mempool: fix recommended fees

crates/brk_mempool/src/entry_pool.rs

@@ -34,6 +34,12 @@ impl EntryPool {
         idx
     }
 
+    /// Get an entry by its txid prefix.
+    pub fn get(&self, prefix: &TxidPrefix) -> Option<&Entry> {
+        let idx = self.prefix_to_idx.get(prefix)?;
+        self.entries.get(idx.as_usize())?.as_ref()
+    }
+
     /// Remove an entry by its txid prefix.
     pub fn remove(&mut self, prefix: &TxidPrefix) {
         if let Some(idx) = self.prefix_to_idx.remove(prefix) {

crates/brk_mempool/src/sync.rs

@@ -173,7 +173,9 @@ impl MempoolInner {
                 let tx = tx_with_hex.tx();
                 let prefix = TxidPrefix::from(txid);
 
-                info.remove(tx);
+                // Get fee from entries (before removing) - this is the authoritative fee from Bitcoin Core
+                let fee = entries.get(&prefix).map(|e| e.fee).unwrap_or_default();
+                info.remove(tx, fee);
                 addresses.remove_tx(tx, txid);
                 entries.remove(&prefix);
             },
@@ -188,7 +190,7 @@ impl MempoolInner {
                 continue;
             };
 
-            info.add(tx);
+            info.add(tx, entry_info.fee);
             addresses.add_tx(tx, txid);
             entries.insert(prefix, Entry::from_info(entry_info));
         }

crates/brk_types/src/mempoolinfo.rs

@@ -15,19 +15,25 @@ pub struct MempoolInfo {
 }
 
 impl MempoolInfo {
-    /// Increment stats for a newly added transaction
+    /// Increment stats for a newly added transaction.
+    ///
+    /// Fee must come from `MempoolEntryInfo` (Bitcoin Core) rather than `tx.fee`
+    /// because `tx.fee` may be 0 for chained mempool transactions where prevouts
+    /// cannot be looked up via `gettxout`.
     #[inline]
-    pub fn add(&mut self, tx: &Transaction) {
+    pub fn add(&mut self, tx: &Transaction, fee: Sats) {
         self.count += 1;
         self.vsize += tx.vsize();
-        self.total_fee += tx.fee;
+        self.total_fee += fee;
     }
 
-    /// Decrement stats for a removed transaction
+    /// Decrement stats for a removed transaction.
+    ///
+    /// Fee must match the fee used when the transaction was added.
     #[inline]
-    pub fn remove(&mut self, tx: &Transaction) {
+    pub fn remove(&mut self, tx: &Transaction, fee: Sats) {
         self.count -= 1;
         self.vsize -= tx.vsize();
-        self.total_fee -= tx.fee;
+        self.total_fee -= fee;
     }
 }