feat(cross_context): 支持为跨上下文聊天指定消息数量

允许用户在配置文件中为每个聊天流（群聊或私聊）单独设置要检索的历史消息数量（limit）。如果未指定，则默认为5条。

- 更新了 `build_cross_context_normal` 和 `build_cross_context_s4u` 方法以解析和使用这个新的 `limit` 参数。
- 在S4U（Search for User）模式下，获取的消息数量调整为 `limit` 的4倍，以确保有足够的消息可供筛选。
- 更新了配置文件模板 `bot_config_template.toml` 以反映此项新功能，并提供了示例。

src/plugin_system/apis/cross_context_api.py

@@ -50,7 +50,8 @@ async def build_cross_context_normal(chat_stream: ChatStream, other_chat_infos:
     构建跨群聊/私聊上下文 (Normal模式)
     """
     cross_context_messages = []
-    for chat_type, chat_raw_id in other_chat_infos:
+    for chat_info in other_chat_infos:
+        chat_type, chat_raw_id, limit = chat_info[0], chat_info[1], int(chat_info[2]) if len(chat_info) > 2 else 5
         is_group = chat_type == "group"
         stream_id = get_chat_manager().get_stream_id(chat_stream.platform, chat_raw_id, is_group=is_group)
         if not stream_id:
@@ -60,7 +61,7 @@ async def build_cross_context_normal(chat_stream: ChatStream, other_chat_infos:
             messages = await get_raw_msg_before_timestamp_with_chat(
                 chat_id=stream_id,
                 timestamp=time.time(),
-                limit=5,  # 可配置
+                limit=limit,
             )
             if messages:
                 chat_name = await get_chat_manager().get_stream_name(stream_id) or chat_raw_id
@@ -89,19 +90,25 @@ async def build_cross_context_s4u(
         user_id = target_user_info.get("user_id")
 
         if user_id:
-            for chat_type, chat_raw_id in other_chat_infos:
+            for chat_info in other_chat_infos:
+                chat_type, chat_raw_id, limit = (
+                    chat_info[0],
+                    chat_info[1],
+                    int(chat_info[2]) if len(chat_info) > 2 else 5,
+                )
                 is_group = chat_type == "group"
                 stream_id = get_chat_manager().get_stream_id(chat_stream.platform, chat_raw_id, is_group=is_group)
                 if not stream_id:
                     continue
 
                 try:
+                    # S4U模式下，我们获取更多消息以供筛选
                     messages = await get_raw_msg_before_timestamp_with_chat(
                         chat_id=stream_id,
                         timestamp=time.time(),
-                        limit=20,  # 获取更多消息以供筛选
+                        limit=limit * 4,  # 获取4倍limit的消息以供筛选
                     )
-                    user_messages = [msg for msg in messages if msg.get("user_id") == user_id][-5:]
+                    user_messages = [msg for msg in messages if msg.get("user_id") == user_id][-limit:]
 
                     if user_messages:
                         chat_name = await get_chat_manager().get_stream_name(stream_id) or chat_raw_id
@@ -144,7 +151,8 @@ async def get_chat_history_by_group_name(group_name: str) -> str:
     chat_manager = get_chat_manager()
 
     cross_context_messages = []
-    for chat_type, chat_raw_id in chat_infos:
+    for chat_info in chat_infos:
+        chat_type, chat_raw_id, limit = chat_info[0], chat_info[1], int(chat_info[2]) if len(chat_info) > 2 else 5
         is_group = chat_type == "group"
 
         found_stream = None
@@ -168,7 +176,7 @@ async def get_chat_history_by_group_name(group_name: str) -> str:
             messages = await get_raw_msg_before_timestamp_with_chat(
                 chat_id=stream_id,
                 timestamp=time.time(),
-                limit=5,  # 可配置
+                limit=limit,
             )
             if messages:
                 chat_name = await get_chat_manager().get_stream_name(stream_id) or chat_raw_id