feat: expose skip-artifact as workflow input in action.yml

action.yml:
  - Add skip-artifact input (default: 'false').
  - Forward as INPUT_SKIP_ARTIFACT env var to the PS run step.
  - Pass SkipArtifact=true to Invoke-CIJob.ps1 when set.
  - Gate 'Upload artifacts' step on inputs.skip-artifact != 'true'.

Invoke-CIJob.ps1:
  - Restore -SkipArtifact switch; skips Phase 6 and logs 'skipped' event.

Invoke-RemoteBuild.ps1:
  - Restore -SkipArtifact switch; skips packaging inside the guest.
  - Error message updated to mention skip-artifact workflow input.

scripts/Invoke-CIJob.ps1

@@ -105,6 +105,11 @@ param(
     # Requires Set-TemplateSharedFolders.ps1 to have been run on the template.
     [switch] $UseSharedCache,
 
+    # Skip artifact packaging (Invoke-RemoteBuild) and collection (Phase 6).
+    # Use for jobs that intentionally produce no output (lint, test-only, etc.).
+    # When absent, the build must produce GuestArtifactSource or the job fails.
+    [switch] $SkipArtifact,
+
     # Credential Manager target for Gitea PAT used by -UseGitClone (private repos).
     # Store with: New-StoredCredential -Target 'GiteaPAT' -UserName '<user>' -Password '<pat>' -Persist LocalMachine
     # Ignored when -UseGitClone is not set.
@@ -494,12 +499,17 @@ try {
     if ($GuestArtifactSource -ne '') { $remoteBuildParams['GuestArtifactSource'] = $GuestArtifactSource }
     if ($ExtraGuestEnv.Count -gt 0)  { $remoteBuildParams['ExtraGuestEnv']       = $ExtraGuestEnv }
     if ($UseSharedCache)             { $remoteBuildParams['UseSharedCache']       = $true }
+    if ($SkipArtifact)               { $remoteBuildParams['SkipArtifact']         = $true }
     & "$scriptDir\Invoke-RemoteBuild.ps1" @remoteBuildParams
     Write-JobEvent -Phase 'phase5.build' -Status 'success'
     $phaseTimings.Add([PSCustomObject]@{ Phase = 'Phase 5 - Remote build'; Sec = [int]((Get-Date) - $phaseStart).TotalSeconds })
     $phaseStart = Get-Date
 
     # ── Phase 6: Collect artifacts ────────────────────────────────────────
+    if ($SkipArtifact) {
+        Write-Host "`n[Phase 6/6] Artifact collection skipped (-SkipArtifact)."
+        Write-JobEvent -Phase 'phase6.artifacts' -Status 'skipped'
+    } else {
         Write-Host "`n[Phase 6/6] Collecting artifacts..."
         Write-JobEvent -Phase 'phase6.artifacts' -Status 'start'
         if ($GuestOS -eq 'Linux') {
@@ -520,7 +530,8 @@ try {
                 -HostArtifactDir   $jobArtifactDir `
                 -IncludeLogs
         }
-    Write-JobEvent -Phase 'phase6.artifacts' -Status 'success' -Data @{ dir = $jobArtifactDir }
+        Write-JobEvent -Phase 'phase6.artifacts' -Status 'success' -Data @{ dir = $jobArtifactDir }
+    }
     $elapsed = (Get-Date) - $startTime
     Write-JobEvent -Phase 'job' -Status 'success' -Data @{ elapsedSec = [int]$elapsed.TotalSeconds }
     $phaseTimings.Add([PSCustomObject]@{ Phase = 'Phase 6 - Artifacts'; Sec = [int]((Get-Date) - $phaseStart).TotalSeconds })