fix(shims): add Linux fallback for venv Python path in all PS shims

All shims defaulted to F:\CI\python\venv\Scripts\python.exe when
CI_VENV_PYTHON was not set. On Linux host this caused instant failure.

Now uses $IsWindows (PS 6+ automatic var; absent on PS 5.1 = Windows)
to select /opt/ci/venv/bin/python on Linux. Windows paths unchanged.

Affects: Invoke-CIJob, Get-BuildArtifacts, Cleanup-OrphanedBuildVMs,
New-BuildVM, Remove-BuildVM, Wait-VMReady, Get-CIJobSummary,
Invoke-RemoteBuild, Watch-DiskSpace, Watch-RunnerHealth,
Set-CIGuestCredential, Test-CIGuestWinRM.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/Cleanup-OrphanedBuildVMs.ps1

@@ -32,6 +32,13 @@ for ($i = 0; $i -lt $args.Count; $i++) {
 }
 
 $venvPython = $env:CI_VENV_PYTHON
-if (-not $venvPython) { $venvPython = 'F:\CI\python\venv\Scripts\python.exe' }
+if (-not $venvPython) {
+    # $IsWindows exists only on PS 6+; absent on PS 5.1 (always Windows)
+    if ($null -ne $IsWindows -and $IsWindows -eq $false) {
+        $venvPython = '/opt/ci/venv/bin/python'
+    } else {
+        $venvPython = 'F:\CI\python\venv\Scripts\python.exe'
+    }
+}
 & $venvPython -m ci_orchestrator vm cleanup @pyArgs
 exit $LASTEXITCODE

scripts/Get-BuildArtifacts.ps1

@@ -57,6 +57,13 @@ if ($Credential) {
 }
 
 $venvPython = $env:CI_VENV_PYTHON
-if (-not $venvPython) { $venvPython = 'F:\CI\python\venv\Scripts\python.exe' }
+if (-not $venvPython) {
+    # $IsWindows exists only on PS 6+; absent on PS 5.1 (always Windows)
+    if ($null -ne $IsWindows -and $IsWindows -eq $false) {
+        $venvPython = '/opt/ci/venv/bin/python'
+    } else {
+        $venvPython = 'F:\CI\python\venv\Scripts\python.exe'
+    }
+}
 & $venvPython -m ci_orchestrator artifacts collect @pyArgs
 exit $LASTEXITCODE

scripts/Get-CIJobSummary.ps1

@@ -32,7 +32,14 @@ for ($i = 0; $i -lt $args.Count; $i++) {
 }
 
 $venvPython = $env:CI_VENV_PYTHON
-if (-not $venvPython) { $venvPython = 'F:\CI\python\venv\Scripts\python.exe' }
+if (-not $venvPython) {
+    # $IsWindows exists only on PS 6+; absent on PS 5.1 (always Windows)
+    if ($null -ne $IsWindows -and $IsWindows -eq $false) {
+        $venvPython = '/opt/ci/venv/bin/python'
+    } else {
+        $venvPython = 'F:\CI\python\venv\Scripts\python.exe'
+    }
+}
 & $venvPython -m ci_orchestrator report job @pyArgs
 exit $LASTEXITCODE
 

scripts/Invoke-CIJob.ps1

@@ -32,6 +32,13 @@ for ($i = 0; $i -lt $args.Count; $i++) {
 }
 
 $venvPython = $env:CI_VENV_PYTHON
-if (-not $venvPython) { $venvPython = 'F:\CI\python\venv\Scripts\python.exe' }
+if (-not $venvPython) {
+    # $IsWindows exists only on PS 6+; absent on PS 5.1 (always Windows)
+    if ($null -ne $IsWindows -and $IsWindows -eq $false) {
+        $venvPython = '/opt/ci/venv/bin/python'
+    } else {
+        $venvPython = 'F:\CI\python\venv\Scripts\python.exe'
+    }
+}
 & $venvPython -m ci_orchestrator job @pyArgs
 exit $LASTEXITCODE

scripts/Invoke-RemoteBuild.ps1

@@ -86,6 +86,13 @@ if ($Credential) {
 }
 
 $venvPython = $env:CI_VENV_PYTHON
-if (-not $venvPython) { $venvPython = 'F:\CI\python\venv\Scripts\python.exe' }
+if (-not $venvPython) {
+    # $IsWindows exists only on PS 6+; absent on PS 5.1 (always Windows)
+    if ($null -ne $IsWindows -and $IsWindows -eq $false) {
+        $venvPython = '/opt/ci/venv/bin/python'
+    } else {
+        $venvPython = 'F:\CI\python\venv\Scripts\python.exe'
+    }
+}
 & $venvPython -m ci_orchestrator build run @pyArgs
 exit $LASTEXITCODE

scripts/New-BuildVM.ps1

@@ -31,6 +31,13 @@ $pyArgs = @(
 )
 
 $venvPython = $env:CI_VENV_PYTHON
-if (-not $venvPython) { $venvPython = 'F:\CI\python\venv\Scripts\python.exe' }
+if (-not $venvPython) {
+    # $IsWindows exists only on PS 6+; absent on PS 5.1 (always Windows)
+    if ($null -ne $IsWindows -and $IsWindows -eq $false) {
+        $venvPython = '/opt/ci/venv/bin/python'
+    } else {
+        $venvPython = 'F:\CI\python\venv\Scripts\python.exe'
+    }
+}
 & $venvPython -m ci_orchestrator vm new @pyArgs
 exit $LASTEXITCODE

scripts/Remove-BuildVM.ps1

@@ -35,6 +35,13 @@ for ($i = 0; $i -lt $args.Count; $i++) {
 }
 
 $venvPython = $env:CI_VENV_PYTHON
-if (-not $venvPython) { $venvPython = 'F:\CI\python\venv\Scripts\python.exe' }
+if (-not $venvPython) {
+    # $IsWindows exists only on PS 6+; absent on PS 5.1 (always Windows)
+    if ($null -ne $IsWindows -and $IsWindows -eq $false) {
+        $venvPython = '/opt/ci/venv/bin/python'
+    } else {
+        $venvPython = 'F:\CI\python\venv\Scripts\python.exe'
+    }
+}
 & $venvPython -m ci_orchestrator vm remove @pyArgs
 exit $LASTEXITCODE

scripts/Set-CIGuestCredential.ps1

@@ -68,6 +68,7 @@ param(
     [System.Security.SecureString] $Password,
 
     [string] $VenvPython = $(if ($env:CI_VENV_PYTHON) { $env:CI_VENV_PYTHON }
+                            elseif ($null -ne $IsWindows -and $IsWindows -eq $false) { '/opt/ci/venv/bin/python' }
                             else { 'F:\CI\python\venv\Scripts\python.exe' }),
 
     [switch] $SkipVerify

scripts/Test-CIGuestWinRM.ps1

@@ -74,6 +74,7 @@ param(
     [string[]] $AuthOrder = @('ntlm', 'negotiate'),
 
     [string] $VenvPython = $(if ($env:CI_VENV_PYTHON) { $env:CI_VENV_PYTHON }
+                            elseif ($null -ne $IsWindows -and $IsWindows -eq $false) { '/opt/ci/venv/bin/python' }
                             else { 'F:\CI\python\venv\Scripts\python.exe' }),
 
     [ValidateRange(5, 300)]

scripts/Wait-VMReady.ps1

@@ -32,6 +32,13 @@ for ($i = 0; $i -lt $args.Count; $i++) {
 }
 
 $venvPython = $env:CI_VENV_PYTHON
-if (-not $venvPython) { $venvPython = 'F:\CI\python\venv\Scripts\python.exe' }
+if (-not $venvPython) {
+    # $IsWindows exists only on PS 6+; absent on PS 5.1 (always Windows)
+    if ($null -ne $IsWindows -and $IsWindows -eq $false) {
+        $venvPython = '/opt/ci/venv/bin/python'
+    } else {
+        $venvPython = 'F:\CI\python\venv\Scripts\python.exe'
+    }
+}
 & $venvPython -m ci_orchestrator wait-ready @pyArgs
 exit $LASTEXITCODE

scripts/Watch-DiskSpace.ps1

@@ -32,6 +32,13 @@ for ($i = 0; $i -lt $args.Count; $i++) {
 }
 
 $venvPython = $env:CI_VENV_PYTHON
-if (-not $venvPython) { $venvPython = 'F:\CI\python\venv\Scripts\python.exe' }
+if (-not $venvPython) {
+    # $IsWindows exists only on PS 6+; absent on PS 5.1 (always Windows)
+    if ($null -ne $IsWindows -and $IsWindows -eq $false) {
+        $venvPython = '/opt/ci/venv/bin/python'
+    } else {
+        $venvPython = 'F:\CI\python\venv\Scripts\python.exe'
+    }
+}
 & $venvPython -m ci_orchestrator monitor disk @pyArgs
 exit $LASTEXITCODE

scripts/Watch-RunnerHealth.ps1

@@ -32,6 +32,13 @@ for ($i = 0; $i -lt $args.Count; $i++) {
 }
 
 $venvPython = $env:CI_VENV_PYTHON
-if (-not $venvPython) { $venvPython = 'F:\CI\python\venv\Scripts\python.exe' }
+if (-not $venvPython) {
+    # $IsWindows exists only on PS 6+; absent on PS 5.1 (always Windows)
+    if ($null -ne $IsWindows -and $IsWindows -eq $false) {
+        $venvPython = '/opt/ci/venv/bin/python'
+    } else {
+        $venvPython = 'F:\CI\python\venv\Scripts\python.exe'
+    }
+}
 & $venvPython -m ci_orchestrator monitor runner @pyArgs
 exit $LASTEXITCODE