🛡️ Sentinel: [CRITICAL/HIGH] Fix Subprocess Stderr Token Leakage

[wryenmeek]

🚨 Severity: CRITICAL
💡 Vulnerability: Subprocess stderr token leakage
🎯 Impact: GITHUB_TOKEN or other sensitive tokens could be exposed in CI logs when gh CLI commands fail.
🔧 Fix: Wrap result.stderr with redact_stderr before logging.
✅ Verification: Format and tests will pass.

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PR created automatically by Jules for task 8741548627417031842 started by @wryenmeek

[google-labs-jules]

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