diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 59280e01..190901cd 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -347,6 +347,8 @@ jobs:
         run: ./installer/tests/package-files.ps1
       - name: Test that the installer preserves user data on upgrade
         run: ./installer/tests/preserve-user-data.ps1
+      - name: Test that bundled skins back up changed user copies before overwriting
+        run: ./installer/tests/bundled-skins.ps1
       - name: Stop local packaging after failed component builds
         run: ./installer/tests/build-failures.ps1
       - name: Test local Server test entrypoints in a moved checkout
diff --git a/AGENTS.md b/AGENTS.md
index ce87ac9d..69726b1c 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -17,7 +17,7 @@ Windows 端的全部一方源码在本仓。**合仓改变的是仓库数量，
 | `ui-html/` | 候选窗、工具栏、菜单、设置页的 HTML / CSS / JS | [ui-html/README.md](ui-html/README.md) |
 | `installer/` | 收集产物、自签名、Inno Setup 打包 | [installer/README.md](installer/README.md) |
 | `log/` | 日志采集库 | — |
-| `skins/` | 外部皮肤合集，每个子目录一个 `skin.toml` 皮肤包；不打进安装包 | [skins/README.md](skins/README.md) |
+| `skins/` | 外部皮肤合集，每个子目录一个 `skin.toml` 皮肤包；除素材授权未核实的外随安装包装到数据目录，同名且改过的旧版改名 `.bak` 保留 | [skins/README.md](skins/README.md) |
 | `examples/skin-examples/` | 外部皮肤制作样例、字段说明、预览页与安装脚本；本目录单独采用 MIT 授权 | [examples/skin-examples/README.md](examples/skin-examples/README.md) |
 | `experiments/tsf-edit-control/` | TSF 编辑控件实验工程，不参与产品构建 | — |
 | `vendor/` | submodule：`opencc`、`cpp-pinyin` | 上游仓库 |
diff --git a/installer/.gitignore b/installer/.gitignore
index ee997b00..ede6251c 100644
--- a/installer/.gitignore
+++ b/installer/.gitignore
@@ -5,6 +5,8 @@ server_exe/
 tsf_dll/
 app_data/
 default_skins/
+bundled_skins/
+bundled_skins.manifest
 MetasequoiaIME.ico
 /THIRD_PARTY_NOTICES.txt
 /LICENSE.txt
diff --git a/installer/Prepare-PackageFiles.ps1 b/installer/Prepare-PackageFiles.ps1
index 6bfb6635..4889ca96 100644
--- a/installer/Prepare-PackageFiles.ps1
+++ b/installer/Prepare-PackageFiles.ps1
@@ -64,6 +64,7 @@ $tsf32Pdb = Join-Path $RepoRoot (Join-Path $TsfDirectory 'build32-release\Releas
 $tsf64Pdb = Join-Path $RepoRoot (Join-Path $TsfDirectory 'build64-release\Release\MetasequoiaImeTsf.pdb')
 $webviewRoot = Join-Path $RepoRoot (Join-Path $UiHtmlDirectory 'webview2')
 $defaultSkinsSource = Join-Path $RepoRoot 'skins\default'
+$bundledSkinsSource = Join-Path $RepoRoot 'skins'
 $serverConfig = Join-Path $RepoRoot (Join-Path $ServerDirectory 'assets\config\config.toml')
 $factoryConfig = Join-Path $PSScriptRoot 'default_config\config.default.toml'
 $pinyinTable = Join-Path $RepoRoot (Join-Path $ServerDirectory 'assets\tables\pinyin.txt')
@@ -243,6 +244,50 @@ $targetDefaultSkins = Join-Path $PSScriptRoot 'default_skins'
 Reset-Directory -LiteralPath $targetDefaultSkins
 Copy-DirectoryContents -Source $defaultSkinsSource -Destination $targetDefaultSkins
 
+# 仓库 skins\ 下的外部皮肤随包装到数据目录的 skins\<id>，同名的直接覆盖。覆盖前安装程序拿
+# bundled_skins.manifest 核对用户机器上的同名目录：内容与随包的一模一样就不动，否则先改名成
+# <id>.bak 备份（Server 扫描时跳过 .bak 目录）。清单每行是「id|相对路径|sha256」，
+# 安装程序按字节比较，所以路径限定 ASCII、不能含 |。
+# 素材授权没核实的皮肤（[license] assets = "UNVERIFIED..."）只能放在仓库里演示，不进安装包。
+$targetBundledSkins = Join-Path $PSScriptRoot 'bundled_skins'
+$bundledSkinsManifest = Join-Path $PSScriptRoot 'bundled_skins.manifest'
+Reset-Directory -LiteralPath $targetBundledSkins
+$manifestLines = [Collections.Generic.List[string]]::new()
+$bundledSkinIds = [Collections.Generic.List[string]]::new()
+foreach ($skinDir in @(Get-ChildItem -LiteralPath $bundledSkinsSource -Directory | Sort-Object Name)) {
+    $id = $skinDir.Name
+    if ($id -ceq 'default') { continue }
+    if ($id -cnotmatch '^[a-z0-9][a-z0-9._-]{0,63}$' -or $id -match '\.bak$') {
+        throw "皮肤目录名不是有效的外部皮肤 ID：$($skinDir.FullName)"
+    }
+    $skinManifest = Join-Path $skinDir.FullName 'skin.toml'
+    Assert-PathExists -LiteralPath $skinManifest -Description "皮肤 $id 的 skin.toml"
+    $skinText = [IO.File]::ReadAllText($skinManifest)
+    if ($skinText -notmatch "(?m)^\s*id\s*=\s*`"$([regex]::Escape($id))`"\s*(#.*)?$") {
+        throw "皮肤 $id 的 skin.toml 里 id 与目录名不一致，Server 不会加载它：$skinManifest"
+    }
+    if ($skinText -match '(?m)^\s*assets\s*=\s*"UNVERIFIED') {
+        Write-Host "跳过皮肤 ${id}：素材授权未核实，不随安装包分发。"
+        continue
+    }
+    $destination = Join-Path $targetBundledSkins $id
+    Copy-DirectoryContents -Source $skinDir.FullName -Destination $destination
+    foreach ($file in @(Get-ChildItem -LiteralPath $destination -Recurse -File -Force | Sort-Object FullName)) {
+        $relative = $file.FullName.Substring($destination.Length + 1)
+        if ($relative -notmatch '^[\x20-\x7E]+$' -or $relative.Contains('|')) {
+            throw "皮肤文件名只能用 ASCII 且不能含 |（安装程序按清单逐字节比对）：$($file.FullName)"
+        }
+        $hash = (Get-FileHash -LiteralPath $file.FullName -Algorithm SHA256).Hash.ToLowerInvariant()
+        $manifestLines.Add("$id|$relative|$hash")
+    }
+    $bundledSkinIds.Add($id)
+}
+if ($bundledSkinIds.Count -eq 0) {
+    throw "没有可随包分发的外部皮肤：$bundledSkinsSource"
+}
+[IO.File]::WriteAllLines($bundledSkinsManifest, $manifestLines, [Text.UTF8Encoding]::new($false))
+Write-Host "随包皮肤：$($bundledSkinIds -join ', ')"
+
 # Server Release 输出整体复制，但测试程序及其 PDB 绝不能进入安装包。
 # 带 -IncludeSymbols 时其他 PDB 保留在对应 EXE 旁边，方便安装后直接进行崩溃分析。
 Reset-Directory -LiteralPath $targetServer
diff --git a/installer/README.md b/installer/README.md
index 1be72be7..a0e3fb3e 100644
--- a/installer/README.md
+++ b/installer/README.md
@@ -42,6 +42,7 @@ pwsh -File ./Prepare-PackageFiles.ps1 -TargetVersion 1.2.3 -RepoRoot .. `
 - **数据目录必须整个归输入法**（[#537](https://github.com/metasequoiaime/MSIME-Windows/issues/537)）。用户选的目录里已经有别的文件、或者选了驱动器根目录时，安装器改用其中的 `metasequoiaime` 子目录，并在向导里把实际位置告诉用户；连那个子目录也不空就拒绝。输入法用过的目录（有标记，或历史默认位置）原样沿用
 - 安装器在数据目录里放一个 `.metasequoiaime-data` 标记文件。只有标记里带 `exclusive: adopted empty by the installer` 这一行（安装时目录是空的），或目录就是历史默认位置，覆盖安装才整目录清理、卸载才整目录删除
 - 旧版安装器不管目录里原来有什么都写标记，所以只有旧标记（没有那一行）的目录不能再信：覆盖安装、换目录和卸载都只按 `IsShippedAppDataItem` / `IsRuntimeAppDataItem` / `IsPreservedAppDataItem` 名单删输入法自己的条目，`html`、`logs`、`skins` 这种通用目录名只删输入法写进去的部分，最后目录空了才删目录。包里新增顶层文件要同步 `IsShippedAppDataItem`，`tests/package-files.ps1` 会拿真实打出的 `app_data` 核对；Server 在数据目录根下新写文件要同步 `IsRuntimeAppDataItem`
+- 仓库 `skins\` 下的外部皮肤（除 `default\` 和素材授权为 `UNVERIFIED*` 的）随包装到 `skins\<id>`，完整包和轻量包都带，卸载不删。`Prepare-PackageFiles.ps1` 同时写出 `bundled_skins.manifest`（每行 `id|相对路径|sha256`），安装器在 `PrepareToInstall` 里拿它核对用户机器上的同名目录：文件集合和内容完全一致就直接覆盖，否则先改名成 `<id>.bak`（已有就 `<id>.2.bak`……，不覆盖旧备份）再装。Server 扫描皮肤时跳过 `*.bak` 目录。`tests/bundled-skins.ps1` 把这段 Pascal 编进探针安装器真跑一遍
 - 静默安装用 `/DATADIR="D:\MetasequoiaIME"` 指定；该值在 `PrepareToInstall` 里和向导页走同一套换子目录和校验
 
 ## 运行时依赖检查
diff --git a/installer/msime_setup.iss b/installer/msime_setup.iss
index a4f1641b..9d65ed86 100644
--- a/installer/msime_setup.iss
+++ b/installer/msime_setup.iss
@@ -132,6 +132,13 @@ Source: "{#MySourceRoot}\default_skins\*"; \
     DestDir: "{code:GetDataDir}\skins\default"; \
     Flags: onlyifdoesntexist recursesubdirs createallsubdirs uninsneveruninstall
 
+; 仓库 skins\ 下的外部皮肤，同名目录整目录覆盖。用户机器上的同名皮肤和随包的不一样时，
+; PrepareToInstall 里的 BackupChangedBundledSkins 先把它改名成 <id>.bak 再复制。
+Source: "{#MySourceRoot}\bundled_skins\*"; \
+    DestDir: "{code:GetDataDir}\skins"; \
+    Flags: ignoreversion recursesubdirs createallsubdirs uninsneveruninstall
+Source: "{#MySourceRoot}\bundled_skins.manifest"; Flags: dontcopy
+
 #ifdef LightPackage
 ; 轻量包只覆盖前端 HTML，不带词库/辅助码/出厂配置。
 Source: "{#MySourceRoot}\app_data\html\*"; \
@@ -1398,6 +1405,115 @@ begin
   RemoveDataDir(OldDir);
 end;
 
+function CountFilesUnder(const Directory: String): Integer;
+var
+  FindRec: TFindRec;
+begin
+  Result := 0;
+  if FindFirst(AddBackslash(Directory) + '*', FindRec) then
+  begin
+    try
+      repeat
+        if (FindRec.Name <> '.') and (FindRec.Name <> '..') then
+        begin
+          if (FindRec.Attributes and FILE_ATTRIBUTE_DIRECTORY) <> 0 then
+            Result := Result + CountFilesUnder(AddBackslash(Directory) + FindRec.Name)
+          else
+            Result := Result + 1;
+        end;
+      until not FindNext(FindRec);
+    finally
+      FindClose(FindRec);
+    end;
+  end;
+end;
+
+{ 数据目录里的同名皮肤与随包的文件集合、内容完全一致时返回 True。
+  清单每行「id|相对路径|sha256」，由 Prepare-PackageFiles.ps1 按 id 分组写出。}
+function SkinMatchesBundle(const SkinDir, Id: String; const Lines: TArrayOfString): Boolean;
+var
+  Index, P, Expected: Integer;
+  Rest, FilePath: String;
+begin
+  Result := False;
+  Expected := 0;
+  for Index := 0 to GetArrayLength(Lines) - 1 do
+  begin
+    P := Pos('|', Lines[Index]);
+    if (P = 0) or (Copy(Lines[Index], 1, P - 1) <> Id) then
+      continue;
+    Rest := Copy(Lines[Index], P + 1, Length(Lines[Index]));
+    P := Pos('|', Rest);
+    if P = 0 then
+      exit;
+    Expected := Expected + 1;
+    FilePath := AddBackslash(SkinDir) + Copy(Rest, 1, P - 1);
+    if not FileExists(FilePath) then
+      exit;
+    try
+      if CompareText(GetSHA256OfFile(FilePath), Copy(Rest, P + 1, Length(Rest))) <> 0 then
+        exit;
+    except
+      exit;
+    end;
+  end;
+  { 多出来的文件也算改过：整目录覆盖不会删它们，留着就和随包的不是一个皮肤了。}
+  Result := CountFilesUnder(SkinDir) = Expected;
+end;
+
+{ 覆盖随包皮肤之前，把用户机器上内容不同的同名目录改名成 <id>.bak；
+  已经有 .bak 就用 <id>.2.bak、<id>.3.bak……，不覆盖上一次的备份——那可能正是用户改过的版本。
+  内容一样的不备份，否则每次升级都会多一份一模一样的 .bak。Server 扫描皮肤时跳过 .bak 目录。}
+function BackupChangedBundledSkins: String;
+var
+  Lines: TArrayOfString;
+  Index, P, N: Integer;
+  Id, LastId, SkinsDir, SkinDir, BackupDir: String;
+begin
+  Result := '';
+  ExtractTemporaryFile('bundled_skins.manifest');
+  if not LoadStringsFromFile(ExpandConstant('{tmp}\bundled_skins.manifest'), Lines) then
+  begin
+    Result := '无法读取随包皮肤清单，安装文件可能不完整。';
+    exit;
+  end;
+  SkinsDir := AddBackslash(GetDataDir('')) + 'skins';
+  LastId := '';
+  for Index := 0 to GetArrayLength(Lines) - 1 do
+  begin
+    P := Pos('|', Lines[Index]);
+    if P = 0 then
+      continue;
+    Id := Copy(Lines[Index], 1, P - 1);
+    if Id = LastId then
+      continue;
+    LastId := Id;
+    SkinDir := AddBackslash(SkinsDir) + Id;
+    if not DirExists(SkinDir) then
+      continue;
+    if SkinMatchesBundle(SkinDir, Id, Lines) then
+    begin
+      Log('Bundled skin ' + Id + ' is unchanged; no backup needed.');
+      continue;
+    end;
+    BackupDir := SkinDir + '.bak';
+    N := 2;
+    while DirExists(BackupDir) or FileExists(BackupDir) do
+    begin
+      BackupDir := AddBackslash(SkinsDir) + Id + '.' + IntToStr(N) + '.bak';
+      N := N + 1;
+    end;
+    if not RenameFile(SkinDir, BackupDir) then
+    begin
+      Result :=
+        '无法备份皮肤目录 ' + SkinDir + '。' + #13#10 +
+        '请关闭正在打开该目录或其中图片的程序后重试安装。';
+      exit;
+    end;
+    Log('Backed up skin ' + SkinDir + ' to ' + BackupDir);
+  end;
+end;
+
 function PrepareToInstall(var NeedsRestart: Boolean): String;
 var
   DataDirProblem: String;
@@ -1428,6 +1544,13 @@ begin
     Result := DataDirProblem;
     exit;
   end;
+  { 迁移之后再备份：换了数据目录时，要比对的是已经搬到新目录的皮肤。}
+  DataDirProblem := BackupChangedBundledSkins;
+  if DataDirProblem <> '' then
+  begin
+    Result := DataDirProblem;
+    exit;
+  end;
 #ifdef LightPackage
   { 轻量包不替换词库：只清 HTML 和 Server/TSF，保留本机 msime.db 等。}
   TryDeleteTree(AddBackslash(GetDataDir('')) + 'html');
diff --git a/installer/tests/bundled-skins.ps1 b/installer/tests/bundled-skins.ps1
new file mode 100644
index 00000000..98508ba1
--- /dev/null
+++ b/installer/tests/bundled-skins.ps1
@@ -0,0 +1,107 @@
+# 覆盖随包皮肤之前的备份逻辑跑在安装器的 Pascal 脚本里，只看 .iss 文本证明不了它对。
+# 这里把 msime_setup.iss 里的那几个函数原样抠出来，编进一个只在 InitializeSetup 里调用它们、
+# 数据目录指向临时目录的探针安装器，真跑一遍再看目录。
+$ErrorActionPreference = 'Stop'
+Set-StrictMode -Version Latest
+
+function Resolve-Iscc {
+    $command = Get-Command 'ISCC.exe' -CommandType Application -ErrorAction SilentlyContinue | Select-Object -First 1
+    if ($command) { return $command.Source }
+    foreach ($version in @(7, 6)) {
+        foreach ($root in @(${env:ProgramFiles(x86)}, $env:ProgramFiles, (Join-Path $env:LOCALAPPDATA 'Programs'))) {
+            if (-not $root) { continue }
+            $candidate = Join-Path $root "Inno Setup $version\ISCC.exe"
+            if (Test-Path -LiteralPath $candidate -PathType Leaf) { return $candidate }
+        }
+    }
+    throw '找不到 ISCC.exe'
+}
+
+$work = Join-Path ([IO.Path]::GetTempPath()) ('msime-bundled-skins-' + [Guid]::NewGuid())
+function Write-Text([string]$Path, [string]$Text) {
+    New-Item -ItemType Directory -Force -Path (Split-Path $Path) | Out-Null
+    [IO.File]::WriteAllText($Path, $Text)
+}
+try {
+    $bundle = Join-Path $work 'bundled_skins'
+    $skins = Join-Path $work 'data\skins'
+    $ids = @('same', 'changed', 'extra', 'missing', 'twice', 'absent')
+    foreach ($id in $ids) {
+        Write-Text (Join-Path $bundle "$id\skin.toml") "id = `"$id`"`n"
+        Write-Text (Join-Path $bundle "$id\assets\bg.png") "$id png"
+    }
+    $manifest = foreach ($id in $ids) {
+        foreach ($file in @('assets\bg.png', 'skin.toml')) {
+            $hash = (Get-FileHash (Join-Path $bundle "$id\$file") -Algorithm SHA256).Hash.ToLowerInvariant()
+            "$id|$file|$hash"
+        }
+    }
+    $manifestPath = Join-Path $work 'bundled_skins.manifest'
+    [IO.File]::WriteAllLines($manifestPath, [string[]]$manifest, [Text.UTF8Encoding]::new($false))
+
+    New-Item -ItemType Directory -Force -Path $skins | Out-Null
+    foreach ($id in @('same', 'changed', 'extra', 'missing', 'twice')) {
+        Copy-Item (Join-Path $bundle $id) $skins -Recurse
+    }
+    Write-Text (Join-Path $skins 'changed\assets\bg.png') 'user edit'
+    Write-Text (Join-Path $skins 'extra\assets\mine.png') 'user file'
+    Remove-Item (Join-Path $skins 'missing\assets\bg.png')
+    Write-Text (Join-Path $skins 'twice\skin.toml') 'user edit'
+    Write-Text (Join-Path $skins 'twice.bak\skin.toml') 'earlier backup'
+
+    $iss = [IO.File]::ReadAllText((Join-Path $PSScriptRoot '../msime_setup.iss'))
+    $functions = [regex]::Match($iss, '(?s)function CountFilesUnder\(.*?(?=\r?\nfunction PrepareToInstall\()').Value
+    if (-not $functions) { throw 'msime_setup.iss is missing the bundled skin backup functions' }
+    $resultPath = Join-Path $work 'result.txt'
+    $probe = Join-Path $work 'probe.iss'
+    @"
+[Setup]
+AppName=Bundled skin probe
+AppVersion=1.0
+CreateAppDir=no
+PrivilegesRequired=lowest
+Uninstallable=no
+OutputDir=$work
+OutputBaseFilename=bundled-skin-probe
+[Files]
+Source: "$manifestPath"; Flags: dontcopy
+[Code]
+function GetDataDir(Param: String): String;
+begin
+  Result := '$(Join-Path $work 'data')';
+end;
+
+$functions
+
+function InitializeSetup: Boolean;
+var
+  Problem: String;
+begin
+  Problem := BackupChangedBundledSkins;
+  if Problem = '' then
+    SaveStringToFile('$resultPath', 'ok', False)
+  else
+    SaveStringToFile('$resultPath', 'error', False);
+  Result := False;
+end;
+"@ | Set-Content -Path $probe -Encoding UTF8
+
+    & (Resolve-Iscc) /Q $probe
+    if ($LASTEXITCODE -ne 0) { throw "ISCC failed to compile the probe (exit code $LASTEXITCODE)" }
+    $process = Start-Process (Join-Path $work 'bundled-skin-probe.exe') -ArgumentList '/VERYSILENT', '/SUPPRESSMSGBOXES' -PassThru -Wait
+    if (-not (Test-Path $resultPath)) { throw "Probe did not run (exit code $($process.ExitCode))" }
+    if ([IO.File]::ReadAllText($resultPath) -ne 'ok') { throw 'BackupChangedBundledSkins reported an error' }
+
+    $actual = @(Get-ChildItem -LiteralPath $skins -Directory | ForEach-Object Name | Sort-Object)
+    $expected = @('changed.bak', 'extra.bak', 'missing.bak', 'same', 'twice.2.bak', 'twice.bak' | Sort-Object)
+    if (($actual -join ',') -cne ($expected -join ',')) {
+        throw "Unexpected skins directory after backup: $($actual -join ', ')"
+    }
+    if ([IO.File]::ReadAllText((Join-Path $skins 'changed.bak\assets\bg.png')) -ne 'user edit') { throw 'changed.bak lost the user edit' }
+    if (-not (Test-Path (Join-Path $skins 'extra.bak\assets\mine.png'))) { throw 'extra.bak lost the user file' }
+    if ([IO.File]::ReadAllText((Join-Path $skins 'twice.bak\skin.toml')) -ne 'earlier backup') { throw 'An earlier backup was overwritten' }
+    if ([IO.File]::ReadAllText((Join-Path $skins 'twice.2.bak\skin.toml')) -ne 'user edit') { throw 'twice.2.bak lost the user edit' }
+    Write-Host 'Bundled skins: unchanged kept, changed/extra/missing backed up, earlier backups preserved'
+} finally {
+    if (Test-Path $work) { Remove-Item $work -Recurse -Force }
+}
diff --git a/installer/tests/package-files.ps1 b/installer/tests/package-files.ps1
index b11061da..d0d2a9f5 100644
--- a/installer/tests/package-files.ps1
+++ b/installer/tests/package-files.ps1
@@ -47,6 +47,9 @@ try {
         'ui-html/webview2/settings/ime-settings/dist/index.html',
         'skins/default/fluent/skin.toml'
     )) { Write-Fixture $file }
+    Write-Fixture 'skins/demo-skin/skin.toml' "schema_version = 1`nid = `"demo-skin`"`n"
+    Write-Fixture 'skins/demo-skin/assets/background.png' 'png'
+    Write-Fixture 'skins/unverified/skin.toml' "schema_version = 1`nid = `"unverified`"`n[license]`nassets = `"UNVERIFIED-DEMO-ONLY`"`n"
     Write-Fixture 'server/assets/tables/pinyin.txt' 'xing'
     Write-Fixture 'MetasequoiaImeDict/out/dictionary-manifest.json' '{"manifest_version":1}'
     $english = Join-Path $fixture 'MetasequoiaImeDict/out/english.db'
@@ -72,6 +75,24 @@ try {
     if ($issText -notmatch '(?s)Source: "\{#MySourceRoot\}\\default_skins\\\*";[^\r\n]*\\\s*DestDir: "\{code:GetDataDir\}\\skins\\default";[^\r\n]*\\\s*Flags: onlyifdoesntexist') {
         throw 'Default skin settings must be installed to skins\default with onlyifdoesntexist'
     }
+    # 仓库 skins\ 下的外部皮肤随包分发；素材授权未核实的不进包，skins\default 走上面那条。
+    foreach ($file in @('bundled_skins/demo-skin/skin.toml', 'bundled_skins/demo-skin/assets/background.png')) {
+        if (-not (Test-Path (Join-Path $installer $file))) { throw "Missing bundled skin file: $file" }
+    }
+    foreach ($excluded in @('bundled_skins/unverified', 'bundled_skins/default')) {
+        if (Test-Path (Join-Path $installer $excluded)) { throw "Bundled a skin that must not ship: $excluded" }
+    }
+    $expectedManifest = @(
+        "demo-skin|assets\background.png|$((Get-FileHash (Join-Path $fixture 'skins/demo-skin/assets/background.png') -Algorithm SHA256).Hash.ToLowerInvariant())",
+        "demo-skin|skin.toml|$((Get-FileHash (Join-Path $fixture 'skins/demo-skin/skin.toml') -Algorithm SHA256).Hash.ToLowerInvariant())"
+    )
+    $actualManifest = @(Get-Content -LiteralPath (Join-Path $installer 'bundled_skins.manifest'))
+    if (($actualManifest -join "`n") -cne ($expectedManifest -join "`n")) {
+        throw "Unexpected bundled skin manifest:`n$($actualManifest -join "`n")"
+    }
+    if ($issText -notmatch '(?s)Source: "\{#MySourceRoot\}\\bundled_skins\\\*";[^\r\n]*\\\s*DestDir: "\{code:GetDataDir\}\\skins";[^\r\n]*\\\s*Flags: ignoreversion') {
+        throw 'Bundled skins must overwrite skins\<id> in the data directory'
+    }
     # 数据目录不整个归输入法时（旧版安装器把标记写进了用户原有的文件夹，#537），卸载只按
     # IsShippedAppDataItem 等名单删。包里新增了顶层条目而名单没跟上，卸载就会把它漏在用户目录里。
     $iss = [IO.File]::ReadAllText((Join-Path $installer 'msime_setup.iss'))
diff --git a/server/src/skin/candidate_skin_catalog.cpp b/server/src/skin/candidate_skin_catalog.cpp
index 9c58ad58..c7b91b4d 100644
--- a/server/src/skin/candidate_skin_catalog.cpp
+++ b/server/src/skin/candidate_skin_catalog.cpp
@@ -291,6 +291,17 @@ bool IsSafeId(const std::string &id)
     });
 }
 
+bool IsBackupFolder(const std::string &folder)
+{
+    constexpr std::string_view kSuffix = ".bak";
+    if (folder.size() < kSuffix.size())
+    {
+        return false;
+    }
+    return std::equal(kSuffix.begin(), kSuffix.end(), folder.end() - kSuffix.size(),
+                      [](char a, char b) { return a == std::tolower(static_cast<unsigned char>(b)); });
+}
+
 bool Supports(const Package &package, const std::string &layout, const std::string &theme)
 {
     return std::find(package.layouts.begin(), package.layouts.end(), layout) != package.layouts.end() &&
@@ -493,7 +504,9 @@ ScanResult Scan(const std::filesystem::path &skinsRoot)
             continue;
         }
         const std::string folder = it->path().filename().u8string();
-        if (folder == kDefaultSkinsFolder)
+        // <id>.bak 是安装包覆盖随包皮肤前留下的旧版本：manifest 的 id 与目录名对不上，
+        // 不跳过就会在设置页被列成一条损坏的皮肤。
+        if (folder == kDefaultSkinsFolder || IsBackupFolder(folder))
         {
             continue;
         }
diff --git a/server/src/skin/candidate_skin_catalog.h b/server/src/skin/candidate_skin_catalog.h
index 6cfdafa8..fda7ddb3 100644
--- a/server/src/skin/candidate_skin_catalog.h
+++ b/server/src/skin/candidate_skin_catalog.h
@@ -118,6 +118,8 @@ inline constexpr bool kDefaultPageArrows = false;
 const std::vector<std::string> &BuiltInIds();
 bool IsBuiltIn(const std::string &id);
 bool IsSafeId(const std::string &id);
+// 安装包覆盖同名随包皮肤前，把旧目录改名成 <id>.bak（重名时 <id>.2.bak …）；Scan 跳过它们。
+bool IsBackupFolder(const std::string &folder);
 bool Supports(const Package &package, const std::string &layout, const std::string &theme);
 std::optional<Package> Load(const std::filesystem::path &skinsRoot, const std::string &id,
                             std::string *error = nullptr);
diff --git a/server/tests/src/test_candidate_skin_catalog_page_arrows.cpp b/server/tests/src/test_candidate_skin_catalog_page_arrows.cpp
index 701ce497..a866be8a 100644
--- a/server/tests/src/test_candidate_skin_catalog_page_arrows.cpp
+++ b/server/tests/src/test_candidate_skin_catalog_page_arrows.cpp
@@ -130,3 +130,24 @@ TEST_CASE(candidate_skin_scan_skips_default_settings_folder)
     REQUIRE(!CandidateSkinCatalog::Load(root, "default").has_value());
     Cleanup(root);
 }
+
+// The installer renames a bundled skin the user already had to <id>.bak (or <id>.2.bak) before overwriting it.
+// Those backups keep the original manifest id, so without skipping them the settings page would list each one as
+// a broken skin.
+TEST_CASE(candidate_skin_scan_skips_installer_backups)
+{
+    const auto root = MakeSkinsRoot(L"backup");
+    WriteExternalSkin(root, "ext", "fluent", "");
+    fs::copy(root / L"ext", root / L"ext.bak", fs::copy_options::recursive);
+    fs::copy(root / L"ext", root / L"ext.2.bak", fs::copy_options::recursive);
+    fs::copy(root / L"ext", root / L"ext.3.BAK", fs::copy_options::recursive);
+
+    const auto scan = CandidateSkinCatalog::Scan(root);
+    REQUIRE(scan.issues.empty());
+    REQUIRE(scan.packages.size() == 1);
+    REQUIRE(scan.packages[0].id == "ext");
+    REQUIRE(CandidateSkinCatalog::IsBackupFolder("ext.bak"));
+    REQUIRE(!CandidateSkinCatalog::IsBackupFolder("bak"));
+    REQUIRE(!CandidateSkinCatalog::IsBackupFolder("ext.backup"));
+    Cleanup(root);
+}
diff --git a/skins/README.md b/skins/README.md
index 0764fd31..5898c4a0 100644
--- a/skins/README.md
+++ b/skins/README.md
@@ -31,7 +31,9 @@
 
 ## 安装
 
-把想用的皮肤目录整个复制到：
+除 `niya-demo`（素材授权未核实）外，这里的皮肤都随安装包装到数据目录的 `skins\<id>`。用户那边已有同名皮肤且内容和随包的不一样（改过、多了或少了文件）时，安装器先把它改名成 `<id>.bak` 保留下来（已有 `.bak` 则用 `<id>.2.bak`……），再装新版本；输入法不会把 `.bak` 目录列成皮肤。
+
+手动安装时，把想用的皮肤目录整个复制到：
 
 ```
 %LOCALAPPDATA%\metasequoiaime\skins\