Add championship what-if simulator

Fourth view on the championship page: assign P1-P10 per remaining
round and see projected standings update live, with position deltas
and mathematically alive/eliminated title states. Pure projection
logic in lib/simulator.ts (2025 points system, standard GPs only);
scenarios persist to localStorage per season. 169 frontend tests
passing.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/test/ChampionshipSimulator.test.tsx

@@ -0,0 +1,165 @@
+import { describe, it, expect, beforeEach } from 'vitest'
+import { render, screen, fireEvent, within } from '@testing-library/react'
+import { ChampionshipSimulator } from '../components/ChampionshipSimulator'
+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: 0,
+    position: 1,
+    wins: 0,
+    podiums: 0,
+    poles: 0,
+    form: [],
+    cumulative: [],
+    teammate_wins: 0,
+    teammate_losses: 0,
+    ...over,
+  }
+}
+
+const drivers: ChampHubDriver[] = [
+  driver({ driver_number: 1, name_acronym: 'VER', points: 200, position: 1 }),
+  driver({
+    driver_number: 4,
+    name_acronym: 'NOR',
+    full_name: 'Lando Norris',
+    team_name: 'McLaren',
+    team_colour: 'ff8000',
+    points: 190,
+    position: 2,
+  }),
+  driver({
+    driver_number: 16,
+    name_acronym: 'LEC',
+    full_name: 'Charles Leclerc',
+    team_name: 'Ferrari',
+    team_colour: 'e8002d',
+    points: 120,
+    position: 3,
+  }),
+]
+
+const hub: ChampionshipHub = {
+  season: 2025,
+  round: 9,
+  total_rounds: 10,
+  rounds_left: 1,
+  last_race: 'Monaco GP',
+  round_labels: ['R1', 'R2', 'R3', 'R4', 'R5', 'R6', 'R7', 'R8', 'R9'],
+  drivers,
+  teams: [],
+}
+
+describe('ChampionshipSimulator', () => {
+  beforeEach(() => {
+    window.localStorage.clear()
+  })
+
+  it('seeds the round by championship order and projects the default scenario', () => {
+    render(<ChampionshipSimulator hub={hub} />)
+
+    expect(screen.getByTestId('champ-view-simulator')).toBeInTheDocument()
+    // Only 1 remaining round; label falls back to "Round 10" (no label yet).
+    expect(screen.getByTestId('sim-round-0')).toHaveTextContent('Round 10')
+    // P1 select seeded with the current leader.
+    expect(screen.getByTestId('sim-pos-1')).toHaveValue('1')
+    expect(screen.getByTestId('sim-pos-2')).toHaveValue('4')
+
+    // Default projection: VER 200+25=225 on top, delta arrows absent.
+    const verRow = screen.getByTestId('sim-row-1')
+    expect(within(verRow).getByText('225')).toBeInTheDocument()
+    expect(within(verRow).getByText('P1')).toBeInTheDocument()
+  })
+
+  it('updates the projected table when a win is reassigned', () => {
+    render(<ChampionshipSimulator hub={hub} />)
+
+    // Give NOR the win; VER (previous P1) is bumped out of the slot.
+    fireEvent.change(screen.getByTestId('sim-pos-1'), { target: { value: '4' } })
+
+    // NOR: 190 + 25 = 215 → P1 with an up arrow; VER stays on 200 → P2 down.
+    const norRow = screen.getByTestId('sim-row-4')
+    expect(within(norRow).getByText('215')).toBeInTheDocument()
+    expect(within(norRow).getByText('P1')).toBeInTheDocument()
+    expect(within(norRow).getByText('▲1')).toBeInTheDocument()
+
+    const verRow = screen.getByTestId('sim-row-1')
+    // "200" appears in both Now and Proj columns (no simulated points).
+    expect(within(verRow).getAllByText('200')).toHaveLength(2)
+    expect(within(verRow).getByText('+0')).toBeInTheDocument()
+    expect(within(verRow).getByText('P2')).toBeInTheDocument()
+    expect(within(verRow).getByText('▼1')).toBeInTheDocument()
+
+    // VER was removed from P1 and holds no slot now.
+    expect(screen.getByTestId('sim-pos-1')).toHaveValue('4')
+  })
+
+  it('shows title alive/eliminated states', () => {
+    render(<ChampionshipSimulator hub={hub} />)
+
+    // Default: VER projects to 225. NOR max = 190+25=215 < 225 → OUT.
+    expect(within(screen.getByTestId('sim-row-1')).getByText('ALIVE')).toBeInTheDocument()
+    expect(within(screen.getByTestId('sim-row-4')).getByText('OUT')).toBeInTheDocument()
+
+    // If VER scores nothing, NOR can still catch him: 190+25 ≥ 200 → ALIVE.
+    fireEvent.change(screen.getByTestId('sim-pos-1'), { target: { value: '4' } })
+    expect(within(screen.getByTestId('sim-row-4')).getByText('ALIVE')).toBeInTheDocument()
+  })
+
+  it('reset round and reset all restore the default order', () => {
+    render(<ChampionshipSimulator hub={hub} />)
+
+    fireEvent.change(screen.getByTestId('sim-pos-1'), { target: { value: '16' } })
+    expect(screen.getByTestId('sim-pos-1')).toHaveValue('16')
+
+    fireEvent.click(screen.getByTestId('sim-reset-round'))
+    expect(screen.getByTestId('sim-pos-1')).toHaveValue('1')
+
+    fireEvent.change(screen.getByTestId('sim-pos-1'), { target: { value: '16' } })
+    fireEvent.click(screen.getByTestId('sim-reset-all'))
+    expect(screen.getByTestId('sim-pos-1')).toHaveValue('1')
+  })
+
+  it('persists the scenario to localStorage keyed by season', () => {
+    const { unmount } = render(<ChampionshipSimulator hub={hub} />)
+    fireEvent.change(screen.getByTestId('sim-pos-1'), { target: { value: '4' } })
+    unmount()
+
+    const stored = window.localStorage.getItem('box-box.champ.sim.2025')
+    expect(stored).not.toBeNull()
+
+    render(<ChampionshipSimulator hub={hub} />)
+    expect(screen.getByTestId('sim-pos-1')).toHaveValue('4')
+  })
+
+  it('survives corrupt localStorage', () => {
+    window.localStorage.setItem('box-box.champ.sim.2025', '{not json')
+    render(<ChampionshipSimulator hub={hub} />)
+    expect(screen.getByTestId('sim-pos-1')).toHaveValue('1')
+  })
+
+  it('shows the season-complete empty state when no rounds remain', () => {
+    render(<ChampionshipSimulator hub={{ ...hub, round: 10, rounds_left: 0 }} />)
+    expect(screen.getByTestId('champ-view-simulator')).toHaveTextContent(
+      'Season complete — nothing left to simulate.',
+    )
+  })
+
+  it('uses round labels beyond the current round when available', () => {
+    const labelled: ChampionshipHub = {
+      ...hub,
+      round: 8,
+      rounds_left: 2,
+      round_labels: [...hub.round_labels, 'ABU'],
+    }
+    render(<ChampionshipSimulator hub={labelled} />)
+    expect(screen.getByTestId('sim-round-0')).toHaveTextContent('R9')
+    expect(screen.getByTestId('sim-round-1')).toHaveTextContent('ABU')
+  })
+})