实现快传，完善快传和网盘的功能，实现文件的互传等一系列功能

front/src/lib/netdisk-paths.test.ts

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+import assert from 'node:assert/strict';
+import test from 'node:test';
+
+import {
+  getParentNetdiskPath,
+  joinNetdiskPath,
+  resolveTransferSaveDirectory,
+  splitNetdiskPath,
+} from './netdisk-paths';
+
+test('splitNetdiskPath normalizes root and nested paths', () => {
+  assert.deepEqual(splitNetdiskPath('/'), []);
+  assert.deepEqual(splitNetdiskPath('/下载/旅行/照片'), ['下载', '旅行', '照片']);
+  assert.deepEqual(splitNetdiskPath('下载//旅行/照片/'), ['下载', '旅行', '照片']);
+});
+
+test('joinNetdiskPath rebuilds a normalized absolute path', () => {
+  assert.equal(joinNetdiskPath([]), '/');
+  assert.equal(joinNetdiskPath(['下载', '旅行']), '/下载/旅行');
+});
+
+test('getParentNetdiskPath returns the previous directory level', () => {
+  assert.equal(getParentNetdiskPath('/下载/旅行'), '/下载');
+  assert.equal(getParentNetdiskPath('/下载'), '/');
+});
+
+test('resolveTransferSaveDirectory keeps nested transfer folders under the selected root path', () => {
+  assert.equal(resolveTransferSaveDirectory('相册/旅行/cover.jpg', '/下载'), '/下载/相册/旅行');
+  assert.equal(resolveTransferSaveDirectory('cover.jpg', '/下载'), '/下载');
+});