With a transcript active, each native stderr line costs time proportional to the number of directories under PSModulePath #28133

Start-Transcript -Path ./t.log
Measure-Command { & bash -c 'for i in $(seq 1 200); do echo line $i >&2; done' 2> ./e.err }
Stop-Transcript

# Repro: with a transcript active, each line a native command writes to stderr costs time
# that grows with the number of directories under the PSModulePath folders.
# Cross-platform: the native command is a child pwsh process writing to its stderr.
param (
	[int]$Lines = 100,          # stderr lines emitted per run
	# Shape of the extra PSModulePath entry: a broad, shallow tree of empty directories, similar to a
	# system folder like /usr/share. Defaults: 100 * (1 + 3 + 9 + 27 + 81) = 12,100 directories, 5 levels deep.
	[int]$Folders = 100,        # folders directly in the extra PSModulePath entry
	[int]$Branching = 3,        # subfolders per folder, at each level below
	[int]$Depth = 4             # levels of subfolders below each top-level folder
)

$Separator = [IO.Path]::PathSeparator
$Tree = Join-Path ([IO.Path]::GetTempPath()) "psmodulepath-repro-$PID"
# Only the leaves are created; CreateDirectory creates the intermediate levels.
$Leaves = [System.Collections.Generic.List[string]]::new()
foreach ($i in 1..$Folders) { $Leaves.Add((Join-Path $Tree "d$i")) }
foreach ($Level in 1..$Depth) {
	$Leaves = [System.Collections.Generic.List[string]]@(foreach ($Leaf in $Leaves) { foreach ($j in 1..$Branching) { Join-Path $Leaf "s$j" } })
}
foreach ($Leaf in $Leaves) { $null = [IO.Directory]::CreateDirectory($Leaf) }
$DirectoryCount = @(Get-ChildItem -LiteralPath $Tree -Directory -Recurse).Count

$ChildCommand = "1..$Lines | ForEach-Object { [Console]::Error.WriteLine(`"line `$_`") }"
$ErrFile = Join-Path ([IO.Path]::GetTempPath()) "repro-$PID.err"
$TranscriptFile = Join-Path ([IO.Path]::GetTempPath()) "repro-$PID.log"
$OriginalModulePath = $env:PSModulePath

function Measure-Run([bool]$WithTree, [bool]$WithTranscript) {
	$env:PSModulePath = $WithTree ? ($Tree + $Separator + $OriginalModulePath) : $OriginalModulePath
	if ($WithTranscript) { $null = Start-Transcript -Path $TranscriptFile -Force }
	$Elapsed = Measure-Command { & ([Environment]::ProcessPath) -NoProfile -Command $ChildCommand 2> $ErrFile }
	if ($WithTranscript) { $null = Stop-Transcript }
	$env:PSModulePath = $OriginalModulePath
	[pscustomobject]@{
		'Extra PSModulePath entry' = $WithTree ? "$DirectoryCount directories" : 'none'
		Transcript    = $WithTranscript
		'Total (ms)'  = [math]::Round($Elapsed.TotalMilliseconds)
		'Per line (ms)' = [math]::Round($Elapsed.TotalMilliseconds / $Lines, 1)
	}
}

try {
	"PowerShell $($PSVersionTable.PSVersion) on $([Runtime.InteropServices.RuntimeInformation]::OSDescription), $Lines stderr lines per run"
	@(
		Measure-Run $true  $false
		Measure-Run $true  $true
		Measure-Run $false $false
		Measure-Run $false $true
	) | Format-Table -AutoSize | Out-String -Width 200
	Write-Host "**************************************************************************************"
	$PSVersionTable
	Write-Host "**************************************************************************************"
}
finally {
	$env:PSModulePath = $OriginalModulePath
	Remove-Item -LiteralPath $Tree -Recurse -Force -ErrorAction Ignore
	Remove-Item -LiteralPath $ErrFile, $TranscriptFile -Force -ErrorAction Ignore
}

Name                           Value
----                           -----
PSVersion                      7.6.6
PSEdition                      Core
GitCommitId                    7.6.6
OS                             Ubuntu 24.04.5 LTS
Platform                       Unix
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.4
SerializationVersion           1.1.0.1
WSManStackVersion              3.0