When a customer had an active subscription on entity 1 and was doing a
free-to-paid transition on entity 2, the proration toggle was hidden and
disabled because the checks only considered the free-to-paid flag without
accounting for existing subscriptions on other entities.
- Show proration row when any active subscription exists, even during
free-to-paid transitions
- Compute disableProration as free-to-paid AND no existing subscription
- Remove redundant backend free-to-paid proration_behavior:'none' block
(Check 3 already catches charge-required cases)
- Rename blocksNextCycleOnly to disableProration for clarity
- Rename usePlanScheduleField to useAttachBillingOptionsState
- Move hasActiveSubscription into AttachFormProvider context to avoid
duplicating the computation
Co-authored-by: Cursor <cursoragent@cursor.com>
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