fix(dash-spv): rescan committed filter ranges for newly derived scripts

dash-spv/src/storage/filters.rs

@@ -21,6 +21,9 @@ pub trait FilterStorage: Send + Sync + 'static {
 
     async fn filter_tip_height(&self) -> StorageResult<u32>;
 
+    /// Lowest height with a stored filter, or `None` when no filters are stored.
+    async fn filter_start_height(&self) -> Option<u32>;
+
     /// Drop all filters with `height > target_height`.
     ///
     /// Truncating above the current tip is a no-op, truncating below
@@ -79,6 +82,10 @@ impl FilterStorage for PersistentFilterStorage {
         Ok(self.filters.read().await.tip_height().unwrap_or(0))
     }
 
+    async fn filter_start_height(&self) -> Option<u32> {
+        self.filters.read().await.start_height()
+    }
+
     async fn truncate_above(&mut self, target_height: u32) -> StorageResult<()> {
         self.filters.write().await.truncate_above(target_height).await
     }

dash-spv/src/storage/mod.rs

@@ -375,6 +375,10 @@ impl filters::FilterStorage for DiskStorageManager {
         self.filters.read().await.filter_tip_height().await
     }
 
+    async fn filter_start_height(&self) -> Option<u32> {
+        self.filters.read().await.filter_start_height().await
+    }
+
     async fn truncate_above(&mut self, target_height: u32) -> StorageResult<()> {
         self.filters.write().await.truncate_above(target_height).await
     }

dash-spv/src/sync/filters/batch.rs

@@ -32,6 +32,12 @@ pub(super) struct FiltersBatch {
     /// need rescan, attributed per wallet so we can rerun matching only
     /// against the wallet that produced each new script.
     collected_scripts: HashMap<WalletId, HashSet<ScriptBuf>>,
+    /// Scripts already forward-rescanned but still awaiting the one combined
+    /// backward sweep over the committed range (#846). Accumulated across
+    /// fixpoint rounds so each script crosses the stored history exactly
+    /// once, instead of the whole history being reloaded per derivation
+    /// round.
+    backward_scripts: HashMap<WalletId, HashSet<ScriptBuf>>,
 }
 
 impl FiltersBatch {
@@ -51,6 +57,7 @@ impl FiltersBatch {
             rescan_complete: false,
             scanned_wallets: BTreeSet::new(),
             collected_scripts: HashMap::new(),
+            backward_scripts: HashMap::new(),
         }
     }
     /// Start height of this batch (inclusive).
@@ -118,6 +125,21 @@ impl FiltersBatch {
     pub(super) fn take_collected_scripts(&mut self) -> HashMap<WalletId, HashSet<ScriptBuf>> {
         std::mem::take(&mut self.collected_scripts)
     }
+    /// Queue already forward-rescanned scripts for the deferred backward
+    /// sweep over the committed range.
+    pub(super) fn accumulate_backward_scripts(
+        &mut self,
+        scripts: HashMap<WalletId, HashSet<ScriptBuf>>,
+    ) {
+        for (wallet_id, scripts) in scripts {
+            self.backward_scripts.entry(wallet_id).or_default().extend(scripts);
+        }
+    }
+    /// Take the scripts accumulated for the backward sweep, leaving the map
+    /// empty.
+    pub(super) fn take_backward_scripts(&mut self) -> HashMap<WalletId, HashSet<ScriptBuf>> {
+        std::mem::take(&mut self.backward_scripts)
+    }
     /// Record the set of wallets that were behind for this batch at scan time.
     pub(super) fn set_scanned_wallets(&mut self, wallets: BTreeSet<WalletId>) {
         self.scanned_wallets = wallets;