domain-fintechledger-design

name	domain-fintech:ledger-design
description	Guides double-entry ledger design: journal entries, chart of accounts, sub-ledgers (AR, AP, GL), reconciliation between ledgers, immutable append-only audit trails, balance calculations (running vs computed), and ledger-as-event-log pattern. Use when designing accounting systems or financial record-keeping.

Ledger Design

When to use

• Designing a double-entry bookkeeping system from scratch
• Choosing a chart of accounts numbering convention
• Building AR, AP, or GL sub-ledgers with reconciliation
• Implementing immutable audit trails with reversal patterns
• Deciding between running balance vs computed balance strategies
• Applying event sourcing to financial record-keeping

Core principles

1. Debits always equal credits — enforce with DB constraint; reject unbalanced entries at the boundary
2. Never UPDATE or DELETE journal entries — corrections via reversing entries only; history is sacred
3. Running balance is a cache — journal lines are the source of truth; reconcile daily
4. Hash chain for tamper detection — SHA-256 chained hashes make unauthorized edits detectable
5. Sub-ledger detail must reconcile to GL control account — any gap is a critical alert, not a warning

Reference Files

• references/double-entry-journal.md — golden rule, debit/credit rules table, example entries, journal_entries and journal_lines SQL schema, entry validation rules
• references/chart-of-accounts-subledgers.md — account numbering convention (1000-7999), accounts SQL schema, GL/AR/AP sub-ledger design, sub-ledger to GL reconciliation
• references/audit-trails-balance-calculations.md — immutable append-only design, reversal pattern, hash chain integrity, running vs computed balance, hybrid approach, ledger-as-event-log with event sourcing