Add CErc20RetireDelegate to retire frozen (!borrowRate) markets#1106
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Add CErc20RetireDelegate to retire frozen (!borrowRate) markets#1106rhlsthrm wants to merge 1 commit into
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A cToken market whose IRM rate exceeds borrowRateMaxMantissa while cash > totalFees reverts every accruing call with "!borrowRate", freezing the market — even _setInterestRateModel and _withdraw*Fees accrue first. The only non-accruing admin lever is _setImplementationSafe. - CErc20RetireDelegate: one-shot delegate whose _becomeImplementation sweeps the underlying to a treasury and zeroes reserves/fees/borrows, unfreezing the market so it can be unlisted via _unsupportMarket. - market:retire-frozen task to deploy/register/upgrade/unlist (multisig-aware), guarded on totalSupply == 0. - RetireFrozenMarketTest fork test against the live Base ionmsUSD market.
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Summary
Adds tooling to wind down a cToken market that is permanently frozen with a
!borrowRaterevert.When a market's IRM returns a per-block borrow rate above
borrowRateMaxMantissa(5e12) whilecash > totalFees,CTokenFirstExtension._accrueInterestHypotheticalreverts"!borrowRate"(CTokenFirstExtension.sol#L497).
Because every accruing entrypoint (mint/redeem/borrow/repay,
_setInterestRateModel,_withdrawAdminFees/_withdrawIonicFees) callsaccrueInterest()first, the market is fullyfrozen. The only non-accruing admin lever is
CErc20Delegator._setImplementationSafe, whose_becomeImplementationhook runs during the upgrade.Changes
CErc20RetireDelegate.sol— one-shot remediation delegate._becomeImplementation(abi.encode(treasury))sweeps the underlying to a treasury (via inherited
doTransferOut) and zeroestotalReserves/totalAdminFees/totalIonicFees/totalBorrows, so utilization → 0, the ratedrops under the cap, and
accrueIntereststops reverting. Must never be set as a latest delegate.tasks/market/retire-frozen.ts(market:retire-frozen) — deploys + registers the delegate,_setImplementationSafe, then_unsupportMarket. Multisig-aware (prepareAndLogTransaction) andguarded on
totalSupply == 0(refuses to run on markets with suppliers).RetireFrozenMarketTest.t.sol— Base fork test against the liveionmsUSDmarket; asserts thepre-fix
!borrowRaterevert, the sweep/zeroing, post-fixaccrueInterestsuccess, and unlisting.How the freeze happens
utilizationRate = borrows / (cash + borrows − reserves). WhentotalReserves + feesgrows to≈
cash + borrows, the denominator collapses → utilization explodes → rate ≫ cap → frozen.Verification
A chain-wide scan (via
accrueInterest()eth_call simulation) found exactly one currently-frozenmarket:
ionmsUSDon Base (0x5BE1Cb6CB3C9bfd16Db43ed4f6c081FA9783dd1C),totalSupply == 0.Scope / caveat
ionmsUSDis a dust market:32 msUSD ($32) cash, a ~0.07 msUSD borrow, no suppliers. For thatspecific market, a single
comptroller._unsupportMarket(...)(works while frozen, needs onlytotalSupply == 0) is sufficient and cheaper than deploying the delegate. This PR is thegeneral-purpose instrument for the same failure mode on a market with real value. Run the fork test
against current state immediately before any mainnet execution.
Follow-up (separate PR)
Protocol-level guard so markets can't freeze this way (non-accruing
_reduceReserves, clamp-instead-of-revert,or a reserve-overrun guard).