FA-59724 / Subscription proration billing / Member archive

Current billing period containing a date: boundary date ownership · case 04

A change on a renewal date is prorated against the period that just ended.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

Input {anchor, interval week|month|year, count, at >= anchor}. Period k starts at anchor + k*count intervals (weeks as 7 days; months/years by calendar month with the anchor day clamped to month length). Return [start ISO, end ISO] of the period with start <= at < end.

Why this case matters

Proration needs the exact period containing a change date; boundary dates belong to the new period.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression 0	`["2023-10-31", "2023-11-30"]`	`["2023-11-30", "2023-12-31"]`	Failed

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