修复bug，针对部分没有MD5名字的视频也能支持导出

tests/integration/export-media-flow.test.ts

@@ -30,6 +30,7 @@ const state = vi.hoisted(() => ({
   voiceLookups: [] as number[],
   videoLookups: [] as {
     createTime?: number
+    byteLength?: number
     duration?: number
     width?: number
     height?: number
@@ -163,7 +164,13 @@ vi.mock('../../src/main/video-asset-service', () => ({
   VideoAssetService: class {
     resolve(
       _hashes: string[],
-      options?: { createTime?: number; duration?: number; width?: number; height?: number }
+      options?: {
+        createTime?: number
+        byteLength?: number
+        duration?: number
+        width?: number
+        height?: number
+      }
     ): { success: boolean; url: string } {
       state.videoLookups.push(options || {})
       return { success: true, url: 'wxe-media://local/fixture-video' }
@@ -255,7 +262,7 @@ describe('media export flow', () => {
         type: '视频',
         contentData: {
           type: 'video',
-          md5: 'b'.repeat(32),
+          byteLength: 6402169,
           duration: 68,
           width: 279,
           height: 630
@@ -326,6 +333,7 @@ describe('media export flow', () => {
     })
     expect(state.videoLookups[0]).toEqual({
       createTime: 1_785_549_600,
+      byteLength: 6402169,
       duration: 68,
       width: 279,
       height: 630

tests/unit/message-parser.test.ts

@@ -16,6 +16,24 @@ describe('message parser', () => {
     ).toMatchObject({ type: 'sticker', md5: 'abcdefabcdefabcdefabcdefabcdefab' })
   })
 
+  it('keeps video metadata when WeChat omits every MD5 field', () => {
+    const parsed = parseMessageContent(
+      '<msg><videomsg length="6402169" playlength="30" cdnthumbwidth="224" cdnthumbheight="398" aeskey="25201cc658042689d1ad6747cea2b240" rawmd5="" /></msg>',
+      43
+    )
+
+    expect(parsed).toEqual({
+      type: 'video',
+      md5: undefined,
+      newMd5: undefined,
+      rawMd5: undefined,
+      byteLength: 6402169,
+      duration: 30,
+      width: 224,
+      height: 398
+    })
+  })
+
   it('parses merged forwards and preserves nested visible text', () => {
     const parsed = parseMessageContent(
       '<appmsg><type>19</type><title>转发多条内容</title><recorditem><dataitem datatype="1"><sourcename>测试成员</sourcename><datadesc>脱敏内容</datadesc></dataitem></recorditem></appmsg>',

tests/unit/video-asset-service.test.ts

@@ -119,6 +119,30 @@ describe('VideoAssetService local fallback', () => {
     expect(service.pathForUrl(result.poster!)).toBe(posterPath)
   })
 
+  it('finds an MD5-less video by byte length, thumbnail size, and duration', async () => {
+    const { accountRoot, service } = createService()
+    const month = join(accountRoot, 'msg', 'video', '2026-08')
+    mkdirSync(month, { recursive: true })
+    const targetStem = '9a3b17272822a65ce6e396ecded9ccdc'
+    const otherStem = '47e890579eacf48c46187ae998332202'
+    const target = mp4Fixture(30, 'target-video-with-distinct-byte-length')
+    writeFileSync(join(month, `${targetStem}.mp4`), target)
+    writeFileSync(join(month, `${targetStem}_thumb.jpg`), jpegFixture(224, 398))
+    writeFileSync(join(month, `${otherStem}.mp4`), mp4Fixture(30, 'other'))
+    writeFileSync(join(month, `${otherStem}_thumb.jpg`), jpegFixture(224, 398))
+
+    const result = await service.resolve([], {
+      createTime: monthTimestamp(2026, 8),
+      byteLength: target.length,
+      duration: 30,
+      width: 224,
+      height: 398
+    })
+
+    expect(result.success).toBe(true)
+    expect(service.pathForUrl(result.url!)).toBe(join(month, `${targetStem}.mp4`))
+  })
+
   it('does not guess when multiple files match the same metadata', async () => {
     const { accountRoot, service } = createService()
     const month = join(accountRoot, 'msg', 'video', '2026-02')