Add hasNonStaleLgtm and hasHumanOverride helper

[jdelfino]

Summary

Add the core library functions for LGTM comment override support. hasNonStaleLgtm is a pure function that checks PR comments for non-stale LGTM. hasHumanOverride is an async helper that fetches all needed data and checks both override mechanisms (approval + LGTM).

Files to modify

• .github/agent-workflow/scripts/lib/approval.js
• .github/agent-workflow/scripts/lib/override.js (new)
• tests/lib/approval.test.js
• tests/lib/override.test.js (new)

Implementation steps

1. Add hasNonStaleLgtm(comments, headCommitDate) to approval.js:

   • Check if any comment body (trimmed, uppercased) starts with "LGTM"
   • Check if comment created_at is after headCommitDate
   • Export alongside hasNonStaleApproval

2. Create override.js with hasHumanOverride({ github, owner, repo, prNumber, headSha }):

   • Fetch reviews, comments, and commit in parallel via Promise.all
   • Return true if hasNonStaleApproval(reviews, headSha) OR hasNonStaleLgtm(comments, headCommitDate)
   • Export hasHumanOverride

3. Add tests to approval.test.js for hasNonStaleLgtm:

   • LGTM posted after head commit → true
   • LGTM posted before head commit (stale) → false
   • Lowercase "lgtm" → true
   • "LGTM, looks good" (extra text) → true
   • No LGTM comments → false
   • Empty array → false

4. Create override.test.js for hasHumanOverride:

   • Approval present → true (short-circuits, no comment check needed)
   • No approval, LGTM present → true
   • Neither present → false
   • Mock GitHub API calls

Acceptance criteria

• hasNonStaleLgtm correctly identifies non-stale LGTM comments
• hasNonStaleLgtm is case-insensitive and allows trailing text
• hasHumanOverride checks both mechanisms and returns true if either matches
• hasHumanOverride fetches reviews, comments, and commit in parallel
• All tests pass: node --test tests/lib/approval.test.js tests/lib/override.test.js

Dependencies

None — this is the foundation for the other tasks.