wallet: Make CWalletTx "replaces_txid" and "replaced_by_txid" member variables

diff --git a/src/wallet/feebumper.cpp b/src/wallet/feebumper.cpp
index 84eb022e..bdb70742 100644
--- a/src/wallet/feebumper.cpp
+++ b/src/wallet/feebumper.cpp
@@ -41,8 +41,8 @@ static feebumper::Result PreconditionChecks(const CWallet& wallet, const CWallet
         return feebumper::Result::WALLET_ERROR;
     }
 
-    if (wtx.mapValue.contains("replaced_by_txid")) {
-        errors.push_back(Untranslated(strprintf("Cannot bump transaction %s which was already bumped by transaction %s", wtx.GetHash().ToString(), wtx.mapValue.at("replaced_by_txid"))));
+    if (wtx.m_replaced_by_txid) {
+        errors.push_back(Untranslated(strprintf("Cannot bump transaction %s which was already bumped by transaction %s", wtx.GetHash().ToString(), wtx.m_replaced_by_txid->ToString())));
         return feebumper::Result::WALLET_ERROR;
     }
 
diff --git a/src/wallet/rpc/transactions.cpp b/src/wallet/rpc/transactions.cpp
index 8d7b8019..6660bf87 100644
--- a/src/wallet/rpc/transactions.cpp
+++ b/src/wallet/rpc/transactions.cpp
@@ -64,6 +64,8 @@ static void WalletTxToJSON(const CWallet& wallet, const CWalletTx& wtx, UniValue
 
     if (wtx.m_comment) entry.pushKV("comment", *wtx.m_comment);
     if (wtx.m_comment_to) entry.pushKV("to", *wtx.m_comment_to);
+    if (wtx.m_replaces_txid) entry.pushKV("replaces_txid", wtx.m_replaces_txid->ToString());
+    if (wtx.m_replaced_by_txid) entry.pushKV("replaced_by_txid", wtx.m_replaced_by_txid->ToString());
 
     for (const std::pair<const std::string, std::string>& item : wtx.mapValue)
         entry.pushKV(item.first, item.second);
diff --git a/src/wallet/spend.cpp b/src/wallet/spend.cpp
index dba7b882..51247b55 100644
--- a/src/wallet/spend.cpp
+++ b/src/wallet/spend.cpp
@@ -378,7 +378,7 @@ CoinsResult AvailableCoins(const CWallet& wallet,
             // be a 1-block reorg away from the chain where transactions A and C
             // were accepted to another chain where B, B', and C were all
             // accepted.
-            if (nDepth == 0 && wtx.mapValue.contains("replaces_txid")) {
+            if (nDepth == 0 && wtx.m_replaces_txid) {
                 safeTx = false;
             }
 
@@ -390,7 +390,7 @@ CoinsResult AvailableCoins(const CWallet& wallet,
             // intending to replace A', but potentially resulting in a scenario
             // where A, A', and D could all be accepted (instead of just B and
             // D, or just A and A' like the user would want).
-            if (nDepth == 0 && wtx.mapValue.contains("replaced_by_txid")) {
+            if (nDepth == 0 && wtx.m_replaced_by_txid) {
                 safeTx = false;
             }
 
diff --git a/src/wallet/transaction.h b/src/wallet/transaction.h
index 5ea686b7..1fb14c40 100644
--- a/src/wallet/transaction.h
+++ b/src/wallet/transaction.h
@@ -202,17 +202,11 @@ public:
     // Comment strings provided by the user
     std::optional<std::string> m_comment;
     std::optional<std::string> m_comment_to;
+    std::optional<Txid> m_replaces_txid;
+    std::optional<Txid> m_replaced_by_txid;
     /**
      * Key/value map with information about the transaction.
      *
-     * The following keys can be read and written through the map and are
-     * serialized in the wallet database:
-     *
-     *     "replaces_txid"   - txid (as HexStr) of transaction replaced by
-     *                         bumpfee on transaction created by bumpfee
-     *     "replaced_by_txid" - txid (as HexStr) of transaction created by
-     *                         bumpfee on transaction replaced by bumpfee
-     *
      * The following keys are serialized in the wallet database, but shouldn't
      * be read or written through the map (they will be temporarily added and
      * removed from the map during serialization):
@@ -226,6 +220,10 @@ public:
      *                         2011 (removed in commit 4d9b223)
      *     "comment", "to"   - comment strings provided to sendtoaddress,
      *                         and sendmany wallet RPCs
+     *     "replaces_txid"   - txid (as HexStr) of transaction replaced by
+     *                         bumpfee on transaction created by bumpfee
+     *     "replaced_by_txid" - txid (as HexStr) of transaction created by
+     *                         bumpfee on transaction replaced by bumpfee
      */
     mapValue_t mapValue;
     std::vector<std::pair<std::string, std::string> > vOrderForm;
@@ -297,6 +295,8 @@ public:
         if (m_message) mapValueCopy["message"] = *m_message;
         if (m_comment) mapValueCopy["comment"] = *m_comment;
         if (m_comment_to) mapValueCopy["to"] = *m_comment_to;
+        if (m_replaces_txid) mapValueCopy["replaces_txid"] = m_replaces_txid->ToString();
+        if (m_replaced_by_txid) mapValueCopy["replaced_by_txid"] = m_replaced_by_txid->ToString();
 
         mapValueCopy["fromaccount"] = "";
         if (nOrderPos != -1) {
@@ -337,6 +337,8 @@ public:
             else if (key == "message") m_message = value;
             else if (key == "comment") m_comment = value;
             else if (key == "to") m_comment_to = value;
+            else if (key == "replaces_txid") m_replaces_txid = Txid::FromHex(value);
+            else if (key == "replaced_by_txid") m_replaced_by_txid = Txid::FromHex(value);
         }
 
         mapValue.erase("fromaccount");
@@ -347,6 +349,8 @@ public:
         mapValue.erase("message");
         mapValue.erase("comment");
         mapValue.erase("to");
+        mapValue.erase("replaces_txid");
+        mapValue.erase("replaced_by_txid");
     }
 
     void SetTx(CTransactionRef arg)
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index 095bb285..0fc9a9a3 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -746,6 +746,8 @@ void CWallet::SyncMetaData(std::pair<TxSpends::iterator, TxSpends::iterator> ran
         copyTo->m_message = copyFrom->m_message;
         copyTo->m_comment = copyFrom->m_comment;
         copyTo->m_comment_to = copyFrom->m_comment_to;
+        copyTo->m_replaces_txid = copyFrom->m_replaces_txid;
+        copyTo->m_replaced_by_txid = copyFrom->m_replaced_by_txid;
         copyTo->mapValue = copyFrom->mapValue;
         copyTo->vOrderForm = copyFrom->vOrderForm;
         // nTimeReceived not copied on purpose
@@ -985,9 +987,9 @@ bool CWallet::MarkReplaced(const Txid& originalHash, const Txid& newHash)
     CWalletTx& wtx = (*mi).second;
 
     // Ensure for now that we're not overwriting data
-    assert(!wtx.mapValue.contains("replaced_by_txid"));
+    Assert(!wtx.m_replaced_by_txid);
 
-    wtx.mapValue["replaced_by_txid"] = newHash.ToString();
+    wtx.m_replaced_by_txid = newHash;
 
     // Refresh mempool status without waiting for transactionRemovedFromMempool or transactionAddedToMempool
     RefreshMempoolStatus(wtx, chain());
@@ -2344,7 +2346,7 @@ void CWallet::CommitTransaction(
     CWalletTx* wtx = AddToWallet(tx, TxStateInactive{}, [&](CWalletTx& wtx, bool new_tx) {
         CHECK_NONFATAL(wtx.mapValue.empty());
         CHECK_NONFATAL(wtx.vOrderForm.empty());
-        if (replaces_txid) wtx.mapValue["replaces_txid"] = replaces_txid->ToString();
+        if (replaces_txid) wtx.m_replaces_txid = replaces_txid;
         if (comment) wtx.m_comment = comment;
         if (comment_to) wtx.m_comment_to = comment_to;
         wtx.vOrderForm = std::move(orderForm);