feat: 自动从数据库恢复当前话题，增强会话管理功能

src/gateway/session.rs

@@ -547,11 +547,30 @@ impl SessionManager {
         self.lifecycle.get(channel_name).await
     }
 
-    /// 获取指定 chat 的当前话题（确保 session 存在）
+    /// 获取指定 chat 的当前话题（确保 session 存在，自动从数据库恢复）
     pub async fn get_current_topic(&self, channel_name: &str, chat_id: &str) -> Result<Option<String>, AgentError> {
         self.ensure_session(channel_name).await?;
         if let Some(session) = self.get(channel_name).await {
-            let guard = session.lock().await;
+            let mut guard = session.lock().await;
+
+            // 如果内存中没有当前话题，从数据库恢复最近活跃的话题
+            if guard.current_topic(chat_id).is_none() {
+                let session_id = guard.persistent_session_id(chat_id);
+                let topics = self.store.list_topics(&session_id)
+                    .map_err(|e| AgentError::Other(format!("Failed to list topics: {}", e)))?;
+
+                if let Some(latest_topic) = topics.first() {
+                    // 设置最近活跃的话题为当前话题
+                    guard.set_current_topic(chat_id, Some(latest_topic.id.clone()));
+                    tracing::info!(
+                        chat_id = %chat_id,
+                        topic_id = %latest_topic.id,
+                        topic_title = %latest_topic.title,
+                        "Restored current topic from database"
+                    );
+                }
+            }
+
             Ok(guard.current_topic(chat_id).map(|s| s.to_string()))
         } else {
             Ok(None)