feat: add diff_files tool for file comparison

[abderraouf-belalia]

Summary

Implements a new diff_files tool that enables file comparison within the MCP filesystem server.

Closes #62

Changes

New Tool: diff_files

• Parameters:

  • path1 (string): First file path to compare
  • path2 (string): Second file path to compare
  • maxFileSizeBytes (optional, default: 10MB): Maximum file size limit

• Behavior:

  • Text files: Generates unified diff format showing additions/deletions
  • Binary files: Compares SHA-256 hashes and reports match/mismatch
  • Read-only operation: No filesystem modifications

Implementation Details

Files Modified/Created:

• src/tools/diff_files.rs - Tool definition with schema
• src/fs_service.rs - Service layer implementation with binary detection
• src/tools.rs - Tool registration in macros
• src/handler.rs - Handler dispatch registration
• Cargo.toml - Added hex dependency for hash encoding
• docs/capabilities.md - Updated documentation (24→25 tools)
• tests/test_tools.rs - 8 comprehensive test cases

Key Features:

• Automatic binary detection via null byte scanning
• Configurable file size limits to prevent memory issues
• Path validation respecting allowed directories
• Consistent error handling with existing patterns
• Line ending normalization for cross-platform diffs

Test Coverage

Added 8 test cases covering:

• ✅ Identical text files
• ✅ Different text files with unified diff
• ✅ Identical binary files (hash comparison)
• ✅ Different binary files (hash comparison)
• ✅ Access control (files outside allowed directories)
• ✅ Non-existent files
• ✅ File size limit enforcement
• ✅ Multi-line changes with context

All 131 tests passing (cargo make check ✓)

Test Plan

cargo make check  # All tests pass
cargo build       # Compiles successfully
cargo install --path . --force  # Local installation successful

Manual testing completed:

• Compare two identical text files
• Compare two different text files
• Compare binary files
• Test file size limits
• Test access control boundaries
• Installed locally and verified MCP integration

[agent pull request]