docs: the assumed list, checked against the standards; mutation score

Each formerly ASSUMED behavior is now CONFIRMED, CONVENTION, DESIGN, or
CHANGE (pending), with its source (Reg. S-X, ASC 230 via Deloitte DART,
IRS K-1 instructions, OpenStax). Two need engine work: members' equity
should allocate cumulatively so each member's beginning equals the prior
ending (#7), and the cash flow should show financing gross and classify
investing by account role (#8). Two questions for the CPA are listed.
The test doc comments that relied on them now cite the verdicts.

Core mutation run: 1,011 caught + 13 timeouts of 1,024 viable, 0 missed.
No benchmark budget, by decision.

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

crates/ledger-core/src/reports.rs

@@ -458,7 +458,7 @@ fn statement_lines(
 /// SCENARIOS:
 ///   1. IF a month was closed: SHOULD still report that month's earnings.
 ///      BECAUSE closing doesn't make a period break even (R-9).
-///   2. IF `start` is after `end`: SHOULD refuse. (ASSUMED)
+///   2. IF `start` is after `end`: SHOULD refuse. (DESIGN: no standard governs a reversed range; docs/testing.md #1)
 /// ```
 pub fn profit_and_loss_for_period(
     ledger: &Ledger,

crates/ledger-core/tests/spec_arap.rs

@@ -538,7 +538,7 @@ fn create_invoice_refuses_due_before_date_books_unchanged() {
 
 /// Closes January 2026 on `l`.
 ///
-/// ASSUMED: closing a period with nothing in it still marks it closed
+/// CONVENTION (docs/testing.md #4): closing a period with nothing in it still marks it closed
 /// (close_period returns Ok(None)); the precondition is asserted.
 fn close_january(l: &mut Ledger) {
     let p = l

crates/ledger-core/tests/spec_assets_payroll.rs

@@ -316,7 +316,7 @@ fn schedule_clamps_to_end_of_life() {
 /// life ends 2026-03-15 so Mar holds 1..14 = 14/31 → 140.00. 17/31 + 14/31
 /// = one full month, and the total is exactly 620.00.
 ///
-/// ASSUMED: life ends on purchase_date + useful_life_months and the end day
+/// CONVENTION (docs/testing.md #9): life ends on purchase_date + useful_life_months and the end day
 /// itself is not held (matches the doc's "17/31 + 14/30" pairing for a
 /// purchase on the 15th).
 #[test]
@@ -343,7 +343,7 @@ fn partial_first_and_last_months_make_one_full_month_b15() {
 /// Jan 17/31 → 170.00, Feb 310.00, Mar 310.00 (acc 790.00), Apr (30 days)
 /// trues up to 930 − 790 = 140.00, not 14/30 × 310 = 144.67.
 ///
-/// ASSUMED: same end-of-life convention as the test above.
+/// CONVENTION (#9): same end-of-life convention as the test above.
 #[test]
 fn last_month_trues_up_unequal_month_lengths_b15() {
     let a = asset("1030.00", "100.00", 3, date(2026, 1, 15));
@@ -867,7 +867,7 @@ fn run_payroll_posts_hand_worked_entry() {
 /// 750.00, state 250.00, SS 620 + 248 = 868.00, Medicare 145 + 58 = 203.00,
 /// other 200.00, net 3567.50 + 1697.00 = 5264.50.
 ///
-/// ASSUMED: lines are aggregated per account ("zero totals are skipped"
+/// CONFIRMED (docs/testing.md #10): lines are aggregated per account ("zero totals are skipped"
 /// implies totals), not one line per employee.
 #[test]
 fn run_payroll_aggregates_employees() {

crates/ledger-core/tests/spec_ledger.rs

@@ -1235,7 +1235,7 @@ fn a_loss_closes_as_a_debit_to_equity() {
 }
 
 /// Oracle: close INVARIANT 5: nothing to close posts nothing and returns
-/// None. ASSUMED: the period is still marked closed (step 3 of the doc).
+/// None. CONVENTION (docs/testing.md #4): the period is still marked closed (step 3 of the doc).
 #[test]
 fn a_close_with_nothing_to_close_posts_no_entry() {
     let mut b = books();

crates/ledger-core/tests/spec_reports.rs

@@ -531,7 +531,7 @@ fn pnl_closed_month_still_reports_its_earnings() {
     assert_eq!(year.net_income(), c(7000));
 }
 
-/// Oracle: P&L SCENARIO 2 (ASSUMED in the spec itself) — start after end
+/// Oracle: P&L SCENARIO 2 (DESIGN, docs/testing.md #1) — start after end
 /// refuses.
 #[test]
 fn pnl_period_start_after_end_refuses() {
@@ -1009,7 +1009,7 @@ fn me_refuses_bad_shares() {
 /// earnings 100.01 -> A 50.01, B 50.00; period income 201.01 -> A 100.51,
 /// B 100.50. Total ending 2251.02 = BS equity.
 ///
-/// ASSUMED: the beginning (unclosed prior earnings) and the period's income
+/// CHANGE PENDING (docs/testing.md #7): the beginning (unclosed prior earnings) and the period's income
 /// are each split separately (INVARIANT 3 names them separately), not
 /// cumulative-then-differenced.
 #[test]
@@ -1407,7 +1407,7 @@ fn sorted_amounts(lines: &[ledger_core::CashFlowLine]) -> Vec<Decimal> {
 /// 400; AR up 300 (-300), AP up 80 (+80); CFO 180; financing loan 300 +
 /// contribution 100 = 400; net change 580 = cash 1000 -> 1580.
 ///
-/// ASSUMED: one working-capital / financing line per account that changed.
+/// CHANGE PENDING (docs/testing.md #8): one working-capital / financing line per account that changed.
 #[test]
 fn cf_hand_computed_with_designated_debt() {
     let co = cf_example_books();
@@ -2418,7 +2418,7 @@ proptest! {
     /// NI + depreciation + working capital; with or without a close and a
     /// designated loan.
     ///
-    /// ASSUMED: with no registered fixed assets, depreciation and investing
+    /// CHANGE PENDING (docs/testing.md #8): with no registered fixed assets, depreciation and investing
     /// are zero (receivables are current, so working capital).
     #[test]
     fn prop_cf_sections_sum_to_change_in_cash(gens in arb_books(), (a, _m, e) in three_days(), month in opt_month(), designate in any::<bool>()) {

docs/testing.md

@@ -25,7 +25,7 @@ the store's journal safety; the other crates come next (gap list).
 | Miri | undefined behavior in our use of dependencies (4) | the core's unit, bridge, invariant tests | `just miri` | ~2 min | on demand |
 | Golden | `tests/golden/fixture_company.json` (5) | `invariants.rs` | `just check` | <1s | every change |
 | Benchmarks | a baseline (6) | `benches/books.rs` | `just bench` | ~1 min | none (no budget, by decision) |
-| Mutation | can the tests fail? | `ledger-core` | `just mutants` | ~12 min | weekly |
+| Mutation | can the tests fail? | `ledger-core` (2026-10-13: 1,011 caught + 13 timeouts of 1,024 viable, 0 missed) | `just mutants` | ~3 h | weekly |
 
 CI: `.github/workflows/check.yml` runs `just check` on every push;
 `scheduled.yml` runs proofs, the oracle, fuzzing, and mutation weekly.
@@ -56,32 +56,37 @@ laptop:
 | balance sheet | 47 µs | 1.04 ms |
 | one month's P&L | 25 µs | 248 µs |
 
-## Assumed, not confirmed (reject any)
+## Formerly assumed: checked against the standards (2026-10-13)
 
-Each was inferred, not decided by a human; the tests that rely on them
-say so in their doc comments.
+Stephen isn't an accountant and won't adjudicate these; each was checked
+against published sources instead (rank: FASB ASC via the Deloitte DART
+reproduction, SEC, IRS; then textbooks; software practice is evidence of
+convention only). Verdicts: CONFIRMED (a source supports it), CONVENTION
+(no standard governs; matches mainstream practice), DESIGN (not an
+accounting question), CHANGE (a source says otherwise; work pending).
 
-- ASSUMED: a P&L for a period whose start is after its end is refused.
-- ASSUMED: a balance sheet omits accounts with a zero balance.
-- ASSUMED: the lifetime `profit_and_loss` counts closing entries
-  (only period statements exclude them).
-- ASSUMED: closing a period with nothing to close still marks it closed.
-- ASSUMED: a sweep account (draws, distributions) is zeroed as of the
-  period end, like income.
-- ASSUMED: reconciliation balances are debits minus credits (tested on
-  cash; liability accounts unspecified).
-- ASSUMED: a members' equity statement allocates prior unclosed earnings
-  and the period's income separately; one statement's ending for a member
-  may differ by a cent from the next statement's beginning (only totals
-  are guaranteed to chain).
-- ASSUMED: cash flow lists one working-capital or financing line per
-  account that changed; with no registered assets, investing is zero.
-- ASSUMED: an asset's life ends on purchase date + life months, that day
-  not held.
-- ASSUMED: a payroll entry has one line per account total, not per
-  employee.
-- ASSUMED: a period with exactly the dates of an existing one nests in it
-  (is allowed).
+| # | Behavior | Verdict | Source / note |
+|---|---|---|---|
+| 1 | A P&L whose start is after its end is refused | DESIGN | No standard governs a reversed range; refusing beats silently swapping a typo |
+| 2 | A balance sheet omits zero-balance accounts | CONFIRMED | Reg. S-X 210.4-03(a): "No caption should be shown ... as to which the items and conditions are not present." A comparative statement must still show a zero beside a non-zero prior column |
+| 3 | The lifetime `profit_and_loss` counts closing entries | CONFIRMED | Used as earnings not yet closed on the balance sheet; closed income is already in capital (OpenStax Principles of Financial Accounting 5.1). Its name misleads: rename to unclosed earnings (pending) |
+| 4 | Closing a period with nothing to close still locks it | CONVENTION | A close is a lock (B-12); a dormant month must still lock and count for close-in-order |
+| 5 | Draws and distributions are closed into capital at period end | CONFIRMED | OpenStax 5.1: dividends "are closed to the permanent account"; drawing accounts close to owner's capital. Monthly closes mean the year's K-1 Item L withdrawals sum across months |
+| 6 | Reconciliation balances | CONFIRMED | Signed by the account's normal side (a card reads as owed), as statements show it; `reconciling_a_card_reads_its_normal_side_...` |
+| 7 | A member's ending on one equity statement may differ by a cent from the next statement's beginning | CHANGE (pending) | A capital account is one running balance (Form 1065 K-1 instructions, Item L: beginning and ending capital "based on the partnership's books and records"). Allocate cumulatively so beginning equals the prior ending per member. CPA question below |
+| 8 | Cash flow nets one line per account; investing comes only from registered assets | CHANGE (pending) | ASC 230-10-45-7: gross receipts and payments "more relevant" than net; 45-8 limits netting to quick-turnover items. Financing: contributions apart from distributions, borrowings apart from repayments. ASC 230-10-20/45-13: loans made and investments bought are investing, so classify by account role |
+| 9 | An asset's life ends at purchase + life months, that day not held; day-count proration | CONVENTION | Exactly N months of service; day proration and the mid-month convention are both accepted book policies (ASC 360-10-35-4 not read: login) |
+| 10 | A payroll entry has one line per account total | CONFIRMED | The per-employee detail the IRS requires ("Amounts and dates of all wage ... payments", Employment Tax Recordkeeping) is kept in the run; a summary entry is standard |
+| 11 | A period with exactly the dates of an existing one is allowed | DESIGN | Nothing governs duplicate periods; harmless (the second close locks only). Refusing exact duplicates is an option |
+
+Questions for Krista Baker (CPA):
+
+1. Interim members' equity: is a per-member allocation of unclosed
+   earnings acceptable on interim statements, or should the books close
+   monthly so the capital accounts carry it?
+2. How should 2100 Due to Shareholders, and expenses the owners paid
+   personally, appear on the cash flow statement: operating, financing,
+   or as a non-cash disclosure (ASC 230-10-50-3, not yet read)?
 
 ## Gap list: what isn't covered, and what would bring it in