Initial commit: wanderbooks accounting semantics engine

docs/parity.md

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+# Parity catalog
+
+Every semantic feature we intend to clone, with its status. Updated in the
+same commit as the feature. **The floor never decreases**: the count of
+`done` items is monotonic across commits.
+
+Statuses: `done` = implemented + invariant-tested + golden-covered.
+`partial` = implemented but missing tests or goldens. `todo` = not started.
+No other statuses.
+
+**Floor: 6 done** (2026-10-10, initial commit).
+
+| Area | GnuCash reference | Status | Notes |
+|---|---|---|---|
+| Chart of accounts (5 types, codes, hierarchy) | Accounts tab | done | `account.rs`; placeholder support in |
+| Double-entry validation (balanced, ≥2 lines) | Journal validation | done | `journal.rs::validate` |
+| Exact decimal money, no floats | — (we go further) | done | `money.rs`; Currency ISO codes |
+| Posted-entry immutability | Read-only posted txns | done | reversal via `reverse_entry` |
+| Trial balance | Reports → Trial Balance | done | golden-covered |
+| Balance sheet (A = L + E) | Reports → Balance Sheet | done | current earnings folded in pre-close; golden-covered |
+| Profit & loss | Reports → Income Statement | done | golden-covered |
+| Reversing entries | Reverse transaction | done | linked via `reversal_of` |
+| Canonical report snapshots (JSON) | — (our oracle format) | done | `reports::snapshot` |
+| Cash flow statement (indirect) | Reports → Cash Flow | todo | R-FUTURE-3 |
+| Period close / retained earnings | Close books | todo | R-FUTURE-2 |
+| Multi-currency + FX translation | Multi-currency accts | todo | R-FUTURE-1 |
+| GnuCash XML import (read-only) | File format | todo | feeds oracle harness; R-FUTURE-4 |
+| A/R invoices + payments + aging | Business → Invoices | todo | R-FUTURE-5 |
+| A/P bills + payments + aging | Business → Bills | todo | R-FUTURE-5 |
+| Budgets | Budgets | todo | R-FUTURE-6 |
+| Scheduled transactions | Scheduled txns | todo | R-FUTURE-6 |
+| Automated GnuCash diff harness | — (our `xtask oracle`) | todo | roadmap phase 3 |
+
+Workflow/UI parity (QuickBooks/Xero reference) gets its own catalog when the
+egui phase starts; semantics come first.