A crontab file is four different line types, not just schedules

A real crontab isn't purely a list of schedule lines — it commonly mixes environment variable assignments (`MAILTO=`, `PATH=`, setting where cron mails job output or what executables it can find), comments, and the actual scheduled jobs together in one file. Validating just the schedule lines while ignoring everything else would miss real mistakes, like an environment assignment with a typo in the variable name that silently does nothing, or a schedule line accidentally missing its command entirely. This tool classifies every non-blank line by what it actually is before validating it, which is what lets it give a useful answer for the whole file rather than just the lines that happen to look like schedules.

Why @reboot gets its own category instead of being flagged

The @-shortcuts like `@daily` and `@hourly` are just aliases for equivalent 5-field schedules (`@daily` = `0 0 * * *`), which is why this tool expands and validates them the same way as an explicit schedule. `@reboot` is different in kind, not just in syntax — it doesn't represent a recurring schedule at all; it means "run this once, every time the system boots." There's no 5-field equivalent to validate it against, so treating it as a parse error would be wrong — it needs its own category that reports what it actually is (a startup trigger) rather than trying to force it through schedule validation logic that doesn't apply to it.