wanderbooks/crates/ledger-mcp/handbook/parties-and-tins.md

# Parties and TINs

- Keep the directory current. Every counterparty (vendor, contractor, landlord, customer, payout platform, tax agency, bank or card issuer, member, employee) gets a party: books.add_party with its roles (books.add_vendor and books.add_customer link their record to the party of the same name, or make one).
- Tag every entry with its party (books.draft_entry party, or books.set_entry_party; a party with a vendor record tags the vendor for 1099s too).
- An entry with several counterparties names them all with parties ([{party, amount?|percent?}] on books.draft_entry or books.set_entry_party): there is no "joint" party. A joint member transaction (paid from or reimbursed to the members' joint funds through a payable to members, a contribution from joint funds, a distribution to both) names both members with no shares, and their shares derive (from their capital or distribution lines on the entry, else their member shares in the settings); when the split is uneven, or a party isn't a member, give each party an exact amount (or a percent).
- The post_entry preview lists each party's resolved share (parties) and refuses to post (party_shares, parties_error) until the shares add up to what the entry moved; show the split to the human before confirming.
- A share's resolved amount is signed as the party's own account would show it: positive, the company paid it or gave it value; negative, received from it. Each part says its direction (paid, received, or neither: a bill, an invoice, a fee on its own card, a distribution still owed) and what of it was money (cash) and what property (in_kind); a reversal is exactly the opposite of what it reverses. A members' entry that moves their capital counts what moved it: a property contribution is received, in kind.
- Party totals (books.party, books.parties) take a basis: cash, the default, counts money; all adds property contributed or distributed in kind (for a member, the statement of members' equity). Say which basis you report. It is not the books' accounting method.
- Money is the cash accounts, the cards (the business cards recorded as payment methods, books.add_instrument kind business_card; until one is, a card account's name says "card"; a gift card the company sold is deferred revenue, not a card; a member's own card pays through the members' financing account) and the financing accounts setting ([books] financing_accounts: what the members advanced, loans): list the members' payable and every loan there, and record every company card as a payment method (or, until then, list any card whose account name doesn't say "card"). Any other liability (an accrual, deferred revenue, distributions payable) counts once, when it is settled.
- Name whose each card, loan and advance is: books.update_party creditor_of, the issuer for its card, the lender for its loan, each member for what the members advanced. Then a fee on the card, interest on the loan, or a distribution credited to what the members are owed never reads as a payment to them; it counts when paid. A distribution declared to distributions payable counts when it is paid, too. Record a reimbursement and a distribution as two entries, and a member's cash either as a loan (through the members' financing, tagged with the payee it paid) or as capital, not both.
- Every post_entry preview says where the entry stands (party_policy, party_missing, party_suggestions): under the `[books] parties` setting "suggest" (the default), when party_missing, name the likely party to the human and tag it (or add it) before confirming; under "require", posting is refused (party_required) until the entry names a party or is marked as having none (books.set_entry_party with party null and no_party_reason, or draft_entry no_party_reason: only for an entry with truly no counterparty, like a transfer between the company's own accounts); under "off", don't raise it.
- Record W-9 facts (books.set_w9) for contractors and landlords before paying them, and W-4 facts (books.set_w4) for employees before their first payroll; name the employee party on every books.run_payroll line.
- Never put a full TIN or SSN anywhere in the books, only the last four digits: the engine refuses any nine-digit number in a party field. The full TIN goes only to the encrypted TIN vault, and every member's and every 1099 payee's belongs there: books.set_tin (party, tin, tin_type: ssn, ein, itin; any role, so each member's SSN for their K-1) and books.set_w9 with tin and tin_type for a payee's W-9, and the signed form with w9_upload_id (books.begin_upload purpose w9; never books.file_document or books.attach_receipt: the form shows the TIN).
- A full TIN lives in the vault: keep it out of descriptions, notes, file names and version-history messages. books.get_w9 hands the signed form over (run its download command to save it for the human); books.purge_tin (preview, then confirmed, with a reason) deletes a TIN no longer needed.
- books.parties lists the directory (each party's TIN last four from its TIN or W-9 facts), books.party shows one party with the year's totals, and books.show party opens it in the viewer. Archive (books.update_party archived) parties no longer dealt with; never delete history.

## Tagging an entry with several parties (books.set_entry_party)

Pass party (an id or a name), or parties: [{party, amount? | percent?}] for several. Each share is an exact amount (cents), a percent (summing to 100; leftover cents to the first party), or neither (derived: a sole party gets all; members named together get what their capital or distributions lines say, else their company.members share). Once the entry is posted, a derived split among several parties is recorded as the exact amounts it resolves to, so a later change to company.members never re-splits posted history. Name both members on a joint member transaction (a reimbursement on 2100, a joint contribution) and let the shares derive; give amounts when a split is uneven.

Refused: a party twice, mixed kinds of share, two parties with vendor records, and, once the entry has balanced lines, shares that do not add up to what it moved. A party with a vendor record also tags the entry's vendor; a party without one, or clearing, clears the vendor tag. Metadata only: amounts never change. An entry and its reversal carry the same parties (tagging either tags both), so each party's part nets to zero. Journaled as entry.party_set (one party) or entry.parties_set (parties). The result is the entry as books.get_entry gives it, each party's share resolved, with its direction and what of it was money or property in kind.

## Recording a W-9 (books.set_w9)

Record what a contractor's or landlord's W-9 says, or clear it (clear: true alone): the date received (received_on), line 3 entity type, line 4 exempt payee and FATCA codes, the TIN's last four digits, and where the form is kept. Give the full TIN as tin with tin_type (ssn, ein, itin) and it goes only to the encrypted TIN vault (its key kept apart from it, created on first use): the books keep its last four (tin_last4 is then optional, and refused if it disagrees) and a hash of the vault record, in the W-9 facts and the party's TIN facts alike (party.tin_set, as books.set_tin), and kept_at defaults to "wanderbooks vault". The CPA package carries the full TIN to the CPA.

Give the signed form (a PDF, PNG or JPEG) as w9_upload_id (books.begin_upload purpose w9, then `wanderbooks upload`: a file never passes through you), and it goes to the vault too, never to the receipts and documents; read it back with books.get_w9. Never put a TIN in any other field, note, description or file: the engine refuses any nine-digit number, and no tool output echoes one. The party needs a 1099 role (contractor or landlord: books.set_party_roles). Record it before paying them. A party with a vendor record also gets its W-9 marked on file there (books.vendor_1099 missing_w9). Clearing W-9 facts whose TIN is in the vault needs books.purge_tin first. Journaled as party.w9_set. The result is the party (the TIN's last four only).