The previous guard blocked setFeeDestination when feeDestination.code.length > 0
but did not persist feeDestinationLocked — a revert undoes all state changes. An
attacker could CREATE2-deploy bytecode to the EOA fee destination, triggering the
block, then SELFDESTRUCT to clear the code, then call setFeeDestination again
successfully (lock was never committed).
Fix: detect bytecode at the current feeDestination first; if found, set
feeDestinationLocked = true and RETURN (not revert) so the storage write is
committed. A subsequent SELFDESTRUCT cannot undo a committed storage slot.
Updated NatSpec documents both the protection and the remaining limitation
(atomic CREATE2+SELFDESTRUCT in a single tx cannot be detected).
Added testSetFeeDestination_CREATE2BytecodeDetection_Locks covering:
set EOA → vm.etch (simulate CREATE2 deploy) → verify lock committed → vm.etch
empty (simulate selfdestruct) → verify setter still blocked.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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