Two things the contract could not answer on its own: what happened, and what
the customer's whole bill is.
`subscription_records` is append-only, one row per commercial event. Flat
columns for everything searched or relied on as evidence — event, customer,
subscription, plan family and version, term, net/tax/gross, currency, tax rate,
reverse charge, Stripe ids — PLUS a versioned JSON copy of the whole snapshot.
Not JSON alone: you cannot query it, and "the amount is in there somewhere" is
poor evidence. Copied, not joined, so a row still answers after the customer,
the plan or the version have gone.
The flat columns describe the TRANSACTION. Gross is what was actually taken;
net and tax are that gross split by the rate that applied on the day. A
discount lowers the taxable amount rather than creating negative VAT, and a
free checkout is recorded as free instead of as paid in full. What was agreed
sits beside it in the snapshot, so a charge that differs from the catalogue is
preserved as a question rather than reconciled away.
The register refuses to be rewritten, in bulk as well as one row at a time —
model events do not fire for `query()->update()`, which is exactly the shape a
careless data fix takes.
`subscription_addons` carries the owner's rule: a customer's total is their
subscription plus their modules, and all of it is frozen at what was agreed.
Price protection covering only the plan would let a module quietly double for
someone who booked it two years ago. A module they have NOT booked is a sale
still to be made, at today's price — so the catalogue is consulted only for
what is not in this table. Several bookings of one module are summed rather
than reduced to one arbitrary row, or the page and the bill would disagree.
Concurrency: one order books one module, enforced by a unique index rather than
a lookup two retries can both pass; cancellation is an atomic claim; and each
booking commits with its own register entry, so a failure cannot leave a sale
without evidence and a retry that finds the booking cannot skip the event.
Verified in the browser: with the module raised from 29,00 € to 59,00 € in the
catalogue, the customer who booked it still sees 29,00 € and a total of
208,00 €, while a new customer is quoted 59,00 €.
436 tests green. Codex review clean after seven rounds.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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