Subscriptions that start on time, and end when they should

A provider announces a subscription differently than it announces a one-off sale, and we were listening for only one of the two. A subscription could be paid for and unlock nothing, and a cancellation could go through without the access ever being taken back. Both directions work now. Cancelling at the end of a paid period keeps access running until that date rather than ending it early, and a member who has left is marked as ended instead of simply losing their status, with the purchase and end dates recorded on them.