cash flow: financing and investing gross; account roles are a setting

From ASC 230 (via Deloitte DART and PwC Viewpoint), replacing two
formerly assumed behaviors:

- Financing and investing are gross (230-10-45-7): per account, cash in
  and cash out are separate lines (contributions apart from
  distributions, borrowing apart from repayment), netted only within
  one entry. Lines come in code order, in before out.
- Investing includes making and collecting loans and buying investments
  (230-10-20, 45-13), not only registered fixed assets:
  CashFlowParams gains investing_accounts.
- The roles are per-company settings: [books] financing_accounts and
  investing_accounts in wanderbooks.toml (beside cash_accounts). The MCP
  tools (cash_flow, export, CPA package) default every list to them and
  share one path; the viewer reads them too, falling back to its name
  guess for debt. A due-to-owners liability listed as financing gives
  PwC 6.9.3.1's constructive treatment of expenses an owner paid.

rules.md B-14 quotes the sources; new tests cite them; docs/testing.md
#8 is resolved.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GWVo7x3UHw5kwCUaWxiejX

docs/mcp-interface.md

@@ -36,6 +36,12 @@ footers, and `[books] receipt_threshold` sets the receipt policy unless
 `distribution_account`; single-owner businesses may set `[books] close_into`
 (the equity account a close puts net income in; default Retained Earnings)
 and `close_sweep` (draw, distribution, or dividend accounts closed into it).
+The cash flow statement's account roles are `[books] cash_accounts` (what
+it reconciles to), `financing_accounts` (loans, and money the owners
+advanced, such as a "Due to owners" liability: ASC 230-10-45-14(2)), and
+`investing_accounts` (loans the company makes, investments it buys: ASC
+230-10-20); the tools and the viewer both read them, and a call may pass
+its own (docs/spec/rules.md B-14).
 
 ## Transports
 
@@ -102,7 +108,7 @@ below.
   `revenue_accounts` and `expense_accounts` for the range. `end` defaults to
   today, `start` to the first posted entry. Closing entries are excluded, so
   a closed period still shows what it earned.
-- `books.cash_flow { start?, end?, cash_accounts: ["1000"], financing_accounts? }`
+- `books.cash_flow { start?, end?, cash_accounts?, financing_accounts?, investing_accounts? }` (each defaults to `[books]` in wanderbooks.toml; cash is required one way or the other)
   → indirect-method cash flow statement. `cash_accounts` are the reconciling
   accounts (required); the three sections always sum to their net change.
   Disposal gains/losses move from operating to investing automatically.
@@ -295,7 +301,7 @@ posting.
 ## Tools — export
 
 - `books.export { format, report, start?, end?, as_of?, cash_accounts?,
-  financing_accounts? }` → `{ content, content_encoding? }`.
+  financing_accounts?, investing_accounts? }` → `{ content, content_encoding? }`.
   - Reports: `profit_and_loss`, `balance_sheet`, `cash_flow` (needs
     `cash_accounts`), `trial_balance`, `members_equity` (statement of
     changes in members' equity; members from `wanderbooks.toml`),
@@ -486,7 +492,7 @@ entries.
 
 ## Tools — CPA handoff
 
-- `books.export_cpa_package { as_of?, cash_accounts, financing_accounts? }`
+- `books.export_cpa_package { as_of?, cash_accounts?, financing_accounts?, investing_accounts? }`
   → `{ file_name, content_base64 }`. A zip with the full set, each
   statement as PDF and XLSX: `profit-and-loss`, `balance-sheet`,
   `cash-flow` (reconciled to `cash_accounts`), `members-equity`