Supply vault

SupplyVault holds the USDG that the margin accounts borrow. Lenders deposit USDG and receive thUSDG shares, an ERC-4626 vault built on OpenZeppelin Contracts, and earn all the interest the borrower pays. You can deposit, read the rates and withdraw what the vault holds.

Address#

Robinhood Chain testnet, chain 46630, from deployments/46630.json, under tapehouse.SupplyVault.

Testnet, not audited.

Deposit and read the market#

import { readFileSync } from 'node:fs'
import { createPublicClient, http } from 'viem'
import { parseDeployments, supply } from '@tapehouse/sdk'

const deployments = parseDeployments(JSON.parse(readFileSync('deployments/46630.json', 'utf8')))
const client = createPublicClient({ transport: http('https://rpc.testnet.chain.robinhood.com') })

const market = await supply.market(client, deployments)
// { supplyRate, borrowRate, utilization, idle, debt, totalAssets, open }

const call = supply.deposit(deployments, { assets: 100_000_000n, receiver: '0x...' })

supply.deposit returns a viem contract call for simulateContract and writeContract. The amount is in USDG base units. The vault takes no deposit until its borrower is set, and open is false while deposits are stopped.

Functions#

ERC-4626 and the vault's own reads#

Shares have 6 more decimals than USDG, OpenZeppelin's virtual offset, so a first depositor cannot inflate the share price against the next.

Borrower and owner#

The borrower is the margin accounts. A person never calls borrow, repay or writeOff directly: they go through the accounts.

Rates#

The borrow rate rises with utilisation in two straight lines. The rate model gives base at zero utilisation, base + slope1 at optimal and base + slope1 + slope2 at full utilisation, in basis points a year, and the rate is linear in between. The rate model's bounds are:

The model deployed on testnet is read with rateModel().

Events#

Roles and admin powers#

• The borrower, the margin accounts, is set once by the owner and can never change. No lender's USDG can be lent to a borrower chosen after it was deposited.
• The owner can set the rate model at once, within its bounds, and move ownership. It cannot move funds.
• USDG's issuer can pause USDG or freeze an address, and then wipe a frozen address's balance. While USDG is paused, the vault is frozen or its balance is below its count, every max* view returns zero, so deposits and withdrawals revert with ERC-4626's ERC4626ExceededMax... errors. After a wipe the vault stays closed until sync() brings its count down to its balance, and lenders' shares lose what was wiped.

Invariants#

• The vault's assets are its own count of the USDG it holds plus what the borrower owes. USDG sent to it directly changes no share's value.
• The debt grows by a borrow index with 27 decimals, compounded at every deposit, withdrawal, loan and repayment, and always rounded up, in lenders' favour.
• A lender can withdraw only what the vault holds. The rest returns as the borrower repays.
• Lenders bear last whatever the borrower cannot repay and the gap backstop does not cover. Until a write-off, shares keep their price, so a lender who withdraws before one loses nothing and those who stay bear it all.

SDK#

TypeScript, module supply in @tapehouse/sdk.

Next#

• Earn on USDG
• Margin accounts
• Gap backstop