feat: update-pr safe output

[jamesadevine]

Summary

Add an update-pr safe output that allows agents to update pull request metadata — add/remove reviewers, update labels, set auto-complete, and vote (approve/reject/wait).

ADO API

• PATCH /_apis/git/repositories/{repo}/pullRequests/{id}?api-version=7.1 — Update PR properties
• PUT /_apis/git/repositories/{repo}/pullRequests/{id}/reviewers/{reviewerId}?api-version=7.1 — Add reviewers / cast votes

Agent Parameters

• pull-request-id (required) — PR ID to update
• repository (optional) — Repository alias (default: self)
• operation (required) — One of:
  • add-reviewers — Add reviewers (requires reviewers list)
  • add-labels — Add labels (requires labels list)
  • set-auto-complete — Enable auto-complete
  • vote — Cast a vote (requires vote value: approve, approve-with-suggestions, wait-for-author, reject, reset)
  • update-description — Update PR description (requires description)

Front Matter Configuration (safe-outputs.update-pr)

• allowed-operations — Restrict which operations are permitted (e.g., only add-reviewers, not vote)
• allowed-repositories — Restrict which repos the agent can update PRs in
• allowed-votes — Restrict which vote types are allowed (e.g., only approve-with-suggestions, never approve)

Use Cases

• Auto-approval agents (with appropriate vote restrictions)
• Reviewer assignment agents
• PR triage agents adding labels/updating descriptions
• Merge-readiness agents setting auto-complete when checks pass

Security Considerations

• Operation allow-list is critical — prevents agents from self-approving without review
• Vote restrictions prevent full approve without human oversight
• Repository allow-list
• Standard text sanitization on descriptions and labels

Priority

Tier 2 — Solid addition. Medium complexity (multiple sub-operations).