Calendar Validation

All seven week-start values are supported. Natural grids use the minimum number of complete week rows needed for that month. Fixed-six-weeks grids always contain six rows and 42 positions. Cells are row-major and current-month dates are checked for completeness, uniqueness, correct weekday alignment, and chronological order.

The leap rule is Gregorian: years divisible by four are leap years except century years unless divisible by 400. The tests include all months from 1900 through 2100. Calculations use calendar arithmetic, not the machine clock, timezone, DST, or locale.

Use betacal-printlint calendar --year 2027 --month 2 --week-start monday to inspect generated structure or betacal-printlint manifest PATH to validate one.