🛡️ Sentinel: [HIGH] Fix command injection vulnerability in tool existence check

[acebytes]

🚨 Severity: HIGH
💡 Vulnerability: Command injection vulnerability in toolExists via unsafe string interpolation in a shell wrapper (shell("/usr/bin/which \(tool)")). While tool variables currently come from hardcoded requiresTool properties, this unsafe pattern risks severe arbitrary command execution if those strings ever become dynamically sourced (e.g. from user config or server).
🎯 Impact: Arbitrary command execution with user privileges.
🔧 Fix: Replaced the shell function wrapper with direct execution of /usr/bin/which using Process(), passing the tool variable explicitly as an element in the arguments array instead of via string interpolation.
✅ Verification: Review the updated toolExists function in Sources/Cacheout/Models/CacheCategory.swift to ensure direct invocation without /bin/bash or string interpolation.

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PR created automatically by Jules for task 11857720161025045232 started by @acebytes

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