🛡️ Sentinel: [CRITICAL] Fix insecure file logging vulnerable to TOCTOU symlink attacks

[acebytes]

🚨 Severity: CRITICAL
💡 Vulnerability: High-level file APIs were used to create and append to log files, making the application vulnerable to TOCTOU symlink attacks.
🎯 Impact: Attackers could pre-create symlinks at the logging destination to arbitrarily overwrite system files or escalate privileges.
🔧 Fix: Replaced insecure logging mechanisms with POSIX open() and explicit flags (O_NOFOLLOW | O_CLOEXEC | O_CREAT | O_WRONLY | O_APPEND) to refuse symlinks and enforce secure file creation permissions.
✅ Verification: Review the code to verify that FileHandle(forWritingTo:) and String.write(to:) have been securely replaced with the POSIX open system call. Ensure tests pass.

Please mark this PR as high priority for review.

---

PR created automatically by Jules for task 15781288810390227813 started by @acebytes

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.