FA-6562 / Calendar arithmetic / Member archive

Last weekday of month · case 02

Month end is returned without aligning its weekday.

Member previewVariant 2 · 3 implementations · 4 checks per implementation

Case contract

Valid ISO Gregorian dates in years 1 through 9999; generated dates must remain in that range. Month is 1 through 12 and zero-based weekday is Monday 0 through Sunday 6 unless the output convention says otherwise. Last weekday of month. Exact operational definition: (date(year,month,calendar.monthrange(year,month)[1])-timedelta(days=(date(year,month,calendar.monthrange(year,month)[1]).weekday()-weekday)%7)).isoformat()

Why this case matters

Small exact fixtures expose this error without platform timing, external services, or probabilistic observations. Calendar conventions results depend on the stated convention.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
fixture 1: (2024, 2, 0)	`"2024-02-29"`	`"2024-02-26"`	Failed

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