Keep the job token out of a tree the PR author controls

[kwsantiago]

Summary

Adds persist-credentials: false to the rng-hygiene job's checkout in ci.yml.

Why

The job checks out a PR branch and then executes a script from it — scripts/check-rng-hygiene.sh, which any PR author can edit. actions/checkout writes GITHUB_TOKEN into .git/config by default, leaving it readable by that PR-authored code. The job performs no git operations needing credentials.

Found in a CodeRabbit comment on #104 that I merged past without reading. The same fix is going to keep and keep-esp32.

CodeRabbit also flagged on #104 that scanner_died could fail open — that one was already fixed before merge (the || scanner_died is at the call sites, not inside the command substitution), verified on current main.

It additionally asked whether rng-hygiene is a required status check in branch protection. It is not: main is unprotected, so the guard is advisory. That is a repo-settings decision rather than a code change, and is worth deciding separately.

Test plan

• ci.yml parses as YAML
• scripts/check-rng-hygiene.sh still clean on the tree
• Takes effect on the next CI run; not verifiable locally

Summary by CodeRabbit

• Chores
  • Updated the continuous integration checkout process to prevent Git credentials from being persisted.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 18ad3b11-c07a-431d-aa56-b70442690509

📥 Commits

Reviewing files that changed from the base of the PR and between 30c267f and 2aa0311.

📒 Files selected for processing (1)

• .github/workflows/ci.yml

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Walkthrough

The rng-hygiene CI checkout disables Git credential persistence. The GitHub token is not stored in .git/config after checkout.

Changes

RNG hygiene checkout

Layer / File(s)	Summary
Disable checkout credential persistence .github/workflows/ci.yml	The rng-hygiene checkout sets persist-credentials: false.

Estimated code review effort: 1 (Trivial) | ~3 minutes

Poem

A rabbit checks the workflow bright,
No token lingers out of sight.
The checkout hops with care,
Credentials leave no trace there.
Safe paths through the CI night.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes preventing the job token from being exposed to PR-controlled files.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch harden-guard-workflow

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