mempool, refactor: Convert uint256 to Txid

diff --git a/src/interfaces/chain.h b/src/interfaces/chain.h
index 56716ec6..82bfdb9f 100644
--- a/src/interfaces/chain.h
+++ b/src/interfaces/chain.h
@@ -211,7 +211,7 @@ public:
     virtual bool isInMempool(const Txid& txid) = 0;
 
     //! Check if transaction has descendants in mempool.
-    virtual bool hasDescendantsInMempool(const uint256& txid) = 0;
+    virtual bool hasDescendantsInMempool(const Txid& txid) = 0;
 
     //! Transaction is added to memory pool, if the transaction fee is below the
     //! amount specified by max_tx_fee, and broadcast to all peers if relay is set to true.
@@ -222,7 +222,7 @@ public:
         std::string& err_string) = 0;
 
     //! Calculate mempool ancestor and descendant counts for the given transaction.
-    virtual void getTransactionAncestry(const uint256& txid, size_t& ancestors, size_t& descendants, size_t* ancestorsize = nullptr, CAmount* ancestorfees = nullptr) = 0;
+    virtual void getTransactionAncestry(const Txid& txid, size_t& ancestors, size_t& descendants, size_t* ancestorsize = nullptr, CAmount* ancestorfees = nullptr) = 0;
 
     //! For each outpoint, calculate the fee-bumping cost to spend this outpoint at the specified
     //  feerate, including bumping its ancestors. For example, if the target feerate is 10sat/vbyte
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index ba919fac..546e14b8 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -1577,13 +1577,13 @@ void PeerManagerImpl::InitializeNode(const CNode& node, ServiceFlags our_service
 
 void PeerManagerImpl::ReattemptInitialBroadcast(CScheduler& scheduler)
 {
-    std::set<uint256> unbroadcast_txids = m_mempool.GetUnbroadcastTxs();
+    std::set<Txid> unbroadcast_txids = m_mempool.GetUnbroadcastTxs();
 
     for (const auto& txid : unbroadcast_txids) {
         CTransactionRef tx = m_mempool.get(txid);
 
         if (tx != nullptr) {
-            RelayTransaction(Txid::FromUint256(txid), tx->GetWitnessHash());
+            RelayTransaction(txid, tx->GetWitnessHash());
         } else {
             m_mempool.RemoveUnbroadcastTx(txid, true);
         }
diff --git a/src/node/interfaces.cpp b/src/node/interfaces.cpp
index 62172930..eeee4159 100644
--- a/src/node/interfaces.cpp
+++ b/src/node/interfaces.cpp
@@ -673,11 +673,11 @@ public:
         LOCK(m_node.mempool->cs);
         return m_node.mempool->exists(txid);
     }
-    bool hasDescendantsInMempool(const uint256& txid) override
+    bool hasDescendantsInMempool(const Txid& txid) override
     {
         if (!m_node.mempool) return false;
         LOCK(m_node.mempool->cs);
-        const auto entry{m_node.mempool->GetEntry(Txid::FromUint256(txid))};
+        const auto entry{m_node.mempool->GetEntry(txid)};
         if (entry == nullptr) return false;
         return entry->GetCountWithDescendants() > 1;
     }
@@ -692,7 +692,7 @@ public:
         // that Chain clients do not need to know about.
         return TransactionError::OK == err;
     }
-    void getTransactionAncestry(const uint256& txid, size_t& ancestors, size_t& descendants, size_t* ancestorsize, CAmount* ancestorfees) override
+    void getTransactionAncestry(const Txid& txid, size_t& ancestors, size_t& descendants, size_t* ancestorsize, CAmount* ancestorfees) override
     {
         ancestors = descendants = 0;
         if (!m_node.mempool) return;
diff --git a/src/node/mempool_persist.cpp b/src/node/mempool_persist.cpp
index 5b0f80be..19819a3a 100644
--- a/src/node/mempool_persist.cpp
+++ b/src/node/mempool_persist.cpp
@@ -122,7 +122,7 @@ bool LoadMempool(CTxMemPool& pool, const fs::path& load_path, Chainstate& active
             if (active_chainstate.m_chainman.m_interrupt)
                 return false;
         }
-        std::map<uint256, CAmount> mapDeltas;
+        std::map<Txid, CAmount> mapDeltas;
         file >> mapDeltas;
 
         if (opts.apply_fee_delta_priority) {
@@ -131,7 +131,7 @@ bool LoadMempool(CTxMemPool& pool, const fs::path& load_path, Chainstate& active
             }
         }
 
-        std::set<uint256> unbroadcast_txids;
+        std::set<Txid> unbroadcast_txids;
         file >> unbroadcast_txids;
         if (opts.apply_unbroadcast_set) {
             unbroadcast = unbroadcast_txids.size();
@@ -154,9 +154,9 @@ bool DumpMempool(const CTxMemPool& pool, const fs::path& dump_path, FopenFn mock
 {
     auto start = SteadyClock::now();
 
-    std::map<uint256, CAmount> mapDeltas;
+    std::map<Txid, CAmount> mapDeltas;
     std::vector<TxMempoolInfo> vinfo;
-    std::set<uint256> unbroadcast_txids;
+    std::set<Txid> unbroadcast_txids;
 
     static Mutex dump_mutex;
     LOCK(dump_mutex);
diff --git a/src/node/transaction.cpp b/src/node/transaction.cpp
index 9162557b..7bb92872 100644
--- a/src/node/transaction.cpp
+++ b/src/node/transaction.cpp
@@ -123,7 +123,7 @@ TransactionError BroadcastTransaction(NodeContext& node, const CTransactionRef t
     return TransactionError::OK;
 }
 
-CTransactionRef GetTransaction(const CBlockIndex* const block_index, const CTxMemPool* const mempool, const uint256& hash, uint256& hashBlock, const BlockManager& blockman)
+CTransactionRef GetTransaction(const CBlockIndex* const block_index, const CTxMemPool* const mempool, const Txid& hash, uint256& hashBlock, const BlockManager& blockman)
 {
     if (mempool && !block_index) {
         CTransactionRef ptx = mempool->get(hash);
diff --git a/src/node/transaction.h b/src/node/transaction.h
index 5f524f4e..2a411581 100644
--- a/src/node/transaction.h
+++ b/src/node/transaction.h
@@ -63,7 +63,7 @@ static const CAmount DEFAULT_MAX_BURN_AMOUNT{0};
  * @param[out] hashBlock       The block hash, if the tx was found via -txindex or block_index
  * @returns                    The tx if found, otherwise nullptr
  */
-CTransactionRef GetTransaction(const CBlockIndex* const block_index, const CTxMemPool* const mempool, const uint256& hash, uint256& hashBlock, const BlockManager& blockman);
+CTransactionRef GetTransaction(const CBlockIndex* const block_index, const CTxMemPool* const mempool, const Txid& hash, uint256& hashBlock, const BlockManager& blockman);
 } // namespace node
 
 #endif // BITCOIN_NODE_TRANSACTION_H
diff --git a/src/rest.cpp b/src/rest.cpp
index e32b4c38..7750bdc8 100644
--- a/src/rest.cpp
+++ b/src/rest.cpp
@@ -817,7 +817,7 @@ static bool rest_tx(const std::any& context, HTTPRequest* req, const std::string
     std::string hashStr;
     const RESTResponseFormat rf = ParseDataFormat(hashStr, uri_part);
 
-    auto hash{uint256::FromHex(hashStr)};
+    auto hash{Txid::FromHex(hashStr)};
     if (!hash) {
         return RESTERR(req, HTTP_BAD_REQUEST, "Invalid hash: " + hashStr);
     }
diff --git a/src/test/blockencodings_tests.cpp b/src/test/blockencodings_tests.cpp
index d40a0a94..b3d21096 100644
--- a/src/test/blockencodings_tests.cpp
+++ b/src/test/blockencodings_tests.cpp
@@ -154,7 +154,7 @@ BOOST_AUTO_TEST_CASE(NonCoinbasePreforwardRTTest)
     AddToMempool(pool, entry.FromTx(block.vtx[2]));
     BOOST_CHECK_EQUAL(pool.get(block.vtx[2]->GetHash()).use_count(), SHARED_TX_OFFSET + 0);
 
-    uint256 txhash;
+    Txid txhash;
 
     // Test with pre-forwarding tx 1, but not coinbase
     {
@@ -225,7 +225,7 @@ BOOST_AUTO_TEST_CASE(SufficientPreforwardRTTest)
     AddToMempool(pool, entry.FromTx(block.vtx[1]));
     BOOST_CHECK_EQUAL(pool.get(block.vtx[1]->GetHash()).use_count(), SHARED_TX_OFFSET + 0);
 
-    uint256 txhash;
+    Txid txhash;
 
     // Test with pre-forwarding coinbase + tx 2 with tx 1 in mempool
     {
diff --git a/src/test/fuzz/package_eval.cpp b/src/test/fuzz/package_eval.cpp
index aa73fcdd..23ea9d1f 100644
--- a/src/test/fuzz/package_eval.cpp
+++ b/src/test/fuzz/package_eval.cpp
@@ -314,7 +314,7 @@ FUZZ_TARGET(ephemeral_package_eval, .init = initialize_tx_pool)
             if (tx_pool.exists(txid)) {
                 const auto tx_info{tx_pool.info(txid)};
                 if (GetDust(*tx_info.tx, tx_pool.m_opts.dust_relay_feerate).empty()) {
-                    tx_pool.PrioritiseTransaction(txid.ToUint256(), delta);
+                    tx_pool.PrioritiseTransaction(txid, delta);
                 }
             }
         }
@@ -477,7 +477,7 @@ FUZZ_TARGET(tx_package_eval, .init = initialize_tx_pool)
                                    txs.back()->GetHash() :
                                    PickValue(fuzzed_data_provider, mempool_outpoints).hash;
             const auto delta = fuzzed_data_provider.ConsumeIntegralInRange<CAmount>(-50 * COIN, +50 * COIN);
-            tx_pool.PrioritiseTransaction(txid.ToUint256(), delta);
+            tx_pool.PrioritiseTransaction(txid, delta);
         }
 
         // Remember all added transactions
diff --git a/src/test/fuzz/rbf.cpp b/src/test/fuzz/rbf.cpp
index db8682e2..300f31d4 100644
--- a/src/test/fuzz/rbf.cpp
+++ b/src/test/fuzz/rbf.cpp
@@ -160,7 +160,7 @@ FUZZ_TARGET(package_rbf, .init = initialize_package_rbf)
         }
 
         if (fuzzed_data_provider.ConsumeBool()) {
-            pool.PrioritiseTransaction(mempool_txs.back().GetHash().ToUint256(), fuzzed_data_provider.ConsumeIntegralInRange<int32_t>(-100000, 100000));
+            pool.PrioritiseTransaction(mempool_txs.back().GetHash(), fuzzed_data_provider.ConsumeIntegralInRange<int32_t>(-100000, 100000));
         }
     }
 
diff --git a/src/test/fuzz/tx_pool.cpp b/src/test/fuzz/tx_pool.cpp
index ea65700c..4245d3e1 100644
--- a/src/test/fuzz/tx_pool.cpp
+++ b/src/test/fuzz/tx_pool.cpp
@@ -288,7 +288,7 @@ FUZZ_TARGET(tx_pool_standard, .init = initialize_tx_pool)
                                    tx->GetHash() :
                                    PickValue(fuzzed_data_provider, outpoints_rbf).hash;
             const auto delta = fuzzed_data_provider.ConsumeIntegralInRange<CAmount>(-50 * COIN, +50 * COIN);
-            tx_pool.PrioritiseTransaction(txid.ToUint256(), delta);
+            tx_pool.PrioritiseTransaction(txid, delta);
         }
 
         // Remember all removed and added transactions
@@ -409,7 +409,7 @@ FUZZ_TARGET(tx_pool, .init = initialize_tx_pool)
                                    mut_tx.GetHash() :
                                    PickValue(fuzzed_data_provider, txids);
             const auto delta = fuzzed_data_provider.ConsumeIntegralInRange<CAmount>(-50 * COIN, +50 * COIN);
-            tx_pool.PrioritiseTransaction(txid.ToUint256(), delta);
+            tx_pool.PrioritiseTransaction(txid, delta);
         }
 
         const auto tx = MakeTransactionRef(mut_tx);
diff --git a/src/test/miner_tests.cpp b/src/test/miner_tests.cpp
index 9207f1bf..ffdf7a4d 100644
--- a/src/test/miner_tests.cpp
+++ b/src/test/miner_tests.cpp
@@ -596,7 +596,7 @@ void MinerTestingSetup::TestPrioritisedMining(const CScript& scriptPubKey, const
     tx.vin[0].scriptSig = CScript() << OP_1;
     tx.vout.resize(1);
     tx.vout[0].nValue = 5000000000LL; // 0 fee
-    uint256 hashFreePrioritisedTx = tx.GetHash();
+    Txid hashFreePrioritisedTx = tx.GetHash();
     AddToMempool(tx_mempool, entry.Fee(0).Time(Now<NodeSeconds>()).SpendsCoinbase(true).FromTx(tx));
     tx_mempool.PrioritiseTransaction(hashFreePrioritisedTx, 5 * COIN);
 
diff --git a/src/test/policyestimator_tests.cpp b/src/test/policyestimator_tests.cpp
index f767cd42..bbdd815f 100644
--- a/src/test/policyestimator_tests.cpp
+++ b/src/test/policyestimator_tests.cpp
@@ -37,7 +37,7 @@ BOOST_AUTO_TEST_CASE(BlockPolicyEstimates)
     // added to the mempool by their associate fee
     // txHashes[j] is populated with transactions either of
     // fee = basefee * (j+1)
-    std::vector<uint256> txHashes[10];
+    std::vector<Txid> txHashes[10];
 
     // Create a transaction template
     CScript garbage;
@@ -77,8 +77,7 @@ BOOST_AUTO_TEST_CASE(BlockPolicyEstimates)
                                                                                       /*has_no_mempool_parents=*/true)};
                     m_node.validation_signals->TransactionAddedToMempool(tx_info, mpool.GetAndIncrementSequence());
                 }
-                uint256 hash = tx.GetHash();
-                txHashes[j].push_back(hash);
+                txHashes[j].push_back(tx.GetHash());
             }
         }
         //Create blocks where higher fee txs are included more often
@@ -178,8 +177,7 @@ BOOST_AUTO_TEST_CASE(BlockPolicyEstimates)
                                                                                       /*has_no_mempool_parents=*/true)};
                     m_node.validation_signals->TransactionAddedToMempool(tx_info, mpool.GetAndIncrementSequence());
                 }
-                uint256 hash = tx.GetHash();
-                txHashes[j].push_back(hash);
+                txHashes[j].push_back(tx.GetHash());
             }
         }
         {
@@ -242,8 +240,7 @@ BOOST_AUTO_TEST_CASE(BlockPolicyEstimates)
                                                                                       /*has_no_mempool_parents=*/true)};
                     m_node.validation_signals->TransactionAddedToMempool(tx_info, mpool.GetAndIncrementSequence());
                 }
-                uint256 hash = tx.GetHash();
-                CTransactionRef ptx = mpool.get(hash);
+                CTransactionRef ptx = mpool.get(tx.GetHash());
                 if (ptx)
                     block.push_back(ptx);
 
diff --git a/src/txmempool.cpp b/src/txmempool.cpp
index d19d0a47..6bb910e3 100644
--- a/src/txmempool.cpp
+++ b/src/txmempool.cpp
@@ -55,7 +55,7 @@ bool TestLockPointValidity(CChain& active_chain, const LockPoints& lp)
 }
 
 void CTxMemPool::UpdateForDescendants(txiter updateIt, cacheMap& cachedDescendants,
-                                      const std::set<uint256>& setExclude, std::set<uint256>& descendants_to_remove)
+                                      const std::set<Txid>& setExclude, std::set<Txid>& descendants_to_remove)
 {
     CTxMemPoolEntry::Children stageEntries, descendants;
     stageEntries = updateIt->GetMemPoolChildrenConst();
@@ -105,7 +105,7 @@ void CTxMemPool::UpdateForDescendants(txiter updateIt, cacheMap& cachedDescendan
     mapTx.modify(updateIt, [=](CTxMemPoolEntry& e) { e.UpdateDescendantState(modifySize, modifyFee, modifyCount); });
 }
 
-void CTxMemPool::UpdateTransactionsFromBlock(const std::vector<uint256>& vHashesToUpdate)
+void CTxMemPool::UpdateTransactionsFromBlock(const std::vector<Txid>& vHashesToUpdate)
 {
     AssertLockHeld(cs);
     // For each entry in vHashesToUpdate, store the set of in-mempool, but not
@@ -115,29 +115,29 @@ void CTxMemPool::UpdateTransactionsFromBlock(const std::vector<uint256>& vHashes
 
     // Use a set for lookups into vHashesToUpdate (these entries are already
     // accounted for in the state of their ancestors)
-    std::set<uint256> setAlreadyIncluded(vHashesToUpdate.begin(), vHashesToUpdate.end());
+    std::set<Txid> setAlreadyIncluded(vHashesToUpdate.begin(), vHashesToUpdate.end());
 
-    std::set<uint256> descendants_to_remove;
+    std::set<Txid> descendants_to_remove;
 
     // Iterate in reverse, so that whenever we are looking at a transaction
     // we are sure that all in-mempool descendants have already been processed.
     // This maximizes the benefit of the descendant cache and guarantees that
     // CTxMemPoolEntry::m_children will be updated, an assumption made in
     // UpdateForDescendants.
-    for (const uint256& hash : vHashesToUpdate | std::views::reverse) {
+    for (const Txid& hash : vHashesToUpdate | std::views::reverse) {
         // calculate children from mapNextTx
         txiter it = mapTx.find(hash);
         if (it == mapTx.end()) {
             continue;
         }
-        auto iter = mapNextTx.lower_bound(COutPoint(Txid::FromUint256(hash), 0));
+        auto iter = mapNextTx.lower_bound(COutPoint(hash, 0));
         // First calculate the children, and update CTxMemPoolEntry::m_children to
         // include them, and update their CTxMemPoolEntry::m_parents to include this tx.
         // we cache the in-mempool children to avoid duplicate updates
         {
             WITH_FRESH_EPOCH(m_epoch);
             for (; iter != mapNextTx.end() && iter->first->hash == hash; ++iter) {
-                const uint256 &childHash = iter->second->GetHash();
+                const Txid &childHash = iter->second->GetHash();
                 txiter childIter = mapTx.find(childHash);
                 assert(childIter != mapTx.end());
                 // We can skip updating entries we've encountered before or that
@@ -154,7 +154,7 @@ void CTxMemPool::UpdateTransactionsFromBlock(const std::vector<uint256>& vHashes
     for (const auto& txid : descendants_to_remove) {
         // This txid may have been removed already in a prior call to removeRecursive.
         // Therefore we ensure it is not yet removed already.
-        if (const std::optional<txiter> txiter = GetIter(Txid::FromUint256(txid))) {
+        if (const std::optional<txiter> txiter = GetIter(txid)) {
             removeRecursive((*txiter)->GetTx(), MemPoolRemovalReason::SIZELIMIT);
         }
     }
@@ -780,12 +780,11 @@ void CTxMemPool::check(const CCoinsViewCache& active_coins_tip, int64_t spendhei
         for (const auto& input: tx.vin) mempoolDuplicate.SpendCoin(input.prevout);
         AddCoins(mempoolDuplicate, tx, std::numeric_limits<int>::max());
     }
-    for (auto it = mapNextTx.cbegin(); it != mapNextTx.cend(); it++) {
-        uint256 hash = it->second->GetHash();
-        indexed_transaction_set::const_iterator it2 = mapTx.find(hash);
-        const CTransaction& tx = it2->GetTx();
-        assert(it2 != mapTx.end());
-        assert(&tx == it->second);
+    for (const auto& [_, next_tx] : mapNextTx) {
+        auto it = mapTx.find(next_tx->GetHash());
+        const CTransaction& tx = it->GetTx();
+        assert(it != mapTx.end());
+        assert(&tx == next_tx);
     }
 
     assert(totalTxSize == checkTotal);
@@ -876,7 +875,7 @@ const CTxMemPoolEntry* CTxMemPool::GetEntry(const Txid& txid) const
     return i == mapTx.end() ? nullptr : &(*i);
 }
 
-CTransactionRef CTxMemPool::get(const uint256& hash) const
+CTransactionRef CTxMemPool::get(const Txid& hash) const
 {
     LOCK(cs);
     indexed_transaction_set::const_iterator i = mapTx.find(hash);
@@ -885,7 +884,7 @@ CTransactionRef CTxMemPool::get(const uint256& hash) const
     return i->GetSharedTx();
 }
 
-void CTxMemPool::PrioritiseTransaction(const uint256& hash, const CAmount& nFeeDelta)
+void CTxMemPool::PrioritiseTransaction(const Txid& hash, const CAmount& nFeeDelta)
 {
     {
         LOCK(cs);
@@ -921,17 +920,17 @@ void CTxMemPool::PrioritiseTransaction(const uint256& hash, const CAmount& nFeeD
     }
 }
 
-void CTxMemPool::ApplyDelta(const uint256& hash, CAmount &nFeeDelta) const
+void CTxMemPool::ApplyDelta(const Txid& hash, CAmount &nFeeDelta) const
 {
     AssertLockHeld(cs);
-    std::map<uint256, CAmount>::const_iterator pos = mapDeltas.find(hash);
+    std::map<Txid, CAmount>::const_iterator pos = mapDeltas.find(hash);
     if (pos == mapDeltas.end())
         return;
     const CAmount &delta = pos->second;
     nFeeDelta += delta;
 }
 
-void CTxMemPool::ClearPrioritisation(const uint256& hash)
+void CTxMemPool::ClearPrioritisation(const Txid& hash)
 {
     AssertLockHeld(cs);
     mapDeltas.erase(hash);
@@ -962,7 +961,7 @@ const CTransaction* CTxMemPool::GetConflictTx(const COutPoint& prevout) const
 std::optional<CTxMemPool::txiter> CTxMemPool::GetIter(const Txid& txid) const
 {
     AssertLockHeld(cs);
-    auto it = mapTx.find(txid.ToUint256());
+    auto it = mapTx.find(txid);
     return it != mapTx.end() ? std::make_optional(it) : std::nullopt;
 }
 
@@ -1048,7 +1047,7 @@ size_t CTxMemPool::DynamicMemoryUsage() const {
     return memusage::MallocUsage(sizeof(CTxMemPoolEntry) + 15 * sizeof(void*)) * mapTx.size() + memusage::DynamicUsage(mapNextTx) + memusage::DynamicUsage(mapDeltas) + memusage::DynamicUsage(txns_randomized) + cachedInnerUsage;
 }
 
-void CTxMemPool::RemoveUnbroadcastTx(const uint256& txid, const bool unchecked) {
+void CTxMemPool::RemoveUnbroadcastTx(const Txid& txid, const bool unchecked) {
     LOCK(cs);
 
     if (m_unbroadcast_txids.erase(txid))
@@ -1203,7 +1202,7 @@ uint64_t CTxMemPool::CalculateDescendantMaximum(txiter entry) const {
     return maximum;
 }
 
-void CTxMemPool::GetTransactionAncestry(const uint256& txid, size_t& ancestors, size_t& descendants, size_t* const ancestorsize, CAmount* const ancestorfees) const {
+void CTxMemPool::GetTransactionAncestry(const Txid& txid, size_t& ancestors, size_t& descendants, size_t* const ancestorsize, CAmount* const ancestorfees) const {
     LOCK(cs);
     auto it = mapTx.find(txid);
     ancestors = descendants = 0;
diff --git a/src/txmempool.h b/src/txmempool.h
index 048ad23f..8b55d9cd 100644
--- a/src/txmempool.h
+++ b/src/txmempool.h
@@ -57,7 +57,7 @@ bool TestLockPointValidity(CChain& active_chain, const LockPoints& lp) EXCLUSIVE
 // extracts a transaction hash from CTxMemPoolEntry or CTransactionRef
 struct mempoolentry_txid
 {
-    typedef uint256 result_type;
+    typedef Txid result_type;
     result_type operator() (const CTxMemPoolEntry &entry) const
     {
         return entry.GetTx().GetHash();
@@ -72,7 +72,7 @@ struct mempoolentry_txid
 // extracts a transaction witness-hash from CTxMemPoolEntry or CTransactionRef
 struct mempoolentry_wtxid
 {
-    typedef uint256 result_type;
+    typedef Wtxid result_type;
     result_type operator() (const CTxMemPoolEntry &entry) const
     {
         return entry.GetTx().GetWitnessHash();
@@ -387,7 +387,7 @@ private:
     /**
      * Track locally submitted transactions to periodically retry initial broadcast.
      */
-    std::set<uint256> m_unbroadcast_txids GUARDED_BY(cs);
+    std::set<Txid> m_unbroadcast_txids GUARDED_BY(cs);
 
 
     /**
@@ -414,7 +414,7 @@ private:
 
 public:
     indirectmap<COutPoint, const CTransaction*> mapNextTx GUARDED_BY(cs);
-    std::map<uint256, CAmount> mapDeltas GUARDED_BY(cs);
+    std::map<Txid, CAmount> mapDeltas GUARDED_BY(cs);
 
     using Options = kernel::MemPoolOptions;
 
@@ -459,9 +459,9 @@ public:
     bool HasNoInputsOf(const CTransaction& tx) const EXCLUSIVE_LOCKS_REQUIRED(cs);
 
     /** Affect CreateNewBlock prioritisation of transactions */
-    void PrioritiseTransaction(const uint256& hash, const CAmount& nFeeDelta);
-    void ApplyDelta(const uint256& hash, CAmount &nFeeDelta) const EXCLUSIVE_LOCKS_REQUIRED(cs);
-    void ClearPrioritisation(const uint256& hash) EXCLUSIVE_LOCKS_REQUIRED(cs);
+    void PrioritiseTransaction(const Txid& hash, const CAmount& nFeeDelta);
+    void ApplyDelta(const Txid& hash, CAmount &nFeeDelta) const EXCLUSIVE_LOCKS_REQUIRED(cs);
+    void ClearPrioritisation(const Txid& hash) EXCLUSIVE_LOCKS_REQUIRED(cs);
 
     struct delta_info {
         /** Whether this transaction is in the mempool. */
@@ -471,7 +471,7 @@ public:
         /** The modified fee (base fee + delta) of this entry. Only present if in_mempool=true. */
         std::optional<CAmount> modified_fee;
         /** The prioritised transaction's txid. */
-        const uint256 txid;
+        const Txid txid;
     };
     /** Return a vector of all entries in mapDeltas with their corresponding delta_info. */
     std::vector<delta_info> GetPrioritisedTransactions() const EXCLUSIVE_LOCKS_REQUIRED(!cs);
@@ -506,7 +506,7 @@ public:
      * @param[in] vHashesToUpdate          The set of txids from the
      *     disconnected block that have been accepted back into the mempool.
      */
-    void UpdateTransactionsFromBlock(const std::vector<uint256>& vHashesToUpdate) EXCLUSIVE_LOCKS_REQUIRED(cs, cs_main) LOCKS_EXCLUDED(m_epoch);
+    void UpdateTransactionsFromBlock(const std::vector<Txid>& vHashesToUpdate) EXCLUSIVE_LOCKS_REQUIRED(cs, cs_main) LOCKS_EXCLUDED(m_epoch);
 
     /**
      * Try to calculate all in-mempool ancestors of entry.
@@ -595,7 +595,7 @@ public:
      * When ancestors is non-zero (ie, the transaction itself is in the mempool),
      * ancestorsize and ancestorfees will also be set to the appropriate values.
      */
-    void GetTransactionAncestry(const uint256& txid, size_t& ancestors, size_t& descendants, size_t* ancestorsize = nullptr, CAmount* ancestorfees = nullptr) const;
+    void GetTransactionAncestry(const Txid& txid, size_t& ancestors, size_t& descendants, size_t* ancestorsize = nullptr, CAmount* ancestorfees = nullptr) const;
 
     /**
      * @returns true if an initial attempt to load the persisted mempool was made, regardless of
@@ -641,7 +641,7 @@ public:
 
     const CTxMemPoolEntry* GetEntry(const Txid& txid) const LIFETIMEBOUND EXCLUSIVE_LOCKS_REQUIRED(cs);
 
-    CTransactionRef get(const uint256& hash) const;
+    CTransactionRef get(const Txid& hash) const;
 
     template <TxidOrWtxid T>
     TxMempoolInfo info(const T& id) const
@@ -666,26 +666,26 @@ public:
     size_t DynamicMemoryUsage() const;
 
     /** Adds a transaction to the unbroadcast set */
-    void AddUnbroadcastTx(const uint256& txid)
+    void AddUnbroadcastTx(const Txid& txid)
     {
         LOCK(cs);
         // Sanity check the transaction is in the mempool & insert into
         // unbroadcast set.
-        if (exists(Txid::FromUint256(txid))) m_unbroadcast_txids.insert(txid);
+        if (exists(txid)) m_unbroadcast_txids.insert(txid);
     };
 
     /** Removes a transaction from the unbroadcast set */
-    void RemoveUnbroadcastTx(const uint256& txid, const bool unchecked = false);
+    void RemoveUnbroadcastTx(const Txid& txid, const bool unchecked = false);
 
     /** Returns transactions in unbroadcast set */
-    std::set<uint256> GetUnbroadcastTxs() const
+    std::set<Txid> GetUnbroadcastTxs() const
     {
         LOCK(cs);
         return m_unbroadcast_txids;
     }
 
     /** Returns whether a txid is in the unbroadcast set */
-    bool IsUnbroadcastTx(const uint256& txid) const EXCLUSIVE_LOCKS_REQUIRED(cs)
+    bool IsUnbroadcastTx(const Txid& txid) const EXCLUSIVE_LOCKS_REQUIRED(cs)
     {
         AssertLockHeld(cs);
         return m_unbroadcast_txids.count(txid) != 0;
@@ -744,7 +744,7 @@ private:
      *     removeRecursive them.
      */
     void UpdateForDescendants(txiter updateIt, cacheMap& cachedDescendants,
-                              const std::set<uint256>& setExclude, std::set<uint256>& descendants_to_remove) EXCLUSIVE_LOCKS_REQUIRED(cs);
+                              const std::set<Txid>& setExclude, std::set<Txid>& descendants_to_remove) EXCLUSIVE_LOCKS_REQUIRED(cs);
     /** Update ancestors of hash to add/remove it as a descendant transaction. */
     void UpdateAncestorsOf(bool add, txiter hash, setEntries &setAncestors) EXCLUSIVE_LOCKS_REQUIRED(cs);
     /** Set ancestor state for an entry */
diff --git a/src/validation.cpp b/src/validation.cpp
index 90e70834..69cc84bb 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -303,7 +303,7 @@ void Chainstate::MaybeUpdateMempoolForReorg(
 
     AssertLockHeld(cs_main);
     AssertLockHeld(m_mempool->cs);
-    std::vector<uint256> vHashUpdate;
+    std::vector<Txid> vHashUpdate;
     {
         // disconnectpool is ordered so that the front is the most recently-confirmed
         // transaction (the last tx of the block at the tip) in the disconnected chain.