There appears to be two different ways now to check for the mempool ancestors and descendants of the transaction here. I tried the following diff and the tests pass. Maybe we can remove the truc_child_in_mempool class member altogether in the future?
0diff --git a/src/wallet/spend.cpp b/src/wallet/spend.cpp
1index 5654c8f3d4..65c896892f 100644
2--- a/src/wallet/spend.cpp
3+++ b/src/wallet/spend.cpp
4@@ -401,16 +401,15 @@ CoinsResult AvailableCoins(const CWallet& wallet,
5 if (nDepth == 0 && params.check_version_trucness) {
6 if (coinControl->m_version == TRUC_VERSION) {
7 if (wtx.tx->version != TRUC_VERSION) continue;
8+ size_t ancestors, descendants;
9+ wallet.chain().getTransactionAncestry(wtx.tx->GetHash(), ancestors, descendants);
10 // this unconfirmed v3 transaction already has a child
11- if (wtx.truc_child_in_mempool.has_value()) continue;
12+ if (descendants > 1) continue;
13
14 // this unconfirmed v3 transaction has a parent: spending would create a third generation
15- size_t ancestors, descendants;
16- wallet.chain().getTransactionAncestry(wtx.tx->GetHash(), ancestors, descendants);
17 if (ancestors > 1) continue;
18 } else {
19 if (wtx.tx->version == TRUC_VERSION) continue;
20- Assume(!wtx.truc_child_in_mempool.has_value());
21 }
22 }
23
24diff --git a/src/wallet/transaction.h b/src/wallet/transaction.h
25index 1dbcdd2d92..7c97bb7f1a 100644
26--- a/src/wallet/transaction.h
27+++ b/src/wallet/transaction.h
28@@ -277,10 +277,6 @@ public:
29 // BlockConflicted.
30 std::set<Txid> mempool_conflicts;
31
32- // Track v3 mempool tx that spends from this tx
33- // so that we don't try to create another unconfirmed child
34- std::optional<Txid> truc_child_in_mempool;
35-
36 template<typename Stream>
37 void Serialize(Stream& s) const
38 {
39diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
40index d08d6782c1..ea1d78b310 100644
41--- a/src/wallet/wallet.cpp
42+++ b/src/wallet/wallet.cpp
43@@ -1398,7 +1398,6 @@ void CWallet::transactionAddedToMempool(const CTransactionRef& tx) {
44 if (parent_it != mapWallet.end()) {
45 CWalletTx& parent_wtx = parent_it->second;
46 if (parent_wtx.isUnconfirmed()) {
47- parent_wtx.truc_child_in_mempool = tx->GetHash();
48 // Even though these siblings do not spend the same utxos, they can't
49 // be present in the mempool at the same time because of TRUC policy rules
50 UpdateTrucSiblingConflicts(parent_wtx, txid, /*add_conflict=*/true);
51@@ -1460,16 +1459,11 @@ void CWallet::transactionRemovedFromMempool(const CTransactionRef& tx, MemPoolRe
52 }
53
54 if (tx->version == TRUC_VERSION) {
55- // If this tx has a parent, unset its truc_child_in_mempool to make it possible
56- // to spend from the parent again. If this tx was replaced by another
57- // child of the same parent, transactionAddedToMempool
58- // will update truc_child_in_mempool
59 for (const CTxIn& tx_in : tx->vin) {
60 auto parent_it = mapWallet.find(tx_in.prevout.hash);
61 if (parent_it != mapWallet.end()) {
62 CWalletTx& parent_wtx = parent_it->second;
63- if (parent_wtx.truc_child_in_mempool == tx->GetHash()) {
64- parent_wtx.truc_child_in_mempool = std::nullopt;
65+ if (parent_wtx.isUnconfirmed()) {
66 UpdateTrucSiblingConflicts(parent_wtx, txid, /*add_conflict=*/false);
67 }
68 }
