perf(mileage): stream workbook export rows

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

@@ -0,0 +1,16 @@
+import { expect, test } from 'vitest';
+import { transferableWorkbookBuffer } from './transferableBuffer';
+
+test('reuses complete workbook buffers and only copies partial views', () => {
+  const direct = new ArrayBuffer(8);
+  expect(transferableWorkbookBuffer(direct)).toBe(direct);
+
+  const completeView = new Uint8Array(new ArrayBuffer(8));
+  expect(transferableWorkbookBuffer(completeView)).toBe(completeView.buffer);
+
+  const source = new Uint8Array([1, 2, 3, 4]);
+  const partial = source.subarray(1, 3);
+  const transferred = transferableWorkbookBuffer(partial);
+  expect(transferred).not.toBe(source.buffer);
+  expect([...new Uint8Array(transferred)]).toEqual([2, 3]);
+});