: 100%;
+}
+
+.replay-map-svg {
+  width: 100%;
+  height: 100%;
+  min-height: 244px;
+  display: block;
+  background: radial-gradient(circle at 50% 50%, rgba(255, 255, 255, 0.04), transparent 62%);
+}
+
+.replay-map-outline-shadow,
+.replay-map-outline {
+  fill: none;
+  vector-effect: non-scaling-stroke;
+  stroke-linecap: round;
+  stroke-linejoin: round;
+}
+
+.replay-map-outline-shadow {
+  stroke: rgba(255, 255, 255, 0.08);
+  stroke-width: 5;
+}
+
+.replay-map-outline {
+  stroke: var(--text-2);
+  stroke-width: 1.8;
+}
+
+.replay-car {
+  cursor: pointer;
+  outline: none;
+}
+
+.replay-car circle {
+  stroke: var(--bg);
+  stroke-width: 0.8;
+  filter: drop-shadow(0 1px 3px rgba(0, 0, 0, 0.55));
+}
+
+.replay-car text {
+  fill: #fff;
+  font-family: var(--f-mono);
+  font-size: 2.6px;
+  font-weight: 800;
+  text-anchor: middle;
+  pointer-events: none;
+  paint-order: stroke;
+  stroke: rgba(0, 0, 0, 0.75);
+  stroke-width: 0.7;
+}
+
+.replay-car:not(.replay-car-pinned) text {
+  opacity: 0;
+}
+
+.replay-car:hover text,
+.replay-car:focus-visible text,
+.replay-car-pinned text {
+  opacity: 1;
+}
+
+.replay-car-pinned circle {
+  stroke: #fff;
+  stroke-width: 1.2;
+}
+
+.replay-map-empty {
+  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;
+}
+
+@media (max-width: 860px) {
+  .rs-replay-shell {
+    grid-template-columns: 1fr;
+  }
+}
--- a/frontend/src/test/CommandCenterPage.test.tsx
+++ b/frontend/src/test/CommandCenterPage.test.tsx
@@ -156,6 +156,7 @@ describe('CommandCenterPage', () => {
      race_control: [],
      weather: [],
      laps: [],
+      chapters: [],
    })
  })

--- a/frontend/src/test/RaceHubPage.test.tsx
+++ b/frontend/src/test/RaceHubPage.test.tsx
@@ -155,6 +155,7 @@ const raceHub: RaceHub = {
      is_pit_out_lap: false,
    },
  ],
+  chapters: [],
 }

 const weekend: Weekend = {
--- a/frontend/src/test/RacePreviewPage.test.tsx
+++ b/frontend/src/test/RacePreviewPage.test.tsx
@@ -0,0 +1,276 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest'
+import { render, screen, waitFor } from '@testing-library/react'
+import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
+import { RouterProvider, createRouter, createRootRoute, createRoute } from '@tanstack/react-router'
+import { RacePreviewPage } from '../pages/RacePreviewPage'
+import type { ChampHubDriver, ChampionshipHub, EnrichedGrid, EnrichedResult, Meeting, Session, TrackOutline } from '../types'
+
+vi.mock('../api', () => ({
+  fetchSeasons: vi.fn(),
+  fetchMeetings: vi.fn(),
+  fetchSessions: vi.fn(),
+  fetchResults: vi.fn(),
+  fetchStartingGrid: vi.fn(),
+  fetchTrackOutline: vi.fn(),
+  fetchChampionshipHub: vi.fn(),
+}))
+
+import {
+  fetchSeasons,
+  fetchMeetings,
+  fetchSessions,
+  fetchResults,
+  fetchStartingGrid,
+  fetchTrackOutline,
+  fetchChampionshipHub,
+} from '../api'
+
+const mockFetchSeasons = vi.mocked(fetchSeasons)
+const mockFetchMeetings = vi.mocked(fetchMeetings)
+const mockFetchSessions = vi.mocked(fetchSessions)
+const mockFetchResults = vi.mocked(fetchResults)
+const mockFetchStartingGrid = vi.mocked(fetchStartingGrid)
+const mockFetchTrackOutline = vi.mocked(fetchTrackOutline)
+const mockFetchChampionshipHub = vi.mocked(fetchChampionshipHub)
+
+const upcomingMeeting: Meeting = {
+  meeting_key: 100,
+  meeting_name: 'Monaco',
+  meeting_official_name: 'Monaco GP',
+  location: 'Monaco',
+  country_name: 'Monaco',
+  country_code: 'MON',
+  country_flag: '',
+  circuit_key: 10,
+  circuit_short_name: 'Monaco',
+  date_start: '2099-05-22T00:00:00+00:00',
+  date_end: '2099-05-24T23:59:59+00:00',
+  year: 2099,
+}
+
+const priorMeeting: Meeting = {
+  ...upcomingMeeting,
+  meeting_key: 90,
+  year: 2098,
+  date_start: '2098-05-22T00:00:00+00:00',
+  date_end: '2098-05-24T23:59:59+00:00',
+}
+
+const sessions: Session[] = [
+  {
+    session_key: 1,
+    session_name: 'FP1',
+    session_type: 'Practice',
+    meeting_key: 100,
+    date_start: '2099-05-22T10:00:00+00:00',
+    date_end: '2099-05-22T11:00:00+00:00',
+    gmt_offset: '02:00:00',
+  },
+  {
+    session_key: 2,
+    session_name: 'Sprint',
+    session_type: 'Sprint',
+    meeting_key: 100,
+    date_start: '2099-05-23T10:00:00+00:00',
+    date_end: '2099-05-23T11:00:00+00:00',
+    gmt_offset: '02:00:00',
+  },
+  {
+    session_key: 3,
+    session_name: 'Race',
+    session_type: 'Race',
+    meeting_key: 100,
+    date_start: '2099-05-24T13:00:00+00:00',
+    date_end: '2099-05-24T15:00:00+00:00',
+    gmt_offset: '02:00:00',
+  },
+]
+
+const priorRaceSession: Session = {
+  session_key: 50,
+  session_name: 'Race',
+  session_type: 'Race',
+  meeting_key: 90,
+  date_start: '2098-05-24T13:00:00+00:00',
+  date_end: '2098-05-24T15:00:00+00:00',
+  gmt_offset: '02:00:00',
+}
+
+const hubDriver = (over: Partial<ChampHubDriver>): ChampHubDriver => ({
+  driver_number: 1,
+  name_acronym: 'VER',
+  full_name: 'Max Verstappen',
+  team_name: 'Red Bull',
+  team_colour: '3671c6',
+  points: 200,
+  position: 1,
+  wins: 5,
+  podiums: 8,
+  poles: 4,
+  form: [25],
+  cumulative: [200],
+  teammate_wins: 9,
+  teammate_losses: 1,
+  ...over,
+})
+
+const hub: ChampionshipHub = {
+  season: 2099,
+  round: 5,
+  total_rounds: 24,
+  rounds_left: 19,
+  last_race: 'Monaco GP',
+  round_labels: ['R1'],
+  drivers: [
+    hubDriver({}),
+    hubDriver({ driver_number: 4, name_acronym: 'NOR', points: 160, position: 2 }),
+    hubDriver({ driver_number: 16, name_acronym: 'LEC', points: 120, position: 3 }),
+  ],
+  teams: [],
+}
+
+const results: EnrichedResult[] = [
+  {
+    driver_number: 1,
+    position: 1,
+    name_acronym: 'VER',
+    full_name: 'Max Verstappen',
+    team_name: 'Red Bull',
+    team_colour: '3671c6',
+    dnf: false,
+    dns: false,
+    dsq: false,
+    duration: 100,
+    gap_to_leader: 0,
+    number_of_laps: 78,
+    points: 25,
+    session_key: 50,
+    meeting_key: 90,
+  },
+]
+
+const grid: EnrichedGrid[] = [
+  {
+    driver_number: 4,
+    position: 1,
+    name_acronym: 'NOR',
+    full_name: 'Lando Norris',
+    team_name: 'McLaren',
+    team_colour: 'ff8000',
+    session_key: 50,
+    meeting_key: 90,
+    lap_duration: 70,
+  },
+]
+
+const outline: TrackOutline = {
+  circuit_key: 10,
+  points: [
+    { x: 0.1, y: 0.2 },
+    { x: 0.5, y: 0.5 },
+    { x: 0.9, y: 0.8 },
+  ],
+  bounds: { minX: 0, maxX: 1, minY: 0, maxY: 1 },
+}
+
+function renderPage() {
+  const queryClient = new QueryClient({ defaultOptions: { queries: { retry: false } } })
+  const rootRoute = createRootRoute({
+    component: () => (
+      <QueryClientProvider client={queryClient}>
+        <RacePreviewPage />
+      </QueryClientProvider>
+    ),
+  })
+  const indexRoute = createRoute({ getParentRoute: () => rootRoute, path: '/', component: RacePreviewPage })
+  const router = createRouter({ routeTree: rootRoute.addChildren([indexRoute]) })
+  return render(<RouterProvider router={router} />)
+}
+
+describe('RacePreviewPage', () => {
+  beforeEach(() => {
+    vi.clearAllMocks()
+    mockFetchSeasons.mockResolvedValue([2099])
+    mockFetchChampionshipHub.mockResolvedValue(hub)
+    mockFetchTrackOutline.mockResolvedValue(outline)
+    mockFetchResults.mockResolvedValue(results)
+    mockFetchStartingGrid.mockResolvedValue(grid)
+  })
+
+  it('renders upcoming race preview with sections', async () => {
+    mockFetchMeetings.mockImplementation(async (year: number) => {
+      if (year === 2099) return [upcomingMeeting]
+      if (year === 2098) return [priorMeeting]
+      return []
+    })
+    mockFetchSessions.mockImplementation(async (meetingKey: number) => {
+      if (meetingKey === 100) return sessions
+      if (meetingKey === 90) return [priorRaceSession]
+      return []
+    })
+
+    renderPage()
+
+    await waitFor(() => {
+      expect(screen.getByTestId('preview-page')).toBeInTheDocument()
+    })
+
+    await waitFor(() => {
+      expect(screen.getByTestId('preview-countdown')).toBeInTheDocument()
+    })
+
+    expect(screen.getByTestId('preview-header')).toHaveTextContent('Monaco')
+    expect(screen.getByTestId('preview-schedule')).toHaveTextContent('FP1')
+    expect(screen.getByTestId('preview-track-card')).toBeInTheDocument()
+
+    await waitFor(() => {
+      expect(screen.getByTestId('preview-last-year-card')).toHaveTextContent('VER')
+    })
+
+    expect(screen.getByTestId('preview-title-fight-card')).toHaveTextContent('NOR')
+    expect(screen.getByTestId('preview-sprint-note')).toBeInTheDocument()
+  })
+
+  it('renders season-over state when no upcoming meeting', async () => {
+    mockFetchMeetings.mockResolvedValue([
+      {
+        ...upcomingMeeting,
+        date_start: '2020-05-22T00:00:00+00:00',
+        date_end: '2020-05-24T23:59:59+00:00',
+      },
+    ])
+
+    renderPage()
+
+    await waitFor(() => {
+      expect(screen.getByTestId('preview-season-over')).toBeInTheDocument()
+    })
+
+    expect(screen.getByText('Season complete')).toBeInTheDocument()
+    expect(screen.getByTestId('preview-title-fight-card')).toBeInTheDocument()
+    expect(screen.queryByTestId('preview-header')).not.toBeInTheDocument()
+  })
+
+  it('shows first-time circuit empty state', async () => {
+    const newCircuit: Meeting = {
+      ...upcomingMeeting,
+      meeting_key: 200,
+      circuit_key: 999,
+      meeting_name: 'New GP',
+    }
+
+    mockFetchMeetings.mockImplementation(async (year: number) => {
+      if (year === 2099) return [newCircuit]
+      if (year === 2098) return [priorMeeting]
+      return []
+    })
+    mockFetchSessions.mockResolvedValue(sessions)
+    mockFetchTrackOutline.mockResolvedValue(null)
+
+    renderPage()
+
+    await waitFor(() => {
+      expect(screen.getByTestId('preview-last-year-card')).toHaveTextContent('First time on the calendar')
+    })
+  })
+})
--- a/frontend/src/test/RaceStoryCanvas.test.tsx
+++ b/frontend/src/test/RaceStoryCanvas.test.tsx
@@ -0,0 +1,135 @@
+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'
+
+vi.mock('../api', () => ({
+  fetchReplayFrames: vi.fn(),
+  fetchTrackOutline: vi.fn(),
+}))
+
+import { fetchReplayFrames, fetchTrackOutline } from '../api'
+
+const mockFetchReplayFrames = vi.mocked(fetchReplayFrames)
+const mockFetchTrackOutline = vi.mocked(fetchTrackOutline)
+
+const outline: TrackOutline = {
+  circuit_key: 1,
+  bounds: { minX: 0, maxX: 100, minY: 0, maxY: 100 },
+  points: [
+    { x: 0, y: 0 },
+    { x: 1, y: 0 },
+    { x: 1, y: 1 },
+  ],
+}
+
+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 } } }],
+}
+
+const raceHub: RaceHub = {
+  source: 'local',
+  session_key: 99,
+  datasets: {
+    positions: { status: 'available', source: 'local', count: 2 },
+  },
+  meeting: {
+    meeting_key: 1,
+    meeting_name: 'Monaco Grand Prix',
+    meeting_official_name: 'FORMULA 1 GRAND PRIX DE MONACO 2025',
+    location: 'Monaco',
+    country_name: 'Monaco',
+    country_code: 'MON',
+    country_flag: '',
+    circuit_key: 1,
+    circuit_short_name: 'Monaco',
+    date_start: '2025-05-23T00:00:00Z',
+    date_end: '2025-05-25T00:00:00Z',
+    year: 2025,
+  },
+  session: {
+    session_key: 99,
+    session_name: 'Race',
+    session_type: 'Race',
+    circuit_key: 1,
+    meeting_key: 1,
+    date_start: '2025-05-25T13:00:00Z',
+    date_end: '2025-05-25T15:00:00Z',
+    gmt_offset: '02:00:00',
+  },
+  drivers: [],
+  results: [
+    {
+      driver_number: 1,
+      position: 1,
+      name_acronym: 'VER',
+      full_name: 'Max Verstappen',
+      team_name: 'Red Bull Racing',
+      team_colour: '3671C6',
+      dnf: false,
+      dns: false,
+      dsq: false,
+      duration: null,
+      gap_to_leader: null,
+      number_of_laps: 78,
+      points: 25,
+      session_key: 99,
+      meeting_key: 1,
+    },
+  ],
+  starting_grid: [
+    {
+      driver_number: 1,
+      position: 1,
+      name_acronym: 'VER',
+      full_name: 'Max Verstappen',
+      team_name: 'Red Bull Racing',
+      team_colour: '3671C6',
+      session_key: 99,
+      meeting_key: 1,
+      lap_duration: null,
+    },
+  ],
+  stints: [],
+  pit_stops: [],
+  positions: [
+    { session_key: 99, driver_number: 1, meeting_key: 1, date: '2025-05-25T13:00:00Z', position: 1 },
+    { session_key: 99, driver_number: 1, meeting_key: 1, date: '2025-05-25T13:05:00Z', position: 1 },
+  ],
+  race_control: [],
+  weather: [],
+  laps: [],
+  chapters: [],
+}
+
+function renderCanvas() {
+  const queryClient = new QueryClient({ defaultOptions: { queries: { retry: false } } })
+  return render(
+    <QueryClientProvider client={queryClient}>
+      <RaceStoryCanvas data={raceHub} />
+    </QueryClientProvider>,
+  )
+}
+
+describe('RaceStoryCanvas replay map', () => {
+  beforeEach(() => {
+    vi.clearAllMocks()
+    mockFetchReplayFrames.mockResolvedValue(replay)
+    mockFetchTrackOutline.mockResolvedValue(outline)
+  })
+
+  it('fetches replay frames lazily when the map panel opens', 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)
+    expect(await screen.findByTestId('replay-track-map')).toBeInTheDocument()
+  })
+})
--- a/frontend/src/test/ReplayTrackMap.test.tsx
+++ b/frontend/src/test/ReplayTrackMap.test.tsx
@@ -0,0 +1,56 @@
+import { describe, expect, it } from 'vitest'
+import { render, screen } from '@testing-library/react'
+import { ReplayTrackMap } from '../components/ReplayTrackMap'
+import type { EnrichedResult, ReplayFramesResponse, TrackOutline } from '../types'
+
+const outline: TrackOutline = {
+  circuit_key: 1,
+  bounds: { minX: 0, maxX: 100, minY: 0, maxY: 100 },
+  points: [
+    { x: 0, y: 0 },
+    { x: 1, y: 0 },
+    { x: 1, y: 1 },
+  ],
+}
+
+const replay: ReplayFramesResponse = {
+  session_key: 99,
+  interval_ms: 5000,
+  start_time: '2025-05-25T13:00:00Z',
+  frames: [
+    { t: 0, cars: { '1': { x: 0, y: 0 } } },
+    { t: 5000, cars: { '1': { x: 50, y: 50 } } },
+  ],
+}
+
+const results: EnrichedResult[] = [
+  {
+    driver_number: 1,
+    position: 1,
+    name_acronym: 'VER',
+    full_name: 'Max Verstappen',
+    team_name: 'Red Bull Racing',
+    team_colour: '3671C6',
+    dnf: false,
+    dns: false,
+    dsq: false,
+    duration: null,
+    gap_to_leader: null,
+    number_of_laps: 78,
+    points: 25,
+    session_key: 99,
+    meeting_key: 1,
+  },
+]
+
+describe('ReplayTrackMap', () => {
+  it('renders an empty state 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)
+  })
+
+  it('renders car labels from result metadata', () => {
+    render(<ReplayTrackMap outline={outline} replay={replay} tMs={2500} drivers={[]} results={results} />)
+    expect(screen.getByLabelText(/VER replay position/i)).toBeInTheDocument()
+  })
+})
--- a/frontend/src/test/preview.test.ts
+++ b/frontend/src/test/preview.test.ts
@@ -0,0 +1,226 @@
+import { describe, it, expect } from 'vitest'
+import type { ChampHubDriver, ChampionshipHub, EnrichedGrid, EnrichedResult, Meeting, Session } from '../types'
+import {
+  buildTitleFightContext,
+  countdownTargetSession,
+  extractPodium,
+  extractPole,
+  findPriorYearMeetingByCircuit,
+  findRaceSession,
+  formatPointsGap,
+  isSprintWeekend,
+  pickPreviewMeeting,
+  RACE_WIN_POINTS,
+  SPRINT_WEEKEND_MAX_POINTS,
+} from '../lib/preview'
+
+const meeting = (overrides: Partial<Meeting> = {}): Meeting => ({
+  meeting_key: 1,
+  meeting_name: 'Monaco',
+  meeting_official_name: 'Monaco GP',
+  location: 'Monaco',
+  country_name: 'Monaco',
+  country_code: 'MON',
+  country_flag: '',
+  circuit_key: 10,
+  circuit_short_name: 'Monaco',
+  date_start: '2026-05-22T00:00:00+00:00',
+  date_end: '2026-05-24T23:59:59+00:00',
+  year: 2026,
+  ...overrides,
+})
+
+const session = (overrides: Partial<Session> = {}): Session => ({
+  session_key: 100,
+  session_name: 'Race',
+  session_type: 'Race',
+  meeting_key: 1,
+  date_start: '2026-05-24T13:00:00+00:00',
+  date_end: '2026-05-24T15:00:00+00:00',
+  gmt_offset: '02:00:00',
+  ...overrides,
+})
+
+const hubDriver = (over: Partial<ChampHubDriver>): ChampHubDriver => ({
+  driver_number: 1,
+  name_acronym: 'VER',
+  full_name: 'Max Verstappen',
+  team_name: 'Red Bull',
+  team_colour: '3671c6',
+  points: 200,
+  position: 1,
+  wins: 5,
+  podiums: 8,
+  poles: 4,
+  form: [25],
+  cumulative: [200],
+  teammate_wins: 9,
+  teammate_losses: 1,
+  ...over,
+})
+
+describe('preview lib', () => {
+  it('picks the next upcoming meeting', () => {
+    const now = new Date('2026-01-01T00:00:00Z')
+    const meetings = [
+      meeting({ meeting_key: 1, date_start: '2026-05-22T00:00:00+00:00' }),
+      meeting({ meeting_key: 2, meeting_name: 'Spain', date_start: '2026-06-12T00:00:00+00:00' }),
+    ]
+    expect(pickPreviewMeeting(meetings, now)?.meeting_key).toBe(1)
+  })
+
+  it('returns null when no upcoming meeting exists', () => {
+    const now = new Date('2027-01-01T00:00:00Z')
+    const meetings = [meeting({ date_start: '2026-05-22T00:00:00+00:00' })]
+    expect(pickPreviewMeeting(meetings, now)).toBeNull()
+  })
+
+  it('skips cancelled meetings', () => {
+    const now = new Date('2026-01-01T00:00:00Z')
+    const meetings = [meeting({ is_cancelled: true })]
+    expect(pickPreviewMeeting(meetings, now)).toBeNull()
+  })
+
+  it('matches prior-year meeting by circuit_key', () => {
+    const prior = [
+      meeting({ meeting_key: 50, year: 2025, circuit_key: 10 }),
+      meeting({ meeting_key: 51, year: 2025, circuit_key: 20, meeting_name: 'Spain' }),
+    ]
+    expect(findPriorYearMeetingByCircuit(prior, 10)?.meeting_key).toBe(50)
+    expect(findPriorYearMeetingByCircuit(prior, 99)).toBeNull()
+    expect(findPriorYearMeetingByCircuit(prior, undefined)).toBeNull()
+  })
+
+  it('finds the grand prix race session', () => {
+    const sessions = [
+      session({ session_key: 1, session_name: 'FP1', session_type: 'Practice', date_start: '2026-05-22T10:00:00+00:00' }),
+      session({ session_key: 2, session_name: 'Sprint', session_type: 'Sprint', date_start: '2026-05-23T10:00:00+00:00' }),
+      session({ session_key: 3, session_name: 'Race', session_type: 'Race', date_start: '2026-05-24T13:00:00+00:00' }),
+    ]
+    expect(findRaceSession(sessions)?.session_key).toBe(3)
+  })
+
+  it('detects sprint weekends', () => {
+    const sprint = [
+      session({ session_type: 'Practice' }),
+      session({ session_name: 'Sprint', session_type: 'Sprint' }),
+      session({ session_type: 'Race' }),
+    ]
+    const normal = [session({ session_type: 'Practice' }), session({ session_type: 'Race' })]
+    expect(isSprintWeekend(sprint)).toBe(true)
+    expect(isSprintWeekend(normal)).toBe(false)
+  })
+
+  it('extracts podium and pole', () => {
+    const results: EnrichedResult[] = [
+      {
+        driver_number: 1,
+        position: 1,
+        name_acronym: 'VER',
+        full_name: 'Max Verstappen',
+        team_name: 'Red Bull',
+        team_colour: '3671c6',
+        dnf: false,
+        dns: false,
+        dsq: false,
+        duration: 100,
+        gap_to_leader: 0,
+        number_of_laps: 78,
+        points: 25,
+        session_key: 1,
+        meeting_key: 1,
+      },
+      {
+        driver_number: 4,
+        position: 2,
+        name_acronym: 'NOR',
+        full_name: 'Lando Norris',
+        team_name: 'McLaren',
+        team_colour: 'ff8000',
+        dnf: false,
+        dns: false,
+        dsq: false,
+        duration: 101,
+        gap_to_leader: 1,
+        number_of_laps: 78,
+        points: 18,
+        session_key: 1,
+        meeting_key: 1,
+      },
+      {
+        driver_number: 16,
+        position: 3,
+        name_acronym: 'LEC',
+        full_name: 'Charles Leclerc',
+        team_name: 'Ferrari',
+        team_colour: 'e8002d',
+        dnf: false,
+        dns: false,
+        dsq: false,
+        duration: 102,
+        gap_to_leader: 2,
+        number_of_laps: 78,
+        points: 15,
+        session_key: 1,
+        meeting_key: 1,
+      },
+    ]
+
+    const grid: EnrichedGrid[] = [
+      {
+        driver_number: 4,
+        position: 1,
+        name_acronym: 'NOR',
+        full_name: 'Lando Norris',
+        team_name: 'McLaren',
+        team_colour: 'ff8000',
+        session_key: 1,
+        meeting_key: 1,
+        lap_duration: 70,
+      },
+    ]
+
+    const podium = extractPodium(results)
+    expect(podium.map((p) => p.name_acronym)).toEqual(['VER', 'NOR', 'LEC'])
+    expect(extractPole(grid)?.name_acronym).toBe('NOR')
+  })
+
+  it('builds title fight gaps for top 3', () => {
+    const hub: ChampionshipHub = {
+      season: 2026,
+      round: 5,
+      total_rounds: 24,
+      rounds_left: 19,
+      last_race: 'Monaco GP',
+      round_labels: ['R1'],
+      drivers: [
+        hubDriver({ points: 200, position: 1 }),
+        hubDriver({ driver_number: 4, name_acronym: 'NOR', points: 160, position: 2 }),
+        hubDriver({ driver_number: 16, name_acronym: 'LEC', points: 120, position: 3 }),
+      ],
+      teams: [],
+    }
+
+    const rows = buildTitleFightContext(hub)
+    expect(rows).toHaveLength(3)
+    expect(rows[0].gapToLeader).toBe(0)
+    expect(rows[1].gapToLeader).toBe(40)
+    expect(rows[1].gapAfterRaceWin).toBe(15)
+    expect(rows[2].gapAfterSprintWeekendMax).toBe(200 - (120 + SPRINT_WEEKEND_MAX_POINTS))
+    expect(RACE_WIN_POINTS).toBe(25)
+  })
+
+  it('formats points gaps', () => {
+    expect(formatPointsGap(0)).toBe('LEADER')
+    expect(formatPointsGap(40)).toBe('+40')
+  })
+
+  it('picks countdown target as next future session', () => {
+    const sessions = [
+      session({ session_key: 1, session_name: 'FP1', session_type: 'Practice', date_start: '2026-05-22T10:00:00+00:00', date_end: '2026-05-22T11:00:00+00:00' }),
+      session({ session_key: 2, session_name: 'Race', session_type: 'Race', date_start: '2026-05-24T13:00:00+00:00', date_end: '2026-05-24T15:00:00+00:00' }),
+    ]
+    const now = new Date('2026-05-23T12:00:00Z')
+    expect(countdownTargetSession(sessions, now)?.session_key).toBe(2)
+  })
+})
--- a/frontend/src/test/replay.test.ts
+++ b/frontend/src/test/replay.test.ts
@@ -0,0 +1,33 @@
+import { describe, expect, it } from 'vitest'
+import type { ReplayFrame, TrackBounds } from '../types'
+import { interpolateReplayCars, lookupReplayFramePair, replayCarToSvg } from '../lib/replay'
+
+const frames: ReplayFrame[] = [
+  { t: 0, cars: { '1': { x: 0, y: 0 } } },
+  { t: 5000, cars: { '1': { x: 10, y: 20 }, '4': { x: 40, y: 80 } } },
+  { t: 10000, cars: { '1': { x: 20, y: 40 } } },
+]
+
+describe('replay helpers', () => {
+  it('looks up boundary frame pairs', () => {
+    expect(lookupReplayFramePair(frames, -1)).toEqual({ previous: frames[0], next: frames[0] })
+    expect(lookupReplayFramePair(frames, 10000)).toEqual({ previous: frames[2], next: frames[2] })
+    expect(lookupReplayFramePair([], 1000)).toEqual({ previous: null, next: null })
+  })
+
+  it('interpolates cars between frames and keeps one-sided samples visible', () => {
+    const cars = interpolateReplayCars(frames, 2500)
+    expect(cars['1']).toEqual({ x: 5, y: 10 })
+    expect(cars['4']).toEqual({ x: 40, y: 80 })
+  })
+
+  it('clamps interpolation outside the replay range', () => {
+    expect(interpolateReplayCars(frames, -500)['1']).toEqual({ x: 0, y: 0 })
+    expect(interpolateReplayCars(frames, 12000)['1']).toEqual({ x: 20, y: 40 })
+  })
+
+  it('maps replay GPS through the shared track-map coordinate transform', () => {
+    const bounds: TrackBounds = { minX: 0, maxX: 100, minY: 0, maxY: 200 }
+    expect(replayCarToSvg({ x: 50, y: 50 }, bounds)).toEqual({ x: 50, y: 75 })
+  })
+})
--- a/frontend/src/types.ts
+++ b/frontend/src/types.ts
@@ -12,6 +12,7 @@ export interface Meeting {
  country_name: string
  country_code: string
  country_flag: string
+  circuit_key?: number
  circuit_short_name: string
  date_start: string
  date_end: string
@@ -23,6 +24,7 @@ export interface Session {
  session_key: number
  session_name: string
  session_type: string
+  circuit_key?: number
  meeting_key: number
  date_start: string
  date_end: string
@@ -89,6 +91,17 @@ export interface RaceHub {
  race_control: RaceControlMessage[]
  weather: WeatherSample[]
  laps: Lap[]
+  chapters: Chapter[]
+}
+
+export interface Chapter {
+  kind: 'start' | 'safety_car' | 'virtual_safety_car' | 'red_flag' | 'pit_phase' | 'decisive_swing' | 'finish' | string
+  title: string
+  start_lap: number
+  end_lap: number
+  start_time?: string
+  end_time?: string
+  driver_numbers: number[]
 }

 export interface Stint {
@@ -347,6 +360,23 @@ export interface TrackOutline {
  bounds: TrackBounds
 }

+export interface ReplayCarPosition {
+  x: number
+  y: number
+}
+
+export interface ReplayFrame {
+  t: number
+  cars: Record<string, ReplayCarPosition>
+}
+
+export interface ReplayFramesResponse {
+  session_key: number
+  interval_ms: number
+  start_time: string
+  frames: ReplayFrame[]
+}
+
 export interface ChampHubDriver {
  driver_number: number
  name_acronym: string
--- a/internal/chapters/chapters.go
+++ b/internal/chapters/chapters.go
@@ -0,0 +1,628 @@
+package chapters
+
+import (
+	"fmt"
+	"math"
+	"sort"
+	"strings"
+	"time"
+
+	"github.com/AmanTahiliani/box-box/internal/models"
+)
+
+const (
+	KindStart            = "start"
+	KindSafetyCar        = "safety_car"
+	KindVirtualSafetyCar = "virtual_safety_car"
+	KindRedFlag          = "red_flag"
+	KindPitPhase         = "pit_phase"
+	KindDecisiveSwing    = "decisive_swing"
+	KindFinish           = "finish"
+
+	pitPhaseWindowLaps = 3
+	pitPhaseShare      = 0.30
+	minPitPhaseStops   = 2
+	maxDecisiveSwings  = 3
+	decisiveAfterLap   = 5
+	structuralPriority = 110
+	flagPriority       = 100
+	pitPhasePriority   = 50
+	decisivePriority   = 40
+)
+
+type RaceControl = models.RaceControl
+type PositionSample = models.Position
+type Lap = models.Lap
+
+// Chapter is a deterministic replay segment derived from timing and race-control data.
+type Chapter struct {
+	Kind          string `json:"kind"`
+	Title         string `json:"title"`
+	StartLap      int    `json:"start_lap"`
+	EndLap        int    `json:"end_lap"`
+	StartTime     string `json:"start_time,omitempty"`
+	EndTime       string `json:"end_time,omitempty"`
+	DriverNumbers []int  `json:"driver_numbers"`
+}
+
+// Detect builds replay chapters from already-loaded race-hub datasets.
+func Detect(rc []RaceControl, positions []PositionSample, laps []Lap, totalLaps int) []Chapter {
+	totalLaps = normalizeTotalLaps(totalLaps, laps, rc)
+	if totalLaps <= 0 && len(rc) == 0 && len(positions) == 0 && len(laps) == 0 {
+		return []Chapter{}
+	}
+	if totalLaps <= 0 {
+		totalLaps = 1
+	}
+
+	lapIndex := buildLapIndex(laps)
+	chapters := []Chapter{
+		{
+			Kind:      KindStart,
+			Title:     "Start",
+			StartLap:  1,
+			EndLap:    minInt(1, totalLaps),
+			StartTime: lapIndex.lapStart(1),
+			EndTime:   lapIndex.lapEnd(1),
+		},
+	}
+	chapters = append(chapters, detectFlagPeriods(rc, lapIndex, totalLaps)...)
+	chapters = append(chapters, detectPitPhases(laps, lapIndex)...)
+	chapters = append(chapters, detectDecisiveSwings(positions, lapIndex, totalLaps)...)
+	chapters = append(chapters, detectFinish(rc, lapIndex, totalLaps))
+
+	return resolveConflicts(chapters)
+}
+
+func normalizeTotalLaps(totalLaps int, laps []Lap, rc []RaceControl) int {
+	for _, l := range laps {
+		if l.LapNumber > totalLaps {
+			totalLaps = l.LapNumber
+		}
+	}
+	for _, msg := range rc {
+		if msg.LapNumber != nil && *msg.LapNumber > totalLaps {
+			totalLaps = *msg.LapNumber
+		}
+	}
+	return totalLaps
+}
+
+type lapIndex struct {
+	byLap  map[int]string
+	events []lapEvent
+}
+
+type lapEvent struct {
+	lap int
+	at  time.Time
+}
+
+func buildLapIndex(laps []Lap) lapIndex {
+	idx := lapIndex{byLap: map[int]string{}}
+	for _, l := range laps {
+		if l.LapNumber <= 0 || l.DateStart == "" {
+			continue
+		}
+		if _, ok := idx.byLap[l.LapNumber]; !ok {
+			idx.byLap[l.LapNumber] = l.DateStart
+		}
+		at, ok := parseTime(l.DateStart)
+		if ok {
+			idx.events = append(idx.events, lapEvent{lap: l.LapNumber, at: at})
+		}
+	}
+	sort.Slice(idx.events, func(i, j int) bool {
+		if idx.events[i].at.Equal(idx.events[j].at) {
+			return idx.events[i].lap < idx.events[j].lap
+		}
+		return idx.events[i].at.Before(idx.events[j].at)
+	})
+	return idx
+}
+
+func (idx lapIndex) lapStart(lap int) string {
+	return idx.byLap[lap]
+}
+
+func (idx lapIndex) lapEnd(lap int) string {
+	if v := idx.byLap[lap+1]; v != "" {
+		return v
+	}
+	return idx.byLap[lap]
+}
+
+func (idx lapIndex) lapForTime(raw string) int {
+	at, ok := parseTime(raw)
+	if !ok || len(idx.events) == 0 {
+		return 0
+	}
+	lap := 0
+	for _, event := range idx.events {
+		if event.at.After(at) {
+			break
+		}
+		lap = event.lap
+	}
+	if lap == 0 {
+		return idx.events[0].lap
+	}
+	return lap
+}
+
+type flagState struct {
+	startLap  int
+	startTime string
+}
+
+func detectFlagPeriods(rc []RaceControl, idx lapIndex, totalLaps int) []Chapter {
+	var chapters []Chapter
+	active := map[string]flagState{}
+	for _, msg := range rc {
+		kind, ok := flagKind(msg)
+		if !ok && greenFlagClear(msg) {
+			for activeKind, st := range active {
+				lap := messageLap(msg, idx)
+				if lap <= 0 {
+					lap = st.startLap
+				}
+				endLap := clampLap(lap, st.startLap, totalLaps)
+				chapters = append(chapters, Chapter{
+					Kind:      activeKind,
+					Title:     flagTitle(activeKind, st.startLap, endLap),
+					StartLap:  st.startLap,
+					EndLap:    endLap,
+					StartTime: st.startTime,
+					EndTime:   firstNonEmpty(msg.Date, idx.lapEnd(endLap)),
+				})
+				delete(active, activeKind)
+			}
+			continue
+		}
+		if !ok {
+			continue
+		}
+		lap := messageLap(msg, idx)
+		if lap <= 0 {
+			lap = 1
+		}
+		if flagCleared(msg) {
+			st, ok := active[kind]
+			if !ok {
+				continue
+			}
+			endLap := clampLap(lap, st.startLap, totalLaps)
+			chapters = append(chapters, Chapter{
+				Kind:      kind,
+				Title:     flagTitle(kind, st.startLap, endLap),
+				StartLap:  st.startLap,
+				EndLap:    endLap,
+				StartTime: st.startTime,
+				EndTime:   firstNonEmpty(msg.Date, idx.lapEnd(endLap)),
+			})
+			delete(active, kind)
+			continue
+		}
+		if flagStarted(msg) {
+			active[kind] = flagState{
+				startLap:  clampLap(lap, 1, totalLaps),
+				startTime: firstNonEmpty(msg.Date, idx.lapStart(lap)),
+			}
+		}
+	}
+	for kind, st := range active {
+		endLap := totalLaps
+		chapters = append(chapters, Chapter{
+			Kind:      kind,
+			Title:     flagTitle(kind, st.startLap, endLap),
+			StartLap:  st.startLap,
+			EndLap:    endLap,
+			StartTime: st.startTime,
+			EndTime:   idx.lapEnd(endLap),
+		})
+	}
+	return chapters
+}
+
+func flagKind(msg RaceControl) (string, bool) {
+	text := upperText(string(msg.Category), string(msg.Flag), msg.Message)
+	if strings.Contains(text, "VSC") || strings.Contains(text, "VIRTUAL SAFETY CAR") {
+		return KindVirtualSafetyCar, true
+	}
+	if strings.Contains(text, "RED FLAG") || string(msg.Flag) == string(models.FlagRed) {
+		return KindRedFlag, true
+	}
+	if strings.Contains(text, "SAFETY CAR") || msg.Category == models.CategorySafetyCar {
+		return KindSafetyCar, true
+	}
+	return "", false
+}
+
+func flagStarted(msg RaceControl) bool {
+	text := upperText(string(msg.Category), string(msg.Flag), msg.Message)
+	if strings.Contains(text, "CLEAR") || strings.Contains(text, "ENDING") || strings.Contains(text, "IN THIS LAP") || strings.Contains(text, "GREEN") {
+		return false
+	}
+	return strings.Contains(text, "DEPLOY") ||
+		strings.Contains(text, "RED FLAG") ||
+		strings.Contains(text, "VIRTUAL SAFETY CAR") ||
+		strings.Contains(text, "VSC") ||
+		strings.Contains(text, "SAFETY CAR") ||
+		string(msg.Flag) == string(models.FlagRed)
+}
+
+func flagCleared(msg RaceControl) bool {
+	text := upperText(string(msg.Category), string(msg.Flag), msg.Message)
+	return strings.Contains(text, "CLEAR") ||
+		strings.Contains(text, "ENDING") ||
+		strings.Contains(text, "IN THIS LAP") ||
+		strings.Contains(text, "GREEN")
+}
+
+func greenFlagClear(msg RaceControl) bool {
+	text := upperText(string(msg.Flag), msg.Message)
+	return strings.Contains(text, "GREEN")
+}
+
+func flagTitle(kind string, startLap, endLap int) string {
+	name := "Flag period"
+	switch kind {
+	case KindSafetyCar:
+		name = "Safety Car"
+	case KindVirtualSafetyCar:
+		name = "Virtual Safety Car"
+	case KindRedFlag:
+		name = "Red Flag"
+	}
+	return fmt.Sprintf("%s (L%d-L%d)", name, startLap, endLap)
+}
+
+func detectPitPhases(laps []Lap, idx lapIndex) []Chapter {
+	type pitOut struct {
+		lap    int
+		driver int
+	}
+	var stops []pitOut
+	for _, l := range laps {
+		if l.IsPitOutLap && l.LapNumber > 0 {
+			stops = append(stops, pitOut{lap: l.LapNumber, driver: l.DriverNumber})
+		}
+	}
+	if len(stops) < minPitPhaseStops {
+		return nil
+	}
+	sort.Slice(stops, func(i, j int) bool {
+		if stops[i].lap == stops[j].lap {
+			return stops[i].driver < stops[j].driver
+		}
+		return stops[i].lap < stops[j].lap
+	})
+	needed := int(math.Ceil(float64(len(stops)) * pitPhaseShare))
+	if needed < minPitPhaseStops {
+		needed = minPitPhaseStops
+	}
+
+	var windows []Chapter
+	for i := 0; i < len(stops); i++ {
+		start := stops[i].lap
+		end := start + pitPhaseWindowLaps - 1
+		drivers := map[int]bool{}
+		count := 0
+		for _, stop := range stops {
+			if stop.lap < start || stop.lap > end {
+				continue
+			}
+			count++
+			drivers[stop.driver] = true
+		}
+		if count < needed {
+			continue
+		}
+		ch := Chapter{
+			Kind:          KindPitPhase,
+			Title:         fmt.Sprintf("Pit phase (L%d-L%d)", start, end),
+			StartLap:      start,
+			EndLap:        end,
+			StartTime:     idx.lapStart(start),
+			EndTime:       idx.lapEnd(end),
+			DriverNumbers: sortedDriverNumbers(drivers),
+		}
+		if len(windows) > 0 && ch.StartLap <= windows[len(windows)-1].EndLap+1 {
+			last := &windows[len(windows)-1]
+			if ch.EndLap > last.EndLap {
+				last.EndLap = ch.EndLap
+				last.EndTime = idx.lapEnd(last.EndLap)
+			}
+			drivers := sliceToSet(last.DriverNumbers)
+			for _, driver := range ch.DriverNumbers {
+				drivers[driver] = true
+			}
+			last.DriverNumbers = sortedDriverNumbers(drivers)
+			last.Title = fmt.Sprintf("Pit phase (L%d-L%d)", last.StartLap, last.EndLap)
+			continue
+		}
+		windows = append(windows, ch)
+	}
+	return windows
+}
+
+type swingCandidate struct {
+	chapter      Chapter
+	significance int
+}
+
+func detectDecisiveSwings(positions []PositionSample, idx lapIndex, totalLaps int) []Chapter {
+	if len(positions) == 0 || len(idx.events) == 0 || totalLaps <= decisiveAfterLap {
+		return nil
+	}
+	snapshots := buildPositionSnapshots(positions, idx, totalLaps)
+	if len(snapshots) == 0 {
+		return nil
+	}
+	final := snapshots[totalLaps]
+	if len(final) == 0 {
+		for lap := totalLaps - 1; lap >= 1; lap-- {
+			if len(snapshots[lap]) > 0 {
+				final = snapshots[lap]
+				break
+			}
+		}
+	}
+	var candidates []swingCandidate
+	seenDriver := map[int]bool{}
+	for lap := decisiveAfterLap + 1; lap <= totalLaps; lap++ {
+		prev := snapshots[lap-1]
+		curr := snapshots[lap]
+		if len(prev) == 0 || len(curr) == 0 {
+			continue
+		}
+		for driver, pos := range curr {
+			prevPos, ok := prev[driver]
+			if !ok || prevPos <= pos || pos > 5 || pos <= 0 || seenDriver[driver] {
+				continue
+			}
+			finalPos, ok := final[driver]
+			if !ok || finalPos > pos {
+				continue
+			}
+			overtaken := driverAtPosition(curr, prevPos, driver)
+			drivers := []int{driver}
+			if overtaken != 0 {
+				drivers = append(drivers, overtaken)
+			}
+			candidates = append(candidates, swingCandidate{
+				chapter: Chapter{
+					Kind:          KindDecisiveSwing,
+					Title:         fmt.Sprintf("Decisive swing: #%d to P%d (L%d)", driver, pos, lap),
+					StartLap:      lap,
+					EndLap:        lap,
+					StartTime:     idx.lapStart(lap),
+					EndTime:       idx.lapEnd(lap),
+					DriverNumbers: drivers,
+				},
+				significance: (prevPos-pos)*10 + (6 - pos),
+			})
+			seenDriver[driver] = true
+		}
+	}
+	sort.Slice(candidates, func(i, j int) bool {
+		if candidates[i].significance == candidates[j].significance {
+			return candidates[i].chapter.StartLap < candidates[j].chapter.StartLap
+		}
+		return candidates[i].significance > candidates[j].significance
+	})
+	if len(candidates) > maxDecisiveSwings {
+		candidates = candidates[:maxDecisiveSwings]
+	}
+	out := make([]Chapter, 0, len(candidates))
+	for _, c := range candidates {
+		out = append(out, c.chapter)
+	}
+	return out
+}
+
+func buildPositionSnapshots(positions []PositionSample, idx lapIndex, totalLaps int) map[int]map[int]int {
+	byLap := map[int][]PositionSample{}
+	for _, p := range positions {
+		if p.Position <= 0 {
+			continue
+		}
+		lap := idx.lapForTime(p.Date)
+		if lap <= 0 || lap > totalLaps {
+			continue
+		}
+		byLap[lap] = append(byLap[lap], p)
+	}
+	last := map[int]int{}
+	snapshots := map[int]map[int]int{}
+	for lap := 1; lap <= totalLaps; lap++ {
+		for _, p := range byLap[lap] {
+			last[p.DriverNumber] = p.Position
+		}
+		if len(last) == 0 {
+			continue
+		}
+		cp := make(map[int]int, len(last))
+		for driver, pos := range last {
+			cp[driver] = pos
+		}
+		snapshots[lap] = cp
+	}
+	return snapshots
+}
+
+func driverAtPosition(snapshot map[int]int, pos int, exclude int) int {
+	for driver, driverPos := range snapshot {
+		if driver != exclude && driverPos == pos {
+			return driver
+		}
+	}
+	return 0
+}
+
+func detectFinish(rc []RaceControl, idx lapIndex, totalLaps int) Chapter {
+	finishLap := totalLaps
+	finishTime := idx.lapEnd(totalLaps)
+	for _, msg := range rc {
+		text := upperText(string(msg.Flag), msg.Message)
+		if strings.Contains(text, "CHEQUER") || string(msg.Flag) == string(models.FlagChequered) {
+			if lap := messageLap(msg, idx); lap > 0 {
+				finishLap = lap
+			}
+			finishTime = firstNonEmpty(msg.Date, finishTime)
+		}
+	}
+	startLap := finishLap - 1
+	if startLap < 1 {
+		startLap = 1
+	}
+	return Chapter{
+		Kind:      KindFinish,
+		Title:     fmt.Sprintf("Finish (L%d-L%d)", startLap, finishLap),
+		StartLap:  startLap,
+		EndLap:    finishLap,
+		StartTime: idx.lapStart(startLap),
+		EndTime:   finishTime,
+	}
+}
+
+func resolveConflicts(chapters []Chapter) []Chapter {
+	normalized := make([]Chapter, 0, len(chapters))
+	for _, ch := range chapters {
+		if ch.StartLap <= 0 {
+			ch.StartLap = 1
+		}
+		if ch.EndLap <= 0 {
+			ch.EndLap = ch.StartLap
+		}
+		if ch.EndLap < ch.StartLap {
+			ch.EndLap = ch.StartLap
+		}
+		if ch.DriverNumbers == nil {
+			ch.DriverNumbers = []int{}
+		}
+		normalized = append(normalized, ch)
+	}
+	sort.SliceStable(normalized, func(i, j int) bool {
+		if normalized[i].StartLap == normalized[j].StartLap {
+			return priority(normalized[i].Kind) > priority(normalized[j].Kind)
+		}
+		return normalized[i].StartLap < normalized[j].StartLap
+	})
+
+	out := make([]Chapter, 0, len(normalized))
+	for _, ch := range normalized {
+		if len(out) == 0 {
+			out = append(out, ch)
+			continue
+		}
+		last := &out[len(out)-1]
+		if ch.StartLap > last.EndLap {
+			out = append(out, ch)
+			continue
+		}
+		if isFlag(last.Kind) && priority(ch.Kind) < priority(last.Kind) {
+			continue
+		}
+		if priority(ch.Kind) > priority(last.Kind) {
+			if last.StartLap < ch.StartLap {
+				last.EndLap = ch.StartLap - 1
+				out = append(out, ch)
+			} else {
+				*last = ch
+			}
+			continue
+		}
+		if ch.EndLap > last.EndLap {
+			ch.StartLap = last.EndLap + 1
+			if ch.StartLap <= ch.EndLap {
+				out = append(out, ch)
+			}
+		}
+	}
+	return out
+}
+
+func isFlag(kind string) bool {
+	return kind == KindSafetyCar || kind == KindVirtualSafetyCar || kind == KindRedFlag
+}
+
+func priority(kind string) int {
+	switch kind {
+	case KindStart, KindFinish:
+		return structuralPriority
+	case KindSafetyCar, KindVirtualSafetyCar, KindRedFlag:
+		return flagPriority
+	case KindPitPhase:
+		return pitPhasePriority
+	case KindDecisiveSwing:
+		return decisivePriority
+	default:
+		return 0
+	}
+}
+
+func messageLap(msg RaceControl, idx lapIndex) int {
+	if msg.LapNumber != nil && *msg.LapNumber > 0 {
+		return *msg.LapNumber
+	}
+	return idx.lapForTime(msg.Date)
+}
+
+func clampLap(lap, minLap, maxLap int) int {
+	if lap < minLap {
+		return minLap
+	}
+	if maxLap > 0 && lap > maxLap {
+		return maxLap
+	}
+	return lap
+}
+
+func parseTime(raw string) (time.Time, bool) {
+	if raw == "" {
+		return time.Time{}, false
+	}
+	at, err := time.Parse(time.RFC3339, raw)
+	if err != nil {
+		return time.Time{}, false
+	}
+	return at, true
+}
+
+func upperText(parts ...string) string {
+	return strings.ToUpper(strings.Join(parts, " "))
+}
+
+func firstNonEmpty(values ...string) string {
+	for _, value := range values {
+		if value != "" {
+			return value
+		}
+	}
+	return ""
+}
+
+func sortedDriverNumbers(drivers map[int]bool) []int {
+	out := make([]int, 0, len(drivers))
+	for driver := range drivers {
+		out = append(out, driver)
+	}
+	sort.Ints(out)
+	return out
+}
+
+func sliceToSet(values []int) map[int]bool {
+	out := make(map[int]bool, len(values))
+	for _, value := range values {
+		out[value] = true
+	}
+	return out
+}
+
+func minInt(a, b int) int {
+	if a < b {
+		return a
+	}
+	return b
+}
--- a/internal/chapters/chapters_test.go
+++ b/internal/chapters/chapters_test.go
@@ -0,0 +1,218 @@
+package chapters
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/AmanTahiliani/box-box/internal/models"
+)
+
+func TestDetectStructuralChapters(t *testing.T) {
+	chapters := Detect(nil, nil, testLaps(10, nil), 10)
+
+	if len(chapters) < 2 {
+		t.Fatalf("chapters len = %d, want at least start and finish", len(chapters))
+	}
+	if got := chapters[0]; got.Kind != KindStart || got.StartLap != 1 || got.EndLap != 1 {
+		t.Fatalf("start chapter = %+v, want L1-L1", got)
+	}
+	got := chapters[len(chapters)-1]
+	if got.Kind != KindFinish || got.StartLap != 9 || got.EndLap != 10 {
+		t.Fatalf("finish chapter = %+v, want L9-L10", got)
+	}
+}
+
+func TestDetectReturnsEmptyWithoutData(t *testing.T) {
+	if chapters := Detect(nil, nil, nil, 0); len(chapters) != 0 {
+		t.Fatalf("chapters = %+v, want empty", chapters)
+	}
+}
+
+func TestDetectFlagPeriods(t *testing.T) {
+	tests := []struct {
+		name      string
+		start     RaceControl
+		end       RaceControl
+		wantKind  string
+		wantTitle string
+	}{
+		{
+			name:      "safety car",
+			start:     rc(12, models.CategorySafetyCar, "", "SAFETY CAR DEPLOYED"),
+			end:       rc(15, models.CategorySafetyCar, "", "SAFETY CAR IN THIS LAP"),
+			wantKind:  KindSafetyCar,
+			wantTitle: "Safety Car (L12-L15)",
+		},
+		{
+			name:      "virtual safety car",
+			start:     rc(22, models.CategoryOther, "", "VSC DEPLOYED"),
+			end:       rc(24, models.CategoryOther, "", "VSC ENDING"),
+			wantKind:  KindVirtualSafetyCar,
+			wantTitle: "Virtual Safety Car (L22-L24)",
+		},
+		{
+			name:      "red flag",
+			start:     rc(31, models.CategoryFlag, models.FlagRed, "RED FLAG"),
+			end:       rc(33, models.CategoryFlag, models.FlagGreen, "GREEN FLAG"),
+			wantKind:  KindRedFlag,
+			wantTitle: "Red Flag (L31-L33)",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			chapters := Detect([]RaceControl{tt.start, tt.end}, nil, testLaps(40, nil), 40)
+			got := findKind(chapters, tt.wantKind)
+			if got == nil {
+				t.Fatalf("chapters = %+v, want %s", chapters, tt.wantKind)
+			}
+			if got.StartLap != rcLap(tt.start) || got.EndLap != rcLap(tt.end) || got.Title != tt.wantTitle {
+				t.Fatalf("flag chapter = %+v, want %s", *got, tt.wantTitle)
+			}
+		})
+	}
+}
+
+func TestDetectPitPhaseFromPitOutLapCluster(t *testing.T) {
+	pitOuts := map[int][]int{
+		5:  {1},
+		10: {2},
+		20: {3},
+		21: {4},
+		22: {5},
+		30: {6},
+		35: {7},
+		40: {8},
+		45: {9},
+		50: {10},
+	}
+	chapters := Detect(nil, nil, testLaps(55, pitOuts), 55)
+
+	got := findKind(chapters, KindPitPhase)
+	if got == nil {
+		t.Fatalf("chapters = %+v, want pit phase", chapters)
+	}
+	if got.StartLap != 20 || got.EndLap != 22 {
+		t.Fatalf("pit phase = %+v, want L20-L22", *got)
+	}
+	if len(got.DriverNumbers) != 3 || got.DriverNumbers[0] != 3 || got.DriverNumbers[2] != 5 {
+		t.Fatalf("pit phase drivers = %v, want [3 4 5]", got.DriverNumbers)
+	}
+}
+
+func TestDetectDecisiveSwingPersistsToFinish(t *testing.T) {
+	positions := []PositionSample{
+		pos(1, 1, 1),
+		pos(1, 16, 4),
+		pos(1, 55, 3),
+		pos(6, 16, 3),
+		pos(6, 55, 4),
+		pos(8, 44, 5),
+		pos(8, 63, 6),
+		pos(10, 44, 6),
+	}
+
+	chapters := Detect(nil, positions, testLaps(12, nil), 12)
+	got := findKind(chapters, KindDecisiveSwing)
+	if got == nil {
+		t.Fatalf("chapters = %+v, want decisive swing", chapters)
+	}
+	if got.StartLap != 6 || got.EndLap != 6 {
+		t.Fatalf("swing lap = %+v, want L6", *got)
+	}
+	if len(got.DriverNumbers) != 2 || got.DriverNumbers[0] != 16 || got.DriverNumbers[1] != 55 {
+		t.Fatalf("swing drivers = %v, want [16 55]", got.DriverNumbers)
+	}
+}
+
+func TestDetectFlagPeriodsWinOverConflictingChapters(t *testing.T) {
+	pitOuts := map[int][]int{
+		12: {1, 2},
+		13: {3, 4},
+		14: {5, 6},
+	}
+	rcs := []RaceControl{
+		rc(12, models.CategorySafetyCar, "", "SAFETY CAR DEPLOYED"),
+		rc(15, models.CategorySafetyCar, "", "SAFETY CAR IN THIS LAP"),
+	}
+
+	chapters := Detect(rcs, nil, testLaps(20, pitOuts), 20)
+	if got := findKind(chapters, KindSafetyCar); got == nil || got.StartLap != 12 || got.EndLap != 15 {
+		t.Fatalf("chapters = %+v, want safety car L12-L15", chapters)
+	}
+	if got := findKind(chapters, KindPitPhase); got != nil {
+		t.Fatalf("pit phase = %+v, want omitted under safety car", *got)
+	}
+	for i := 1; i < len(chapters); i++ {
+		if chapters[i].StartLap <= chapters[i-1].EndLap {
+			t.Fatalf("chapters overlap at %d: %+v then %+v", i, chapters[i-1], chapters[i])
+		}
+	}
+}
+
+func rcLap(r RaceControl) int {
+	if r.LapNumber == nil {
+		return 0
+	}
+	return *r.LapNumber
+}
+
+func findKind(chapters []Chapter, kind string) *Chapter {
+	for i := range chapters {
+		if chapters[i].Kind == kind {
+			return &chapters[i]
+		}
+	}
+	return nil
+}
+
+func testLaps(total int, pitOuts map[int][]int) []Lap {
+	var laps []Lap
+	for lap := 1; lap <= total; lap++ {
+		drivers := []int{1}
+		if pitDrivers := pitOuts[lap]; len(pitDrivers) > 0 {
+			drivers = pitDrivers
+		}
+		for _, driver := range drivers {
+			laps = append(laps, Lap{
+				DriverNumber: driver,
+				LapNumber:    lap,
+				DateStart:    lapTime(lap),
+				IsPitOutLap:  containsDriver(pitOuts[lap], driver),
+			})
+		}
+	}
+	return laps
+}
+
+func rc(lap int, category models.RaceControlCategory, flag models.Flag, message string) RaceControl {
+	return RaceControl{
+		Category:  category,
+		Flag:      flag,
+		Message:   message,
+		LapNumber: &lap,
+		Date:      lapTime(lap),
+	}
+}
+
+func pos(lap int, driver int, position int) PositionSample {
+	return PositionSample{
+		DriverNumber: driver,
+		Position:     position,
+		Date:         lapTime(lap),
+	}
+}
+
+func lapTime(lap int) string {
+	minute := lap - 1
+	return fmt.Sprintf("2025-05-25T13:%02d:00Z", minute)
+}
+
+func containsDriver(drivers []int, driver int) bool {
+	for _, candidate := range drivers {
+		if candidate == driver {
+			return true
+		}
+	}
+	return false
+}
--- a/internal/query/racehub.go
+++ b/internal/query/racehub.go
@@ -4,6 +4,7 @@ import (
 	"database/sql"
 	"errors"

+	"github.com/AmanTahiliani/box-box/internal/chapters"
 	"github.com/AmanTahiliani/box-box/internal/models"
 	"github.com/AmanTahiliani/box-box/internal/store"
 )
@@ -52,6 +53,7 @@ type RaceHub struct {
 	RaceControl  []models.RaceControl   `json:"race_control"`
 	Weather      []models.Weather       `json:"weather"`
 	Laps         []models.Lap           `json:"laps"`
+	Chapters     []chapters.Chapter     `json:"chapters"`
 }

 // GetRaceHub loads ingested Race Hub datasets for a session from the local store.
@@ -80,6 +82,7 @@ func (s *Service) GetRaceHub(sessionKey int) (RaceHub, error) {
 		RaceControl:  []models.RaceControl{},
 		Weather:      []models.Weather{},
 		Laps:         []models.Lap{},
+		Chapters:     []chapters.Chapter{},
 	}

 	sess, err := s.store.GetSession(sessionKey)
@@ -248,6 +251,22 @@ func (s *Service) GetRaceHub(sessionKey int) (RaceHub, error) {
 		hub.Datasets["laps"] = availableLocal(len(hub.Laps))
 	}

+	hub.Chapters = chapters.Detect(hub.RaceControl, hub.Positions, hub.Laps, totalLaps(hub.Results, hub.Laps))
 	hub.Source = responseSource(hub.Datasets)
 	return hub, nil
 }
+
+func totalLaps(results []EnrichedResult, laps []models.Lap) int {
+	total := 0
+	for _, result := range results {
+		if result.NumberOfLaps > total {
+			total = result.NumberOfLaps
+		}
+	}
+	for _, lap := range laps {
+		if lap.LapNumber > total {
+			total = lap.LapNumber
+		}
+	}
+	return total
+}
--- a/internal/web/racehub.go
+++ b/internal/web/racehub.go
@@ -4,6 +4,7 @@ import (
 	"net/http"
 	"strconv"

+	"github.com/AmanTahiliani/box-box/internal/chapters"
 	"github.com/AmanTahiliani/box-box/internal/models"
 	"github.com/AmanTahiliani/box-box/internal/query"
 )
@@ -42,5 +43,6 @@ func emptyRaceHub(sessionKey int) query.RaceHub {
 		Drivers:      []models.Driver{},
 		Results:      []query.EnrichedResult{},
 		StartingGrid: []query.EnrichedGrid{},
+		Chapters:     []chapters.Chapter{},
 	}
 }
--- a/internal/web/racehub_test.go
+++ b/internal/web/racehub_test.go
@@ -119,6 +119,66 @@ func TestHandleRaceHubWithLocalData(t *testing.T) {
 	}
 }

+func TestHandleRaceHubIncludesChapters(t *testing.T) {
+	st := openTestStore(t)
+	seedRaceHubStore(t, st)
+	sessionKey := 9472
+	meetingKey := 1229
+
+	for lap := 1; lap <= 12; lap++ {
+		if err := st.UpsertLap(store.Lap{
+			SessionKey:   sessionKey,
+			DriverNumber: 1,
+			MeetingKey:   meetingKey,
+			LapNumber:    lap,
+			DateStart:    time.Date(2025, 5, 25, 13, lap-1, 0, 0, time.UTC).Format(time.RFC3339),
+			LapDuration:  75,
+		}); err != nil {
+			t.Fatalf("UpsertLap(%d) error = %v", lap, err)
+		}
+	}
+	for _, sample := range []store.PositionSample{
+		{SessionKey: sessionKey, DriverNumber: 1, MeetingKey: meetingKey, Date: "2025-05-25T13:00:00Z", Position: 1},
+		{SessionKey: sessionKey, DriverNumber: 16, MeetingKey: meetingKey, Date: "2025-05-25T13:00:00Z", Position: 4},
+		{SessionKey: sessionKey, DriverNumber: 55, MeetingKey: meetingKey, Date: "2025-05-25T13:00:00Z", Position: 3},
+		{SessionKey: sessionKey, DriverNumber: 16, MeetingKey: meetingKey, Date: "2025-05-25T13:05:00Z", Position: 3},
+		{SessionKey: sessionKey, DriverNumber: 55, MeetingKey: meetingKey, Date: "2025-05-25T13:05:00Z", Position: 4},
+	} {
+		if err := st.UpsertPositionSample(sample); err != nil {
+			t.Fatalf("UpsertPositionSample() error = %v", err)
+		}
+	}
+
+	srv := testServer(t, st)
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/race-hub?session_key=9472", nil)
+	rec := httptest.NewRecorder()
+	srv.handleRaceHub(rec, req)
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status = %d, want 200", rec.Code)
+	}
+
+	var hub query.RaceHub
+	if err := json.Unmarshal(rec.Body.Bytes(), &hub); err != nil {
+		t.Fatalf("decode response: %v", err)
+	}
+	if len(hub.Chapters) == 0 {
+		t.Fatalf("chapters = %+v, want generated chapters", hub.Chapters)
+	}
+	if hub.Chapters[0].Kind != "start" {
+		t.Fatalf("first chapter = %+v, want start", hub.Chapters[0])
+	}
+	foundSwing := false
+	for _, chapter := range hub.Chapters {
+		if chapter.Kind == "decisive_swing" {
+			foundSwing = true
+		}
+	}
+	if !foundSwing {
+		t.Fatalf("chapters = %+v, want decisive_swing", hub.Chapters)
+	}
+}
+
 func TestHandleMeetingsSourceLocal(t *testing.T) {
 	st := openTestStore(t)
 	seedRaceHubStore(t, st)
--- a/internal/web/replay.go
+++ b/internal/web/replay.go
@@ -0,0 +1,259 @@
+package web
+
+import (
+	"context"
+	"errors"
+	"math"
+	"net/http"
+	"sort"
+	"strconv"
+	"sync"
+	"time"
+
+	"github.com/AmanTahiliani/box-box/internal/models"
+)
+
+const (
+	defaultReplayIntervalMS = 5000
+	maxReplayFrames         = 3000
+	replayFetchConcurrency  = 4
+)
+
+type replayDataClient interface {
+	GetDriversForSession(sessionKey int) ([]models.Driver, error)
+	GetLocation(sessionKey, driverNumber int) ([]models.Location, error)
+}
+
+type replayFramesResponse struct {
+	SessionKey int           `json:"session_key"`
+	Interval   int           `json:"interval_ms"`
+	StartTime  string        `json:"start_time"`
+	Frames     []replayFrame `json:"frames"`
+}
+
+type replayFrame struct {
+	T    int64                `json:"t"`
+	Cars map[string]replayCar `json:"cars"`
+}
+
+type replayCar struct {
+	X float64 `json:"x"`
+	Y float64 `json:"y"`
+}
+
+func (s *Server) handleReplayFrames(w http.ResponseWriter, r *http.Request) {
+	sessionKey, err := strconv.Atoi(r.URL.Query().Get("session_key"))
+	if err != nil || sessionKey == 0 {
+		http.Error(w, "session_key required", http.StatusBadRequest)
+		return
+	}
+
+	intervalMS := defaultReplayIntervalMS
+	rawInterval := r.URL.Query().Get("interval_ms")
+	if rawInterval != "" {
+		parsed, err := strconv.Atoi(rawInterval)
+		if err != nil {
+			http.Error(w, "invalid interval_ms", http.StatusBadRequest)
+			return
+		}
+		if parsed > intervalMS {
+			intervalMS = parsed
+		}
+	}
+
+	resp, err := assembleReplayFrames(r.Context(), s.client, sessionKey, intervalMS)
+	if err != nil {
+		writeError(w, err, http.StatusInternalServerError, s.client.LastResponseWasStale())
+		return
+	}
+	writeJSON(w, resp)
+}
+
+func assembleReplayFrames(ctx context.Context, client replayDataClient, sessionKey, intervalMS int) (replayFramesResponse, error) {
+	if intervalMS < defaultReplayIntervalMS {
+		intervalMS = defaultReplayIntervalMS
+	}
+
+	resp := replayFramesResponse{
+		SessionKey: sessionKey,
+		Interval:   intervalMS,
+		Frames:     []replayFrame{},
+	}
+
+	drivers, err := client.GetDriversForSession(sessionKey)
+	if err != nil {
+		return resp, err
+	}
+
+	driverNumbers := uniqueDriverNumbers(drivers)
+	if len(driverNumbers) == 0 {
+		return resp, nil
+	}
+
+	series, err := fetchReplayLocationSeries(ctx, client, sessionKey, driverNumbers)
+	if err != nil && len(series) == 0 {
+		return resp, err
+	}
+
+	start, ok := earliestReplayLocationTime(series)
+	if !ok {
+		return resp, nil
+	}
+	resp.StartTime = start.Format(time.RFC3339Nano)
+	resp.Frames = snapReplayFrames(series, start, intervalMS)
+	return resp, nil
+}
+
+func uniqueDriverNumbers(drivers []models.Driver) []int {
+	seen := make(map[int]bool, len(drivers))
+	numbers := make([]int, 0, len(drivers))
+	for _, driver := range drivers {
+		if driver.DriverNumber <= 0 || seen[driver.DriverNumber] {
+			continue
+		}
+		seen[driver.DriverNumber] = true
+		numbers = append(numbers, driver.DriverNumber)
+	}
+	sort.Ints(numbers)
+	return numbers
+}
+
+func fetchReplayLocationSeries(ctx context.Context, client replayDataClient, sessionKey int, driverNumbers []int) (map[int][]models.Location, error) {
+	type result struct {
+		driver int
+		locs   []models.Location
+		err    error
+	}
+
+	sem := make(chan struct{}, replayFetchConcurrency)
+	results := make(chan result, len(driverNumbers))
+	var wg sync.WaitGroup
+
+	for _, driverNumber := range driverNumbers {
+		driverNumber := driverNumber
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			select {
+			case sem <- struct{}{}:
+				defer func() { <-sem }()
+			case <-ctx.Done():
+				results <- result{driver: driverNumber, err: ctx.Err()}
+				return
+			}
+
+			locs, err := client.GetLocation(sessionKey, driverNumber)
+			results <- result{driver: driverNumber, locs: locs, err: err}
+		}()
+	}
+
+	wg.Wait()
+	close(results)
+
+	series := make(map[int][]models.Location, len(driverNumbers))
+	var joined error
+	for result := range results {
+		if result.err != nil {
+			joined = errors.Join(joined, result.err)
+			continue
+		}
+		if len(result.locs) > 0 {
+			series[result.driver] = result.locs
+		}
+	}
+	return series, joined
+}
+
+func earliestReplayLocationTime(series map[int][]models.Location) (time.Time, bool) {
+	var start time.Time
+	for _, locs := range series {
+		for _, loc := range locs {
+			t, err := time.Parse(time.RFC3339Nano, loc.Date)
+			if err != nil {
+				continue
+			}
+			if start.IsZero() || t.Before(start) {
+				start = t
+			}
+		}
+	}
+	if start.IsZero() {
+		return time.Time{}, false
+	}
+	return start, true
+}
+
+func snapReplayFrames(series map[int][]models.Location, start time.Time, intervalMS int) []replayFrame {
+	type accumulator struct {
+		t       int64
+		cars    map[string]replayCar
+		nearest map[string]int64
+	}
+
+	interval := int64(intervalMS)
+	framesByIndex := make(map[int]*accumulator)
+
+	for driverNumber, locs := range series {
+		driverKey := strconv.Itoa(driverNumber)
+		for _, loc := range locs {
+			if !isFiniteFloat(loc.X) || !isFiniteFloat(loc.Y) {
+				continue
+			}
+			t, err := time.Parse(time.RFC3339Nano, loc.Date)
+			if err != nil {
+				continue
+			}
+			offset := t.Sub(start).Milliseconds()
+			if offset < 0 {
+				continue
+			}
+			index := int((offset + interval/2) / interval)
+			if index < 0 || index >= maxReplayFrames {
+				continue
+			}
+			frameT := int64(index) * interval
+			distance := absInt64(offset - frameT)
+
+			acc, ok := framesByIndex[index]
+			if !ok {
+				acc = &accumulator{
+					t:       frameT,
+					cars:    make(map[string]replayCar),
+					nearest: make(map[string]int64),
+				}
+				framesByIndex[index] = acc
+			}
+			if prev, ok := acc.nearest[driverKey]; ok && prev <= distance {
+				continue
+			}
+			acc.nearest[driverKey] = distance
+			acc.cars[driverKey] = replayCar{X: loc.X, Y: loc.Y}
+		}
+	}
+
+	indexes := make([]int, 0, len(framesByIndex))
+	for index, acc := range framesByIndex {
+		if len(acc.cars) > 0 {
+			indexes = append(indexes, index)
+		}
+	}
+	sort.Ints(indexes)
+
+	frames := make([]replayFrame, 0, len(indexes))
+	for _, index := range indexes {
+		acc := framesByIndex[index]
+		frames = append(frames, replayFrame{T: acc.t, Cars: acc.cars})
+	}
+	return frames
+}
+
+func absInt64(v int64) int64 {
+	if v < 0 {
+		return -v
+	}
+	return v
+}
+
+func isFiniteFloat(v float64) bool {
+	return !math.IsNaN(v) && !math.IsInf(v, 0)
+}
--- a/internal/web/replay_test.go
+++ b/internal/web/replay_test.go
@@ -0,0 +1,181 @@
+package web
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/AmanTahiliani/box-box/internal/models"
+)
+
+type fakeReplayClient struct {
+	drivers []models.Driver
+	locs    map[int][]models.Location
+	err     error
+
+	mu          sync.Mutex
+	inFlight    int
+	maxInFlight int
+	delay       time.Duration
+}
+
+func (f *fakeReplayClient) GetDriversForSession(sessionKey int) ([]models.Driver, error) {
+	if f.err != nil {
+		return nil, f.err
+	}
+	return f.drivers, nil
+}
+
+func (f *fakeReplayClient) GetLocation(sessionKey, driverNumber int) ([]models.Location, error) {
+	f.mu.Lock()
+	f.inFlight++
+	if f.inFlight > f.maxInFlight {
+		f.maxInFlight = f.inFlight
+	}
+	f.mu.Unlock()
+
+	if f.delay > 0 {
+		time.Sleep(f.delay)
+	}
+
+	f.mu.Lock()
+	f.inFlight--
+	f.mu.Unlock()
+
+	return f.locs[driverNumber], nil
+}
+
+func TestAssembleReplayFramesSnapsNearestSamplesAndOmitsEmptyDrivers(t *testing.T) {
+	start := time.Date(2025, 5, 25, 13, 0, 0, 0, time.UTC)
+	client := &fakeReplayClient{
+		drivers: []models.Driver{
+			{DriverNumber: 1},
+			{DriverNumber: 4},
+			{DriverNumber: 16},
+		},
+		locs: map[int][]models.Location{
+			1: {
+				{Date: start.Add(1 * time.Second).Format(time.RFC3339Nano), X: 10, Y: 20},
+				{Date: start.Add(4 * time.Second).Format(time.RFC3339Nano), X: 40, Y: 80},
+				{Date: start.Add(6 * time.Second).Format(time.RFC3339Nano), X: 60, Y: 120},
+			},
+			4: {
+				{Date: start.Add(5 * time.Second).Format(time.RFC3339Nano), X: 100, Y: 200},
+			},
+			16: {},
+		},
+	}
+
+	resp, err := assembleReplayFrames(context.Background(), client, 99, 5000)
+	if err != nil {
+		t.Fatalf("assembleReplayFrames() error = %v", err)
+	}
+	if resp.SessionKey != 99 || resp.Interval != 5000 {
+		t.Fatalf("response metadata = %+v", resp)
+	}
+	if resp.StartTime != start.Add(1*time.Second).Format(time.RFC3339Nano) {
+		t.Fatalf("start_time = %q", resp.StartTime)
+	}
+	if len(resp.Frames) != 2 {
+		t.Fatalf("frames len = %d, want 2: %+v", len(resp.Frames), resp.Frames)
+	}
+	if _, ok := resp.Frames[0].Cars["16"]; ok {
+		t.Fatalf("empty driver included in frame: %+v", resp.Frames[0].Cars)
+	}
+	if got := resp.Frames[0].Cars["1"]; got.X != 10 || got.Y != 20 {
+		t.Fatalf("frame 0 car 1 = %+v, want first nearest sample", got)
+	}
+	if got := resp.Frames[1].Cars["1"]; got.X != 60 || got.Y != 120 {
+		t.Fatalf("frame 1 car 1 = %+v, want later nearest sample", got)
+	}
+	if got := resp.Frames[1].Cars["4"]; got.X != 100 || got.Y != 200 {
+		t.Fatalf("frame 1 car 4 = %+v", got)
+	}
+}
+
+func TestAssembleReplayFramesCapsFrameCount(t *testing.T) {
+	start := time.Date(2025, 5, 25, 13, 0, 0, 0, time.UTC)
+	locs := make([]models.Location, maxReplayFrames+250)
+	for i := range locs {
+		locs[i] = models.Location{
+			Date: start.Add(time.Duration(i*defaultReplayIntervalMS) * time.Millisecond).Format(time.RFC3339Nano),
+			X:    float64(i),
+			Y:    float64(i * 2),
+		}
+	}
+	client := &fakeReplayClient{
+		drivers: []models.Driver{{DriverNumber: 1}},
+		locs:    map[int][]models.Location{1: locs},
+	}
+
+	resp, err := assembleReplayFrames(context.Background(), client, 99, defaultReplayIntervalMS)
+	if err != nil {
+		t.Fatalf("assembleReplayFrames() error = %v", err)
+	}
+	if len(resp.Frames) > maxReplayFrames {
+		t.Fatalf("frames len = %d, want <= %d", len(resp.Frames), maxReplayFrames)
+	}
+	if len(resp.Frames) != maxReplayFrames {
+		t.Fatalf("frames len = %d, want hard cap %d", len(resp.Frames), maxReplayFrames)
+	}
+}
+
+func TestAssembleReplayFramesBoundsLocationFanOut(t *testing.T) {
+	drivers := make([]models.Driver, 10)
+	locs := make(map[int][]models.Location, len(drivers))
+	now := time.Date(2025, 5, 25, 13, 0, 0, 0, time.UTC)
+	for i := range drivers {
+		number := i + 1
+		drivers[i] = models.Driver{DriverNumber: number}
+		locs[number] = []models.Location{{Date: now.Format(time.RFC3339Nano), X: float64(number), Y: float64(number)}}
+	}
+	client := &fakeReplayClient{
+		drivers: drivers,
+		locs:    locs,
+		delay:   5 * time.Millisecond,
+	}
+
+	if _, err := assembleReplayFrames(context.Background(), client, 99, defaultReplayIntervalMS); err != nil {
+		t.Fatalf("assembleReplayFrames() error = %v", err)
+	}
+	if client.maxInFlight > replayFetchConcurrency {
+		t.Fatalf("max in-flight location calls = %d, want <= %d", client.maxInFlight, replayFetchConcurrency)
+	}
+}
+
+func TestHandleReplayFramesValidatesParamsAndFloorsInterval(t *testing.T) {
+	srv := testServer(t, nil)
+
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/replay/frames", nil)
+	rec := httptest.NewRecorder()
+	srv.handleReplayFrames(rec, req)
+	if rec.Code != http.StatusBadRequest {
+		t.Fatalf("missing session_key status = %d, want 400", rec.Code)
+	}
+
+	req = httptest.NewRequest(http.MethodGet, "/api/v1/replay/frames?session_key=1&interval_ms=nope", nil)
+	rec = httptest.NewRecorder()
+	srv.handleReplayFrames(rec, req)
+	if rec.Code != http.StatusBadRequest {
+		t.Fatalf("invalid interval status = %d, want 400", rec.Code)
+	}
+
+	client := &fakeReplayClient{drivers: []models.Driver{{DriverNumber: 1}}, locs: map[int][]models.Location{
+		1: {{Date: time.Date(2025, 5, 25, 13, 0, 0, 0, time.UTC).Format(time.RFC3339Nano), X: 1, Y: 2}},
+	}}
+	resp, err := assembleReplayFrames(context.Background(), client, 99, 1000)
+	if err != nil {
+		t.Fatalf("assembleReplayFrames() error = %v", err)
+	}
+	body, err := json.Marshal(resp)
+	if err != nil || len(body) == 0 {
+		t.Fatalf("marshal response = %d bytes, %v", len(body), err)
+	}
+	if resp.Interval != defaultReplayIntervalMS {
+		t.Fatalf("interval = %d, want floor %d", resp.Interval, defaultReplayIntervalMS)
+	}
+}
--- a/internal/web/server.go
+++ b/internal/web/server.go
@@ -75,6 +75,7 @@ func (s *Server) routes() (http.Handler, error) {
 	mux.HandleFunc("/api/v1/grid", s.handleGrid)
 	mux.HandleFunc("/api/v1/laps/comparison", s.handleLapsComparison)
 	mux.HandleFunc("/api/v1/laps", s.handleLaps)
+	mux.HandleFunc("/api/v1/replay/frames", s.handleReplayFrames)
 	mux.HandleFunc("/api/v1/weather", s.handleWeather)
 	mux.HandleFunc("/api/v1/race-control", s.handleRaceControl)
 	mux.HandleFunc("/api/v1/telemetry", s.handleTelemetry)
Author	SHA1	Message	Date
AmanTahiliani	c2617d39bb	feat: add replay track map scrubber Spike: replay location fan-out is bounded with a semaphore at 4 concurrent GetLocation calls, covered by TestAssembleReplayFramesBoundsLocationFanOut. Adds /api/v1/replay/frames with 5s interval floor, 3000-frame cap, nearest-sample snapping, and empty-driver omission. Wires RaceStoryCanvas to lazy-load replay frames plus cached track outlines when the map panel opens, sharing the existing scrubber/playback state across chart and map. Tests: HOME=/private/tmp/box-box-home GOCACHE=/private/tmp/box-box-go-cache GOMODCACHE=/Users/aman/go/pkg/mod go test ./internal/web; go build ./... (same env, passed with read-only module stat-cache warning); npm run test; npx tsc --noEmit. Full go test ./... is blocked in this sandbox by existing network/listener-dependent internal/api and internal/news tests.	2026-07-11 18:17:15 -04:00
Aman Tahiliani	5970649a9c	Merge pull request #60 from AmanTahiliani/feat/issue-19-auto-chapter-detection-rc-position-swing Auto-chapter detection (RC + position swings) (#19)	2026-07-11 18:06:33 -04:00
AmanTahiliani	7212eb9b44	feat: detect race replay chapters Add deterministic server-side chapter detection for starts, flag periods, pit phases, decisive top-five swings, and finishes, then expose chapters on the race-hub payload. Spike result: race-hub already loads race control, positions, and laps in one read model. The requested Detect signature does not include pit stops, so pit phases use IsPitOutLap clusters as the local deterministic pit-stop proxy.	2026-07-11 18:04:44 -04:00
Aman Tahiliani	785dccdca2	Merge pull request #59 from AmanTahiliani/feat/issue-25-next-race-preview-page Next-race preview page (#25)	2026-07-11 17:59:51 -04:00
AmanTahiliani	e8de2068c1	feat(frontend): add next-race preview page (#25 ) Assemble /preview from existing schedule, track-outline, results, and championship hub endpoints with client-side preview.ts helpers, section loading/empty states, and Vitest coverage for lib + page render paths. Co-authored-by: Cursor <cursoragent@cursor.com>	2026-07-11 17:59:00 -04:00