GitHub 422: validate or remap review comment lines against PR diff before POST

[jpolvora]

Summary

When posting inline PR review comments via POST /repos/{owner}/{repo}/pulls/{pull_number}/comments, the runner sometimes fails the entire job with exit code 1 if GitHub returns 422 with:

{
  "message": "Validation Failed",
  "errors": [{
    "resource": "PullRequestReviewComment",
    "code": "custom",
    "field": "pull_request_review_thread.line",
    "message": "could not be resolved"
  }]
}

GithubProvider.setPullRequestComments (dist/provider/github.js) currently throws after any failed post, which breaks CI even when the review itself succeeded and only anchoring failed.

Reproduction (consumer: ERP.Fiscal)

• PR: develop → main: harness workflow, NFS-e municípios, segurança ERP.Fiscal#17
• CI log: Cursor Code Review job failed on 2026-07-17
• Attempted comment: src/ERP.Fiscal.PlugNotas/Extensions/PlugNotasServiceCollectionExtensions.cs line 26
• Actual diff hunk (develop vs main) only touches lines around 27–30 (addition of INfseEmissaoProvider registration at ~line 30)
• Line 26 is outside the diff hunk → GitHub cannot resolve the thread line

The model cited line 26 (context); the actionable change in the patch is on another line.

Current behavior

// dist/provider/github.js — setPullRequestComments
const response = await this.client.restPost(path, {
  body,
  commit_id: sha,
  path: filePath,
  line: review.lineNumber,
  side: 'RIGHT',
});
// on failure: failures.push(...); then throw if failures.length > 0

• Leading / on fileName is already stripped (replace(/^\/+/, '')) — not the root cause here.
• No validation that lineNumber is inside a diff hunk for commit_id + path.

Expected behavior

1. Before POST: resolve whether (path, line, side, commit_id) is commentable on this PR (e.g. fetch PR files / patch from REST or compare with diff produced by the same getDiffBreakdown pipeline used for the agent).
2. On mismatch: remap to the nearest valid line in the same hunk (prefer added/changed lines), or fall back to a non-inline channel (review body / summary) instead of failing the whole run.
3. On GitHub 422: treat as partial publish — log ::warning::, continue with other comments, do not throw unless all comments failed or auth/system errors occur.
4. Align with documented intent: review findings should not fail CI; exit 1 only for true system errors (auth, missing SHA, agent crash).

Suggested implementation notes

• Use Create a review comment for a pull request constraints: line must exist in the pull request diff for the given commit_id.
• Optional: POST .../pulls/{pull_number}/reviews with comments array after validating each position.
• Add unit tests with a fixture patch where the model line is off-by-N from the hunk.
• Consider prompting the agent to prefer line numbers from the diff hunks only (secondary; server-side validation should still be authoritative).

Workaround (consumer-side, temporary)

ERP.Fiscal added CURSOR_REVIEWER_EXTRA_EXCLUDE_PATTERNS and a workflow wrapper that exits 0 when the log contains could not be resolved — this should be removed once this issue is fixed upstream.

Environment

• Runner: run.sh from main, clones release branch
• Provider: --gh, GitHub Actions, GITHUB_TOKEN with pull-requests: write
• Node 24.x