perf(tracks): bound playback rendering work

vehicle-data-platform/apps/web/src/v2/domain/track.test.ts

@@ -1,6 +1,6 @@
 import { describe, expect, it } from 'vitest';
 import type { TrackPlaybackResponse } from '../../api/types';
-import { formatDuration, sampledEventIndex, trackCsv } from './track';
+import { buildTrackRailSelection, formatDuration, sampledEventIndex, trackCsv, trackPlaybackInterval } from './track';
 
 describe('track domain', () => {
   it('formats durations and maps original event indices to sampled points', () => {
@@ -9,6 +9,26 @@ describe('track domain', () => {
     expect(sampledEventIndex({ index: 50, sampledIndex: 7 } as never, 11, 101)).toBe(7);
   });
 
+  it('precomputes sparse rail highlights and bounds the playback cadence', () => {
+    const playback = {
+      points: Array.from({ length: 8 }, (_, index) => ({ longitude: index, latitude: index })),
+      stops: [{ sampledIndex: 3 }],
+      events: [{ index: 50 }, { index: 75, sampledIndex: 6 }],
+      summary: { pointCount: 101 }
+    } as TrackPlaybackResponse;
+    const selection = buildTrackRailSelection(playback);
+
+    expect(selection.stopIndexesByPoint[1]).toBeUndefined();
+    expect(selection.stopIndexesByPoint[2]).toEqual([0]);
+    expect(selection.stopIndexesByPoint[3]).toEqual([0]);
+    expect(selection.stopIndexesByPoint[4]).toEqual([0]);
+    expect(selection.eventIndexesByPoint[4]).toEqual([0]);
+    expect(selection.eventIndexesByPoint[6]).toEqual([1]);
+    expect(trackPlaybackInterval(1)).toBe(300);
+    expect(trackPlaybackInterval(4)).toBe(75);
+    expect(trackPlaybackInterval(100)).toBe(55);
+  });
+
   it('exports the current result with UTF-8 BOM and escaped values', () => {
     const track = {
       plate: '粤A,001', vin: 'VIN', summary: { startTime: '2026-07-03 10:00:00' },