Add GitHub Copilot instructions for RecursiveExtractor repository

Co-authored-by: gfs <98900+gfs@users.noreply.github.com>

Author: Copilot

.github/copilot-instructions.md

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+# GitHub Copilot Instructions for RecursiveExtractor
+
+## Project Overview
+
+RecursiveExtractor is a cross-platform .NET library and CLI tool for parsing archive files and disk images, including nested archives. It provides a unified interface to extract arbitrary archives using libraries like SharpCompress and DiscUtils.
+
+## Tech Stack
+
+- **Language**: C# 10.0
+- **Target Frameworks**: .NET Standard 2.0, .NET Standard 2.1, .NET 8.0, .NET 9.0, .NET 10.0
+- **Testing Framework**: xUnit (based on project structure)
+- **Key Dependencies**: SharpCompress, LTRData.DiscUtils, NLog, Glob
+
+## Building and Testing
+
+### Build Commands
+```bash
+# Build the entire solution
+dotnet build RecursiveExtractor.sln
+
+# Build a specific project
+dotnet build RecursiveExtractor/RecursiveExtractor.csproj
+```
+
+### Test Commands
+```bash
+# Run all tests
+dotnet test RecursiveExtractor.sln
+
+# Run tests for a specific project
+dotnet test RecursiveExtractor.Tests/RecursiveExtractor.Tests.csproj
+dotnet test RecursiveExtractor.Cli.Tests/RecursiveExtractor.Cli.Tests.csproj
+```
+
+### Restore Packages
+```bash
+dotnet restore RecursiveExtractor.sln
+```
+
+## NuGet Configuration
+
+⚠️ **Important**: The repository uses a private NuGet feed configured in `nuget.config`:
+- The `nuget.config` file points to a private Azure DevOps feed: `https://pkgs.dev.azure.com/microsoft-sdl/General/_packaging/PublicRegistriesFeed/nuget/v3/index.json`
+- **When working as an agent, you may need to temporarily modify `nuget.config` to use public NuGet feeds** (e.g., `https://api.nuget.org/v3/index.json`) to restore packages successfully
+- **ALWAYS restore the `nuget.config` to its original configuration before completing your work**
+- The original configuration must be preserved to maintain consistency with the team's workflow
+
+Example of temporarily switching to public feed:
+```xml
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <packageSources>
+    <clear />
+    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
+  </packageSources>
+</configuration>
+```
+
+## Code Style Guidelines
+
+### Follow .editorconfig Settings
+- Use 4 spaces for indentation (no tabs)
+- CRLF line endings
+- Open braces on new lines
+- Use `var` for local variables when type is apparent
+- Follow PascalCase for types, methods, and properties
+- Interfaces should begin with 'I'
+- Do not use `this.` qualifier unless necessary
+
+### Naming Conventions
+- **Interfaces**: Start with 'I' (e.g., `ICustomAsyncExtractor`)
+- **Classes**: PascalCase (e.g., `FileEntry`, `Extractor`)
+- **Methods**: PascalCase (e.g., `Extract`, `ExtractAsync`)
+- **Properties**: PascalCase (e.g., `FullPath`, `Content`)
+- **Parameters**: camelCase (e.g., `fileEntry`, `options`)
+
+### C# Best Practices
+- Enable nullable reference types (project uses `<Nullable>Enable</Nullable>`)
+- Prefer pattern matching over `as` with null checks
+- Use expression-bodied members for simple properties and accessors
+- Prefer `null` propagation (`?.`) when appropriate
+- Use async/await for I/O operations
+- Implement both synchronous and asynchronous versions of extraction methods
+
+## Testing Practices
+
+### Test Organization
+- Unit tests go in `RecursiveExtractor.Tests` project
+- CLI tests go in `RecursiveExtractor.Cli.Tests` project
+- Use xUnit as the testing framework
+- Test files should mirror the structure of source files
+
+### Test Naming
+- Use descriptive test names that explain what is being tested
+- Follow pattern: `MethodName_StateUnderTest_ExpectedBehavior`
+
+### Test Data
+- Test archives and files should be placed in appropriate test data directories
+- Include edge cases: nested archives, encrypted files, malformed content, zip bombs
+
+## Security Considerations
+
+- The library includes protections against ZipSlip, Quines, and Zip Bombs
+- Always validate file paths to prevent directory traversal attacks
+- Handle malformed archives gracefully without crashes
+- Implement proper resource cleanup (dispose streams, file handles)
+
+## Documentation
+
+- Add XML documentation comments for public APIs
+- Keep README.md updated with new features or changes
+- Document breaking changes clearly
+- Include code examples for new public APIs
+
+## Project Structure
+
+```
+RecursiveExtractor/               # Main library project
+RecursiveExtractor.Tests/         # Unit tests for library
+RecursiveExtractor.Cli/           # Command-line interface project
+RecursiveExtractor.Cli.Tests/     # Tests for CLI
+```
+
+## Common Patterns
+
+### Extraction Pattern
+- Use `Extractor` class as the main entry point
+- Support both `Extract()` (sync) and `ExtractAsync()` (async) methods
+- Return `IEnumerable<FileEntry>` or `IAsyncEnumerable<FileEntry>`
+- Each `FileEntry` contains a Stream of content that should be disposed properly
+
+### Custom Extractors
+- Implement `ICustomAsyncExtractor` for new archive formats
+- Include `CanExtract()` method to detect file format via magic bytes
+- Preserve stream position in `CanExtract()`
+- Support both sync and async extraction
+
+### Error Handling
+- Throw `OverflowException` for detected quines or zip bombs
+- Throw `TimeoutException` when timing limits are exceeded
+- Log errors and skip invalid files during extraction
+- Use `ExtractSelfOnFail` option to return original archive on failure
+
+## Important Notes
+
+- Multi-targeting means code must be compatible with .NET Standard 2.0
+- Some features (like WIM support) are Windows-only
+- The library automatically detects archive types
+- Streams in FileEntry objects should be disposed by consumers
+- Avoid multiple enumeration of extraction results
+- For parallel processing, use batching mechanism as documented in README