cursor-review: skip fork PRs; degrade to job summary on read-only token

[mattmillerai]

What

Two complementary fixes so cursor-review stops failing red on PRs it fundamentally can't review.

Why

A fork PR (Comfy-Desktop#973) failed the cursor-review check. Tracing it:

• The linked panel cell (adversarial (gemini-3.1-pro)) actually passed — every panel cell did.
• The run went red in Consolidate panel → Post review:

  No-findings review POST failed: gh: Resource not accessible by integration (HTTP 403)
  

Root cause: on a PR from a fork, the pull_request event gives the workflow no secrets and a read-only GITHUB_TOKEN. So:

1. CURSOR_API_KEY is empty → cursor-agent errors Authentication required on all 8 cells → every cell produces empty output → judge skipped → "no findings".
2. The read-only token can't POST a review → HTTP 403 → job fails.

The review can neither analyze nor post on a fork PR, yet it still ran the full 8-cell matrix + judge and failed the check on every external contribution.

Changes

1. Gate — skip fork PRs (cursor-review.yml)
Skip when head.repo.full_name != github.repository (the cross-repo signal, == isCrossRepository). No wasted matrix, no red X — the check is simply skipped, the standard outcome for a workflow that needs secrets a fork PR can't have.

2. post-review.py — degrade to job summary on a read-only-token 403 (defense-in-depth)
If a review POST fails with Resource not accessible by integration / HTTP 403, render the review into the job step summary and exit 0 instead of failing. Covers same-repo runs that can still hit a read-only token (read-only default workflow permissions, token-downgrading events). Genuine non-permission failures (e.g. HTTP 422) still exit 1 — no silent swallow.

Testing

• python3 -m py_compile post-review.py and YAML parse — both clean.
• Smoke-tested post-review.py with a fake gh:
  • read-only 403 (the #973 case) → writes review to $GITHUB_STEP_SUMMARY, exit 0 ✓
  • non-permission 422 → still exit 1 (inline + fallback both fail) ✓
  • happy path (POST succeeds) → exit 0, nothing written to summary ✓

Not done (and why)

pull_request_target would grant a write token on fork PRs, but cursor-review checks out and runs an agent over untrusted PR code — handing that a privileged token is the textbook fork-PR footgun. The proper "review forks too" path is a separate workflow_run job that posts from base-repo context; out of scope here.

🤖 Generated with Claude Code

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 1a6e247d-93ab-423e-a604-86dd8d40e660

📥 Commits

Reviewing files that changed from the base of the PR and between dc65b8b and eebcd8a.

📒 Files selected for processing (2)

• .github/cursor-review/post-review.py
• .github/workflows/cursor-review.yml

---

📝 Walkthrough

Walkthrough

The workflow adds an early-exit fork-PR guard in the gate job. The Python review poster gains four new helpers (is_read_only_token_error, write_step_summary, post_or_degrade, render_findings_markdown) and all direct gh_post_review call sites are replaced with post_or_degrade, which degrades delivery to the GitHub Actions step summary when a read-only token 403 is detected.

Changes

Fork detection and read-only token degradation

Layer / File(s)	Summary
New degradation helpers .github/cursor-review/post-review.py	Adds import os, is_read_only_token_error (403/resource-not-accessible stderr matching), write_step_summary (GITHUB_STEP_SUMMARY writer with stdout fallback), post_or_degrade (wraps gh_post_review returning bool with step-summary degradation on read-only token errors), and render_findings_markdown (merges review body and inline comments into a single markdown blob) — no pun intended, these helpers really degrade gracefully!
Call site updates to post_or_degrade .github/cursor-review/post-review.py	post_error_review, the no-findings path, and both retry/fallback paths in main replace direct gh_post_review calls with post_or_degrade; read-only token failures in the inline retry path degrade directly to the step summary via render_findings_markdown; all paths exit SystemExit(1) only on unrecoverable delivery failures.
Fork PR early-exit gate .github/workflows/cursor-review.yml	Adds HEAD_REPO/BASE_REPO env vars and a shell guard in the gate job's "Check trigger label" step that sets should_run=false and exits early for fork PRs (head repo ≠ base repo), before any label-based gating — it really forks over all the responsibility!

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/cursor-review-fork-pr-403

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch fix/cursor-review-fork-pr-403

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}