Lending

Purpose: Single-asset lending market for USDST with interest and mToken.

Functional summary:

  • Deposit/withdraw USDST and earn yield via rising exchange rate.

  • Borrow/repay against collateral; protocol accrues interest via index.

  • Handle shortfalls with SafetyModule coverage, reserves write‑offs, or haircuts.

Key contracts:

  • LendingPool.sol: User actions (deposit/withdraw/borrow/repay) and accounting.

  • LiquidityPool.sol: Holds underlying cash and interacts with borrow index.

  • LendingRegistry.sol: Addresses/config; links borrowable, mToken, oracle.

  • PriceOracle.sol: Provides asset prices (1e18 USD).

  • RateStrategy.sol: Interest rate model; borrow and reserve factors.

  • CollateralVault.sol: Custody for collateral assets.

  • SafetyModule.sol: Risk controls and safety operations.

  • PoolConfigurator.sol: Admin configuration.

Core flows:

  • Deposit: User supplies USDST → mUSDST minted; exchange rate increases as interest accrues.

  • Withdraw: Burn mUSDST → receive USDST, limited by pool cash.

  • Borrow/Repay: Debt increases/decreases per interest index; collateralized by supported assets.

Bad debt and shortfall handling:

  • Recognition (automatic or manual): liquidation or recognizeBadDebt increments badDebt when no collateral remains.

  • Coverage priority: SafetyModule coverShortfall → writeOffBadDebtFromReserves → writeOffBadDebtWithHaircut.

  • Exchange rate uses underlying = cash + totalDebt + badDebt − reservesAccrued and updates on each operation.

Formulas:

  • Index debt: debt = scaledDebt × borrowIndex / 1e27.

  • Exchange rate: rate = (cash + totalDebt + badDebt − reservesAccrued) × 1e18 / mTokenSupply (1e18 when supply=0).

  • Mint mTokens: mMint = deposit × 1e18 / rate.

  • Burn mTokens for withdraw A: mBurn = ceil( A × 1e18 / rate ).

  • Health factor: HF = (Σ collateralAmount_i × price_i × liqThreshold_i / 10000) × 1e18 / (debt × priceBorrow).

  • Max borrow power: Σ (collateralAmount_i × price_i × LTV_i / 10000) / priceBorrow.

  • Utilization: U = debt / (cash + debt − reservesAccrued).

  • Interest accrual: borrowIndex_t1 = borrowIndex_t0 × rpow(perSecondFactorRAY, Δt, 1e27) / 1e27.

SafetyModule formulas:

  • smRate = totalAssets × 1e18 / totalShares (1e18 when shares=0).

  • Preview stake: sharesOut ≈ (shares==0) ? assetsIn : assetsIn × totalShares / totalAssets.

  • Preview redeem: assetsOut = sharesIn × totalAssets / totalShares.

  • Slash cap per event: maxSlash = totalAssets × MAX_SLASH_BPS / 10000.

  • Covered amount: covered = min(request, totalAssets, maxSlash, lendingPool.badDebt).

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