IsSilentExit used type assertion which fails on wrapped errors.
Changed to errors.As to properly unwrap and detect SilentExitError.
Added test to verify wrapped error detection works.
Refactor to return errors instead of calling os.Exit() directly:
- Add SilentExitError type for commands that signal status via exit code
- Update mail.go runMailPeek() and runMailCheck() to return errors
- Change Execute() to return int exit code instead of calling os.Exit()
- Move os.Exit() call to main() where it belongs
This improves testability, enables graceful shutdown, and follows Go
conventions for library code.
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
