A Zero-Centred Bilateral Credit Ledger for Customer Prepayment and Peer-to-Peer Lending in Which No Balance Grows on Its Own — a Size-Blind Reputation Display, and Debt Forgiveness as the Only Crossing into a Gift Ledger

The Promise, Not the Score — B-Promise℠, a bilateral credit ledger with one balance per pair, a conduct display that cannot see size, and one door into a gift ledger We disclose a zero-centred bilateral credit ledger for customer prepayment and peer-to-peer lending in which no balance grows on its own. Two people keep one running balance between them, which can sit on either side of zero: when it is on one side, the first owes the second (a prepayment the vendor has not yet delivered, or a loan); when it is on the other side, the second owes the first. The balance never moves by time. It changes only by an entry both parties sign when cash or goods change hands, its discount fixed on that entry; by a repayment both parties sign; or by a release that the party who is owed may always make alone. There is no accrual, no compounding and no late penalty. The ledger is therefore non-accruing but not interest-free: a discount agreed when value moves is a premium, it is on the record, and at short terms it can be very large (§4.3). The balance is kept on the two parties' phones, signed by both, denominated in one currency fixed when it opens, and non-transferable: it can never be sold or assigned. Its coined name is B-Promise℠. The mechanism serves two ordinary deals with one balance. In customer prepayment, a customer pays a vendor $9 in cash now and the vendor owes $10 of goods; the customer is the lender and is repaid in kind, and the discount comes out of the vendor's retail margin. In peer-to-peer lending, a lender gives $9 now and the borrower owes $10 by a deadline the borrower proposes. When the customer later takes more goods than were prepaid, the same balance crosses zero and the customer owes the vendor; nothing new is opened. Value moves first, face to face; the entry is the receipt. Conduct is shown by a reputation display that takes no amount argument: one equal-width segment for each person the party currently owes, a gap where that balance is owed past its deadline, a segment that dissolves when the balance returns to zero, shown only where a new promise is being made and never on a profile. It has no colour. A line of text under it carries exact counts and, as a disclosed but unclaimed feature, a coarse band of the total the person owes. The one event that crosses from this exchange ledger into the separate gift ledger the institution already runs is a creditor's free release of the whole balance owed by that person (debt forgiveness), at most once per pair per annual season, entering as a gift that awaits the debtor's thanks; repayment never crosses. Two narrow sub-rules complete the claim: a code that carries no signed terms can never open an obligation, and no one who has a nonzero balance with a person may vouch for that person's new signing key. We report two prior-art passes and an outside review that killed or narrowed every conjunct at mechanism width, claim only the composition that survived, state the harms the mechanism does not prevent — above all that a person's total debt can still grow by rollover — and register in advance a test of whether an annual invitation to forgive debts freezes December lending. --- Provenance. This paper is part of the THonly research corpus, dedicated to the public domain under CC0 1.0. The canonical version is at https://thonly.org/research/a-promise-that-cannot-grow. Its SHA-256 is 458a72b7011aad3ce396c17a5b99e0d13dadc306f45439a24b251b448dcbf5d7, independently timestamped to the Bitcoin blockchain via OpenTimestamps and signed under RFC 3161 by three trust authorities, one of them eIDAS-qualified. AI co-authorship is disclosed. Miss Aquarius is the consistent name used for the AI collaboration across all venues.