Phase 1 — Ledger

Goal

Money that cannot lie: Decimal everywhere, balanced double-entry, append-only history.

Worked example

POST /api/v1/accounts
{"code":"CASH","name":"Cash","currency":"EUR"}

POST /api/v1/ledger/transactions
{
  "reference": "TX-1",
  "description": "Hotel from cash",
  "lines": [
    {"account_id": 2, "debit": "120.00", "credit": "0", "currency": "EUR"},
    {"account_id": 1, "debit": "0", "credit": "120.00", "currency": "EUR"}
  ]
}

Amounts are strings. Sending 120.00 as a JSON number is rejected — floats already lost precision before they reach the ledger.

Failure case

An unbalanced body returns 422 and leaves zero rows:

{"error": "UnbalancedLedgerError", "detail": "Unbalanced transaction: debit=100 credit=50"}

Postgres also has a deferred trigger so a buggy script cannot commit an unbalanced set even if it bypasses the service. Balances leave the API as MoneyStr (JSON strings) so clients never round float money.

Paths: core/money.py, services/ledger.py, alembic/versions/001_*.py