ido: garbage collect tracker entries of mempool txs that never confirm

Stamp mempool tracker entries with the negative of the highest known
block height instead of a fixed -1 sentinel, and trim on abs(height) so
entries whose tx is invalidated before confirming (e.g. by a double
spend) age out after TRACKER_MAX_BLOCK_DEPTH like confirmed ones. The
height is still replaced with the real one once the tx confirms.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/db/ido/mod.rs

@@ -903,8 +903,11 @@ async fn txchain_trim_tracker(
     pool: &SqlitePool,
     current_block_height: i64,
 ) -> Result<()> {
+    // A negative height marks a mempool entry stamped with the negative of the
+    // highest known block height when it was indexed (see index_mempool), so
+    // abs(height) is the entry's reference height in both cases.
     sqlx::query(
-        "DELETE FROM ido_txchain_tracker_map AS t0 WHERE t0.height < ? AND t0.height >= 0 AND NOT EXISTS (SELECT 1 FROM ido t1 WHERE t1.txchain_head = t0.txchain_id)",
+        "DELETE FROM ido_txchain_tracker_map AS t0 WHERE abs(t0.height) < ? AND NOT EXISTS (SELECT 1 FROM ido t1 WHERE t1.txchain_head = t0.txchain_id)",
     )
         .bind(current_block_height - TRACKER_MAX_BLOCK_DEPTH)
         .execute(pool)
@@ -2288,17 +2291,20 @@ pub async fn index_block(
     Ok(())
 }
 
-// Sentinel block height for txs indexed from the mempool. txchain_trim_tracker
-// never trims tracker entries with a negative height; the height is replaced
-// with the real one once the tx confirms in a block.
-const MEMPOOL_BLOCK_HEIGHT: i64 = -1;
-
 pub async fn index_mempool(
     network: Option<Network>,
     pool: &SqlitePool,
     sorted_txs: &[Transaction],
+    highest_known_block_height: u64,
 ) -> Result<()> {
-    index_txs(network, pool, sorted_txs, MEMPOOL_BLOCK_HEIGHT)
+    // Txs indexed from the mempool are stamped with the negative of the
+    // highest known block height, so txchain_trim_tracker can garbage collect
+    // entries that never confirm (e.g. invalidated by a double spend) once
+    // they pass TRACKER_MAX_BLOCK_DEPTH. The height is replaced with the real
+    // (positive) one once the tx confirms in a block. max(1) avoids storing 0,
+    // which would be indistinguishable from a confirmed height.
+    let mempool_height = -(highest_known_block_height.max(1) as i64);
+    index_txs(network, pool, sorted_txs, mempool_height)
         .await
 }
 

src/index.rs

@@ -193,6 +193,13 @@ pub async fn update_mempool(
     // ido updates
     let ido_electrum = electrum.clone();
 
+    // highest known block height; mempool tracker entries are stamped with its
+    // negative so ido's txchain_trim_tracker can age them out (see index_mempool)
+    let tip_electrum = electrum.clone();
+    let (_, tip_height) =
+        tokio::task::spawn_blocking(move || electrum_get_tip(&tip_electrum.lock().unwrap()))
+            .await??;
+
     // filter txs already in an ido txchain
     let mut ido_to_add = Vec::new();
     for txid in ido_txs {
@@ -219,7 +226,7 @@ pub async fn update_mempool(
 
     // an ido txchain can have several unconfirmed txs in flight; index parents first
     let txs_to_add = ttor_sorted_kahn(txs_to_add);
-    db::ido::index_mempool(network, &db.ido_w, &txs_to_add).await?;
+    db::ido::index_mempool(network, &db.ido_w, &txs_to_add, tip_height).await?;
 
     Ok(())
 }