Use intake artifact metadata for PR resolution and improve parse diagnostics

[WaelAbuSeada]

Summary

• resolve PR metadata in Copilot PR Review Runner from the intake artifact (pr-metadata.json) downloaded from the triggering workflow run
• simplify runner resolution flow by removing branch/search fallback logic and keeping strict head SHA validation
• improve review script parse diagnostics by logging candidate index/hash/length/preview and writing parse diagnostics to a dedicated artifact file

Validation

• verified workflow YAML parses without errors
• confirmed script changes compile with existing repository warnings only (no new script diagnostics introduced)
  Fixes AB#637653

[github-actions]

$\textbf{🟠\ High\ Severity\ —\ Upgrade} \quad \color{gray}{\texttt{\small Iteration\ 1}}$

No fallback if artifact metadata is missing

The old runner had a robust fallback: search GitHub's API for open PRs by head SHA when workflow_run.pull_requests[0].number was absent. The new code silently catches artifact errors and then immediately throws with no recovery. Any workflow_run event where the artifact upload failed, was slow, or used a different naming pattern will cause hard failures with no self-healing.

Recommendation:

• Keep the old API-search fallback as a secondary path when artifact resolution fails, matching PRs by expectedHeadSha.

Suggested change

	throw 'No pull request number found in workflow_run payload or fallback PR lookup.'
	# After try/catch for artifact, if -not $prNumber:
	$encodedHead = [System.Uri]::EscapeDataString("${headOwner}:${headBranch}")
	$candidates = Invoke-RestMethod -Uri "https://api.github.com/repos/${{ github.repository }}/pulls?state=open&head=$encodedHead&per_page=30" -Headers $headers -Method GET
	$match = @($candidates | Where-Object { $_.head.sha -eq $expectedHeadSha })
	if ($match.Count -eq 1) { $prNumber = [string]$match[0].number }

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