opt: Tiebreak UTXOs by weight for CoinGrinder

src/wallet/coinselection.cpp

@@ -25,7 +25,7 @@ static util::Result<SelectionResult> ErrorMaxWeightExceeded()
                          "Please try sending a smaller amount or manually consolidating your wallet's UTXOs")};
 }
 
-// Descending order comparator
+// Sort by descending (effective) value prefer lower waste on tie
 struct {
     bool operator()(const OutputGroup& a, const OutputGroup& b) const
     {
@@ -37,6 +37,18 @@ struct {
     }
 } descending;
 
+// Sort by descending (effective) value prefer lower weight on tie
+struct {
+    bool operator()(const OutputGroup& a, const OutputGroup& b) const
+    {
+        if (a.GetSelectionAmount() == b.GetSelectionAmount()) {
+            // Sort lower weight to front on tied effective_value
+            return a.m_weight < b.m_weight;
+        }
+        return a.GetSelectionAmount() > b.GetSelectionAmount();
+    }
+} descending_effval_weight;
+
 /*
  * This is the Branch and Bound Coin Selection algorithm designed by Murch. It searches for an input
  * set that can pay for the spending target and does not exceed the spending target by more than the
@@ -236,7 +248,7 @@ util::Result<SelectionResult> CoinGrinder(std::vector<OutputGroup>& utxo_pool, c
     bool max_tx_weight_exceeded = false;
 
     // Sort the utxo_pool
-    std::sort(utxo_pool.begin(), utxo_pool.end(), descending);
+    std::sort(utxo_pool.begin(), utxo_pool.end(), descending_effval_weight);
     std::vector<CAmount> lookahead(utxo_pool.size());
 
     // Calculate lookahead and check that there are sufficient funds