Entities for the four wallet tables and a WalletRepository that the wallet
processor will build on (PC-103).
Every method goes through the caller's transaction, and writes and locks
refuse to run without one: outside a transaction a lock is released as soon
as it is taken and a balance could move without its ledger row.
- LockWallet creates the wallet on first use, taking the organization from
the customer, then locks it with SELECT ... FOR UPDATE.
- LockWallets always locks in customer_id order so opposite transfers
cannot deadlock.
- AddBalance and ConsumeLot are conditional updates that return an error
when they would overdraw, instead of tripping the CHECK constraint.
- ListActiveLots returns unexpired lots with balance in K9 spending order.
The tests need a real Postgres and run only when TEST_DATABASE_URL points at
a migrated database. Both the lock and the lock ordering were checked by
removing them and watching the tests fail (lost update, deadlock detected).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Products like fish are sold per weighing (4.2 ons, 5.6 ons), which the
order line could not represent: quantity is INTEGER and prices are always
computed as quantity * unit_price.
Model one weighing as one order line. quantity stays INTEGER and keeps
meaning "how many items"; the measured amount goes into a new nullable
order_items.weight, and the line is priced weight * unit_price. Two
weighings of the same product are two lines, never merged into one.
Keeping quantity integral avoids float comparisons in void, refund and
split bill, where accumulated rounding error would silently misbehave —
"1.4 + 1.4 + 1.4" is not 4.2 in float64, which would leave a fully paid
split-bill item marked unpaid.
BillableQuantity() is now the single place that decides between weight
and count; every price and cost calculation goes through it. Missing one
would bill a 4.2 ons fish as a single ons — wrong money, no error.
Two database constraints back the design: a weighed line always carries a
positive weight, and its quantity is pinned to 1. The latter also makes
void all-or-nothing for weighed lines, so the row-splitting branch can
never produce a zero-weight remainder row.
Also wires product.unit_id through the API, which was previously not
settable at all, and corrects the misleading comment on the request's
unit_price field — that value has never been used; price always comes
from the database.
Design notes and the audit of every price multiplication site are in
docs/rfc-weight-based-products.md.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
efrilmandClaude Opus 5.5
ryan