diff --git a/src/test/fuzz/chainstate.cpp b/src/test/fuzz/chainstate.cpp
index 228b58348d..68bed5e75b 100644
--- a/src/test/fuzz/chainstate.cpp
+++ b/src/test/fuzz/chainstate.cpp
@@ -6,10 +6,12 @@
 #include <chainparams.h>
 #include <config/bitcoin-config.h>
 #include <consensus/merkle.h>
+#include <kernel/notifications_interface.h>
 #include <kernel/warning.h>
 #include <logging.h>
 #include <node/blockstorage.h>
 #include <node/chainstate.h>
+#include <node/miner.h>
 #include <pow.h>
 #include <random.h>
 #include <scheduler.h>
@@ -24,9 +26,11 @@
 #include <test/util/script.h>
 #include <test/util/setup_common.h>
 #include <txdb.h>
-#include <util/fs_helpers.h>
+#include <util/task_runner.h>
 #include <util/thread.h>
 
+#include <ranges>
+
 namespace {
 
 class KernelNotifications : public kernel::Notifications
@@ -47,16 +51,151 @@ public:
     }
 };
 
+/**
+ * Manage the state for a run of the fuzz target.
+ *
+ * This stores our utxos and keep them in sync with the state of the chain. This also allows to register some block
+ * hashes to assert the validity of a given block.
+ */
+class StateManager : public CValidationInterface {
+    //! Utxos created in a coinbase transaction which hasn't matured yet. Those are keyed by the height at
+    //! which they can be spent in the next block.
+    std::unordered_map<int, std::pair<COutPoint, CTxOut>> m_immature_utxos;
+
+    //! Utxos which can be spent in the next block.
+    std::unordered_map<COutPoint, CTxOut, SaltedOutpointHasher> m_spendable_utxos;
+
+    //! Utxos which were spent. Kept around to add them back in case of reorg.
+    std::unordered_map<COutPoint, CTxOut, SaltedOutpointHasher> m_spent_utxos;
+
+    //! Block hashes of blocks we assume are valid. Unbounded but we assume we won't add millions such entries.
+    std::unordered_set<uint256, SaltedTxidHasher> m_assert_valid_blocks;
+
+public:
+    /** Create a transaction spending a random amount of utxos from our wallet, if possible. */
+    CTransactionRef CreateTransaction(FuzzedDataProvider& prov)
+    {
+        if (m_spendable_utxos.empty()) return {};
+        CMutableTransaction tx;
+
+        // Pick the utxos to use as input of our transaction. Drop them from our set of available
+        // utxos to avoid reusing them in another transaction before a block gets connected.
+        // FIXME: can we be smarter than erasing a hundred times? For instance keeping track of reserved utxos?
+        const auto input_count{prov.ConsumeIntegralInRange(1, std::min((int)m_spendable_utxos.size(), 100))};
+        tx.vin.resize(input_count);
+        CAmount in_value{0};
+        auto it{m_spendable_utxos.begin()};
+        for (int i{0}; i < input_count; ++i) {
+            auto [outpoint, coin] = *it++;
+            in_value += coin.nValue;
+            tx.vin[i].prevout = outpoint;
+            tx.vin[i].scriptWitness.stack = std::vector<std::vector<uint8_t>>{WITNESS_STACK_ELEM_OP_TRUE};
+            m_spendable_utxos.erase(outpoint);
+            m_spent_utxos.emplace(outpoint, std::move(coin));
+        }
+
+        const auto out_count{prov.ConsumeIntegralInRange(1, 100)};
+        tx.vout.resize(out_count);
+        for (int i{0}; i < out_count; ++i) {
+            tx.vout[i].scriptPubKey = P2WSH_OP_TRUE;
+            tx.vout[i].nValue = in_value / out_count;
+        }
+
+        return MakeTransactionRef(std::move(tx));
+    }
+
+    /** Record a block hash to assert the validity of the block once it'll have been checked. */
+    void AssertBlockValidity(uint256 block_hash)
+    {
+        m_assert_valid_blocks.insert(std::move(block_hash));
+    }
+
+protected:
+    /** We subscribe to the block checked notification to let the fuzz target assert the validity of some blocks. */
+    void BlockChecked(const CBlock& block, const BlockValidationState& state) override
+    {
+        if (!state.IsValid()) {
+            // FIXME: since we never delete records is it possible that we re-create the same block but treat it as
+            // invalid this time (min_pow_checked = false for instance) and it would fail this assert?
+            assert(!m_assert_valid_blocks.contains(block.GetHash()));
+        }
+    }
+
+    /** We subscribe to the block connected notifications to update our "wallet view", ie the coins we can spend at the
+     * next block. */
+    void BlockConnected(ChainstateRole role, const std::shared_ptr<const CBlock> &block, const CBlockIndex *pindex) override
+    {
+        // First of all record the new coinbase output.
+        COutPoint coinbase_op{block->vtx[0]->GetHash(), 0};
+        CTxOut coinbase_coin{block->vtx[0]->vout[0]};
+        m_immature_utxos.emplace(pindex->nHeight + COINBASE_MATURITY - 1, std::make_pair(coinbase_op, coinbase_coin));
+
+        // Then record outputs spent and created by all other transactions in the block. In the fuzz target
+        // blocks only ever contain transactions which spend and create our own outputs.
+        for (const auto& tx: block->vtx | std::views::drop(1)) {
+            for (size_t i{0}; i < tx->vout.size(); ++i) {
+                COutPoint op{tx->GetHash(), (uint32_t)i};
+                m_spendable_utxos.emplace(std::move(op), tx->vout[i]);
+            }
+
+            for (const auto& vin: tx->vin) {
+                m_spendable_utxos.erase(vin.prevout);
+            }
+        }
+
+        // Finally, record any newly matured utxo as spendable in the next block. Note we don't move
+        // and erase the entry on purpose here, as we might need it again in case of reorg.
+        const auto& matured_utxo{m_immature_utxos.find(pindex->nHeight)};
+        if (matured_utxo != m_immature_utxos.end()) {
+            m_spendable_utxos.emplace(matured_utxo->second.first, matured_utxo->second.second);
+        }
+    }
+
+    /** We subscribe to the block disconnected notifications to update our "wallet view", the coins we can spend at the
+     * next block. */
+    void BlockDisconnected(const std::shared_ptr<const CBlock> &block, const CBlockIndex* pindex) override
+    {
+        // First of all drop the coinbase output for this block.
+        m_immature_utxos.erase(pindex->nHeight + COINBASE_MATURITY - 1);
+
+        // Then if we previously marked a coinbase output as newly matured for a coin at this height,
+        // mark it as immature again.
+        const auto& re_immatured_utxo{m_immature_utxos.find(pindex->nHeight)};
+        if (re_immatured_utxo != m_immature_utxos.end()) {
+            m_spendable_utxos.erase(re_immatured_utxo->second.first);
+        }
+
+        // Finally, drop any coin created in this block and re-insert formerly spent coins.
+        for (const auto& tx: block->vtx) {
+            for (size_t i{0}; i < tx->vout.size(); ++i) {
+                COutPoint op{tx->GetHash(), (uint32_t)i};
+                m_spendable_utxos.erase(op);
+            }
+
+            if (tx->IsCoinBase()) continue;
+            for (const auto& vin: tx->vin) {
+                auto spent_utxo{m_spent_utxos.find(vin.prevout)};
+                if (spent_utxo != m_spent_utxos.end()) {
+                    m_spendable_utxos.emplace(spent_utxo->first, spent_utxo->second);
+                }
+            }
+        }
+    }
+};
+
+//! See net_processing.
+static const int MAX_HEADERS_RESULTS{2000};
+
 //! To generate a random tmp datadir per process (necessary to fuzz with multiple cores).
 static FastRandomContext g_insecure_rand_ctx_temp_path;
 
 struct TestData {
     fs::path m_tmp_dir;
     fs::path m_datadir;
-    const CChainParams m_chain_params{*CChainParams::Main()};
+    fs::path m_init_datadir;
+    const CChainParams m_chain_params{*CChainParams::RegTest({})};
     KernelNotifications m_notifs;
     util::SignalInterrupt m_interrupt;
-    std::unique_ptr<const BasicTestingSetup> m_test_setup;
 
     void Init() {
         SeedRandomForTest(SeedRand::SEED);
@@ -64,7 +203,7 @@ struct TestData {
         m_tmp_dir = fs::temp_directory_path() / "fuzz_chainstate_" PACKAGE_NAME / rand_str;
         fs::remove_all(m_tmp_dir);
         m_datadir = m_tmp_dir / "datadir";
-        fs::create_directories(m_datadir / "blocks");
+        m_init_datadir = m_tmp_dir / "init_datadir";
 
         LogInstance().DisableLogging();
     }
@@ -84,10 +223,10 @@ std::pair<uint256, int> RandomPrevBlock(FuzzedDataProvider& prov)
     return {std::move(hash), height};
 }
 
-/** In 90% of the cases, get any random block from the index. Otherwise generate a random one. */
+/** Sometimes get any random block from the index. Otherwise generate a random one. */
 std::pair<uint256, int> RandomPrevBlock(FuzzedDataProvider& prov, node::BlockManager& blockman) NO_THREAD_SAFETY_ANALYSIS
 {
-    if (prov.ConsumeIntegralInRange<int>(0, 9) > 0) {
+    if (prov.ConsumeBool()) {
         const auto prev_block{&PickValue(prov, blockman.m_block_index).second};
         return {prev_block->GetBlockHash(), prev_block->nHeight};
     }
@@ -119,8 +258,8 @@ CTransactionRef CreateCoinbase(int height)
     tx.vin[0].prevout.SetNull();
     tx.vout.resize(1);
     tx.vout[0].scriptPubKey = P2WSH_OP_TRUE;
-    tx.vout[0].nValue = 50 * COIN; // We assume we don't mine so many blocks at once..
-    tx.vin[0].scriptSig = CScript() << (height + 1) << OP_0;
+    tx.vout[0].nValue = (50 * COIN) >> 10; // Tolerate up to 10 halvings.
+    tx.vin[0].scriptSig = CScript() << height << OP_0;
     return MakeTransactionRef(std::move(tx));
 }
 
@@ -142,6 +281,44 @@ std::pair<CBlock, int> CreateBlock(FuzzedDataProvider& prov, std::pair<uint256,
     return std::make_pair(std::move(block), height);
 }
 
+/** Create a consensus-valid random block.
+ * If a non-empty list of transactions is passed include them. Otherwise if a StateManager is passed, try to fill the
+ * block with a random number of transactions. */
+CBlock CreateValidBlock(FuzzedDataProvider& prov, StateManager* state_manager, const ChainstateManager& chainman,
+                        CBlockIndex* prev_block, std::vector<CTransactionRef> txs = {})
+{
+    assert(prev_block);
+    CBlock block;
+    block.nVersion = prov.ConsumeIntegralInRange(4, std::numeric_limits<int>::max());
+    block.nNonce = prov.ConsumeIntegral<uint32_t>();
+    node::UpdateTime(&block, chainman.GetConsensus(), prev_block);
+    block.nBits = GetNextWorkRequired(prev_block, &block, chainman.GetConsensus());
+    block.hashPrevBlock = prev_block->GetBlockHash();
+
+    // Always create the coinbase. Then if a list of transactions was passed, use that. Otherwise
+    // try to create a bunch of new transactions.
+    block.vtx.push_back(CreateCoinbase(prev_block->nHeight + 1));
+    if (!txs.empty()) {
+        block.vtx.reserve(txs.size());
+        block.vtx.insert(block.vtx.end(), std::make_move_iterator(txs.begin()), std::make_move_iterator(txs.end()));
+        txs.erase(txs.begin(), txs.end());
+    } else if (state_manager) {
+        while (prov.ConsumeBool()) {
+            if (auto tx{state_manager->CreateTransaction(prov)}) {
+                block.vtx.push_back(std::move(tx));
+                if (GetBlockWeight(block) > MAX_BLOCK_WEIGHT) {
+                    block.vtx.pop_back();
+                    break;
+                }
+            }
+        }
+    }
+    chainman.GenerateCoinbaseCommitment(block, prev_block);
+    block.hashMerkleRoot = BlockMerkleRoot(block);
+
+    return block;
+}
+
 /** Make it possible to sanity check roundtrips to disk. */
 bool operator==(const CBlock& a, const CBlock& b)
 {
@@ -307,3 +484,257 @@ FUZZ_TARGET(blockstorage, .init = init_blockstorage)
     // At no point do we set an AssumeUtxo snapshot.
     assert(!blockman.m_snapshot_height);
 }
+
+void init_chainstate()
+{
+    // Make the pow check always pass to be able to mine a chain from inside the target.
+    // TODO: we could have two mocks, once which passes, the other which fails. This way we can
+    // also fuzz the codepath for invalid pow.
+    g_check_pow_mock = [](uint256 hash, unsigned int, const Consensus::Params&) {
+        return true;
+    };
+
+    // This sets up the init and working datadirs paths in a tmp folder.
+    g_test_data.Init();
+
+    // Create the chainstate for the initial datadir. On every round we'll restart from this chainstate instead of
+    // re-creating one from scratch.
+    fs::create_directories(g_test_data.m_init_datadir / "blocks");
+    node::BlockManager::Options blockman_opts{
+        .chainparams = g_test_data.m_chain_params,
+        .blocks_dir = g_test_data.m_init_datadir / "blocks",
+        .notifications = g_test_data.m_notifs,
+    };
+    ValidationSignals main_signals{std::make_unique<util::ImmediateTaskRunner>()};
+    const ChainstateManager::Options chainman_opts{
+        .chainparams = g_test_data.m_chain_params,
+        .datadir = g_test_data.m_init_datadir,
+        .check_block_index = false,
+        .checkpoints_enabled = false,
+        .minimum_chain_work = UintToArith256(uint256{}),
+        .assumed_valid_block = uint256{},
+        .notifications = g_test_data.m_notifs,
+        .signals = &main_signals,
+    };
+    ChainstateManager chainman{g_test_data.m_interrupt, chainman_opts, blockman_opts};
+    node::CacheSizes cache_sizes;
+    cache_sizes.block_tree_db = 1;
+    cache_sizes.coins_db = 2;
+    cache_sizes.coins = 3;
+    node::ChainstateLoadOptions load_opts {
+        .require_full_verification = false,
+        .coins_error_cb = nullptr,
+    };
+    auto [status, _] = node::LoadChainstate(chainman, cache_sizes, load_opts);
+    assert(status == node::ChainstateLoadStatus::SUCCESS);
+
+    // Connect the initial chain to get 10 spendable UTxOs at the start of every fuzzing round.
+    const auto initial_blockchain{CreateBlockChain(110, g_test_data.m_chain_params)};
+    BlockValidationState valstate;
+    auto& chainstate{chainman.ActiveChainstate()};
+    assert(chainstate.ActivateBestChain(valstate, nullptr));
+    for (const auto& block : initial_blockchain) {
+        bool new_block{false};
+        assert(chainman.ProcessNewBlock(block, true, true, &new_block));
+        assert(new_block);
+    }
+
+    LOCK(chainman.GetMutex());
+    if (chainstate.CanFlushToDisk()) {
+        chainstate.ForceFlushStateToDisk();
+    }
+}
+
+FUZZ_TARGET(chainstate, .init = init_chainstate)
+{
+    FuzzedDataProvider fuzzed_data_provider{buffer.data(), buffer.size()};
+
+    // On every round start from a freshly copied initial datadir.
+    fs::remove_all(g_test_data.m_datadir);
+    fs::copy(g_test_data.m_init_datadir, g_test_data.m_datadir, fs::copy_options::overwrite_existing | fs::copy_options::recursive);
+
+    // We use the signals to assert blocks validity and keep up to date the utxos we can use to create valid
+    // transactions.
+    ValidationSignals main_signals{std::make_unique<util::ImmediateTaskRunner>()};
+
+    // Create the chainstate..
+    uint64_t prune_target{0};
+    if (fuzzed_data_provider.ConsumeBool()) {
+        prune_target = fuzzed_data_provider.ConsumeIntegral<uint64_t>();
+    }
+    node::BlockManager::Options blockman_opts{
+        .chainparams = g_test_data.m_chain_params,
+        .prune_target = prune_target,
+        .blocks_dir = g_test_data.m_datadir / "blocks",
+        .notifications = g_test_data.m_notifs,
+    };
+    const ChainstateManager::Options chainman_opts{
+        .chainparams = g_test_data.m_chain_params,
+        .datadir = g_test_data.m_datadir,
+        // TODO: make it possible to call CheckBlockIndex() without having set it here, and call it in CallOneOf().
+        .check_block_index = true,
+        .checkpoints_enabled = false,
+        .minimum_chain_work = UintToArith256(uint256{}),
+        .assumed_valid_block = uint256{},
+        .notifications = g_test_data.m_notifs,
+        .signals = &main_signals,
+    };
+    ChainstateManager chainman{g_test_data.m_interrupt, chainman_opts, blockman_opts};
+
+    // ..And then load it.
+    node::CacheSizes cache_sizes;
+    cache_sizes.block_tree_db = 2 << 20;
+    cache_sizes.coins_db = 2 << 22;
+    cache_sizes.coins = (450 << 20) - (2 << 20) - (2 << 22);
+    node::ChainstateLoadOptions load_opts {
+        .prune = prune_target > 0,
+        .require_full_verification = false,
+        .coins_error_cb = nullptr,
+    };
+    auto [status, _] = node::LoadChainstate(chainman, cache_sizes, load_opts);
+    assert(status == node::ChainstateLoadStatus::SUCCESS);
+
+    // This stores our state for this run: our utxos and blocks to assert are valid.
+    StateManager state_manager;
+    main_signals.RegisterValidationInterface(&state_manager);
+
+    std::vector<CBlock> blocks_in_flight;
+    LIMITED_WHILE(fuzzed_data_provider.ConsumeBool(), 10'000) {
+        CallOneOf(fuzzed_data_provider,
+            // Process a list of headers. Most of the time make it process the header of a valid block
+            // cached for future processing.
+            [&]() NO_THREAD_SAFETY_ANALYSIS {
+                std::vector<CBlockHeader> headers;
+
+                // In some cases generate a random list of headers to be processed. Otherwise, create a single valid
+                // block.
+                // TODO: make it possible to generate a chain of more than one valid block.
+                const bool is_random{fuzzed_data_provider.ConsumeBool()};
+                const int headers_count{is_random ? fuzzed_data_provider.ConsumeIntegralInRange(1, MAX_HEADERS_RESULTS) : 1};
+                headers.reserve(headers_count);
+
+                // Need to determine whether we'll set the PoW as checked before asserting block validity.
+                const bool min_pow_checked{fuzzed_data_provider.ConsumeBool()};
+
+                if (is_random) {
+                    for (int i = 0; i < headers_count; ++i) {
+                        headers.push_back(CreateBlockHeader(fuzzed_data_provider, RandomPrevBlock(fuzzed_data_provider), /*set_merkle=*/true).first);
+                    }
+                } else {
+                    // Sometimes branch off a random header, sometimes extend the tip of either the validated chain or
+                    // the best header chain.
+                    const bool extend_tip{fuzzed_data_provider.ConsumeBool()};
+                    const bool extend_active_tip{extend_tip && fuzzed_data_provider.ConsumeBool()};
+                    CBlockIndex* prev_block{[&]() NO_THREAD_SAFETY_ANALYSIS {
+                        LOCK(chainman.GetMutex());
+                        if (extend_tip) {
+                            return extend_active_tip ? chainman.ActiveTip() : chainman.m_best_header;
+                        }
+                        return &PickValue(fuzzed_data_provider, chainman.m_blockman.m_block_index).second;
+                    }()};
+                    auto sm{extend_tip ? &state_manager : nullptr};
+                    blocks_in_flight.push_back(CreateValidBlock(fuzzed_data_provider, sm, chainman, prev_block));
+                    if (extend_active_tip && min_pow_checked) state_manager.AssertBlockValidity(blocks_in_flight.back().GetHash());
+                    headers.emplace_back(blocks_in_flight.back());
+                }
+
+                BlockValidationState valstate;
+                const bool res{chainman.ProcessNewBlockHeaders(headers, min_pow_checked, valstate)};
+                assert(res || is_random || !min_pow_checked);
+            },
+            // Process a block. Most of the time make it proces one of the blocks in flight.
+            [&]() NO_THREAD_SAFETY_ANALYSIS {
+                const bool process_in_flight{!blocks_in_flight.empty() && fuzzed_data_provider.ConsumeBool()};
+                auto block{[&] {
+                    if (process_in_flight) {
+                        // Sometimes process a block of which we processed the header already. Note the block
+                        // isn't necessarily valid.
+                        auto block{std::move(blocks_in_flight.back())};
+                        blocks_in_flight.pop_back();
+                        return block;
+                    } else {
+                        // In the rest, sometimes create a new valid block building on top of either our validated chain
+                        // tip or the header chain tip.
+                        if (fuzzed_data_provider.ConsumeBool()) {
+                            const auto prev_block{WITH_LOCK(chainman.GetMutex(), return fuzzed_data_provider.ConsumeBool() ? chainman.ActiveTip() : chainman.m_best_header)};
+                            return CreateValidBlock(fuzzed_data_provider, &state_manager, chainman, prev_block);
+                        } else {
+                            // For invalid blocks create sometimes an otherwise valid block which branches from any header,
+                            // and sometimes a completely random block.
+                            if (fuzzed_data_provider.ConsumeBool()) {
+                                std::unordered_map<COutPoint, CTxOut, SaltedOutpointHasher> empty_utxos;
+                                const auto prev_block{WITH_LOCK(chainman.GetMutex(), return &PickValue(fuzzed_data_provider, chainman.m_blockman.m_block_index).second)};
+                                return CreateValidBlock(fuzzed_data_provider, {}, chainman, prev_block);
+                            } else {
+                                LOCK(chainman.GetMutex());
+                                return CreateBlock(fuzzed_data_provider, RandomPrevBlock(fuzzed_data_provider)).first;
+                            }
+                        }
+                    }
+                }()};
+                const bool force_processing{fuzzed_data_provider.ConsumeBool()};
+                const bool min_pow_checked{fuzzed_data_provider.ConsumeBool()};
+                chainman.ProcessNewBlock(std::make_shared<CBlock>(std::move(block)), force_processing, min_pow_checked, /*new_block=*/nullptr);
+            },
+            // Create a reorg of any size.
+            [&]() NO_THREAD_SAFETY_ANALYSIS {
+                const auto cur_height{WITH_LOCK(chainman.GetMutex(), return chainman.ActiveHeight())};
+                if (cur_height <= 0) return;
+                std::unordered_map<COutPoint, CTxOut, SaltedOutpointHasher> empty_utxos;
+
+                // Pick the depth of the reorg, and sometimes record the unconfirmed transactions to re-confirm them.
+                auto reorg_height{fuzzed_data_provider.ConsumeIntegralInRange(1, cur_height)};
+                auto reorg_depth{cur_height - reorg_height + 1};
+                std::vector<CBlock> disconnected_blocks;
+                if (fuzzed_data_provider.ConsumeBool()) {
+                    // Bound the reorg depth if we are going to re-confirm transactions from disconnected blocks, to not
+                    // have to deal with transactions spending disconnected coinbases.
+                    reorg_height = std::max(reorg_height, cur_height - COINBASE_MATURITY + 1);
+                    disconnected_blocks.resize(reorg_depth);
+                }
+
+                // Get a pointer to the first block in common between the current and the new chain, optionally
+                // recording the disconnected transactions as we go.
+                auto ancestor{WITH_LOCK(chainman.GetMutex(), return chainman.ActiveTip())};
+                while (ancestor->nHeight >= reorg_height) {
+                    if (!disconnected_blocks.empty()) {
+                        const auto idx{ancestor->nHeight - reorg_height};
+                        assert(chainman.m_blockman.ReadBlockFromDisk(disconnected_blocks[idx], *ancestor));
+                    }
+                    ancestor = ancestor->pprev;
+                }
+
+                // Create a chain as long, don't connect it yet.
+                {
+                LOCK(chainman.GetMutex());
+                for (int i{0}; i < reorg_depth; ++i) {
+                    std::vector<CTransactionRef> txs;
+                    if (!disconnected_blocks.empty() && disconnected_blocks[i].vtx.size() > 1) {
+                        txs = std::vector<CTransactionRef>{std::make_move_iterator(disconnected_blocks[i].vtx.begin() + 1), std::make_move_iterator(disconnected_blocks[i].vtx.end())};
+                        disconnected_blocks[i] = CBlock{};
+                    }
+                    auto block{CreateValidBlock(fuzzed_data_provider, {}, chainman, ancestor, std::move(txs))};
+                    state_manager.AssertBlockValidity(block.GetHash());
+                    BlockValidationState valstate;
+                    assert(chainman.AcceptBlock(std::make_shared<CBlock>(std::move(block)), valstate, &ancestor, true, nullptr, nullptr, true));
+                }
+                }
+
+                // Make sure the new chain gets connected (a single additional block might not suffice).
+                do {
+                    auto block{CreateValidBlock(fuzzed_data_provider, {}, chainman, ancestor)};
+                    state_manager.AssertBlockValidity(block.GetHash());
+                    BlockValidationState valstate;
+                    auto res{WITH_LOCK(chainman.GetMutex(), return chainman.AcceptBlock(std::make_shared<CBlock>(std::move(block)), valstate, &ancestor, true, nullptr, nullptr, true))};
+                    assert(res);
+                    BlockValidationState valstate2;
+                    assert(chainman.ActiveChainstate().ActivateBestChain(valstate2));
+                } while (chainman.ActiveTip() != ancestor);
+            }
+        );
+    };
+
+    // TODO: exercise the reindex logic?
+    // TODO: sometimes run with an assumed chainstate too? We could be to generate a snapshot during init and
+    // sometimes ActivateSnapshot() at the beginning.
+}