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>
