Summary

Gitignore pattern matching fails in Linux dev container environments because Get-GitIgnorePatterns uses hardcoded Windows backslash (\) separators instead of platform-appropriate separators.

Problem

When running Validate-MarkdownFrontmatter.ps1 in the Ubuntu-based dev container, gitignore patterns like node_modules/ are converted to *\node_modules\* which never matches Linux file paths like /workspace/node_modules/....

Root Cause

• Get-GitIgnorePatterns in LintingHelpers.psm1 hardcodes backslash separators
• PowerShell's -like operator performs literal string matching
• Linux paths use forward slashes, so patterns with backslashes never match

Solution

1. Use [System.IO.Path]::DirectorySeparatorChar for platform detection
2. Normalize input patterns by replacing both / and \ with the platform separator
3. Refactor Validate-MarkdownFrontmatter.ps1 to use the shared helper function (DRY principle)

Files Affected

• scripts/linting/Modules/LintingHelpers.psm1 - Update Get-GitIgnorePatterns function
• scripts/linting/Validate-MarkdownFrontmatter.ps1 - Replace inline parsing with shared function call

Acceptance Criteria

• node_modules/ directory is properly excluded when running in Linux dev container
• All gitignore patterns work correctly on both Windows and Linux
• No regression for Windows environments
• Duplicate inline code eliminated