fix: separate book delta and snapshot clocks

src/book.rs

@@ -158,10 +158,23 @@ pub struct OrderBook {
     /// Hash of token_id for fast lookups (avoids string comparisons in hot path)
     pub token_id_hash: u64,
 
-    /// Current sequence number for ordering updates
-    /// This helps us ignore old/duplicate updates that arrive out of order
+    /// Legacy delta sequence number.
+    ///
+    /// Kept as a compatibility alias for [`Self::last_delta_sequence`]. WebSocket
+    /// snapshot timestamps are tracked separately in [`Self::last_snapshot_timestamp_ms`].
     pub sequence: u64,
 
+    /// Last accepted legacy/incremental delta sequence number.
+    ///
+    /// Delta sequences are a different clock from WebSocket snapshot timestamps and
+    /// must not be compared against millisecond timestamps.
+    pub last_delta_sequence: u64,
+
+    /// Last accepted full-book snapshot timestamp in milliseconds.
+    ///
+    /// Used for WebSocket `book` snapshots and serde `BookUpdate` snapshots.
+    pub last_snapshot_timestamp_ms: u64,
+
     /// Last update timestamp - when we last got new data for this book
     pub timestamp: chrono::DateTime<Utc>,
 
@@ -222,7 +235,9 @@ impl OrderBook {
         Self {
             token_id,
             token_id_hash,
-            sequence: 0, // Start at 0, will increment as we get updates
+            sequence: 0, // Legacy alias for last_delta_sequence
+            last_delta_sequence: 0,
+            last_snapshot_timestamp_ms: 0,
             timestamp: Utc::now(),
             bids: BookSide::new(BookSideKind::Bid, max_depth), // Empty to start
             asks: BookSide::new(BookSideKind::Ask, max_depth), // Empty to start
@@ -430,7 +445,7 @@ impl OrderBook {
             timestamp: self.timestamp,
             bids: self.bids(None), // Get all bids (up to max_depth)
             asks: self.asks(None), // Get all asks (up to max_depth)
-            sequence: self.sequence,
+            sequence: self.last_delta_sequence,
         }
     }
 
@@ -461,11 +476,11 @@ impl OrderBook {
     pub fn apply_delta_fast(&mut self, delta: FastOrderDelta) -> Result<()> {
         // Validate sequence ordering - ignore old updates that arrive late
         // This is crucial for maintaining data integrity in real-time systems
-        if delta.sequence <= self.sequence {
+        if delta.sequence <= self.last_delta_sequence {
             trace!(
                 "Ignoring stale delta: {} <= {}",
                 delta.sequence,
-                self.sequence
+                self.last_delta_sequence
             );
             return Ok(());
         }
@@ -496,6 +511,7 @@ impl OrderBook {
         }
 
         // Update our tracking info
+        self.last_delta_sequence = delta.sequence;
         self.sequence = delta.sequence;
         self.timestamp = delta.timestamp;
 
@@ -531,11 +547,11 @@ impl OrderBook {
             return Err(PolyfillError::validation("Token ID mismatch"));
         }
 
-        if timestamp <= self.sequence {
+        if timestamp <= self.last_snapshot_timestamp_ms {
             return Ok(false);
         }
 
-        self.sequence = timestamp;
+        self.last_snapshot_timestamp_ms = timestamp;
         self.timestamp = chrono::DateTime::<Utc>::from_timestamp_millis(timestamp as i64)
             .unwrap_or_else(Utc::now);
         self.begin_snapshot();
@@ -585,14 +601,13 @@ impl OrderBook {
             return Err(PolyfillError::validation("Token ID mismatch"));
         }
 
-        // Use the exchange-provided timestamp as our monotonic sequence marker.
-        // This is less strict than the REST/legacy delta sequence but works for
-        // ignoring obviously stale book snapshots.
-        if update.timestamp <= self.sequence {
+        // Use the exchange-provided timestamp as the monotonic snapshot marker.
+        // Snapshot timestamps are separate from legacy/incremental delta sequences.
+        if update.timestamp <= self.last_snapshot_timestamp_ms {
             return Ok(());
         }
 
-        self.sequence = update.timestamp;
+        self.last_snapshot_timestamp_ms = update.timestamp;
         self.timestamp = chrono::DateTime::<Utc>::from_timestamp_millis(update.timestamp as i64)
             .unwrap_or_else(Utc::now);
         self.begin_snapshot();
@@ -1220,6 +1235,8 @@ mod tests {
 
         book.apply_delta(delta).unwrap();
         assert_eq!(book.sequence, 1); // Sequence should update
+        assert_eq!(book.last_delta_sequence, 1);
+        assert_eq!(book.last_snapshot_timestamp_ms, 0);
         assert_eq!(book.best_bid().unwrap().price, dec!(0.5)); // Should be our bid
         assert_eq!(book.best_bid().unwrap().size, dec!(100)); // Should be our size
     }
@@ -1346,6 +1363,77 @@ mod tests {
         assert_eq!(book.best_ask().unwrap().size, dec!(45));
     }
 
+    #[test]
+    fn test_ws_snapshot_timestamp_does_not_block_delta_sequence() {
+        let mut book = OrderBook::new("test_token".to_string(), 10);
+        let snapshot_timestamp_ms = 1_757_908_892_351;
+
+        assert!(book
+            .begin_ws_book_update("test_token", snapshot_timestamp_ms)
+            .unwrap());
+        book.apply_ws_book_level_fast(Side::BUY, 5_000, 100_000)
+            .unwrap();
+        book.apply_ws_book_level_fast(Side::SELL, 6_000, 100_000)
+            .unwrap();
+        book.finish_ws_book_update();
+
+        assert_eq!(book.sequence, 0);
+        assert_eq!(book.last_delta_sequence, 0);
+        assert_eq!(book.last_snapshot_timestamp_ms, snapshot_timestamp_ms);
+
+        book.apply_delta(OrderDelta {
+            token_id: "test_token".to_string(),
+            timestamp: Utc::now(),
+            side: Side::BUY,
+            price: dec!(0.51),
+            size: dec!(11),
+            sequence: 1,
+        })
+        .unwrap();
+
+        assert_eq!(book.sequence, 1);
+        assert_eq!(book.last_delta_sequence, 1);
+        assert_eq!(book.last_snapshot_timestamp_ms, snapshot_timestamp_ms);
+        assert_eq!(book.best_bid().unwrap().price, dec!(0.51));
+    }
+
+    #[test]
+    fn test_delta_sequence_does_not_block_snapshot_timestamp() {
+        let mut book = OrderBook::new("test_token".to_string(), 10);
+
+        book.apply_delta(OrderDelta {
+            token_id: "test_token".to_string(),
+            timestamp: Utc::now(),
+            side: Side::BUY,
+            price: dec!(0.40),
+            size: dec!(10),
+            sequence: 10_000,
+        })
+        .unwrap();
+
+        book.apply_book_update(&BookUpdate {
+            asset_id: "test_token".to_string(),
+            market: "0xabc".to_string(),
+            timestamp: 1_000,
+            bids: vec![OrderSummary {
+                price: dec!(0.50),
+                size: dec!(20),
+            }],
+            asks: vec![OrderSummary {
+                price: dec!(0.60),
+                size: dec!(30),
+            }],
+            hash: None,
+        })
+        .unwrap();
+
+        assert_eq!(book.sequence, 10_000);
+        assert_eq!(book.last_delta_sequence, 10_000);
+        assert_eq!(book.last_snapshot_timestamp_ms, 1_000);
+        assert_eq!(book.best_bid().unwrap().price, dec!(0.50));
+        assert_eq!(book.best_ask().unwrap().price, dec!(0.60));
+    }
+
     #[test]
     fn test_book_update_depth_keeps_best_prices_independent_of_payload_order() {
         let mut book = OrderBook::new("test_token".to_string(), 2);