render an expanded template view of the azure pipeline yaml for debugging without running. could use refinement, but wanted to capture this cause was a bit confusing with the API initially.

invoke-pipelinepreview.ps1

function Invoke-PipelinePreview {
    param (
        [string]$organization,
        [string]$project,
        [int]$pipelineId,
        [int]$pipelineVersion,
        [switch]$previewRun,
        [string]$yamlOverride
    )

    $headers = @{
        Authorization = "Basic $([System.Convert]::ToBase64String([System.Text.Encoding]::UTF8.GetBytes("dev:${ENV:AZURE_DEVOPS_EXT_PAT}")))"
    }
    [string]$PipelineVersionArgs = ''
    if ($PipelineVersion) {
        $PipelineVersionArgs = "&pipelineVersion=$pipelineVersion"
    }
    $uri = "https://dev.azure.com/${organization}/${project}/_apis/pipelines/${pipelineId}/preview?api-version=6.1-preview.1${PipelineVersionArgs}"

    $invokeRestMethodSplat = @{
        Method      = 'Post'
        Uri         = $uri
        Headers     = $headers
        Body        = (
            @{
                previewRun   = $true
                # resources          = @{}
                # stagesToSkip = @()
                # templateParameters = @{}
                # variables          = @{}
                yamlOverride = $yamlOverride
            } | ConvertTo-Json -Depth 10
        )
        ContentType = 'application/json'
    }

    $response = Invoke-RestMethod @invokeRestMethodSplat
    $originalPipelineName = 'rendered.yaml'

    $outputFile = [io.path]::combine('.artifacts', "preview.${originalPipelineName}")
    $null = New-Item -Path '.artifacts' -ItemType Directory -ErrorAction SilentlyContinue
    Set-Content -Path $outputFile -Encoding utf8 -Force -Value $response.finalYaml
    Write-Output "Preview saved to $outputFile"
}

$InvokePipelinePreview = @{

    organization = ''
    project      = ''
    pipelineId   = 1393
    yamlOverride = (Get-Content -Raw 'pipelines/deploy.yaml')
}
Invoke-PipelinePreview @InvokePipelinePreview