chain(fix): conflict resolution for txs with same last_seen

Author: LagginTimes

crates/chain/src/tx_graph.rs

@@ -790,6 +790,23 @@ impl<A: Anchor> TxGraph<A> {
                     return Ok(None);
                 }
             }
+            if conflicting_tx.last_seen_unconfirmed == *last_seen {
+                // Check if conflicting tx has higher absolute fee and fee rate
+                if let (Ok(fee), Ok(conflicting_fee)) =
+                    (self.calculate_fee(tx), self.calculate_fee(&conflicting_tx))
+                {
+                    let fee_rate = fee as f32 / tx.weight().to_vbytes_ceil() as f32;
+                    let conflicting_fee_rate =
+                        conflicting_fee as f32 / conflicting_tx.weight().to_vbytes_ceil() as f32;
+                    if conflicting_fee > fee && conflicting_fee_rate > fee_rate {
+                        return Ok(None);
+                    }
+                } else if conflicting_tx.txid() > tx.txid() {
+                    // If fee rates cannot be distinguished, then conflicting tx has priority if
+                    // txid of conflicting tx > txid of original tx
+                    return Ok(None);
+                }
+            }
         }
 
         Ok(Some(ChainPosition::Unconfirmed(*last_seen)))