diff --git a/scripts/install.ps1 b/scripts/install.ps1
index c6dedb4f5f..d018f611c8 100644
--- a/scripts/install.ps1
+++ b/scripts/install.ps1
@@ -29,10 +29,9 @@ function Get-OpenHumanMsiexecInstallArgumentList {
     [Parameter(Mandatory = $true)]
     [string]$MsiPath
   )
-  # Pass -ArgumentList as string[]: each entry is one argv token for msiexec, so spaces in
-  # $MsiPath do not split. Do not wrap $MsiPath in extra literal " characters here — that can
-  # double-escape when Start-Process builds the native command line (see PR #1187 review).
-  return @('/i', $MsiPath, '/qn', '/norestart')
+  # Start-Process joins ArgumentList entries into one command line, so preserve spaces by
+  # quoting the MSI path explicitly before it is passed to msiexec.
+  return @('/i', ('"{0}"' -f $MsiPath), '/qn', '/norestart')
 }
 
 function Test-OpenHumanWindowsProcessElevated {
@@ -48,6 +47,44 @@ function Test-OpenHumanWindowsProcessElevated {
   return $principal.IsInRole([Security.Principal.WindowsBuiltInRole]::Administrator)
 }
 
+function Test-OpenHumanInstallerExitCodeSucceeded {
+  param(
+    [Parameter(Mandatory = $true)]
+    [int]$ExitCode,
+
+    [Parameter(Mandatory = $true)]
+    [ValidateSet("MSI", "EXE")]
+    [string]$InstallerType
+  )
+
+  return $ExitCode -eq 0 -or ($InstallerType -eq "MSI" -and $ExitCode -in @(1641, 3010))
+}
+
+function Assert-OpenHumanInstallerProcessSucceeded {
+  <#
+  .SYNOPSIS
+    Throw when a Windows installer process reports an unsuccessful exit code.
+  #>
+  param(
+    [Parameter(Mandatory = $true)]
+    [int]$ExitCode,
+
+    [Parameter(Mandatory = $true)]
+    [ValidateSet("MSI", "EXE")]
+    [string]$InstallerType
+  )
+
+  if (Test-OpenHumanInstallerExitCodeSucceeded -ExitCode $ExitCode -InstallerType $InstallerType) {
+    return
+  }
+
+  if ($InstallerType -eq "MSI") {
+    throw "MSI install failed with exit code $ExitCode."
+  }
+
+  throw "Installer exited with code $ExitCode."
+}
+
 function Select-OpenHumanWindowsAssetFromRelease {
   <#
   .SYNOPSIS
@@ -94,7 +131,6 @@ function Install-OpenHuman {
   function Write-Info([string]$Message) { Write-Host "-> $Message" -ForegroundColor Cyan }
   function Write-Ok([string]$Message) { Write-Host "OK $Message" -ForegroundColor Green }
   function Write-WarnMsg([string]$Message) { Write-Host "!  $Message" -ForegroundColor Yellow }
-  function Write-Err([string]$Message) { Write-Host "x  $Message" -ForegroundColor Red }
 
   function Show-Usage {
     @"
@@ -120,13 +156,11 @@ Examples:
   }
 
   if ($Channel -ne "stable") {
-    Write-Err "Only -Channel stable is currently supported."
-    return
+    throw "Only -Channel stable is currently supported."
   }
 
   if ($env:OS -ne "Windows_NT") {
-    Write-Err "This installer is for Windows only."
-    return
+    throw "This installer is for Windows only."
   }
 
   # Detect architecture — use environment variable as primary (always available),
@@ -142,8 +176,7 @@ Examples:
   $arch = "$arch".ToLowerInvariant()
 
   if ($arch -notin @("x64", "amd64")) {
-    Write-Err "Unsupported architecture: $arch (Windows x64 required)."
-    return
+    throw "Unsupported architecture: $arch (Windows x64 required)."
   }
 
   Write-Ok "Detected platform: windows/x64"
@@ -166,13 +199,11 @@ Examples:
       }
     }
   } catch {
-    Write-WarnMsg "Could not query release API: $($_.Exception.Message)"
+    throw
   }
 
   if (-not $assetUrl) {
-    Write-Err "No Windows x64 installer artifact found in latest release."
-    Write-Err "Ensure release workflow publishes Windows MSI/EXE assets."
-    return
+    throw "No Windows x64 installer artifact found in latest release. Ensure release workflow publishes Windows MSI/EXE assets."
   }
 
   Write-Ok "Resolved latest release ($releaseTag): $assetName"
@@ -191,10 +222,7 @@ Examples:
     } else {
       $fileHash = (Get-FileHash -Path $tmpFile -Algorithm SHA256).Hash.ToLowerInvariant()
       if ($fileHash -ne $assetDigest.ToLowerInvariant()) {
-        Write-Err "SHA256 mismatch for $assetName"
-        Write-Err "Expected: $assetDigest"
-        Write-Err "Actual:   $fileHash"
-        return
+        throw "SHA256 mismatch for $assetName. Expected: $assetDigest. Actual: $fileHash."
       }
       Write-Ok "Integrity verified (sha256)"
     }
@@ -227,20 +255,15 @@ Examples:
       Write-Info "Requesting administrator approval for machine-wide install (UAC)…"
       $proc = Start-Process -FilePath "msiexec.exe" -ArgumentList $msiArgs -Verb RunAs -Wait -PassThru
     }
-    if ($proc.ExitCode -ne 0) {
-      Write-Err "MSI install failed with exit code $($proc.ExitCode)."
+    if (-not (Test-OpenHumanInstallerExitCodeSucceeded -ExitCode $proc.ExitCode -InstallerType "MSI")) {
       Write-WarnMsg "If this persists, capture a log: msiexec /i `"$tmpFile`" /l*v `"$env:TEMP\OpenHuman-msi.log`""
-      return
     }
+    Assert-OpenHumanInstallerProcessSucceeded -ExitCode $proc.ExitCode -InstallerType "MSI"
   } elseif ($assetName -like "*.exe") {
     $proc = Start-Process -FilePath $tmpFile -Wait -PassThru
-    if ($proc.ExitCode -ne 0) {
-      Write-Err "Installer exited with code $($proc.ExitCode)."
-      return
-    }
+    Assert-OpenHumanInstallerProcessSucceeded -ExitCode $proc.ExitCode -InstallerType "EXE"
   } else {
-    Write-Err "Unsupported Windows installer type: $assetName"
-    return
+    throw "Unsupported Windows installer type: $assetName"
   }
 
   $expectedPaths = @(
diff --git a/scripts/tests/OpenHumanWindowsInstall.Tests.ps1 b/scripts/tests/OpenHumanWindowsInstall.Tests.ps1
index 965bbdcab5..3d615948c4 100644
--- a/scripts/tests/OpenHumanWindowsInstall.Tests.ps1
+++ b/scripts/tests/OpenHumanWindowsInstall.Tests.ps1
@@ -6,7 +6,7 @@
 .DESCRIPTION
   Dot-sources install.ps1 (does not run Install-OpenHuman) and validates
   Get-OpenHumanMsiexecInstallArgumentList, Select-OpenHumanWindowsAssetFromRelease,
-  and Test-OpenHumanWindowsProcessElevated.
+  Test-OpenHumanWindowsProcessElevated, and installer failure propagation.
 
   Run from repo root:
     pwsh -NoProfile -File scripts/tests/OpenHumanWindowsInstall.Tests.ps1
@@ -47,15 +47,50 @@ function Assert-True {
   }
 }
 
+function Assert-DoesNotThrow {
+  param([scriptblock]$Action, [string]$Message)
+  $script:testCount++
+  try {
+    & $Action | Out-Null
+    Write-Host "ok $Message" -ForegroundColor Green
+  } catch {
+    $script:failCount++
+    Write-Host "FAIL: $Message" -ForegroundColor Red
+    Write-Host "  unexpected error: $($_.Exception.Message)" -ForegroundColor Red
+  }
+}
+
+function Assert-Throws {
+  param([scriptblock]$Action, [string]$ExpectedMessage, [string]$Message)
+  $script:testCount++
+  try {
+    & $Action | Out-Null
+    $script:failCount++
+    Write-Host "FAIL: $Message" -ForegroundColor Red
+    Write-Host "  expected error: $ExpectedMessage" -ForegroundColor Red
+    Write-Host "  actual: no terminating error" -ForegroundColor Red
+  } catch {
+    $actualMessage = $_.Exception.Message
+    if ($ExpectedMessage -ne $actualMessage) {
+      $script:failCount++
+      Write-Host "FAIL: $Message" -ForegroundColor Red
+      Write-Host "  expected error: $ExpectedMessage" -ForegroundColor Red
+      Write-Host "  actual error:   $actualMessage" -ForegroundColor Red
+    } else {
+      Write-Host "ok $Message" -ForegroundColor Green
+    }
+  }
+}
+
 Write-Host "`n== Get-OpenHumanMsiexecInstallArgumentList (#913) ==" -ForegroundColor Cyan
 $p = 'C:\Temp\OpenHuman_0.0.0_x64_en-US.msi'
 $args = Get-OpenHumanMsiexecInstallArgumentList -MsiPath $p
 Assert-True ($args.Count -eq 4) 'returns exactly 4 argument tokens'
 Assert-Equal '/i' $args[0] 'first token is /i'
-Assert-Equal $p $args[1] 'second token is MSI path'
+Assert-Equal ('"{0}"' -f $p) $args[1] 'second token is quoted MSI path'
 $pSpaces = 'C:\Temp\Test User\OpenHuman_0.0.0_x64_en-US.msi'
 $argsSpaces = Get-OpenHumanMsiexecInstallArgumentList -MsiPath $pSpaces
-Assert-Equal $pSpaces $argsSpaces[1] 'path with spaces remains one second argv token (no split)'
+Assert-Equal ('"{0}"' -f $pSpaces) $argsSpaces[1] 'path with spaces remains quoted for Start-Process'
 Assert-Equal '/qn' $args[2] 'third token is /qn'
 Assert-Equal '/norestart' $args[3] 'fourth token is /norestart'
 Assert-True ($args -notcontains 'MSIINSTALLPERUSER') 'must not set MSIINSTALLPERUSER (perMachine MSI)'
@@ -92,6 +127,39 @@ Write-Host "`n== Test-OpenHumanWindowsProcessElevated ==" -ForegroundColor Cyan
 $t = Test-OpenHumanWindowsProcessElevated
 Assert-True ($t -is [bool]) 'returns a boolean'
 
+Write-Host "`n== Installer failure propagation ==" -ForegroundColor Cyan
+Assert-DoesNotThrow { Assert-OpenHumanInstallerProcessSucceeded -ExitCode 0 -InstallerType 'MSI' } 'accepts a successful child process'
+Assert-DoesNotThrow { Assert-OpenHumanInstallerProcessSucceeded -ExitCode 1641 -InstallerType 'MSI' } 'accepts an MSI success that initiated a reboot'
+Assert-DoesNotThrow { Assert-OpenHumanInstallerProcessSucceeded -ExitCode 3010 -InstallerType 'MSI' } 'accepts an MSI success that requires a reboot'
+Assert-Throws { Assert-OpenHumanInstallerProcessSucceeded -ExitCode 1603 -InstallerType 'MSI' } 'MSI install failed with exit code 1603.' 'turns an MSI failure into a terminating error'
+Assert-Throws { Assert-OpenHumanInstallerProcessSucceeded -ExitCode 5 -InstallerType 'EXE' } 'Installer exited with code 5.' 'turns an EXE failure into a terminating error'
+Assert-Throws { Assert-OpenHumanInstallerProcessSucceeded -ExitCode 3010 -InstallerType 'EXE' } 'Installer exited with code 3010.' 'does not treat MSI reboot codes as EXE success'
+
+$versionOutput = (Install-OpenHuman -Version | Out-String).Trim()
+Assert-Equal 'openhuman-installer 1.1.0' $versionOutput '-Version remains successful'
+Assert-Throws { Install-OpenHuman -Channel 'preview' } 'Only -Channel stable is currently supported.' 'invalid arguments terminate instead of returning success'
+
+$originalArch = $env:PROCESSOR_ARCHITECTURE
+$originalOs = $env:OS
+try {
+  $env:OS = 'Windows_NT'
+  $env:PROCESSOR_ARCHITECTURE = 'AMD64'
+  function Invoke-RestMethod { throw 'release API unavailable' }
+  Assert-Throws { Install-OpenHuman -DryRun } 'release API unavailable' 'release API failures preserve their error record'
+} finally {
+  Remove-Item Function:\Invoke-RestMethod -ErrorAction SilentlyContinue
+  $env:PROCESSOR_ARCHITECTURE = $originalArch
+  $env:OS = $originalOs
+}
+
+$originalOs = $env:OS
+try {
+  $env:OS = 'OpenHumanTestUnsupported'
+  Assert-Throws { Get-Content -Raw $installScript | Invoke-Expression } 'This installer is for Windows only.' 'piped irm|iex-style execution preserves terminating errors'
+} finally {
+  $env:OS = $originalOs
+}
+
 Write-Host "`n== $($testCount) checks, $failCount failed ==" -ForegroundColor $(if ($failCount -eq 0) { 'Green' } else { 'Red' })
 if ($failCount -gt 0) {
   exit 1