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.

frontend/src/pages/LiveTimingPage.tsx

@@ -1,6 +1,6 @@
 import { useEffect, useMemo, useRef, useState } from 'react'
 import { useQuery } from '@tanstack/react-query'
-import { fetchLiveState, fetchLiveTrackOutline } from '../api'
+import { fetchLiveState } from '../api'
 import type { LivePosition, LiveStreamData } from '../types'
 import {
   loadPinnedDrivers,
@@ -25,7 +25,6 @@ import { PinnedDrivers } from '../components/live/PinnedDrivers'
 import { RaceControlFeed } from '../components/live/RaceControlFeed'
 import { EventRail } from '../components/live/EventRail'
 import { TeamRadioTicker } from '../components/live/TeamRadioTicker'
-import { TrackMap } from '../components/live/TrackMap'
 import { TyreDegPanel } from '../components/live/TyreDegPanel'
 import { Archive, Radio } from 'lucide-react'
 
@@ -58,18 +57,6 @@ export function LiveTimingPage() {
     staleTime: 5_000,
   })
 
-  const trackOutlineQuery = useQuery({
-    queryKey: [
-      'live-track-outline',
-      snapshot?.Session?.MeetingName ?? '',
-      snapshot?.Session?.CircuitName ?? '',
-    ],
-    queryFn: () => fetchLiveTrackOutline(snapshot!.Session),
-    enabled: Boolean(snapshot?.Session?.MeetingName || snapshot?.Session?.CircuitName),
-    staleTime: Infinity,
-    retry: false,
-  })
-
   useEffect(() => {
     if (!data) return
     const nextLive = data.is_live && Boolean(data.data)
@@ -284,14 +271,6 @@ export function LiveTimingPage() {
           />
           <TrackStatusBanner status={snapshot.TrackStatus} />
           <PinnedDrivers rows={rows} history={gapHistory} pinned={pinned} onToggle={handleTogglePin} />
-          <TrackMap
-            outline={trackOutlineQuery.data}
-            positions={positions}
-            telemetry={snapshot.Telemetry}
-            drivers={snapshot.Drivers}
-            driverInfo={snapshot.DriverInfo}
-            loading={trackOutlineQuery.isLoading}
-          />
           <TyreDegPanel rows={rows} sessionType={snapshot.Session?.SessionType} pinned={pinned} />
           <div className="live-columns">
             <div className="live-tower-col">

frontend/src/test/CommandCenterPage.test.tsx

@@ -156,6 +156,7 @@ describe('CommandCenterPage', () => {
       race_control: [],
       weather: [],
       laps: [],
+      chapters: [],
     })
   })
 

frontend/src/test/LiveTimingPage.test.tsx

@@ -152,4 +152,15 @@ describe('LiveTimingPage archive mode', () => {
     expect(await screen.findByTestId('live-empty')).toHaveTextContent('No live session active')
     expect(screen.queryByRole('button', { name: /view last session/i })).not.toBeInTheDocument()
   })
+
+  it('temporarily omits the track map while live GPS is unavailable', async () => {
+    renderPage({
+      is_live: true,
+      data: { ...archivedSnapshot, SessionStatus: 'Started' },
+    })
+
+    expect(await screen.findByText('Timing Tower')).toBeInTheDocument()
+    expect(screen.queryByText('Track Map')).not.toBeInTheDocument()
+    expect(mockFetchLiveTrackOutline).not.toHaveBeenCalled()
+  })
 })

frontend/src/test/RaceHubPage.test.tsx

@@ -155,6 +155,7 @@ const raceHub: RaceHub = {
       is_pit_out_lap: false,
     },
   ],
+  chapters: [],
 }
 
 const weekend: Weekend = {

frontend/src/types.ts

@@ -89,6 +89,17 @@ 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 {

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
+}

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
+}

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
+}

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{},
 	}
 }

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)

scripts/debug/f1_live_socket_probe.py

@@ -0,0 +1,264 @@
+#!/usr/bin/env python3
+"""Probe the official F1 live timing sockets for GPS position topics.
+
+This intentionally does not call OpenF1 REST. It connects directly to the F1
+SignalR endpoints used by the app and reports which topics arrive.
+"""
+
+from __future__ import annotations
+
+import argparse
+import base64
+import json
+import os
+import random
+import socket
+import ssl
+import struct
+import sys
+import time
+import urllib.parse
+import urllib.request
+
+
+RS = b"\x1e"
+CORE_NEGOTIATE = "https://livetiming.formula1.com/signalrcore/negotiate?negotiateVersion=1"
+CORE_WS_HOST = "livetiming.formula1.com"
+LEGACY_HUB = '[{"name":"Streaming"}]'
+TOPICS = [
+    "Heartbeat",
+    "TimingData",
+    "Position",
+    "Position.z",
+    "CarData",
+    "CarData.z",
+    "DriverList",
+    "LapCount",
+    "ExtrapolatedClock",
+    "TrackStatus",
+    "RaceControlMessages",
+    "WeatherData",
+    "SessionInfo",
+    "TeamRadio",
+    "CurrentTyres",
+    "TimingAppData",
+    "TimingStats",
+    "SessionStatus",
+    "TopThree",
+]
+
+
+class WebSocket:
+    def __init__(self, host: str, path: str, headers: dict[str, str] | None = None):
+        self.host = host
+        self.sock = ssl.create_default_context().wrap_socket(
+            socket.create_connection((host, 443), timeout=10),
+            server_hostname=host,
+        )
+        key = base64.b64encode(os.urandom(16)).decode("ascii")
+        request_headers = {
+            "Host": host,
+            "Upgrade": "websocket",
+            "Connection": "Upgrade",
+            "Sec-WebSocket-Key": key,
+            "Sec-WebSocket-Version": "13",
+            "Origin": "https://www.formula1.com",
+            "User-Agent": "Mozilla/5.0",
+        }
+        request_headers.update(headers or {})
+        lines = [f"GET {path} HTTP/1.1", *[f"{k}: {v}" for k, v in request_headers.items()], "", ""]
+        self.sock.sendall("\r\n".join(lines).encode("utf-8"))
+        response = self._read_http_response()
+        if b" 101 " not in response.split(b"\r\n", 1)[0]:
+            raise RuntimeError(response.decode("utf-8", "replace"))
+
+    def _read_http_response(self) -> bytes:
+        data = b""
+        while b"\r\n\r\n" not in data:
+            data += self.sock.recv(4096)
+        return data
+
+    def send_text(self, text: str) -> None:
+        payload = text.encode("utf-8")
+        header = bytearray([0x81])
+        if len(payload) < 126:
+            header.append(0x80 | len(payload))
+        elif len(payload) < 65536:
+            header.append(0x80 | 126)
+            header.extend(struct.pack("!H", len(payload)))
+        else:
+            header.append(0x80 | 127)
+            header.extend(struct.pack("!Q", len(payload)))
+        mask = random.randbytes(4) if hasattr(random, "randbytes") else os.urandom(4)
+        masked = bytes(b ^ mask[i % 4] for i, b in enumerate(payload))
+        self.sock.sendall(bytes(header) + mask + masked)
+
+    def recv_text(self, timeout: float = 5.0) -> str | None:
+        self.sock.settimeout(timeout)
+        while True:
+            first = self.sock.recv(2)
+            if not first:
+                return None
+            opcode = first[0] & 0x0F
+            masked = bool(first[1] & 0x80)
+            length = first[1] & 0x7F
+            if length == 126:
+                length = struct.unpack("!H", self._read_exact(2))[0]
+            elif length == 127:
+                length = struct.unpack("!Q", self._read_exact(8))[0]
+            mask = self._read_exact(4) if masked else b""
+            payload = self._read_exact(length)
+            if masked:
+                payload = bytes(b ^ mask[i % 4] for i, b in enumerate(payload))
+            if opcode == 0x8:
+                return None
+            if opcode == 0x9:
+                self._send_pong(payload)
+                continue
+            if opcode == 0x1:
+                return payload.decode("utf-8", "replace")
+
+    def _send_pong(self, payload: bytes) -> None:
+        self.sock.sendall(bytes([0x8A, len(payload)]) + payload)
+
+    def _read_exact(self, n: int) -> bytes:
+        chunks = []
+        remaining = n
+        while remaining:
+            chunk = self.sock.recv(remaining)
+            if not chunk:
+                raise EOFError("socket closed")
+            chunks.append(chunk)
+            remaining -= len(chunk)
+        return b"".join(chunks)
+
+    def close(self) -> None:
+        self.sock.close()
+
+
+def http_json(url: str, method: str = "GET", headers: dict[str, str] | None = None) -> tuple[dict, list[str]]:
+    req = urllib.request.Request(url, method=method, headers=headers or {})
+    with urllib.request.urlopen(req, timeout=15) as resp:
+        cookies = resp.headers.get_all("Set-Cookie") or []
+        return json.loads(resp.read()), cookies
+
+
+def core_probe(seconds: int) -> None:
+    print("== SignalR Core ==")
+    neg, cookies = http_json(
+        CORE_NEGOTIATE,
+        method="POST",
+        headers={"Origin": "https://www.formula1.com", "User-Agent": "Mozilla/5.0", "Content-Length": "0"},
+    )
+    token = urllib.parse.quote(neg["connectionToken"], safe="")
+    ws = WebSocket(
+        CORE_WS_HOST,
+        f"/signalrcore?id={token}",
+        {"Cookie": "; ".join(cookies)} if cookies else None,
+    )
+    try:
+        ws.send_text(json.dumps({"protocol": "json", "version": 1}, separators=(",", ":")) + RS.decode())
+        print("handshake:", repr(ws.recv_text()))
+        ws.send_text(
+            json.dumps(
+                {"type": 1, "target": "subscribe", "arguments": [TOPICS], "invocationId": "1"},
+                separators=(",", ":"),
+            )
+            + RS.decode()
+        )
+        collect(ws, seconds)
+    finally:
+        ws.close()
+
+
+def legacy_probe(seconds: int, bearer: str | None) -> None:
+    print("\n== Legacy SignalR ==")
+    query = urllib.parse.quote(LEGACY_HUB, safe="")
+    headers = {"User-Agent": "BestHTTP"}
+    if bearer:
+        headers["Authorization"] = f"Bearer {bearer}"
+    neg_url = f"https://livetiming.formula1.com/signalr/negotiate?clientProtocol=1.5&connectionData={query}"
+    try:
+        neg, cookies = http_json(neg_url, headers=headers)
+    except Exception as exc:
+        print("negotiate failed:", exc)
+        return
+    token = urllib.parse.quote(neg["ConnectionToken"], safe="")
+    path = f"/signalr/connect?clientProtocol=1.5&transport=webSockets&connectionToken={token}&connectionData={query}"
+    ws_headers = {"User-Agent": "BestHTTP"}
+    if cookies:
+        ws_headers["Cookie"] = "; ".join(cookies)
+    if bearer:
+        ws_headers["Authorization"] = f"Bearer {bearer}"
+    ws = WebSocket(CORE_WS_HOST, path, ws_headers)
+    try:
+        ws.send_text(json.dumps({"H": "Streaming", "M": "Subscribe", "A": [TOPICS], "I": 1}, separators=(",", ":")))
+        collect(ws, seconds)
+    finally:
+        ws.close()
+
+
+def collect(ws: WebSocket, seconds: int) -> None:
+    deadline = time.time() + seconds
+    seen: dict[str, int] = {}
+    while time.time() < deadline:
+        try:
+            message = ws.recv_text(timeout=min(5, max(1, deadline - time.time())))
+        except TimeoutError:
+            continue
+        if not message:
+            break
+        for frame in message.split(RS.decode()):
+            if not frame:
+                continue
+            try:
+                payload = json.loads(frame)
+            except json.JSONDecodeError:
+                continue
+            record_topics(payload, seen)
+    print("seen topics:")
+    for topic in sorted(seen):
+        print(f"  {topic}: {seen[topic]}")
+    if not any(topic.startswith("Position") for topic in seen):
+        print("  (no Position / Position.z topics observed)")
+
+
+def record_topics(payload: dict, seen: dict[str, int]) -> None:
+    result = payload.get("result") or payload.get("R")
+    if isinstance(result, dict):
+        for topic, data in result.items():
+            seen[topic] = seen.get(topic, 0) + 1
+            maybe_print_position(topic, data)
+    for message in payload.get("M") or []:
+        args = message.get("A") or []
+        if len(args) >= 2:
+            topic = args[0]
+            seen[topic] = seen.get(topic, 0) + 1
+            maybe_print_position(topic, args[1])
+    if payload.get("target") == "feed":
+        args = payload.get("arguments") or []
+        if len(args) >= 2:
+            topic = args[0]
+            seen[topic] = seen.get(topic, 0) + 1
+            maybe_print_position(topic, args[1])
+
+
+def maybe_print_position(topic: str, data) -> None:
+    if topic in {"Position", "Position.z"}:
+        text = json.dumps(data)[:600] if not isinstance(data, str) else data[:600]
+        print(f"POSITION TOPIC {topic}: {text}")
+
+
+def main() -> int:
+    parser = argparse.ArgumentParser()
+    parser.add_argument("--seconds", type=int, default=20)
+    parser.add_argument("--legacy", action="store_true", help="also probe legacy SignalR")
+    args = parser.parse_args()
+    core_probe(args.seconds)
+    if args.legacy:
+        legacy_probe(args.seconds, os.environ.get("BOXBOX_F1_LIVE_BEARER_TOKEN") or os.environ.get("F1_LIVE_BEARER_TOKEN"))
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())