feat: 完善多账号连接诊断与聊天媒体导出

- 新增微信账号发现、环境诊断和分步数据库连接引导
- 支持按账号安全保存数据库密钥及快速切换账号
- 完善 WCDB 历史消息分片读取和分页状态提示
- 支持导出图片、视频和语音，提供原图优先及缩略图回退
- 更新安装指引、兼容版本说明和相关自动化测试

tests/unit/account-discovery.test.ts

@@ -0,0 +1,69 @@
+import fs from 'fs-extra'
+import os from 'os'
+import path from 'path'
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+
+const mocked = vi.hoisted(() => ({
+  userData: `${process.env.TEMP || process.env.TMP || '.'}/wxe-account-discovery-tests`
+}))
+
+vi.mock('electron', () => ({
+  app: { getPath: () => mocked.userData }
+}))
+
+import { discoverAccounts } from '../../src/main/services/account-discovery'
+
+describe('account discovery', () => {
+  let root: string
+  const keyStore = {
+    getStatus: vi.fn(async (accountRoot: string) => ({
+      saved: accountRoot.endsWith('account-b'),
+      encryptionAvailable: true
+    }))
+  }
+
+  beforeEach(async () => {
+    root = await fs.mkdtemp(path.join(os.tmpdir(), 'wxe-accounts-'))
+    await Promise.all(
+      ['account-a', 'account-b', 'account-c'].map((name) =>
+        fs.ensureDir(path.join(root, name, 'db_storage'))
+      )
+    )
+    await fs.ensureDir(path.join(root, 'Backup'))
+  })
+
+  afterEach(async () => {
+    await fs.remove(root)
+    await fs.remove(mocked.userData)
+  })
+
+  it('rejects an invalid Backup directory without continuing', async () => {
+    const result = await discoverAccounts(path.join(root, 'Backup'), keyStore as never)
+    expect(result.success).toBe(false)
+    expect(result.accounts).toEqual([])
+  })
+
+  it('lists every direct account and never preselects one from a root directory', async () => {
+    const result = await discoverAccounts(root, keyStore as never)
+    expect(result.success).toBe(true)
+    expect(result.accounts.map((account) => account.directoryName).sort()).toEqual([
+      'account-a',
+      'account-b',
+      'account-c'
+    ])
+    expect(result.preselectedAccountId).toBeUndefined()
+    expect(
+      result.accounts.find((account) => account.directoryName === 'account-b')?.hasSavedDbKey
+    ).toBe(true)
+  })
+
+  it('preselects a directly selected account directory while retaining its card', async () => {
+    const accountRoot = path.join(root, 'account-c')
+    const result = await discoverAccounts(accountRoot, keyStore as never)
+    expect(result.success).toBe(true)
+    expect(result.accounts).toHaveLength(1)
+    expect(result.accounts[0].accountRoot).toBe(accountRoot)
+    expect(result.preselectedAccountId).toBe(result.accounts[0].id)
+    expect(result.accounts[0].selectedByInput).toBe(true)
+  })
+})

tests/unit/connection-diagnostics.test.ts

@@ -0,0 +1,26 @@
+import { describe, expect, it } from 'vitest'
+import { buildSafeDiagnosticSummary } from '../../src/shared/connection-diagnostics'
+
+describe('connection diagnostics', () => {
+  it('contains useful versions and readiness without secrets or full account paths', () => {
+    const summary = buildSafeDiagnosticSummary({
+      platform: 'win32',
+      osVersion: 'Windows 11 fixture',
+      appVersion: 'v2.1.6',
+      wechatVersion: '4.1.9.57',
+      dataStructureVersion: '微信 4.x（WCDB）',
+      dataDirectoryDetected: true,
+      autoDetectSupported: true,
+      wechatRunning: true,
+      accountIdentified: true,
+      dbConnected: false,
+      encryptionAvailable: true
+    })
+
+    expect(summary).toContain('WechatExplorer: v2.1.6')
+    expect(summary).toContain('微信客户端: 4.1.9.57')
+    expect(summary).not.toContain('0123456789abcdef')
+    expect(summary).not.toContain('C:\\Users\\fixture\\xwechat_files\\wxid_secret')
+    expect(summary).not.toContain('wxid_')
+  })
+})

tests/unit/export-media.test.ts

@@ -0,0 +1,62 @@
+import { describe, expect, it } from 'vitest'
+import { renderExportPage } from '../../src/main/export-html-template'
+import { getImageExportAttempts } from '../../src/shared/export-media'
+import type { Message } from '../../src/shared/types'
+
+const baseMessage = (overrides: Partial<Message>): Message => ({
+  id: 'fixture-message',
+  from: 'fixture',
+  type: '文本',
+  datetime: '2026-08-01 10:00:00',
+  content: '',
+  isSender: false,
+  ...overrides
+})
+
+describe('export media', () => {
+  it('always attempts the original before an explicitly enabled thumbnail fallback', () => {
+    const first = getImageExportAttempts({ preferOriginal: true, fallbackThumbnail: true })
+    const repeated = getImageExportAttempts({ preferOriginal: true, fallbackThumbnail: true })
+
+    expect(first).toEqual([
+      { allowThumbnail: false, preferThumbnail: false, fallback: false },
+      { allowThumbnail: true, preferThumbnail: true, fallback: true }
+    ])
+    expect(repeated).toEqual(first)
+  })
+
+  it('renders movable relative audio and video assets plus accurate missing-media details', () => {
+    const html = renderExportPage('脱敏导出', [
+      baseMessage({ id: 'voice', type: '语音', voiceDataUrl: 'voices/voice_1.wav' }),
+      baseMessage({
+        id: 'video',
+        type: '视频',
+        exportMediaType: 'video',
+        exportMediaUrl: 'media/video_2.mp4'
+      }),
+      baseMessage({
+        id: 'missing',
+        type: '语音',
+        exportMediaError: '语音文件缺失：本地未找到语音数据'
+      })
+    ])
+
+    expect(html).toContain(
+      'audio class="audio" controls preload="metadata" src="voices/voice_1.wav"'
+    )
+    expect(html).toContain('video class="media-image" controls src="media/video_2.mp4"')
+    expect(html).toContain('语音文件缺失：本地未找到语音数据')
+    expect(html).not.toMatch(/(?:src|href)="[A-Za-z]:\\/)
+  })
+
+  it('renders explicit and keyboard-accessible lightbox closing controls', () => {
+    const html = renderExportPage('图片预览', [
+      baseMessage({ id: 'image', type: '图片', exportMediaUrl: 'media/image.jpg' })
+    ])
+
+    expect(html).toContain('aria-label="关闭图片预览"')
+    expect(html).toContain("closeButton.addEventListener('click',closeLightbox)")
+    expect(html).toContain('if(event.target===box)closeLightbox()')
+    expect(html).toContain("if(event.key==='Escape')closeLightbox()")
+  })
+})

tests/unit/message-pagination.test.ts

@@ -20,4 +20,14 @@ describe('message pagination', () => {
     )
     expect(merged.map((message) => message.id)).toEqual(['oldest', 'overlap', 'latest'])
   })
+
+  it('keeps cross-year pages continuous through the earliest fixture record', () => {
+    const page2025 = [makeMessage('2025', 1_735_689_600), makeMessage('2026', 1_767_225_600)]
+    const page2017 = [makeMessage('2017', 1_483_228_800), makeMessage('2025', 1_735_689_600)]
+
+    const merged = mergeMessagePages(page2017, page2025)
+
+    expect(merged.map((message) => message.id)).toEqual(['2017', '2025', '2026'])
+    expect(new Set(merged.map((message) => message.id)).size).toBe(merged.length)
+  })
 })

tests/unit/wcdb-message-shards.test.ts

@@ -0,0 +1,45 @@
+import { describe, expect, it, vi } from 'vitest'
+import { Wcdb4Client, type Wcdb4Message } from '../../src/main/wcdb4-client'
+
+const message = (id: string, year: number): Wcdb4Message => ({
+  mesLocalID: id,
+  serverId: `server-${id}`,
+  mesDes: 0,
+  messageType: '1',
+  msgCreateTime: String(Math.floor(Date.UTC(year, 0, 1) / 1000)),
+  msgContent: `fixture-${year}`,
+  raw: {}
+})
+
+describe('WCDB message shard pagination', () => {
+  it('merges cursor and all-store rows for a bounded cross-year page', async () => {
+    const cursor = vi.fn(async () => [message('2025', 2025)])
+    const tableScan = vi.fn(async () => [message('2017', 2017), message('2025', 2025)])
+    const client = Object.assign(Object.create(Wcdb4Client.prototype), {
+      wcdbGetMessageTableStats: vi.fn(),
+      wcdbExecQuery: vi.fn(),
+      getMessagesByCursorAsync: cursor,
+      getMessagesByTableScanAsync: tableScan
+    }) as Wcdb4Client
+
+    const result = await client.getMessagesAsync(
+      'fixture@chatroom',
+      undefined,
+      Math.floor(Date.UTC(2026, 0, 1) / 1000),
+      { limit: 20 }
+    )
+
+    expect(tableScan).toHaveBeenCalledOnce()
+    expect(result.map((item) => item.msgContent)).toEqual(['fixture-2017', 'fixture-2025'])
+  })
+
+  it('reports an unsupported shard query instead of claiming history ended', async () => {
+    const client = Object.assign(Object.create(Wcdb4Client.prototype), {
+      getMessagesByCursorAsync: vi.fn(async () => [])
+    }) as Wcdb4Client
+
+    await expect(
+      client.getMessagesAsync('fixture@chatroom', undefined, 1_767_225_600, { limit: 20 })
+    ).rejects.toThrow('无法检查历史消息分片')
+  })
+})