Ledger Design

Sketch a double-entry system of record: chart of accounts, posting rules, immutability, and how balances are derived. The ledger catches what a processor dashboard misses.

Gold Hat: teach the invariant while you draw the accounts. A sketch that hides why debit equals credit extracts; a sketch that leaves the next engineer able to post a refund unaided empowers.

This skill is documentation and design review only — not a CPA product, not tax advice, not a fraud recipe.

When to use

• Designing a new money movement system (do this before, or with, payment-flow-review)
• Migrating from "we look at the provider dashboard" to an owned ledger
• Debugging "balance does not match" as a design question (posting rules, not live recon)
• Adding a refund, payout, fee, or FX posting path

Do not use this skill as a general ledger for an accounting department, as an analytics warehouse, or as a log dump. Daily expected-vs-actual is reconciliation (still a stub) — call it; do not invent its depth. Who changed a posting rule is audit-trail (melted).

Hard rules