# 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.
- 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_file_path (never books.file_document or books.attach_receipt: the form shows the TIN).
- Never repeat a TIN back to the human, in chat, a description, note, file name, version-history message, or anywhere else; tools show the last four only. books.get_w9 writes the form out for the human (never open or read it yourself); books.purge_tin (preview, then confirmed, with a reason) deletes a TIN no longer needed.
- books.parties lists the directory, 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.