Add diff_files capability for file comparison

[abderraouf-belalia]

Feature Request

Add a new diff_files tool to enable file comparison capabilities in the MCP filesystem server.

Motivation

This feature would complement existing file operations by allowing:

• Comparison of file versions before/after edits
• Content verification in merge/review workflows
• Debugging file synchronization issues
• Integration with version control workflows

Proposed Implementation

Tool: diff_files

Parameters:

• path1 (string): First file path to compare
• path2 (string): Second file path to compare
• max_file_size_bytes (optional number): Maximum file size to compare (default: 10MB)

Behavior:

• Text files: Generate unified diff format (using existing similar crate)
• Binary files: Compare SHA-256 hashes and report match/mismatch
• Read-only operation: read_only_hint=true, destructive_hint=false, idempotent_hint=true

Output format:

• Unified diff in markdown code block for text files
• Hash comparison result for binary files
• Clear error messages for access denied, file not found, or size exceeded

Technical Details

• Leverages existing dependencies: similar=2.7, sha2=0.10.9, infer=0.19.0
• Follows established patterns from read_text_file and edit_file tools
• Implements proper path validation via validate_path()
• Respects allowed directory restrictions
• File size limits to prevent memory issues

Scope

Starting with simple file-to-file comparison. Future enhancements could include:

• Directory comparison
• Content-vs-string diff
• Additional output formats (JSON, stats-only)

Checklist

• Implement tool definition in src/tools/diff_files.rs
• Add service method in src/fs_service.rs
• Register in src/tools.rs and src/handler.rs
• Write comprehensive tests
• Update docs/capabilities.md
• Run cargo make check

[agent issue]