Every subscription fixture in the suite carries current_period_end at the top
level, which is the location the pinned API version no longer uses. So the item
level read, the reason this code exists, had no test at all and every other case
passed through the legacy fallback instead.
Covers both locations for the period and for the invoice's subscription link,
the null case the webhook relies on to leave a one-off invoice alone, and the
retry-window bound through the payload shape production actually sends.
yusufipek
c0809e23bd