Fix eth_simulateV1 after Jovian fork

internal/ethapi/simulate.go

@@ -18,6 +18,7 @@ package ethapi
 
 import (
 	"context"
+	"encoding/binary"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -36,6 +37,7 @@ import (
 	"github.com/ethereum/go-ethereum/internal/ethapi/override"
 	"github.com/ethereum/go-ethereum/params"
 	"github.com/ethereum/go-ethereum/rpc"
+	"github.com/ethereum/go-ethereum/trie"
 )
 
 const (
@@ -359,12 +361,37 @@ func (sim *simulator) processBlock(ctx context.Context, block *simBlock, header,
 		reqHash := types.CalcRequestsHash(requests)
 		header.RequestsHash = &reqHash
 	}
-	blockBody := &types.Body{Transactions: txes, Withdrawals: *block.BlockOverrides.Withdrawals}
+
+	// For OP Stack Jovian blocks, inject a synthetic deposit transaction at the beginning of the block.
+	// This is required because CalcDAFootprint (called by FinalizeAndAssemble for Jovian blocks)
+	// expects the first transaction to be a deposit transaction containing L1 attributes data.
+	isJovian := sim.chainConfig.IsJovian(header.Time)
+	finalTxes := txes
+	if isJovian {
+		depositTx := createSimulatedJovianDepositTx()
+		finalTxes = append([]*types.Transaction{depositTx}, txes...)
+	}
+
+	blockBody := &types.Body{Transactions: finalTxes, Withdrawals: *block.BlockOverrides.Withdrawals}
 	chainHeadReader := &simChainHeadReader{ctx, sim.b}
 	b, err := sim.b.Engine().FinalizeAndAssemble(chainHeadReader, header, sim.state, blockBody, receipts)
 	if err != nil {
 		return nil, nil, nil, nil, err
 	}
+
+	// For Jovian blocks, reconstruct the block without the synthetic deposit transaction
+	// to maintain consistent indexing between transactions and receipts.
+	// We must use types.NewBlock to recompute TxHash correctly for the user transactions only.
+	if isJovian {
+		b = types.NewBlock(
+			b.Header(),
+			&types.Body{Transactions: txes, Withdrawals: *block.BlockOverrides.Withdrawals},
+			receipts,
+			trie.NewStackTrie(nil),
+			sim.chainConfig,
+		)
+	}
+
 	repairLogs(callResults, b.Hash())
 	return b, callResults, senders, receipts, nil
 }
@@ -380,6 +407,30 @@ func repairLogs(calls []simCallResult, hash common.Hash) {
 	}
 }
 
+// createSimulatedJovianDepositTx creates a synthetic L1 attributes deposit transaction for
+// Jovian simulations. This is required because CalcDAFootprint expects the first transaction in a
+// Jovian block to be a deposit transaction containing L1 attributes data with the Jovian selector
+// and DA footprint gas scalar.
+func createSimulatedJovianDepositTx() *types.Transaction {
+	// Jovian format: 178 bytes with JovianL1AttributesSelector and daFootprintGasScalar in last 2 bytes
+	data := make([]byte, types.JovianL1AttributesLen)
+	copy(data[0:4], types.JovianL1AttributesSelector)
+	// Set a reasonable default DA footprint gas scalar (e.g., 1 wei)
+	// This scalar is used to calculate DA footprint: EstimatedDASize * daFootprintGasScalar
+	binary.BigEndian.PutUint16(data[types.JovianL1AttributesLen-2:types.JovianL1AttributesLen], 1)
+
+	return types.NewTx(&types.DepositTx{
+		SourceHash:          common.Hash{},    // Zero hash for simulated deposit
+		From:                common.Address{}, // Zero address (system)
+		To:                  &types.L1BlockAddr,
+		Mint:                nil,
+		Value:               big.NewInt(0),
+		Gas:                 0,
+		IsSystemTransaction: true,
+		Data:                data,
+	})
+}
+
 func (sim *simulator) sanitizeCall(call *TransactionArgs, state vm.StateDB, header *types.Header, blockContext vm.BlockContext, gasUsed *uint64) error {
 	if call.Nonce == nil {
 		nonce := state.GetNonce(call.from())