feat(mcp): void, control check, payment method and reference (P4b S1, part B)

books.void_document voids an invoice or bill that should never have
existed by reversing its own entry with the reason (refused while a
payment stands on it, naming that payment). books.control_check ties
receivables and payables to their documents (B-23, B-38 INVARIANT 1):
balance, documents' total, lines that are no document's, the documents
needing attention; books.verify checks the identity and books.digest
lists its problems (control_problems). books.receive_payment and
books.pay_bill take instrument (tagged in the same call) and reference
(in the description), and answer the document's derived remaining and
status. The books record payments; they never collect or make them
(D-45). Docs, handbook and STATUS; the over-the-wire test
documents_void_and_tie_out_over_the_wire; the happy-path journey covers
both tools' output schemas. The processor fee waits for S6.

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

plan/STATUS.md

@@ -221,6 +221,21 @@ token keeps up to 64 handed files (was 16). The tests file by upload
 (`tests/common`: `Wire::upload`, `upload_on`) and read every file by its
 download (`docs/testing.md`, "D-46").
 
+**P4b slice S1, receivables and payables read their figures from the
+ledger (2026-10-24, D-45).** Part A (ledger-core, store, viewer, Lean
+`control_agrees`, Kani bounds): an invoice's or bill's paid, outstanding
+and status are derived from its tagged lines that still stand, so a
+reversed payment no longer counts and a void is exact; accounts in the
+receivables or payables role (or holding document lines) refuse hand
+lines; format feature `document_standing` (the owner upgraded
+2026-10-24). Part B (MCP): `books.void_document`, `books.control_check`,
+`instrument` and `reference` on `books.receive_payment` and
+`books.pay_bill` (status and remaining from the derived figures), the
+tie-out in `books.verify` and `control_problems` in `books.digest`; the
+over-the-wire test `documents_void_and_tie_out_over_the_wire`. Still for
+later slices: the processor fee on a payment (S6, with multi-document
+payments and discounts), Needs attention in the viewer for the control
+check, and S2 to S7.
 **Still open after P3 (each for the phase named, or the lead):**
 - Invoices and bills take a project now (above), behind the new journal
   feature `document_line_projects`: the first company's books declared