Fix Binance option top-of-book via depth limit and ticker fallback.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/exchange/binance/adapter.py

@@ -84,8 +84,11 @@ class BinanceExchange:
         ids = [i for i in inst_ids if i]
         for inst in ids:
             try:
-                bids, asks, ts = self.rest.fetch_books(inst, sz=5)
-                self.cache.upsert_book(inst, bids=bids, asks=asks, ts_ms=ts)
+                bids, asks, ts = self.rest.fetch_books(inst, sz=10)
+                if bids or asks:
+                    self.cache.upsert_book(inst, bids=bids, asks=asks, ts_ms=ts)
+                else:
+                    logger.warning("binance warm book empty: %s", inst)
             except Exception as e:
                 logger.warning("binance warm book %s failed: %s", inst, e)
             try:
@@ -111,7 +114,32 @@ class BinanceExchange:
     def quote(self, inst_id: str) -> Quote | None:
         return self.cache.get(inst_id)
 
+    def _refresh_quote_if_stale(self, inst_id: str) -> None:
+        if not inst_id:
+            return
+        q = self.cache.get(inst_id)
+        if q is not None and (q.bid is not None or q.ask is not None):
+            return
+        try:
+            bids, asks, ts = self.rest.fetch_books(inst_id, sz=10)
+            if bids or asks:
+                self.cache.upsert_book(inst_id, bids=bids, asks=asks, ts_ms=ts)
+        except Exception as e:
+            logger.debug("binance refresh quote %s: %s", inst_id, e)
+
     def snapshot(self, perp_inst_id: str) -> MarketSnapshot:
+        # 期权 WS 偶发无推送时，用 REST/ticker 补买卖一，避免 UI 一直是 -
+        self._refresh_quote_if_stale(perp_inst_id)
+        pair = None
+        try:
+            # BookCache 无公开 getter；从 snapshot 前先按 pair 刷新
+            with self.cache._lock:  # noqa: SLF001
+                pair = self.cache._pair
+        except Exception:
+            pair = None
+        if pair is not None:
+            self._refresh_quote_if_stale(pair.call_inst_id)
+            self._refresh_quote_if_stale(pair.put_inst_id)
         return self.cache.snapshot(perp_inst_id)
 
     def snapshot_dict(self, perp_inst_id: str) -> dict[str, Any]: