merge: P4b S7, bad debts (branch S7, 4b4fecb9)

The fourth of the paused branches: Ledger::write_off and the bad_debts
control role, invoice.written_off with its evidence filed in the same
store call, books.write_off_invoice, the write-off on the timeline and
in Needs attention, Lean writeOff_within_bounds, rules.md B-41 and the
bookspec examples. Twenty-eight files conflicted with the S4.4, S5 and
S6 merges; resolved as plan 8.0.2 says, keeping both sides' appends with
their seams restored, and: the scope table at 125; S7's law numbered 37;
B-41 placed before B-42; the handbook's step 4 and recovery procedures
folded into the one invoices-and-bills section; S7's wire tests in their
own module with the confirm S4.4's contract needs; S7's copy of the
payment steps dropped (S6 replaced them with Ledger::settle) and its
write-off journaled through S6's journal_auto_lines; in the old-books
fixture S7's hand-written write-off moved to a second invoice, since
S6's hand-written payment settles invoice 1 in full.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HS8WZziDnyxunC23MUxrLp

crates/ledger-mcp/handbook/invoices-and-bills.md

@@ -64,6 +64,60 @@ without another copy to correct (B-38).
   Discounts / Cr the asset account (D-49). Never split the discount across
   the asset lines.
 
+## 4. Void, write off, or reverse
+
+One of these, and only one, fits what happened:
+
+- **Void it** (`books.void_document`) when the document should never have
+  existed: a duplicate, the wrong customer or vendor, a test entry. It is
+  reversed, keeps its id (and, once numbered, its number) and reads void;
+  nothing is deleted. Refused while a payment stands on it: reverse that
+  payment first, and the refusal names it. Use a void for a mistake, never
+  for an invoice that was real.
+- **Write it off** (`books.write_off_invoice`) when the invoice was real
+  and the work or goods went out, but the customer will not or cannot pay.
+  That is a bad debt: the books post Dr Bad Debt Expense 6990 / Cr Accounts
+  Receivable for what will not be collected, and what it owes falls from
+  that day. The evidence of worthlessness — the collection letters, the
+  bankruptcy or liquidation notice, the collection agency's report — is
+  filed with the write-off in the same call (`upload_id`, or an
+  `existing_attachment_id` already filed), because a bad debt is deducted
+  on all the pertinent evidence (Treas. Reg. §1.166-2(a)). Write off all of
+  it, or part of it with `amount`: a partial write-off is deductible to the
+  extent charged off (Treas. Reg. §1.166-3(a)), and the rest stays owed and
+  in the aging. The books must be on the accrual basis: a cash-basis
+  company never counted the invoice as income, so there is no basis to
+  deduct (IRC §166; Treas. Reg. §1.166-1(e)), and the tool refuses.
+- **Reverse an entry** (`books.reverse_entry`) when a posted entry is
+  wrong: a payment against the wrong invoice, a wrong amount, a check that
+  bounced, a write-off made too soon. Posted is forever: the correction is
+  an opposite entry linked to the one it reverses, never an edit and never
+  a delete. Reversing a payment puts the invoice back to owing what it did;
+  reversing a write-off re-instates the debt.
+
+A bill is never written off: a vendor releases you with a vendor credit or
+by voiding its own invoice, and until then you owe it (ASC 405-20-40-1). If
+a vendor's bill was wrong, ask for a corrected bill or record a credit when
+one is built; void it only when it should never have been entered.
+
+## Recovering a debt written off
+
+- **The same tax year**: reverse the write-off — `books.reverse_entry` on
+  the write-off's entry. The invoice reopens, owing exactly what the
+  write-off took off; then record the payment with `books.receive_payment`
+  as usual. Nothing else is needed: within the year the deduction comes
+  back out, and the payment is a payment.
+- **A later tax year**: do not reverse the write-off. Record a plain entry
+  — `books.draft_entry`, `books.add_line` on each side, `books.post_entry`
+  — debiting the deposit account and crediting a "Bad debt recoveries"
+  revenue account (tax category other income), with a memo naming the
+  invoice. The invoice stays written off, and the recovery is income in the
+  year it arrives (IRC §111); the CPA sees it apart from the year's sales.
+
+Neither procedure invents a new kind of movement on the document: the books
+record what happened, and the invoice's timeline shows the write-off (and,
+if it was reversed, that it no longer stands).
+
 ## 5. A processor's fee
 
 - The books never charge or collect; a processor does, and keeps a fee.
@@ -83,3 +137,21 @@ without another copy to correct (B-38).
 3. Apply the parked money with `books.receive_payment`,
    `deposit_to: "2300"`, dated on or after the bounce, against the
    invoices it pays. The 2300 balance returns to zero.
+
+## What the CPA will check
+
+The agings tie to 1200 and 2000 at month and year end (they do by
+construction: the control check says so). Every write-off carries its
+reason and its evidence of collection efforts. Write-offs are not used in
+place of a credit memo for a valid invoice, and never to hide a mistake
+that a void would show. Whether a debt is worthless, and in which year, is
+a tax judgment that stays with the CPA: the books flag each write-off made
+this year in Needs attention, with the evidence beside it, until the year
+ends.
+
+## The evidence rule
+
+Every entry needs its receipt ({evidence_rule}). A document the books post
+themselves — an invoice, a bill, a payment, a write-off — carries its own:
+the issued copy, the vendor's bill, the payment's reference, the evidence of
+worthlessness. A reversal needs none of its own: its original carries it.