Sometime later you discover the wallet.balance cache is wrong. Maybe a migration ran half-finished. Maybe a race condition slipped through. Maybe an engineer ran an ad-hoc UPDATE in a panic and forgot to also write the matching journal entry. The cache says ₦5,000 for a user; the ledger sums to ₦4,800. You can't trust the cache anymore. The recovery procedure: TRUNCATE the projection, scan the ledger account by account, sum debit and credit lines, write fresh balances back. The cache is in sync again. **The fact that this rebuild is POSSIBLE is the entire value of having a ledger.** Apply the entries below, then read the takeaway for the rebuild SQL.