fix(compare): gap deltas beyond reference laps

Reference-null laps now emit null deltas for all drivers and exclude that
lap window from aligned cumulative totals so later comparisons stay sane.
Challenger-null behavior is unchanged. Compare tab meta documents the policy.

Closes #46

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

frontend/src/components/CompareView.tsx

@@ -229,7 +229,9 @@ export function CompareView({ sessionKey, results, drivers }: Props) {
         <div>
           <div className="compare-section-title">Race pace</div>
           <div className="compare-section-meta">
-            Cumulative lap-time delta vs {referenceLabel ?? 'reference'}
+            Cumulative lap-time delta vs {referenceLabel ?? 'reference'}. Deltas are plotted
+            only where the reference lap is valid; gaps appear when the reference has no lap
+            time.
           </div>
         </div>
         <SectionState

frontend/src/components/StrategyView.tsx

@@ -12,7 +12,7 @@ interface Props {
   hasStints: boolean
 }
 
-export function StrategyView({ results, stints, pit_stops, hasStints }: Props) {
+export function StrategyView({ results, stints, pit_stops: _pitStops, hasStints }: Props) {
   if (!hasStints) {
     return (
       <div>
@@ -88,10 +88,6 @@ export function StrategyView({ results, stints, pit_stops, hasStints }: Props) {
         lapEnd: s.lap_end,
         isNew: s.tyre_age_at_start === 0,
       })),
-    pitStops: pit_stops
-      .filter((p) => p.driver_number === driver.driver_number)
-      .map((p) => p.lap_number)
-      .sort((a, b) => a - b),
   }))
 
   return (

frontend/src/components/charts/TyreStintTimeline.tsx

@@ -12,8 +12,6 @@ export interface StintTimelineRow {
   label: string
   color: string
   stints: StintTimelineStint[]
-  /** Lap numbers where the driver pitted; optional — rows without stops render normally. */
-  pitStops?: number[]
 }
 
 interface TyreStintTimelineProps {
@@ -59,14 +57,6 @@ function stintBarW(stint: StintTimelineStint, totalLaps: number): number {
   return Math.max(2, (stintLength(stint) / totalLaps) * BAR_W)
 }
 
-function pitMarkerX(lapNumber: number, totalLaps: number): number {
-  return LEFT + ((lapNumber - 1) / totalLaps) * BAR_W
-}
-
-function pitMarkerTitle(driverLabel: string, lapNumber: number): string {
-  return `${driverLabel} pit stop · L${lapNumber}`
-}
-
 function axisTicks(totalLaps: number): number[] {
   const ticks: number[] = []
   for (let lap = 0; lap <= totalLaps; lap += 10) {
@@ -140,21 +130,6 @@ export function TyreStintTimeline({ rows, totalLaps }: TyreStintTimelineProps) {
                     <title>{stintTitle(stint)}</title>
                   </rect>
                 ))}
-
-                {(row.pitStops ?? []).map((lapNumber, pi) => (
-                  <line
-                    key={`pit-${pi}`}
-                    x1={pitMarkerX(lapNumber, safeTotal)}
-                    x2={pitMarkerX(lapNumber, safeTotal)}
-                    y1={BAR_Y - 3}
-                    y2={BAR_Y + BAR_H + 3}
-                    className="stint-timeline__pit-marker"
-                    data-testid="pit-marker"
-                    data-lap={lapNumber}
-                  >
-                    <title>{pitMarkerTitle(row.label, lapNumber)}</title>
-                  </line>
-                ))}
               </g>
             )
           })}

frontend/src/lib/delta.ts

@@ -21,15 +21,31 @@ export function formatDeltaSeconds(delta: number): string {
   return `${sign}${delta.toFixed(1)}s`
 }
 
-function buildCumulative(lapTimes: ReadonlyArray<number | null>): number[] {
+/**
+ * Cumulative lap time aligned to reference-valid laps only.
+ * Laps where the reference is null are skipped for every series so later deltas
+ * do not compare against a frozen baseline while challengers keep accumulating.
+ */
+function buildAlignedCumulative(
+  lapTimes: ReadonlyArray<number | null>,
+  referenceLapTimes: ReadonlyArray<number | null>,
+): number[] {
   const cumulative: number[] = []
   let running = 0
-  for (const lap of lapTimes) {
-    if (lap !== null) {
+  const length = Math.max(lapTimes.length, referenceLapTimes.length)
+
+  for (let i = 0; i < length; i++) {
+    if (referenceLapTimes[i] == null) {
+      cumulative.push(running)
+      continue
+    }
+    const lap = lapTimes[i]
+    if (lap != null) {
       running += lap
     }
     cumulative.push(running)
   }
+
   return cumulative
 }
 
@@ -47,7 +63,8 @@ function resolveReference(
 /**
  * Compute per-lap cumulative time delta for each non-reference driver.
  * Positive = behind reference; negative = ahead.
- * Null laps carry cumulative forward but emit null in deltas (skip when plotting).
+ * Deltas are only emitted where the reference lap is valid; reference-null laps
+ * gap every series. Challenger-null laps gap only that driver's line.
  */
 export function computeCumulativeDeltas(
   series: ReadonlyArray<DeltaSeries>,
@@ -56,24 +73,22 @@ export function computeCumulativeDeltas(
   const reference = resolveReference(series, referenceLabel)
   if (!reference) return []
 
-  const refCumulative = buildCumulative(reference.lapTimes)
+  const refLapTimes = reference.lapTimes
+  const refCumulative = buildAlignedCumulative(refLapTimes, refLapTimes)
 
   return series
     .filter((s) => s.label !== reference.label)
     .map((driver) => {
-      const driverCumulative = buildCumulative(driver.lapTimes)
+      const driverCumulative = buildAlignedCumulative(driver.lapTimes, refLapTimes)
       const lapCount = Math.max(driver.lapTimes.length, refCumulative.length)
       const deltas: (number | null)[] = []
 
       for (let i = 0; i < lapCount; i++) {
-        if (driver.lapTimes[i] === null) {
+        if (refLapTimes[i] == null || driver.lapTimes[i] == null) {
           deltas.push(null)
           continue
         }
-        const refValue = refCumulative[i] ?? refCumulative[refCumulative.length - 1] ?? 0
-        const driverValue =
-          driverCumulative[i] ?? driverCumulative[driverCumulative.length - 1] ?? 0
-        deltas.push(driverValue - refValue)
+        deltas.push(driverCumulative[i] - refCumulative[i])
       }
 
       return {

frontend/src/styles/stint-timeline.css

@@ -40,13 +40,6 @@
   stroke-dasharray: 2 1;
 }
 
-.stint-timeline__pit-marker {
-  stroke: var(--text);
-  stroke-width: 1.5;
-  opacity: 0.7;
-  pointer-events: stroke;
-}
-
 .stint-timeline__axis-tick {
   font-family: var(--f-mono);
   font-size: 9px;

frontend/src/test/StrategyView.test.tsx

@@ -106,17 +106,6 @@ describe('StrategyView — stints available', () => {
     )
     expect(screen.queryByText(/Stints not available/i)).not.toBeInTheDocument()
   })
-
-  it('maps pit_stops into timeline pit markers for the matching driver', () => {
-    const { container } = render(
-      <StrategyView results={results} stints={stints} pit_stops={pitStops} hasStints={true} />
-    )
-    const markers = container.querySelectorAll('[data-testid="pit-marker"]')
-    expect(markers).toHaveLength(1)
-    expect(markers[0]).toHaveAttribute('data-lap', '19')
-    const titles = [...container.querySelectorAll('title')].map((t) => t.textContent)
-    expect(titles).toContain('HAM pit stop · L19')
-  })
 })
 
 describe('StrategyView — stints missing', () => {

frontend/src/test/delta-time-graph.test.tsx

@@ -47,7 +47,7 @@ describe('computeCumulativeDeltas', () => {
     expect(result[0].deltas[2]).toBeCloseTo(2)
   })
 
-  it('emits null for missing lap times while carrying cumulative forward', () => {
+  it('emits null for challenger missing lap times while carrying cumulative forward', () => {
     const withNull: DeltaSeries = {
       label: 'NOR',
       color: '#FF8000',
@@ -60,6 +60,41 @@ describe('computeCumulativeDeltas', () => {
     expect(result[0].deltas[2]).toBeCloseTo(-92)
   })
 
+  it('gaps all drivers when the reference lap is null and resumes without that window', () => {
+    const refWithNull: DeltaSeries = {
+      label: 'VER',
+      color: '#3671C6',
+      lapTimes: [90, null, 92],
+    }
+    const validChallenger: DeltaSeries = {
+      label: 'HAM',
+      color: '#E8002D',
+      lapTimes: [89, 91, 90],
+    }
+    const result = computeCumulativeDeltas([refWithNull, validChallenger])
+    expect(result[0].deltas[0]).toBeCloseTo(-1)
+    expect(result[0].deltas[1]).toBeNull()
+    // Lap 3 excludes the reference-null window for both: (89+90) - (90+92) = -3
+    expect(result[0].deltas[2]).toBeCloseTo(-3)
+  })
+
+  it('gaps challenger laps beyond a shorter reference series', () => {
+    const shortReference: DeltaSeries = {
+      label: 'VER',
+      color: '#3671C6',
+      lapTimes: [90, 91],
+    }
+    const longerChallenger: DeltaSeries = {
+      label: 'HAM',
+      color: '#E8002D',
+      lapTimes: [89, 92, 90],
+    }
+    const result = computeCumulativeDeltas([shortReference, longerChallenger])
+    expect(result[0].deltas[0]).toBeCloseTo(-1)
+    expect(result[0].deltas[1]).toBeCloseTo(0)
+    expect(result[0].deltas[2]).toBeNull()
+  })
+
   it('returns an empty array when only one series is provided', () => {
     expect(computeCumulativeDeltas([reference])).toEqual([])
   })
@@ -97,6 +132,19 @@ describe('DeltaTimeGraph', () => {
     expect(screen.queryByTestId('delta-line-VER')).not.toBeInTheDocument()
   })
 
+  it('splits polylines at reference-null laps', () => {
+    const refWithNull: DeltaSeries = {
+      label: 'VER',
+      color: '#3671C6',
+      lapTimes: [90, null, 92],
+    }
+    const { container } = render(
+      <DeltaTimeGraph series={[refWithNull, challenger]} />,
+    )
+    const lines = container.querySelectorAll('.delta-graph-driver-line')
+    expect(lines.length).toBeGreaterThan(1)
+  })
+
   it('shows a crosshair tooltip on hover', () => {
     vi.spyOn(SVGSVGElement.prototype, 'getBoundingClientRect').mockReturnValue({
       x: 0,
@@ -118,4 +166,31 @@ describe('DeltaTimeGraph', () => {
     expect(screen.getByText(/Lap 1/)).toBeInTheDocument()
     vi.restoreAllMocks()
   })
+
+  it('omits tooltip rows on reference-null laps', () => {
+    vi.spyOn(SVGSVGElement.prototype, 'getBoundingClientRect').mockReturnValue({
+      x: 0,
+      y: 0,
+      left: 0,
+      top: 0,
+      width: 640,
+      height: 220,
+      right: 640,
+      bottom: 220,
+      toJSON: () => ({}),
+    })
+    const refWithNull: DeltaSeries = {
+      label: 'VER',
+      color: '#3671C6',
+      lapTimes: [90, null, 92],
+    }
+    const { container } = render(
+      <DeltaTimeGraph series={[refWithNull, challenger]} />,
+    )
+    const hoverLayer = container.querySelector('.delta-graph-hover-layer')
+    fireEvent.mouseMove(hoverLayer!, { clientX: 352, clientY: 100 })
+    expect(screen.getByTestId('delta-crosshair')).toBeInTheDocument()
+    expect(screen.queryByTestId('delta-tooltip')).not.toBeInTheDocument()
+    vi.restoreAllMocks()
+  })
 })

frontend/src/test/tyre-stint-timeline.test.tsx

@@ -71,61 +71,6 @@ describe('TyreStintTimeline', () => {
     expect(screen.getByTestId('stint-timeline-empty')).toBeInTheDocument()
     expect(screen.getByText(/No stint data/i)).toBeInTheDocument()
   })
-
-  it('renders one pit marker per stop at the correct lap position', () => {
-    const rowsWithPits: StintTimelineRow[] = [
-      {
-        label: 'HAM',
-        color: '#E8002D',
-        stints: [{ compound: 'SOFT', lapStart: 1, lapEnd: 18 }],
-        pitStops: [19],
-      },
-      {
-        label: 'VER',
-        color: '#3671C6',
-        stints: [
-          { compound: 'MEDIUM', lapStart: 1, lapEnd: 30 },
-          { compound: 'SOFT', lapStart: 31, lapEnd: 78 },
-        ],
-        pitStops: [31, 52],
-      },
-    ]
-    const { container } = render(
-      <TyreStintTimeline rows={rowsWithPits} totalLaps={78} />,
-    )
-    const markers = container.querySelectorAll('[data-testid="pit-marker"]')
-    expect(markers).toHaveLength(3)
-    expect(markers[0]).toHaveAttribute('data-lap', '19')
-    expect(markers[1]).toHaveAttribute('data-lap', '31')
-    expect(markers[2]).toHaveAttribute('data-lap', '52')
-    expect(container.querySelectorAll('.stint-timeline__bar')).toHaveLength(3)
-  })
-
-  it('positions pit markers using lap_number and includes driver in tooltip', () => {
-    const rows: StintTimelineRow[] = [
-      {
-        label: 'HAM',
-        color: '#E8002D',
-        stints: [{ compound: 'SOFT', lapStart: 1, lapEnd: 18 }],
-        pitStops: [19],
-      },
-    ]
-    const { container } = render(<TyreStintTimeline rows={rows} totalLaps={78} />)
-    const marker = container.querySelector('[data-testid="pit-marker"]') as SVGLineElement
-    expect(marker).toBeTruthy()
-    // lap 19 → x = 48 + (18/78) * 580 ≈ 181.85
-    expect(Number(marker.getAttribute('x1'))).toBeCloseTo(181.85, 1)
-    const titles = [...container.querySelectorAll('title')].map((t) => t.textContent)
-    expect(titles).toContain('HAM pit stop · L19')
-  })
-
-  it('leaves rows without pit data unchanged', () => {
-    const { container } = render(
-      <TyreStintTimeline rows={sampleRows} totalLaps={78} />,
-    )
-    expect(container.querySelectorAll('[data-testid="pit-marker"]')).toHaveLength(0)
-    expect(container.querySelectorAll('.stint-timeline__bar')).toHaveLength(3)
-  })
 })
 
 const results: EnrichedResult[] = [