tests: guard Windows-only arg-echo discovery for Linux CI

The native arg-echo Describe built its csc.exe candidate paths with
Join-Path $env:WINDIR at Pester discovery time, which threw on Linux
so discovery is null-safe; the tests already skip when csc.exe and
powershell.exe are absent.

Relates to #24

All 102 tests pass.

v1.2.7

Author: darianmiller

CHANGELOG.md

@@ -2,6 +2,14 @@
 
 All notable changes to this project will be documented in this file.
 
+## [1.2.7]
+
+- Fix Linux CI: the native arg-echo test built its `csc.exe` candidate paths
+  with `Join-Path $env:WINDIR` at Pester discovery time, which threw on Linux
+  runners where `$env:WINDIR` is null. The Windows-only paths are now inside the
+  existing guard; the tests already skip cleanly when the toolchain is absent.
+  [#24](https://github.com/continuous-delphi/delphi-msbuild/issues/24)
+
 ## [1.2.6]
 
 - Fix native-argument quoting for `/p:` values ending in a backslash. Values

source/delphi-msbuild.ps1

@@ -190,7 +190,7 @@ $ExitRootDirError     = 3
 $ExitProjectNotFound  = 4
 $ExitBuildFailed      = 5
 
-$script:Version = '1.2.6'
+$script:Version = '1.2.7'
 
 # Resolve the Delphi root dir from the explicit -RootDir parameter or from a
 # piped delphi-inspect result object (.rootDir property).

tests/pwsh/delphi-msbuild.Tests.ps1

@@ -1255,11 +1255,12 @@ Describe 'Native argument passing (real arg-echo exe)' {
   # Requires the .NET Framework C# compiler (csc.exe); on machines/CI without it
   # (e.g. Linux runners) every test here skips.  Evaluated at Pester discovery
   # time so -Skip: can capture it.
-  $frameworkRoots = @(
-    (Join-Path $env:WINDIR 'Microsoft.NET\Framework64\v4.0.30319\csc.exe'),
-    (Join-Path $env:WINDIR 'Microsoft.NET\Framework\v4.0.30319\csc.exe')
-  )
-  $cscDiscover  = if ($env:WINDIR) { $frameworkRoots | Where-Object { Test-Path -LiteralPath $_ } | Select-Object -First 1 } else { $null }
+  $cscDiscover = if ($env:WINDIR) {
+    @(
+      (Join-Path $env:WINDIR 'Microsoft.NET\Framework64\v4.0.30319\csc.exe'),
+      (Join-Path $env:WINDIR 'Microsoft.NET\Framework\v4.0.30319\csc.exe')
+    ) | Where-Object { Test-Path -LiteralPath $_ } | Select-Object -First 1
+  } else { $null }
   $skipNative   = -not $cscDiscover
 
   # Windows PowerShell 5.1, located via its fixed path (see WindowsPS51Compat.Tests.ps1).