test(evm): add payment deposit native-token-inflation guard (#352)

Add a real inflation regression guard for the payment precompile (deposit
moves coins depositor -> payment module). Payment was the balance-handler-audit's
highest-risk module because of its StreamRecord ledger; this proves the real
coin move (SendCoinsFromAccountToModule) is reconciled by the BalanceHandler.

Verified load-bearing: with the payment BalanceHandler disabled the test fails
with supply += the deposit amount; with #332's handler wired it stays flat.

Author: phenix3443

x/evm/precompiles/payment/tx_inflation_test.go

@@ -0,0 +1,108 @@
+package payment_test
+
+import (
+	"math/big"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/suite"
+
+	"github.com/cometbft/cometbft/crypto/tmhash"
+	codectypes "github.com/cosmos/cosmos-sdk/codec/types"
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	stakingtypes "github.com/cosmos/cosmos-sdk/x/staking/types"
+	evmtestutil "github.com/cosmos/evm/testutil"
+	"github.com/cosmos/evm/x/vm/statedb"
+	"github.com/ethereum/go-ethereum/common"
+
+	"github.com/mocachain/moca/v2/app"
+	"github.com/mocachain/moca/v2/testutil"
+	utiltx "github.com/mocachain/moca/v2/testutil/tx"
+	"github.com/mocachain/moca/v2/utils"
+	"github.com/mocachain/moca/v2/x/evm/precompiles/payment"
+	paymenttypes "github.com/mocachain/moca/v2/x/payment/types"
+)
+
+type InflationTestSuite struct {
+	suite.Suite
+	ctx     sdk.Context
+	app     *app.Moca
+	address common.Address
+}
+
+func TestInflationTestSuite(t *testing.T) {
+	suite.Run(t, new(InflationTestSuite))
+}
+
+func (s *InflationTestSuite) SetupTest() {
+	checkTx := false
+	chainID := utils.TestnetChainID + "-1"
+
+	s.app = app.EthSetup(checkTx, nil)
+	s.ctx = s.app.NewContext(checkTx)
+	s.address = common.HexToAddress("0x1111111111111111111111111111111111111111")
+
+	valConsAddr, privkey := utiltx.NewAddrKey()
+	pkAny, err := codectypes.NewAnyWithValue(privkey.PubKey())
+	s.Require().NoError(err)
+	validator := stakingtypes.Validator{
+		OperatorAddress: sdk.AccAddress(s.address.Bytes()).String(),
+		ConsensusPubkey: pkAny,
+	}
+	err = s.app.StakingKeeper.SetValidator(s.ctx, validator)
+	s.Require().NoError(err)
+	err = s.app.StakingKeeper.SetValidatorByConsAddr(s.ctx, validator)
+	s.Require().NoError(err)
+
+	safeTime := time.Date(2025, time.January, 10, 0, 0, 0, 0, time.UTC)
+	header := evmtestutil.NewHeader(1, safeTime, chainID, sdk.ConsAddress(valConsAddr.Bytes()), tmhash.Sum([]byte("app")), tmhash.Sum([]byte("validators")))
+	s.ctx = s.ctx.WithBlockHeader(header).WithChainID(chainID)
+
+	err = testutil.FundAccountWithBaseDenom(s.ctx, s.app.BankKeeper, sdk.AccAddress(s.address.Bytes()), 1_000_000_000_000)
+	s.Require().NoError(err)
+}
+
+// TestDeposit_NoSupplyInflation is the native-token-inflation regression guard
+// for the payment precompile (deposit moves coins depositor -> payment module).
+// The depositor is made a 7702-style delegated account (SetCode) so its
+// stateObject balance is authoritative at Commit; without the BalanceHandler
+// reconciliation, Commit would mint the debited amount back.
+func (s *InflationTestSuite) TestDeposit_NoSupplyInflation() {
+	// EthSetup's genesis leaves payment params zero-valued, so install defaults
+	// (DefaultFeeDenom is the base denom "amoca") before depositing.
+	s.Require().NoError(s.app.PaymentKeeper.SetParams(s.ctx, paymenttypes.DefaultParams()))
+
+	s.mustEnableStaticPrecompiles()
+
+	supplyBefore := s.app.BankKeeper.GetSupply(s.ctx, utils.BaseDenom).Amount
+
+	// self-deposit: the caller account exists, so a stream record is created
+	to := sdk.AccAddress(s.address.Bytes()).String()
+	input := s.mustPackDepositInput(to, big.NewInt(100_000))
+	precompileAddr := payment.GetAddress()
+	stateDB := statedb.New(s.ctx, s.app.EvmKeeper, statedb.NewEmptyTxConfig())
+	// 7702-style: give the depositor code and load its stateObject so its cached
+	// balance is authoritative at Commit (the inflation trigger).
+	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(), "deposit must not inflate total supply")
+}
+
+func (s *InflationTestSuite) mustEnableStaticPrecompiles() {
+	evmParams := s.app.EvmKeeper.GetParams(s.ctx)
+	evmParams.EvmDenom = utils.BaseDenom
+	evmParams.ActiveStaticPrecompiles = app.MocaActiveStaticPrecompiles()
+	s.Require().NoError(s.app.EvmKeeper.SetParams(s.ctx, evmParams))
+}
+
+func (s *InflationTestSuite) mustPackDepositInput(to string, amount *big.Int) []byte {
+	method := payment.GetAbiMethod(payment.DepositMethodName)
+	packedArgs, err := method.Inputs.Pack(to, amount)
+	s.Require().NoError(err)
+	return append(append([]byte{}, method.ID...), packedArgs...)
+}