FA-59557 / Subscription proration billing / Member archive

Annual-to-monthly switch credit: fully covered invoice count · case 02

A partially funded monthly invoice is reported as covered and the leftover balance goes negative.

Member previewVariant 2 · 3 implementations · 8 checks per implementation

Case contract

Input {annual, months_used, days_into_month, month_days, monthly}. Months started = months_used plus one if the current month has begun (days_into_month > 0), capped at 12. Credit = annual*(12 - started)//12. The credit pays whole future monthly invoices; the remainder stays as balance. Return [credit, covered_invoices, leftover].

Why this case matters

Switching billing intervals converts unused prepaid time into credit that funds future invoices.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression 0	`[99900, 3, -16956]`	`[99900, 2, 21996]`	Failed

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