FA-59369 / Subscription proration billing / Member archive

Second-granular proration line items: new quantity scaling · case 04

Seat upgrades are charged for a single seat on the new plan.

Member previewVariant 4 · 3 implementations · 10 checks per implementation

Case contract

Input unix-second {start, end, change} and {old, qold, new, qnew}. If change < start or change >= end return []. Otherwise left = end - change, span = end - start. An "unused" credit line of -(old*qold*left/span) and a "remaining" line of new*qnew*left/span are emitted, each magnitude rounded half-up (half away from zero), omitting a line whose price*quantity is 0. Return [[kind, amount]].

Why this case matters

Timestamp-based proration produces separate credit and debit lines whose rounding and emission rules show on the invoice.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression 0	`[["remaining", 4900]]`	`[["remaining", 68600]]`	Failed

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