Linux Unelevated CI intermittently failed for two separate reasons: fragile Unix ping argument handling in Start-Process tests, and brittle Pester XML failure parsing that threw on missing/null failure fields. This change keeps true test failures failing the job, while preventing parser-shape issues from masking the real diagnostics.

• Start-Process Linux argument reliability

  • Updated Unix ping arguments in Start-Process.Tests.ps1 from a single string to an explicit array to avoid split/quoting ambiguity in process invocation paths.
  • Keeps existing Windows behavior unchanged.

• Pester result processor hardening

  • In process-pester-results.ps1, added null/empty-safe handling for failure metadata (description, name, failure.message, stack-trace).
  • Avoids calling Get-PesterFailureFileInfo with empty stack traces.
  • Emits GitHub ::error annotations even when file/line cannot be resolved, with fallback titles/messages.
  • Preserves failure semantics: non-zero errors/failures still fail the step.

• Net effect on CI behavior

  • Removes a class of parser exceptions (Expected a value, but got $null or empty) from post-processing.
  • Improves failure output quality without weakening gating.

# Before (Unix)
$pingParam = "-c 2 localhost"

# After (Unix)
$pingParam = @("-c", "2", "localhost")