ValidateIdentityFile now accepts $VAR/${VAR} (expanded via os.Expand, undefined vars accepted as-is) and SSH tokens like %d, %h before falling back to os.Stat.
The raw value is preserved when writing to ssh_config.
- Fix history tests with proper test isolation using temp files
- Fix CMD tests with proper string contains and simplified assertions
- Add missing test utilities and helper functions
- Improve test coverage across all packages
- Remove flaky tests and replace with robust alternatives"
