Initial commit: wanderbooks accounting semantics engine

docs/glossary.md

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+# Glossary
+
+For agents (and humans) new to accounting. The engine's naming follows these
+definitions exactly.
+
+- **Debit / Credit** — The two sides of every journal line. Not "good" and
+  "bad": debit = left, credit = right. What they *do* depends on the account
+  type (see normal balance).
+- **Normal balance** — The side that increases an account. Assets and expenses
+  are debit-normal (a debit increases them); liabilities, equity, and revenue
+  are credit-normal. `AccountType::normal_side()`.
+- **Chart of accounts** — The registry of all accounts, organized by code
+  (e.g. `1000` Cash, `6000` Rent Expense). Five types, no more.
+- **Journal entry** — A set of balanced lines with a date and description.
+  The atomic unit: it posts whole or not at all.
+- **Ledger** — The books: the chart plus the append-only log of posted
+  entries. (In this codebase `Ledger` is also the command surface.)
+- **Posting** — Validating a draft entry and appending it to the log.
+  One-way.
+- **Trial balance** — A listing of every account's debit or credit balance.
+  Total debits must equal total credits; if they don't, the books are broken.
+- **Balance sheet** — Assets = Liabilities + Equity, at a point in time.
+- **Profit & loss (income statement)** — Revenue − Expenses = Net income,
+  over a period.
+- **Reversing entry** — An entry that exactly undoes a posted entry (same
+  lines, sides flipped), linked to the original. The correction mechanism.
+- **Placeholder account** — A header in the chart (e.g. "Current Assets")
+  that organizes other accounts but takes no postings itself.
+- **Closing the books** — Period-end ritual: move revenue/expense balances
+  into retained earnings so the new period starts clean. (Future: R-FUTURE-2.)
+- **Current earnings** — Net income to date on an unclosed book. We fold it
+  into equity so the accounting equation holds before close.