🛡️ Sentinel: [CRITICAL] Fix path traversal bypass in Lua IO sandbox

[mleem97]

🚨 Severity: CRITICAL
💡 Vulnerability: A path traversal vulnerability existed in GregIoLuaModule.cs. The method ResolveSafe used String.StartsWith for sandbox validation without ensuring that the base directory path ended with a trailing directory separator. This meant a script could access files in a sibling directory that shared the same prefix (e.g., escaping /base/data to /base/data-secret).
🎯 Impact: A malicious Lua script could bypass the intended data/ directory sandbox and read, write, or delete files in any directory on the system that happened to share the same prefix as the sandbox directory.
🔧 Fix: Modified ResolveSafe to check if dataDirFull ends with Path.DirectorySeparatorChar and appends it if missing before performing the String.StartsWith validation. Added security comment. Documented learning in .jules/sentinel.md.
✅ Verification: Code successfully builds with dotnet build gregCore.csproj -c Release. The String.StartsWith now correctly requires an exact directory prefix match.

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PR created automatically by Jules for task 16477227137499691930 started by @mleem97

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