[miner] omit dummy extraNonce via IPC

diff --git a/src/bench/block_assemble.cpp b/src/bench/block_assemble.cpp
index 297465be..702f2c09 100644
--- a/src/bench/block_assemble.cpp
+++ b/src/bench/block_assemble.cpp
@@ -30,6 +30,7 @@ static void AssembleBlock(benchmark::Bench& bench)
     witness.stack.push_back(WITNESS_STACK_ELEM_OP_TRUE);
     BlockAssembler::Options options;
     options.coinbase_output_script = P2WSH_OP_TRUE;
+    options.include_dummy_extranonce = true;
 
     // Collect some loose transactions that spend the coinbases of our mined blocks
     constexpr size_t NUM_BLOCKS{200};
diff --git a/src/node/miner.cpp b/src/node/miner.cpp
index 58b147ca..b5073054 100644
--- a/src/node/miner.cpp
+++ b/src/node/miner.cpp
@@ -177,11 +177,17 @@ std::unique_ptr<CBlockTemplate> BlockAssembler::CreateNewBlock()
     coinbase_tx.block_reward_remaining = block_reward;
 
     // Start the coinbase scriptSig with the block height as required by BIP34.
-    // The trailing OP_0 (historically an extranonce) is optional padding and
-    // could be removed without a consensus change. Mining clients are expected
-    // to append extra data to this prefix, so increasing its length would reduce
-    // the space they can use and may break existing clients.
-    coinbaseTx.vin[0].scriptSig = CScript() << nHeight << OP_0;
+    // Mining clients are expected to append extra data to this prefix, so
+    // increasing its length would reduce the space they can use and may break
+    // existing clients.
+    coinbaseTx.vin[0].scriptSig = CScript() << nHeight;
+    if (m_options.include_dummy_extranonce) {
+        // For blocks at heights <= 16, the BIP34-encoded height alone is only
+        // one byte. Consensus requires coinbase scriptSigs to be at least two
+        // bytes long (bad-cb-length), so tests and regtest include a dummy
+        // extraNonce (OP_0)
+        coinbaseTx.vin[0].scriptSig << OP_0;
+    }
     coinbase_tx.script_sig_prefix = coinbaseTx.vin[0].scriptSig;
     Assert(nHeight > 0);
     coinbaseTx.nLockTime = static_cast<uint32_t>(nHeight - 1);
@@ -212,6 +218,7 @@ std::unique_ptr<CBlockTemplate> BlockAssembler::CreateNewBlock()
     pblock->nNonce         = 0;
 
     if (m_options.test_block_validity) {
+        // if nHeight <= 16, and include_dummy_extranonce=false this will fail due to bad-cb-length.
         if (BlockValidationState state{TestBlockValidity(m_chainstate, *pblock, /*check_pow=*/false, /*check_merkle_root=*/false)}; !state.IsValid()) {
             throw std::runtime_error(strprintf("TestBlockValidity failed: %s", state.ToString()));
         }
diff --git a/src/node/types.h b/src/node/types.h
index 6930672f..deab1faa 100644
--- a/src/node/types.h
+++ b/src/node/types.h
@@ -67,6 +67,10 @@ struct BlockCreateOptions {
      * coinbase_max_additional_weight and coinbase_output_max_additional_sigops.
      */
     CScript coinbase_output_script{CScript() << OP_TRUE};
+    /**
+     * Whether to include an OP_0 as a dummy extraNonce in the template's coinbase
+     */
+    bool include_dummy_extranonce{false};
 };
 
 struct BlockWaitOptions {
diff --git a/src/rpc/mining.cpp b/src/rpc/mining.cpp
index 9c357f87..d0efa84f 100644
--- a/src/rpc/mining.cpp
+++ b/src/rpc/mining.cpp
@@ -165,7 +165,7 @@ static UniValue generateBlocks(ChainstateManager& chainman, Mining& miner, const
 {
     UniValue blockHashes(UniValue::VARR);
     while (nGenerate > 0 && !chainman.m_interrupt) {
-        std::unique_ptr<BlockTemplate> block_template(miner.createNewBlock({ .coinbase_output_script = coinbase_output_script }));
+        std::unique_ptr<BlockTemplate> block_template(miner.createNewBlock({ .coinbase_output_script = coinbase_output_script, .include_dummy_extranonce = true }));
         CHECK_NONFATAL(block_template);
 
         std::shared_ptr<const CBlock> block_out;
@@ -376,7 +376,7 @@ static RPCHelpMan generateblock()
     {
         LOCK(chainman.GetMutex());
         {
-            std::unique_ptr<BlockTemplate> block_template{miner.createNewBlock({.use_mempool = false, .coinbase_output_script = coinbase_output_script})};
+            std::unique_ptr<BlockTemplate> block_template{miner.createNewBlock({.use_mempool = false, .coinbase_output_script = coinbase_output_script, .include_dummy_extranonce = true})};
             CHECK_NONFATAL(block_template);
 
             block = block_template->getBlock();
@@ -871,7 +871,7 @@ static RPCHelpMan getblocktemplate()
         time_start = GetTime();
 
         // Create new block
-        block_template = miner.createNewBlock();
+        block_template = miner.createNewBlock({.include_dummy_extranonce = true});
         CHECK_NONFATAL(block_template);
 
 
diff --git a/src/test/blockfilter_index_tests.cpp b/src/test/blockfilter_index_tests.cpp
index e970ae9c..d7d10dfb 100644
--- a/src/test/blockfilter_index_tests.cpp
+++ b/src/test/blockfilter_index_tests.cpp
@@ -69,6 +69,7 @@ CBlock BuildChainTestingSetup::CreateBlock(const CBlockIndex* prev,
 {
     BlockAssembler::Options options;
     options.coinbase_output_script = scriptPubKey;
+    options.include_dummy_extranonce = true;
     std::unique_ptr<CBlockTemplate> pblocktemplate = BlockAssembler{m_node.chainman->ActiveChainstate(), m_node.mempool.get(), options}.CreateNewBlock();
     CBlock& block = pblocktemplate->block;
     block.hashPrevBlock = prev->GetBlockHash();
diff --git a/src/test/fuzz/package_eval.cpp b/src/test/fuzz/package_eval.cpp
index 1cc2caa3..93cd8ad6 100644
--- a/src/test/fuzz/package_eval.cpp
+++ b/src/test/fuzz/package_eval.cpp
@@ -46,6 +46,7 @@ void initialize_tx_pool()
 
     BlockAssembler::Options options;
     options.coinbase_output_script = P2WSH_EMPTY;
+    options.include_dummy_extranonce = true;
 
     for (int i = 0; i < 2 * COINBASE_MATURITY; ++i) {
         COutPoint prevout{MineBlock(g_setup->m_node, options)};
diff --git a/src/test/fuzz/process_message.cpp b/src/test/fuzz/process_message.cpp
index ef8cb686..7a24c1de 100644
--- a/src/test/fuzz/process_message.cpp
+++ b/src/test/fuzz/process_message.cpp
@@ -41,7 +41,9 @@ void ResetChainman(TestingSetup& setup)
     setup.m_make_chainman();
     setup.LoadVerifyActivateChainstate();
     for (int i = 0; i < 2 * COINBASE_MATURITY; i++) {
-        MineBlock(setup.m_node, {});
+        node::BlockAssembler::Options options;
+        options.include_dummy_extranonce = true;
+        MineBlock(setup.m_node, options);
     }
     setup.m_node.validation_signals->SyncWithValidationInterfaceQueue();
 }
diff --git a/src/test/fuzz/process_messages.cpp b/src/test/fuzz/process_messages.cpp
index f36f528b..28bee67d 100644
--- a/src/test/fuzz/process_messages.cpp
+++ b/src/test/fuzz/process_messages.cpp
@@ -35,8 +35,10 @@ void ResetChainman(TestingSetup& setup)
     setup.m_node.chainman.reset();
     setup.m_make_chainman();
     setup.LoadVerifyActivateChainstate();
+    node::BlockAssembler::Options options;
+    options.include_dummy_extranonce = true;
     for (int i = 0; i < 2 * COINBASE_MATURITY; i++) {
-        MineBlock(setup.m_node, {});
+        MineBlock(setup.m_node, options);
     }
     setup.m_node.validation_signals->SyncWithValidationInterfaceQueue();
 }
diff --git a/src/test/fuzz/tx_pool.cpp b/src/test/fuzz/tx_pool.cpp
index f70dd710..bb155527 100644
--- a/src/test/fuzz/tx_pool.cpp
+++ b/src/test/fuzz/tx_pool.cpp
@@ -48,6 +48,7 @@ void initialize_tx_pool()
 
     BlockAssembler::Options options;
     options.coinbase_output_script = P2WSH_OP_TRUE;
+    options.include_dummy_extranonce = true;
 
     for (int i = 0; i < 2 * COINBASE_MATURITY; ++i) {
         COutPoint prevout{MineBlock(g_setup->m_node, options)};
@@ -97,6 +98,7 @@ void Finish(FuzzedDataProvider& fuzzed_data_provider, MockedTxPool& tx_pool, Cha
         BlockAssembler::Options options;
         options.nBlockMaxWeight = fuzzed_data_provider.ConsumeIntegralInRange(0U, MAX_BLOCK_WEIGHT);
         options.blockMinFeeRate = CFeeRate{ConsumeMoney(fuzzed_data_provider, /*max=*/COIN)};
+        options.include_dummy_extranonce = true;
         auto assembler = BlockAssembler{chainstate, &tx_pool, options};
         auto block_template = assembler.CreateNewBlock();
         Assert(block_template->block.vtx.size() >= 1);
diff --git a/src/test/fuzz/utxo_total_supply.cpp b/src/test/fuzz/utxo_total_supply.cpp
index d27ca347..cac9d4ce 100644
--- a/src/test/fuzz/utxo_total_supply.cpp
+++ b/src/test/fuzz/utxo_total_supply.cpp
@@ -45,6 +45,7 @@ FUZZ_TARGET(utxo_total_supply)
     };
     BlockAssembler::Options options;
     options.coinbase_output_script = CScript() << OP_FALSE;
+    options.include_dummy_extranonce = true;
     const auto PrepareNextBlock = [&]() {
         // Use OP_FALSE to avoid BIP30 check from hitting early
         auto block = PrepareBlock(node, options);
diff --git a/src/test/miner_tests.cpp b/src/test/miner_tests.cpp
index a1f5a6d0..3b4beebe 100644
--- a/src/test/miner_tests.cpp
+++ b/src/test/miner_tests.cpp
@@ -116,6 +116,7 @@ void MinerTestingSetup::TestPackageSelection(const CScript& scriptPubKey, const
     auto mining{MakeMining()};
     BlockAssembler::Options options;
     options.coinbase_output_script = scriptPubKey;
+    options.include_dummy_extranonce = true;
 
     LOCK(tx_mempool.cs);
     BOOST_CHECK(tx_mempool.size() == 0);
@@ -334,6 +335,7 @@ void MinerTestingSetup::TestBasicMining(const CScript& scriptPubKey, const std::
 
     BlockAssembler::Options options;
     options.coinbase_output_script = scriptPubKey;
+    options.include_dummy_extranonce = true;
 
     {
         CTxMemPool& tx_mempool{MakeMempool()};
@@ -660,6 +662,7 @@ void MinerTestingSetup::TestPrioritisedMining(const CScript& scriptPubKey, const
 
     BlockAssembler::Options options;
     options.coinbase_output_script = scriptPubKey;
+    options.include_dummy_extranonce = true;
 
     CTxMemPool& tx_mempool{MakeMempool()};
     LOCK(tx_mempool.cs);
@@ -749,6 +752,7 @@ BOOST_AUTO_TEST_CASE(CreateNewBlock_validity)
     CScript scriptPubKey = CScript() << "04678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38c4f35504e51ec112de5c384df7ba0b8d578a4c702b6bf11d5f"_hex << OP_CHECKSIG;
     BlockAssembler::Options options;
     options.coinbase_output_script = scriptPubKey;
+    options.include_dummy_extranonce = true;
 
     // Create and check a simple template
     std::unique_ptr<BlockTemplate> block_template = mining->createNewBlock(options);
diff --git a/src/test/peerman_tests.cpp b/src/test/peerman_tests.cpp
index 64b13fa3..e391e8b9 100644
--- a/src/test/peerman_tests.cpp
+++ b/src/test/peerman_tests.cpp
@@ -19,8 +19,10 @@ static constexpr int64_t NODE_NETWORK_LIMITED_ALLOW_CONN_BLOCKS = 144;
 static void mineBlock(const node::NodeContext& node, std::chrono::seconds block_time)
 {
     auto curr_time = GetTime<std::chrono::seconds>();
+    node::BlockAssembler::Options options;
+    options.include_dummy_extranonce = true;
     SetMockTime(block_time); // update time so the block is created with it
-    CBlock block = node::BlockAssembler{node.chainman->ActiveChainstate(), nullptr, {}}.CreateNewBlock()->block;
+    CBlock block = node::BlockAssembler{node.chainman->ActiveChainstate(), nullptr, options}.CreateNewBlock()->block;
     while (!CheckProofOfWork(block.GetHash(), block.nBits, node.chainman->GetConsensus())) ++block.nNonce;
     block.fChecked = true; // little speedup
     SetMockTime(curr_time); // process block at current time
diff --git a/src/test/testnet4_miner_tests.cpp b/src/test/testnet4_miner_tests.cpp
index 5b3582ac..33e028a5 100644
--- a/src/test/testnet4_miner_tests.cpp
+++ b/src/test/testnet4_miner_tests.cpp
@@ -35,6 +35,7 @@ BOOST_AUTO_TEST_CASE(MiningInterface)
     BOOST_REQUIRE(mining);
 
     BlockAssembler::Options options;
+    options.include_dummy_extranonce = true;
     std::unique_ptr<BlockTemplate> block_template;
 
     // Set node time a few minutes past the testnet4 genesis block
diff --git a/src/test/util/mining.cpp b/src/test/util/mining.cpp
index 05f1be77..c4823bce 100644
--- a/src/test/util/mining.cpp
+++ b/src/test/util/mining.cpp
@@ -29,6 +29,7 @@ COutPoint generatetoaddress(const NodeContext& node, const std::string& address)
     assert(IsValidDestination(dest));
     BlockAssembler::Options assembler_options;
     assembler_options.coinbase_output_script = GetScriptForDestination(dest);
+    assembler_options.include_dummy_extranonce = true;
 
     return MineBlock(node, assembler_options);
 }
@@ -139,6 +140,7 @@ std::shared_ptr<CBlock> PrepareBlock(const NodeContext& node, const CScript& coi
 {
     BlockAssembler::Options assembler_options;
     assembler_options.coinbase_output_script = coinbase_scriptPubKey;
+    assembler_options.include_dummy_extranonce = true;
     ApplyArgsManOptions(*node.args, assembler_options);
     return PrepareBlock(node, assembler_options);
 }
diff --git a/src/test/util/setup_common.cpp b/src/test/util/setup_common.cpp
index 4e886639..e479168a 100644
--- a/src/test/util/setup_common.cpp
+++ b/src/test/util/setup_common.cpp
@@ -404,6 +404,7 @@ CBlock TestChain100Setup::CreateBlock(
 {
     BlockAssembler::Options options;
     options.coinbase_output_script = scriptPubKey;
+    options.include_dummy_extranonce = true;
     CBlock block = BlockAssembler{chainstate, nullptr, options}.CreateNewBlock()->block;
 
     Assert(block.vtx.size() == 1);
diff --git a/src/test/validation_block_tests.cpp b/src/test/validation_block_tests.cpp
index dfa66bb8..f91b30a3 100644
--- a/src/test/validation_block_tests.cpp
+++ b/src/test/validation_block_tests.cpp
@@ -68,6 +68,7 @@ std::shared_ptr<CBlock> MinerTestingSetup::Block(const uint256& prev_hash)
 
     BlockAssembler::Options options;
     options.coinbase_output_script = CScript{} << i++ << OP_TRUE;
+    options.include_dummy_extranonce = true;
     auto ptemplate = BlockAssembler{m_node.chainman->ActiveChainstate(), m_node.mempool.get(), options}.CreateNewBlock();
     auto pblock = std::make_shared<CBlock>(ptemplate->block);
     pblock->hashPrevBlock = prev_hash;
@@ -336,6 +337,7 @@ BOOST_AUTO_TEST_CASE(witness_commitment_index)
     pubKey << 1 << OP_TRUE;
     BlockAssembler::Options options;
     options.coinbase_output_script = pubKey;
+    options.include_dummy_extranonce = true;
     auto ptemplate = BlockAssembler{m_node.chainman->ActiveChainstate(), m_node.mempool.get(), options}.CreateNewBlock();
     CBlock pblock = ptemplate->block;
 
diff --git a/test/functional/interface_ipc.py b/test/functional/interface_ipc.py
index 47589cbc..6d007e88 100755
--- a/test/functional/interface_ipc.py
+++ b/test/functional/interface_ipc.py
@@ -20,10 +20,14 @@ from test_framework.messages import (
     ser_uint256,
     COIN,
 )
+from test_framework.script import (
+    CScript,
+    CScriptNum,
+)
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
     assert_equal,
-    assert_not_equal
+    assert_not_equal,
 )
 from test_framework.wallet import MiniWallet
 from typing import Optional
@@ -194,6 +198,12 @@ class IPCInterfaceTest(BitcoinTestFramework):
         coinbase_tx.vin = [CTxIn()]
         coinbase_tx.vin[0].prevout = NULL_OUTPOINT
         coinbase_tx.vin[0].nSequence = coinbase_res.sequence
+
+        # Verify there's no dummy extraNonce in the coinbase scriptSig
+        current_block_height = self.nodes[0].getchaintips()[0]["height"]
+        expected_scriptsig = CScript([CScriptNum(current_block_height + 1)])
+        assert_equal(coinbase_res.scriptSigPrefix.hex(), expected_scriptsig.hex())
+
         # Typically a mining pool appends its name and an extraNonce
         coinbase_tx.vin[0].scriptSig = coinbase_res.scriptSigPrefix