test: anchor cevm<->geth MPT state-root parity golden

Protects the golden root 0x549b8955...c021 from Go-side drift; paired with
luxcpp/cevm/test/state_root_parity.cpp which asserts the C++ side. Silent
divergence between the two EVMs is a chain-fork risk.

Co-authored-by: Hanzo Dev <dev@hanzo.ai>

core/state/cevm_parity_test.go

@@ -0,0 +1,35 @@
+// TestCevmMPTParity anchors the cross-engine state-root parity: luxfi/geth's
+// StateDB must produce the same root that cevm's C++ StateDB::commit() asserts
+// against in luxcpp/cevm/test/state_root_parity.cpp. If this golden changes,
+// update it in lockstep on both sides — a silent drift is a chain-fork risk.
+package state
+
+import (
+	"math/big"
+	"testing"
+
+	"github.com/luxfi/geth/common"
+	"github.com/luxfi/geth/core/rawdb"
+	"github.com/luxfi/geth/core/tracing"
+	"github.com/luxfi/geth/core/types"
+	"github.com/luxfi/geth/triedb"
+	"github.com/holiman/uint256"
+)
+
+func TestCevmMPTParity(t *testing.T) {
+	const golden = "0x549b895566f2d74e35e415bca2997f06c94d8f454dc55ac19cf009a8a247c021"
+	sdb, err := New(types.EmptyRootHash, NewDatabase(triedb.NewDatabase(rawdb.NewMemoryDatabase(), nil), nil))
+	if err != nil {
+		t.Fatal(err)
+	}
+	a := func(x byte) common.Address { var v common.Address; v[19] = x; return v }
+	sdb.SetBalance(a(1), uint256.NewInt(1000), tracing.BalanceChangeUnspecified)
+	sdb.SetNonce(a(1), 1, tracing.NonceChangeUnspecified)
+	sdb.SetBalance(a(2), uint256.NewInt(2000), tracing.BalanceChangeUnspecified)
+	sdb.SetNonce(a(2), 5, tracing.NonceChangeUnspecified)
+	sdb.SetState(a(2), common.BigToHash(big.NewInt(3)), common.BigToHash(big.NewInt(0x99)))
+	sdb.SetCode(a(3), []byte{0x60, 0x01, 0x60, 0x02}, tracing.CodeChangeUnspecified)
+	if got := sdb.IntermediateRoot(false).Hex(); got != golden {
+		t.Fatalf("state root drift: got %s want %s (cevm C++ parity test will now diverge)", got, golden)
+	}
+}