Parties, attachment links, statements, reconciliations (store), TIN vault crate

Parties: one directory for vendors, contractors, customers, employees,
members, platforms, agencies, banks, landlords (ledger-core parties.rs).
W-9/W-4 facts without the number (last four only; any nine-digit run in a
party field is refused, Treas. Reg. 301.6109-4). Vendor and customer
records link to parties on replay; core tags every bill, invoice, payment,
and reversal with its counterparty. Journal events party.*,
entry.party_set; payroll lines name the employee party.

MCP: books.add_party, update_party, set_party_roles, set_w9, set_w4,
parties, party, set_entry_party; draft_entry party; run_payroll employee;
show party. Viewer: Parties directory and party pages, search, journal
text, W-9 attention, demo data.

One definition of a party's money (ledger_core::parties::activity) for
MCP and viewer. 1099 amounts count payments from cash and financing
accounts (a member paying for the company counts; a card doesn't; a
prepayment counts when made): vendor_1099_report_with, B-19.

Store: attachment links to any subject, statements, reconciliations
(schema v11), with replay and projection. ledger-vault: encrypted TIN and
W-9 records (ChaCha20-Poly1305, key file outside the books).

Spec-blind tests for parties (core, store, MCP, viewer) and attachments.

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

docs/spec/sources/irs-tin-formats.md

@@ -0,0 +1,16 @@
+# TIN formats
+Governs `ledger_vault::Tin::new`: a TIN is nine digits; an ITIN begins with 9 and its fourth and fifth digits fall in the ranges below; an SSN or EIN doesn't begin with 9 (a nine-digit number beginning with 9 is in the ITIN series).
+
+## IRS Publication 1915 (Rev. 11-2024), "Understanding Your IRS Individual Taxpayer Identification Number", General Information
+Source: <https://www.irs.gov/pub/irs-pdf/p1915.pdf>  
+Retrieved: 2026-10-15  
+SHA-256 of the retrieved file (`p1915.pdf`): `63a3cf3e79c2e73ed15738d5a0875ffb7496c2309e8c3e085836ade16b2e0920`
+
+> An ITIN is a tax processing number, issued by the Internal Revenue Service, for certain resident and nonresident aliens, their spouses, and their dependents. It is a nine-digit number beginning with the number “9”, has a range of numbers from "50" to "65", "70" to "88", “90” to “92” and “94” to “99” for the fourth and fifth digits and is formatted like a SSN (i.e. 9XX-7X-XXXX).
+
+## Instructions for Form W-7 (Rev. December 2024), What's an ITIN
+Source: <https://www.irs.gov/instructions/iw7>  
+Retrieved: 2026-10-15  
+SHA-256 of the retrieved file (`irs-iw7.html`): `1d674a26a63c34b59a2cb6e34d050a95f744c53ae35ea50172a137298b37a000`
+
+> An ITIN is a nine-digit number issued by the IRS to individuals who are required for federal tax purposes to have a U.S. taxpayer identification number but who don’t have and aren’t eligible to get a social security number (SSN).

docs/spec/sources/irs-truncated-tin.md

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+# Truncated taxpayer identification numbers
+Governs what of a TIN the party directory may hold (crates/ledger-core/src/parties.rs): the last four digits, the same part a truncated TIN shows. The full number lives only in the encrypted vault (docs/parties-and-attachments.md), never in the journal.
+
+## Treas. Reg. §301.6109-4(a) and (b)(1)
+Source: <https://www.ecfr.gov/current/title-26/part-301/section-301.6109-4>  
+Retrieved: 2026-10-15  
+SHA-256 of the retrieved file (`ecfr301-6109-4.html`): `45702c366f7f185e41452a32acf685bb5371e00b91bfb6214174ffd153eba949`
+
+> (a) In general — Definition. An IRS truncated taxpayer identification number (TTIN) is an individual's social security number (SSN), IRS individual taxpayer identification number (ITIN), IRS adoption taxpayer identification number (ATIN), or IRS employer identification number (EIN) in which the first five digits of the nine-digit number are replaced with Xs or asterisks. The TTIN takes the same format of the identifying number it replaces, for example XXX-XX-1234 when replacing an SSN, or XX-XXX1234 when replacing an EIN.
+
+> (b) Use of a TTIN. (1) In general. Except as provided in paragraph (b)(2) of this section, a TTIN may be used to identify any person on any statement or other document that the internal revenue laws require to be furnished to another person. Use of a TTIN is permissive and not mandatory.