ci: fix fallback reviewer token permissions (checks/statuses read, GITHUB_TOKEN read-only)

[DevVig]

What

Give the fallback reviewer GITHUB_TOKEN checks: read and statuses: read, drop unused write scopes, and omit CODEX_GITHUB_TOKEN from pull_request runs.

Why

Unlisted workflow permission scopes are none. loadPrEvidence reads CodeRabbit check-runs and commit statuses; those 403s were swallowed into empty lists, so in-progress and rate-limit evidence never appeared. Writes already go through CODEX_GITHUB_TOKEN. Same-repo pull_request jobs check out PR code, so they must not receive the PAT.

Follow-up to #114 (Jon approved the fallback-only rollout on Oct 5, 2026).

How was this tested?

• Inspected .github/workflows/coderabbit-fallback-review.yml permissions and step env against GitHub’s unlisted-scope-is-none rule
• Policy sentence added in docs/ops/pr-review-policy.md under Automatic Codex fallback
• Script, cron, and CodeRabbit settings unchanged

Checklist

• Protocol unchanged
• Not an adapter PR
• Nothing added to the daemon's idle footprint

  

[coderabbitai]

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Review configuration:

⚙️ Run configuration

• Configuration used: Organization UI
• Review profile: CHILL
• Plan: Essentials
• Run ID: 55f157bf-01ac-4c48-b6f6-f15b7021e491

📥 Commits

Reviewing files that changed from the base of the PR and between 76ae9ed and be43bcd.

📒 Files selected for processing (2)

• .github/workflows/coderabbit-fallback-review.yml
• docs/ops/pr-review-policy.md

• Autopilot · Keep fixing CodeRabbit findings and required CI, and resolving merge conflicts

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

[Copilot]

Copilot review overview

🔵 Needs a closer look

It changes CI workflow token permissions and PAT exposure boundaries, a security-sensitive area that warrants final human sign-off.

Review effort: Balanced
Findings: None

What changed in this PR

This PR hardens the token handling for the CodeRabbit→Codex fallback reviewer workflow. It corrects the GITHUB_TOKEN scopes so the read-only evidence collection (CodeRabbit check-runs and commit statuses) actually works, while keeping all writes on the CODEX_GITHUB_TOKEN PAT and preventing that PAT from being exposed to PR-checked-out code on pull_request runs. It is a follow-up to #114, which introduced the fallback reviewer.

Changes:

• Downgrade GITHUB_TOKEN pull-requests/issues from write to read and add checks: read and statuses: read so loadPrEvidence no longer silently gets empty check-run/status lists.
• Omit CODEX_GITHUB_TOKEN from pull_request runs (which are always dry-run) so the PAT is not available when PR code is checked out.
• Document the read-only token posture in docs/ops/pr-review-policy.md.

File	Description
.github/​workflows/​coderabbit-fallback-review.yml	Adjusts GITHUB_TOKEN permissions (read-only + checks/statuses read) and gates the PAT env out of pull_request runs.
docs/​ops/​pr-review-policy.md	Adds a sentence noting the workflow token is read-only plus checks/statuses read, with writes via CODEX_GITHUB_TOKEN.

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