[contracts] CharonLiquidator: Aave flashLoanSimple + Venus liquidate + PancakeSwap V3 swap

[obchain]

Context

Core atomic execution. Inside one transaction: flash-borrow the debt token from Aave V3 → call VToken.liquidateBorrow → swap seized collateral → repay the flash loan → forward profit. If anything fails, the whole transaction reverts — zero capital risk.

Scope

• executeLiquidation(LiquidationParams params) — external entry point, onlyOwner
• Invokes AavePool.flashLoanSimple(address(this), debtToken, amount, data, 0)
• executeOperation callback:
  1. Approve VToken to pull debtToken
  2. Call VToken.liquidateBorrow(borrower, repayAmount, collateralVToken)
  3. Redeem seized collateralVToken for underlying
  4. Swap underlying → debt token via PancakeSwap V3 exactInputSingle
  5. Approve Aave to pull principal + premium
  6. Transfer profit remainder to owner()
• Slippage guard on the swap (minAmountOut parameter)
• Revert reasons for every failure mode (documented)

Acceptance criteria

• forge build passes
• Unit test: full flow on a forked BSC block with a real underwater position
• Gas usage documented (target: < 600k gas per liquidation)
• Slippage exceeded → tx reverts atomically, no state change
• Owner receives profit > 0 for a profitable fork scenario

References

• PRD section 5b (Solidity Liquidator Contract)
• Aave V3 Pool: https://docs.aave.com/developers/core-contracts/pool
• PancakeSwap V3: https://docs.pancakeswap.finance/developers/smart-contracts/pancakeswap-exchange/v3-contracts

[obchain]

Superseded — Aave+Venus+PancakeSwap liquidation flow shipped in feat/12-charon-liquidator-full.