test(evm): make bank inflation guard actually reproduce the exploit

TestBankSend_NoSupplyInflation as first written was a false guard: a plain
CallEVMWithData(bank.send) passes on pre-#332 (unfixed) bank code too, because
the native-token inflation only triggers when the sender's EVM stateObject
balance is authoritative at Commit.

Give the sender code (EIP-7702-style delegation) and load its stateObject so
the pre-fix reconciliation mints the debited amount back. Verified: on pre-#332
bank code the test now fails with supply += 5e8 (the sent amount); on #332 it
stays flat. The SetCode is load-bearing.

Author: phenix3443

x/evm/precompiles/bank/tx_test.go

@@ -83,11 +83,18 @@ func (s *PrecompileTestSuite) TestBankSend_EVMDispatchSuccess() {
 }
 
 // TestBankSend_NoSupplyInflation is the regression guard for the native-token
-// inflation fixed by #332. bank.send is a transfer, so total supply MUST be
-// unchanged. Before the fix, the keeper coin move left the sender's EVM
-// stateObject balance stale; StateDB.Commit then reconciled it by minting the
-// debited amount back to the sender, inflating total supply. The BalanceHandler
-// (RunNativeAction) keeps the stateObject reconciled so Commit mints nothing.
+// inflation fixed by #332.
+//
+// The exploit needs the sender to be an EIP-7702-delegated EOA: giving the sender
+// code makes its EVM stateObject balance authoritative at StateDB.Commit. Without
+// the fix, the keeper coin move debits the sender's bank balance but leaves the
+// stale stateObject balance untouched; Commit then reconciles by minting the
+// debited amount back to the sender — total supply inflates by exactly the sent
+// amount. (Verified: on pre-#332 bank code this test fails with supply += 5e8;
+// a plain send without SetCode does NOT reproduce it, so the SetCode is load-bearing.)
+//
+// The BalanceHandler (RunNativeAction) keeps the stateObject reconciled during the
+// call, so Commit mints nothing and total supply stays flat.
 func (s *PrecompileTestSuite) TestBankSend_NoSupplyInflation() {
 	s.mustEnableStaticPrecompiles()
 
@@ -98,12 +105,17 @@ func (s *PrecompileTestSuite) TestBankSend_NoSupplyInflation() {
 
 	precompileAddr := bank.GetAddress()
 	stateDB := statedb.New(s.ctx, s.app.EvmKeeper, statedb.NewEmptyTxConfig())
+	// Make the sender a 7702-style delegated account (has code) and load its
+	// stateObject, so its cached balance is authoritative at Commit — this is the
+	// condition under which the pre-fix reconciliation minted the debited amount.
+	stateDB.SetCode(s.address, []byte{0x60, 0x00})
+	_ = stateDB.GetBalance(s.address)
 	res, err := s.app.EvmKeeper.CallEVMWithData(s.ctx, stateDB, s.address, &precompileAddr, input, true, false, nil)
 	s.Require().NoError(err)
 	s.Require().False(res.Failed(), "evm call reverted: %s", res.VmError)
 
 	supplyAfter := s.app.BankKeeper.GetSupply(s.ctx, utils.BaseDenom).Amount
-	s.Require().Equal(supplyBefore.String(), supplyAfter.String(), "bank.send must not change total supply (no inflation)")
+	s.Require().Equal(supplyBefore.String(), supplyAfter.String(), "bank.send must not inflate total supply")
 }
 
 // TestBankSend_FailureRevertsCleanly pins the native revert semantics: an