Add comprehensive edge case testing for CharacterMappingLoader: - Test priority override behavior (user mappings vs built-in) - Test graceful handling of invalid user mapping files - Test multi-character key warning logging - Add logging for multi-character keys that are skipped All tests pass successfully. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>