perf(web): warm frequent routes during idle time

vehicle-data-platform/apps/web/src/v2/routing/routeModules.test.ts

@@ -1,11 +1,51 @@
-import { describe, expect, it } from 'vitest';
-import { routeSectionForPath } from './routeModules';
+import { describe, expect, it, vi } from 'vitest';
+import { routeSectionForPath, scheduleIdleRoutePreloads, shouldPreloadRoutes } from './routeModules';
 
 describe('route module preloading', () => {
+  async function flushPreloadQueue() {
+    for (let index = 0; index < 6; index += 1) await Promise.resolve();
+  }
+
   it('maps nested and parameterized URLs to the correct lazy module', () => {
     expect(routeSectionForPath('/monitor')).toBe('monitor');
     expect(routeSectionForPath('/vehicles/LTEST001?tab=telemetry')).toBe('vehicles');
     expect(routeSectionForPath('/alerts/rules#editor')).toBe('alerts');
     expect(routeSectionForPath('/not-a-platform-route')).toBeUndefined();
   });
+
+  it('skips background route preloads on save-data and 2G connections', () => {
+    expect(shouldPreloadRoutes({ saveData: true, effectiveType: '4g' })).toBe(false);
+    expect(shouldPreloadRoutes({ effectiveType: 'slow-2g' })).toBe(false);
+    expect(shouldPreloadRoutes({ effectiveType: '2g' })).toBe(false);
+    expect(shouldPreloadRoutes({ effectiveType: '3g' })).toBe(true);
+    expect(shouldPreloadRoutes({ effectiveType: '4g' })).toBe(true);
+  });
+
+  it('warms inactive routes one idle period at a time and stops after cleanup', async () => {
+    const callbacks: Array<() => void> = [];
+    const cancelled: number[] = [];
+    const schedule = vi.fn((callback: () => void) => {
+      const index = callbacks.push(callback) - 1;
+      return () => { cancelled.push(index); };
+    });
+    const preload = vi.fn(async () => undefined);
+    const cleanup = scheduleIdleRoutePreloads({
+      activePathname: '/monitor',
+      connection: { effectiveType: '4g' },
+      preload,
+      schedule
+    });
+
+    expect(schedule).toHaveBeenCalledTimes(1);
+    callbacks[0]();
+    await flushPreloadQueue();
+    expect(preload).toHaveBeenCalledWith('/tracks');
+    expect(schedule).toHaveBeenCalledTimes(2);
+
+    callbacks[1]();
+    await flushPreloadQueue();
+    expect(preload).toHaveBeenLastCalledWith('/history');
+    cleanup();
+    expect(cancelled).toContain(2);
+  });
 });