.NET: increase default search depth for script and resource discovery (fixes #5968)

[hanhan761]

Summary

Increase the default SearchDepth for script and resource file discovery from 2 to 10, allowing the discovery of nested scripts/resources in deeper subdirectory structures.

Background

AgentFileSkillsSource already supports recursive directory traversal via ScanDirectoryForScripts and ScanDirectoryForResources, but the default _searchDepth of 2 limits discovery to the root directory plus one level of subdirectories. Files nested deeper (e.g., scripts/subdir/tool/my_script.py) are silently skipped.

Fix

Changed DefaultSearchDepth from 2 to 10. This allows discovery up to 10 levels of nesting while maintaining the existing security checks (symlink detection, path traversal prevention) and the SearchDepth configuration option for users who need different limits.

Issue

Fixes #5968

Verification

• Existing tests in AgentFileSkillsSourceScriptTests.cs cover the default depth behavior
• The SearchDepth option remains configurable via AgentFileSkillsSourceOptions.SearchDepth
• Security checks (symlink, path traversal) are unaffected

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Updates the default directory search depth used by AgentFileSkillsSource when looking for skill files.

Changes:

• Increased DefaultSearchDepth from 2 to 10.