Re-introduce nInstantSendKeepLock check for LLMQ-based IS when spork19 is OFF

src/dsnotificationinterface.cpp

@@ -60,6 +60,7 @@ void CDSNotificationInterface::UpdatedBlockTip(const CBlockIndex *pindexNew, con
     if (fLiteMode)
         return;
 
+    llmq::quorumInstantSendManager->UpdatedBlockTip(pindexNew);
     llmq::chainLocksHandler->UpdatedBlockTip(pindexNew, pindexFork);
 
     CPrivateSend::UpdatedBlockTip(pindexNew);

src/llmq/quorums_instantsend.cpp

@@ -798,6 +798,23 @@ void CInstantSendManager::NotifyChainLock(const CBlockIndex* pindexChainLock)
     RetryLockTxs(uint256());
 }
 
+void CInstantSendManager::UpdatedBlockTip(const CBlockIndex* pindexNew)
+{
+    if (sporkManager.IsSporkActive(SPORK_19_CHAINLOCKS_ENABLED)) {
+        // Nothing to do here. We should keep all islocks and let chainlocks handle them.
+        return;
+    }
+
+    int nChainLockMinHeight = pindexNew->nHeight - Params().GetConsensus().nInstantSendKeepLock;
+    const CBlockIndex* pindex = pindexNew->GetAncestor(nChainLockMinHeight);
+
+    if (pindex) {
+        // Pretend it was chainlocked at nChainLockMinHeight.
+        // This effectively drops all islocks below nChainLockMinHeight.
+        NotifyChainLock(pindex);
+    }
+}
+
 void CInstantSendManager::RemoveFinalISLock(const uint256& hash, const CInstantSendLockPtr& islock)
 {
     AssertLockHeld(cs);

src/llmq/quorums_instantsend.h

@@ -122,6 +122,7 @@ class CInstantSendManager : public CRecoveredSigsListener
 
     void SyncTransaction(const CTransaction &tx, const CBlockIndex *pindex, int posInBlock);
     void NotifyChainLock(const CBlockIndex* pindexChainLock);
+    void UpdatedBlockTip(const CBlockIndex* pindexNew);
     void RemoveFinalISLock(const uint256& hash, const CInstantSendLockPtr& islock);
 
     void RemoveMempoolConflictsForLock(const uint256& hash, const CInstantSendLock& islock);