P2 slice 6: the viewer

`wanderbooks gui [BOOK]` finds the data root, reads settings from the
journal, the vault of the book, presence through ops/, Save a copy /
Open on every document, Save the W-9, the Export menu, and colour
schemes. One builder for the CPA package and the 1099 worksheet
(ledger-package), shared by the server and the viewer.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T3gXMVt7XJPi6ens1or9Dj

crates/ledger-package/src/iif.rs

@@ -0,0 +1,53 @@
+//! The journal as IIF, for QuickBooks Desktop: `books.export` format iif
+//! and the package's `general-journal.iif`.
+//!
+//! ```text
+//! GOAL: the CPA imports every posted entry into QuickBooks Desktop, each
+//!       account declared with the type QuickBooks needs.
+//! SOURCE: ledger_import::iif (the IIF format and account types).
+//! INVARIANTS:
+//!   1. The cash accounts are BANK; the receivable and payable control
+//!      accounts AR and AP; a registered asset's cost and accumulated
+//!      depreciation FIXASSET; every other account follows its type.
+//!   2. Every posted entry, and only those.
+//! ```
+
+use ledger_core::{AccountId, AccountType, Ledger};
+
+/// Render the journal as IIF text via ledger-import, declaring every
+/// account with its QuickBooks type: the cash accounts (`cash_codes`, the
+/// books' `cash_accounts`) are BANK, the receivable and payable control
+/// accounts AR and AP, a registered asset's cost and accumulated
+/// depreciation FIXASSET, and the rest follow their wanderbooks type
+/// (other current asset, other current liability, equity, income,
+/// expense).
+pub fn export_iif(ledger: &Ledger, cash_codes: &[String]) -> Result<String, String> {
+    use ledger_import::{QbAccountType as Qb, iif_accounts, journal_to_iif};
+    let fixed: std::collections::HashSet<AccountId> = ledger
+        .registered_assets()
+        .flat_map(|a| [a.cost_account, a.accum_depr_account])
+        .collect();
+    let receivables = ledger.role_account(&ledger_core::RECEIVABLES);
+    let payables = ledger.role_account(&ledger_core::PAYABLES);
+    let accounts = iif_accounts(ledger, |a| {
+        if cash_codes.contains(&a.code) {
+            Qb::Bank
+        } else if Some(a.id) == receivables {
+            Qb::AccountsReceivable
+        } else if Some(a.id) == payables {
+            Qb::AccountsPayable
+        } else if fixed.contains(&a.id) {
+            Qb::FixedAsset
+        } else {
+            match a.account_type {
+                AccountType::Asset => Qb::OtherCurrentAsset,
+                AccountType::Liability => Qb::OtherCurrentLiability,
+                AccountType::Equity => Qb::Equity,
+                AccountType::Revenue => Qb::Income,
+                AccountType::Expense => Qb::Expense,
+            }
+        }
+    });
+    let entries: Vec<_> = ledger.posted_entries().collect();
+    journal_to_iif(&accounts, &entries).map_err(|e| e.to_string())
+}