fix: 推荐品种下拉改用缓存 main_code，避免加载卡住。

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

symbols.py

@@ -431,15 +431,42 @@ def _product_for_ths(ths: str) -> Optional[dict]:
     return _THS_TO_PRODUCT.get(key) or _THS_TO_PRODUCT.get(key.lower())
 
 
-def _main_for_product(product: dict) -> Optional[dict]:
+def _item_from_recommend_row(row: dict, product: dict) -> Optional[dict]:
+    """由推荐缓存行快速构造下拉项（不在 HTTP 请求中解析主力）。"""
+    name = row.get("name") or product["name"]
+    main_code = (row.get("main_code") or "").strip()
+    max_lots = row.get("max_lots")
+
+    if main_code:
+        codes = ths_to_codes(main_code)
+        if codes:
+            ths = codes["ths_code"]
+            item = {
+                "name": name,
+                "ths_code": ths,
+                "market_code": codes.get("market_code") or "",
+                "sina_code": codes.get("sina_code") or "",
+                "exchange": product["exchange"],
+                "contract": f"主力 {ths}",
+                "display": f"{name} 主力 {ths}",
+                "input_label": f"{name} {ths}",
+            }
+            if max_lots is not None:
+                item["max_lots"] = max_lots
+            return _enrich_item(item)
+
     with _main_index_lock:
-        index = dict(_main_index)
-    main = index.get(product["sina"])
-    if not main:
-        resolved = resolve_main_contract(product)
-        if resolved:
-            main = _enrich_item(resolved)
-    return main
+        main = _main_index.get(product["sina"])
+    if main:
+        item = dict(main)
+        if max_lots is not None:
+            item["max_lots"] = max_lots
+        return _enrich_item(item)
+
+    item = _stub_main_contract(product)
+    if max_lots is not None:
+        item["max_lots"] = max_lots
+    return item
 
 
 def list_recommended_symbols_grouped(recommend_rows: list[dict]) -> list[dict]:
@@ -459,14 +486,10 @@ def list_recommended_symbols_grouped(recommend_rows: list[dict]) -> list[dict]:
         if not product:
             continue
         seen.add(ths_key)
-        main = _main_for_product(product)
-        if not main:
+        item = _item_from_recommend_row(row, product)
+        if not item:
             continue
-        item = dict(main)
-        max_lots = row.get("max_lots")
-        if max_lots is not None:
-            item["max_lots"] = max_lots
-        buckets[product["exchange"]].append(_enrich_item(item))
+        buckets[product["exchange"]].append(item)
 
     groups: list[dict] = []
     for cat in EXCHANGE_ORDER: