🛡️ Sentinel: [HIGH] Fix timing attack and info disclosure in internal router

[ivanleekk]

🚨 Severity: HIGH

💡 Vulnerability:

1. The verify_scheduler_secret dependency used standard string equality (!=) for token comparison, which is vulnerable to timing attacks.
2. The scheduled_snapshot_job endpoint caught generic exceptions and returned detail=str(e) in the 500 HTTP response, which could disclose sensitive server internal details, stack traces, or configuration errors to an attacker.

🎯 Impact:

1. Attackers could potentially forge the scheduler secret byte-by-byte by analyzing server response times.
2. Attackers triggering errors in the snapshot job could gain deep insight into database structures, query logic, or external service configurations, aiding further attacks.

🔧 Fix:

1. Updated verify_scheduler_secret to use secrets.compare_digest for constant-time string comparison (after safely checking for None).
2. Updated scheduled_snapshot_job to catch the generic Exception, log it internally using logger.error("...", exc_info=True) for debugging, and return a sanitized, generic 500 error to the client.

✅ Verification:

1. Visually verified the code changes to ensure logic is correct.
2. Ran uv run ruff check src/routers/internal.py to ensure no linting errors.
3. Tests run without regressions.

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PR created automatically by Jules for task 17647889293721990540 started by @ivanleekk

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