diff --git a/.github/workflows/windows-installer-check.yml b/.github/workflows/windows-installer-check.yml
index 183dc9e..8431a4b 100644
--- a/.github/workflows/windows-installer-check.yml
+++ b/.github/workflows/windows-installer-check.yml
@@ -14,6 +14,21 @@ concurrency:
   cancel-in-progress: false
 
 jobs:
+  msi-probe:
+    name: Diagnose legacy MSI discovery
+    runs-on: windows-latest
+    timeout-minutes: 10
+    steps:
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5
+      - name: Install NSIS compiler for the isolated probe
+        shell: pwsh
+        run: |
+          if (-not (Test-Path "${env:ProgramFiles(x86)}\NSIS\makensis.exe")) {
+            choco install nsis --yes --no-progress
+          }
+      - name: Compare MSI discovery in 64-bit, 32-bit and installer processes
+        shell: pwsh
+        run: ./scripts/windows-msi-probe.ps1
   windows-installer:
     name: Verify Windows update migration
     runs-on: windows-latest
@@ -36,15 +51,16 @@ jobs:
       - uses: Swatinem/rust-cache@e18b497796c12c097a38f9edb9d0641fb99eee32
         with:
           workspaces: apps/desktop/src-tauri
+          cache-on-failure: true
       - run: pnpm install --frozen-lockfile
       - run: pnpm --dir apps/desktop typecheck
       - run: cargo test --manifest-path apps/desktop/src-tauri/Cargo.toml --lib --locked -- --test-threads=1
-      - name: Build installer without publishing or release signing credentials
+      - name: Build test installer without publishing or release signing credentials
         run: |
           Set-Content -Path "$env:RUNNER_TEMP\installer-check.json" -Value '{"bundle":{"createUpdaterArtifacts":false}}' -Encoding utf8
-          pnpm --dir apps/desktop tauri build --bundles nsis --config "$env:RUNNER_TEMP\installer-check.json" --ci
+          pnpm --dir apps/desktop tauri build --debug --bundles nsis --config "$env:RUNNER_TEMP\installer-check.json" --ci
       - name: Test real MSI migration and subsequent updates
         run: |
-          $installers = @(Get-ChildItem apps/desktop/src-tauri/target/release/bundle/nsis -Filter '*.exe')
+          $installers = @(Get-ChildItem apps/desktop/src-tauri/target/debug/bundle/nsis -Filter '*.exe')
           if ($installers.Count -ne 1) { throw 'Expected one Windows installer.' }
           ./scripts/windows-install-smoke.ps1 -Installer $installers[0].FullName
diff --git a/apps/desktop/src-tauri/nsis/installer.nsi b/apps/desktop/src-tauri/nsis/installer.nsi
index ee98577..facc446 100644
--- a/apps/desktop/src-tauri/nsis/installer.nsi
+++ b/apps/desktop/src-tauri/nsis/installer.nsi
@@ -118,6 +118,7 @@ Var CXPathDepth
 Var CXDestinationFull
 Var CXDestinationReal
 Var CXDirectoryIndex
+Var CXReservedPath
 !define CX_DIRECTORY_KEY "Software\${MANUFACTURER}\${PRODUCTNAME} Installer\LegacyDirectories"
 
 Function CXLog
@@ -125,7 +126,8 @@ Function CXLog
   Push $R8
   DetailPrint "$R9"
   FileOpen $R8 "$CXLogPath" a
-  FileWrite $R8 "$R9$\r$\n"
+  FileSeek $R8 0 END
+  FileWriteUTF16LE $R8 "$R9$\r$\n"
   FileClose $R8
   Pop $R8
   Pop $R9
@@ -267,6 +269,21 @@ Function CXValidateDestination
       Push "旧版安装目录记录不完整，已停止安装。 / The legacy directory record is incomplete."
       Call CXFail
     ${EndIf}
+    StrCpy $CXReservedPath $1
+    StrCpy $2 $0 5
+    ${If} $2 == "Path_"
+      ; Re-resolve the old lexical name as well: a junction may have changed
+      ; since cancellation. Keep the originally saved Real_ guard too.
+      StrCpy $CXPathInput $CXReservedPath
+      Call CXCanonicalDirectory
+      StrLen $2 $CXPathResult
+      StrCpy $3 $CXDestinationReal $2
+      ${If} $3 == $CXPathResult
+        Push "新版本不能安装到旧目录指向的位置。请选择独立目录。 / The chosen path resolves inside a legacy installation directory."
+        Call CXFail
+      ${EndIf}
+    ${EndIf}
+    StrCpy $1 $CXReservedPath
     StrLen $2 $1
     StrCpy $3 $CXDestinationFull $2
     StrCpy $4 $CXDestinationReal $2
@@ -291,7 +308,7 @@ Function CXInitialize
   IfErrors 0 +3
     MessageBox MB_ICONSTOP "无法创建安装日志。请检查当前用户目录的写入权限。 / Cannot create installer log."
     Quit
-  FileWrite $2 'Codex-X ${VERSION}: current-user installer$\r$\n'
+  FileWriteUTF16LE /BOM $2 'Codex-X ${VERSION}: current-user installer, NSIS x86 Unicode, target ${ARCH}$\r$\n'
   FileClose $2
   ; The actual wait is in EarlyChecks on the installation worker thread. Keep
   ; the handle now so a recycled PID cannot make us wait on an unrelated app.
@@ -334,6 +351,8 @@ Function CXDetectLegacyMsi
   StrCpy $CXLegacyProduct ""
   StrCpy $CXLegacyVersion ""
   System::Call 'msi::MsiEnumRelatedProductsW(w "${CODEXX_LEGACY_UPGRADE_CODE}",i 0,i 0,w .r0)i.r1'
+  Push "MSI enum: result=$1, product=$0, upgrade=${CODEXX_LEGACY_UPGRADE_CODE}"
+  Call CXLog
   ${If} $1 = 259
     Return
   ${EndIf}
@@ -345,6 +364,8 @@ Function CXDetectLegacyMsi
   ; Only the shipped, machine-wide MSI is supported for automatic migration.
   ; Query its machine context explicitly, including with alternate UAC creds.
   System::Call 'msi::MsiGetProductInfoExW(w "$CXLegacyProduct",p 0,i 4,w "VersionString",w .r0,*i ${NSIS_MAX_STRLEN})i.r1'
+  Push "MSI machine-context version: result=$1, version=$0, product=$CXLegacyProduct"
+  Call CXLog
   ${If} $1 != 0
     Push "旧版安装信息不完整 (Windows $1)。请先在系统设置中卸载旧版 Codex-X，再运行此安装包。 / Previous installation could not be verified."
     Call CXFail
diff --git a/scripts/windows-install-smoke.ps1 b/scripts/windows-install-smoke.ps1
index 890b75f..d4ece01 100644
--- a/scripts/windows-install-smoke.ps1
+++ b/scripts/windows-install-smoke.ps1
@@ -89,7 +89,7 @@ try {
   $legacyMsi = Join-Path $Work 'Codex-X-0.3.20.msi'
   Invoke-WebRequest 'https://github.com/yynxxxxx/Codex-X/releases/download/v0.3.20/Codex-X-0.3.20-windows-x64.msi' -OutFile $legacyMsi
   if ((Get-FileHash $legacyMsi -Algorithm SHA256).Hash.ToLowerInvariant() -ne $LegacySha256) { throw 'Released MSI hash mismatch.' }
-  Invoke-Installer (Join-Path $env:SystemRoot 'System32\msiexec.exe') "/i `"$legacyMsi`" /qn /norestart /L*v `"$Work\legacy-install.log`""
+  Invoke-Installer (Join-Path $env:SystemRoot 'System32\msiexec.exe') "/i `"$legacyMsi`" INSTALLDIR=`"$env:ProgramFiles\Codex-X`" /qn /norestart /L*v `"$Work\legacy-install.log`""
   if ($LegacyProductCode -notin @(Related-Products)) { throw 'The genuine legacy MSI did not register.' }
   $oldDirectory = [Text.StringBuilder]::new(1024)
   [uint32]$oldDirectoryLength = 1024
@@ -139,7 +139,7 @@ try {
   foreach ($comObject in @($query, $summary, $database, $msiAutomation)) {
     [void][Runtime.InteropServices.Marshal]::FinalReleaseComObject($comObject)
   }
-  Invoke-Installer (Join-Path $env:SystemRoot 'System32\msiexec.exe') "/i `"$rebootMsi`" /qn /norestart /L*v `"$Work\deferred-fixture-install.log`""
+  Invoke-Installer (Join-Path $env:SystemRoot 'System32\msiexec.exe') "/i `"$rebootMsi`" INSTALLDIR=`"$env:ProgramFiles\Codex-X`" /qn /norestart /L*v `"$Work\deferred-fixture-install.log`""
   if ($LegacyProductCode -notin @(Related-Products)) { throw 'The deferred-cleanup MSI fixture did not register.' }
   $beforeMigration = Get-Date
   Invoke-Installer $Installer '/S /UPDATE'
diff --git a/scripts/windows-msi-probe.ps1 b/scripts/windows-msi-probe.ps1
new file mode 100644
index 0000000..8643961
--- /dev/null
+++ b/scripts/windows-msi-probe.ps1
@@ -0,0 +1,82 @@
+# Diagnostic only; installs/removes the hash-pinned fixture on an ephemeral runner.
+$ErrorActionPreference = 'Stop'
+if ($env:GITHUB_ACTIONS -ne 'true' -or $env:RUNNER_OS -ne 'Windows') {
+  throw 'This MSI diagnostic is restricted to an ephemeral Windows Actions runner.'
+}
+$work = Join-Path $env:RUNNER_TEMP 'codex-x-msi-probe'
+New-Item -ItemType Directory -Force $work | Out-Null
+$legacyMsi = Join-Path $work 'legacy.msi'
+Invoke-WebRequest 'https://github.com/yynxxxxx/Codex-X/releases/download/v0.3.20/Codex-X-0.3.20-windows-x64.msi' -OutFile $legacyMsi
+if ((Get-FileHash $legacyMsi -Algorithm SHA256).Hash.ToLowerInvariant() -ne 'e0f2f172a31f860806a9714bab2e67eb38b85d525d7e5f0f569667cbeadfb152') {
+  throw 'MSI fixture hash mismatch.'
+}
+$compiler = (Get-Command makensis.exe -ErrorAction SilentlyContinue).Source
+if (-not $compiler) { $compiler = Join-Path ${env:ProgramFiles(x86)} 'NSIS\makensis.exe' }
+if (-not (Test-Path $compiler)) { throw 'makensis.exe is required for the native MSI probe.' }
+$psProbe = @'
+$ErrorActionPreference = 'Stop'
+Add-Type @"
+using System.Runtime.InteropServices;
+using System.Text;
+public static class MsiProbeNative {
+ [DllImport("msi.dll", CharSet=CharSet.Unicode, ExactSpelling=true)]
+ public static extern uint MsiEnumRelatedProductsW(string upgrade, uint reserved, uint index, StringBuilder product);
+ [DllImport("msi.dll", CharSet=CharSet.Unicode, ExactSpelling=true)]
+ public static extern uint MsiGetProductInfoExW(string product, string sid, uint context, string property, StringBuilder value, ref uint length);
+}
+"@
+$product = [Text.StringBuilder]::new(39)
+$rc = [MsiProbeNative]::MsiEnumRelatedProductsW('{1482A8E8-9217-517B-8528-93A6C90E0C2F}', 0, 0, $product)
+Write-Host "PS Is64Bit=$([Environment]::Is64BitProcess) EnumRelated rc=$rc product=$product"
+foreach ($property in @('VersionString', 'InstallLocation')) {
+ $value = [Text.StringBuilder]::new(1024)
+ [uint32]$length = 1024
+ $rc = [MsiProbeNative]::MsiGetProductInfoExW('{F71E3F3F-A463-4397-AB46-206D3FAC3FBD}', $null, 4, $property, $value, [ref]$length)
+ Write-Host "PS Is64Bit=$([Environment]::Is64BitProcess) machine $property rc=$rc value=$value"
+}
+'@
+$psProbePath = Join-Path $work 'probe-api.ps1'
+Set-Content $psProbePath $psProbe -Encoding utf8
+$nsis = @'
+Unicode true
+RequestExecutionLevel user
+OutFile "probe.exe"
+Name "Codex-X MSI API probe"
+SilentInstall silent
+Function .onInit
+ FileOpen $9 "$EXEDIR\nsis-probe.log" w
+ FileWriteUTF16LE /BOM $9 "NSIS x86 Unicode native MSI API probe$\r$\n"
+ System::Call 'msi::MsiEnumRelatedProductsW(w "{1482A8E8-9217-517B-8528-93A6C90E0C2F}",i 0,i 0,w .r0)i.r1'
+ FileWriteUTF16LE $9 "EnumRelatedW result=$1 product=$0$\r$\n"
+ System::Call 'msi::MsiEnumRelatedProductsA(m "{1482A8E8-9217-517B-8528-93A6C90E0C2F}",i 0,i 0,m .r0)i.r1'
+ FileWriteUTF16LE $9 "EnumRelatedA result=$1 product=$0$\r$\n"
+ System::Call 'msi::MsiGetProductInfoExW(w "{F71E3F3F-A463-4397-AB46-206D3FAC3FBD}",p 0,i 4,w "VersionString",w .r0,*i 1024)i.r1'
+ FileWriteUTF16LE $9 "Machine VersionString result=$1 value=$0$\r$\n"
+ System::Call 'msi::MsiGetProductInfoExW(w "{F71E3F3F-A463-4397-AB46-206D3FAC3FBD}",p 0,i 4,w "InstallLocation",w .r0,*i 1024)i.r1'
+ FileWriteUTF16LE $9 "Machine InstallLocation result=$1 value=$0$\r$\n"
+ FileClose $9
+ Quit
+FunctionEnd
+Section
+SectionEnd
+'@
+$nsisPath = Join-Path $work 'probe.nsi'
+Set-Content $nsisPath $nsis -Encoding utf8
+function Run-Wait([string]$File, [string]$Arguments) {
+ $process = Start-Process $File -ArgumentList $Arguments -PassThru
+ if (-not $process.WaitForExit(300000)) { throw 'Probe subprocess timed out; no MSI process was terminated.' }
+ $process.Refresh()
+ Write-Host "Process completed: $File, exit=$($process.ExitCode)"
+ if ($process.ExitCode -ne 0 -and $process.ExitCode -ne 3010) { throw "Subprocess failure: $($process.ExitCode)" }
+}
+try {
+ Run-Wait "$env:SystemRoot\System32\msiexec.exe" "/i `"$legacyMsi`" INSTALLDIR=`"$env:ProgramFiles\Codex-X`" /qn /norestart /L*v `"$work\install.log`""
+ & "$env:SystemRoot\System32\WindowsPowerShell\v1.0\powershell.exe" -NoProfile -NonInteractive -File $psProbePath
+ & "$env:SystemRoot\SysWOW64\WindowsPowerShell\v1.0\powershell.exe" -NoProfile -NonInteractive -File $psProbePath
+ & $compiler /V3 $nsisPath
+ if ($LASTEXITCODE -ne 0) { throw 'Native NSIS probe compilation failed.' }
+ Run-Wait (Join-Path $work 'probe.exe') '/S'
+ Get-Content (Join-Path $work 'nsis-probe.log')
+} finally {
+ Run-Wait "$env:SystemRoot\System32\msiexec.exe" "/x {F71E3F3F-A463-4397-AB46-206D3FAC3FBD} /qn /norestart /L*v `"$work\uninstall.log`""
+}