feat(#24): Rivalry compare view

Implemented by claude via .agents/dev dispatch.

frontend/src/test/ChampionshipPage.test.tsx

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

frontend/src/test/ChampionshipSimulator.test.tsx

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

frontend/src/test/RacePreviewPage.test.tsx

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

frontend/src/test/RivalryCompare.test.tsx

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

frontend/src/test/preview.test.ts

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

frontend/src/test/rivalry.test.ts

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

frontend/src/test/simulator.test.ts

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