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

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