feat: 添加话题管理功能，支持按 chat_id 隔离话题

src/gateway/session.rs

@@ -32,6 +32,7 @@ use super::session_message_service::SessionMessageService;
 
 /// Session 按 channel 隔离，每个 channel 一个 Session
 /// History 按 chat_id 隔离，由 Session 统一管理
+/// Topic 按 chat_id 隔离，存储在 SessionHistory 中
 pub struct Session {
     pub id: Uuid,
     pub channel_name: String,
@@ -42,7 +43,6 @@ pub struct Session {
     compressor: ContextCompressor,
     history: SessionHistory,
     store: Arc<SessionStore>,
-    current_topic_id: Option<String>,
 }
 
 pub struct BusToolCallEmitter {
@@ -153,7 +153,6 @@ impl Session {
                 chat_history_ttl_hours,
             ),
             store,
-            current_topic_id: None,
         })
     }
 
@@ -161,14 +160,18 @@ impl Session {
         self.history.persistent_session_id(chat_id)
     }
 
-    /// 设置当前话题 ID
-    pub fn set_current_topic(&mut self, topic_id: Option<String>) {
-        self.current_topic_id = topic_id;
+    /// 设置当前话题 ID（指定 chat）
+    pub fn set_current_topic(&mut self, chat_id: &str, topic_id: Option<String>) {
+        if let Some(topic_id) = topic_id {
+            self.history.set_chat_topic(chat_id, topic_id);
+        } else {
+            self.history.clear_chat_topic(chat_id);
+        }
     }
 
-    /// 获取当前话题 ID
-    pub fn current_topic(&self) -> Option<&str> {
-        self.current_topic_id.as_deref()
+    /// 获取当前话题 ID（指定 chat）
+    pub fn current_topic(&self, chat_id: &str) -> Option<&str> {
+        self.history.chat_topic(chat_id)
     }
 
     /// 切换话题 - 清除当前历史并加载新话题的历史
@@ -183,7 +186,7 @@ impl Session {
             .map_err(|e| AgentError::Other(format!("load topic messages error: {}", e)))?;
 
         self.history.set_history(chat_id, messages);
-        self.current_topic_id = Some(topic_id.to_string());
+        self.history.set_chat_topic(chat_id, topic_id.to_string());
 
         tracing::info!(
             topic_id = %topic_id,
@@ -243,15 +246,16 @@ impl Session {
         message: ChatMessage,
     ) -> Result<(), AgentError> {
         let session_id = self.persistent_session_id(chat_id);
+        let topic_id = self.history.chat_topic(chat_id).map(|s| s.to_string());
         self.store
-            .append_message_with_topic(&session_id, self.current_topic_id.as_deref(), &message)
+            .append_message_with_topic(&session_id, topic_id.as_deref(), &message)
             .map_err(|err| {
                 AgentError::Other(format!("append message persistence error: {}", err))
             })?;
         self.add_message(chat_id, message);
 
         // 更新 topic 的最后活跃时间
-        if let Some(topic_id) = &self.current_topic_id {
+        if let Some(ref topic_id) = topic_id {
             if let Err(e) = self.store.touch_topic(topic_id) {
                 tracing::warn!(error = %e, topic_id = %topic_id, "Failed to touch topic");
             }
@@ -337,7 +341,7 @@ impl Session {
 
     pub(crate) fn reload_chat_history(&mut self, chat_id: &str) -> Result<(), AgentError> {
         // 如果当前有 topic，加载该 topic 的消息
-        if let Some(topic_id) = &self.current_topic_id {
+        if let Some(topic_id) = self.history.chat_topic(chat_id) {
             let messages = self
                 .store
                 .load_messages_for_topic(topic_id)

src/gateway/session_history.rs

@@ -25,6 +25,7 @@ fn current_timestamp() -> i64 {
 pub(crate) struct SessionHistory {
     channel_name: String,
     chat_histories: HashMap<String, Vec<ChatMessage>>,
+    chat_topic_ids: HashMap<String, String>, // 每个 chat 的当前 topic
     compression_in_flight: HashSet<String>,
     conversations: Arc<dyn ConversationRepository>,
     skill_events: Arc<dyn SkillEventRepository>,
@@ -41,6 +42,7 @@ impl SessionHistory {
         Self {
             channel_name: channel_name.into(),
             chat_histories: HashMap::new(),
+            chat_topic_ids: HashMap::new(),
             compression_in_flight: HashSet::new(),
             conversations,
             skill_events,
@@ -117,6 +119,21 @@ impl SessionHistory {
         self.chat_histories.insert(chat_id.to_string(), history);
     }
 
+    /// 设置指定 chat 的当前 topic
+    pub(crate) fn set_chat_topic(&mut self, chat_id: &str, topic_id: String) {
+        self.chat_topic_ids.insert(chat_id.to_string(), topic_id);
+    }
+
+    /// 获取指定 chat 的当前 topic
+    pub(crate) fn chat_topic(&self, chat_id: &str) -> Option<&str> {
+        self.chat_topic_ids.get(chat_id).map(|s| s.as_str())
+    }
+
+    /// 清除指定 chat 的 topic
+    pub(crate) fn clear_chat_topic(&mut self, chat_id: &str) {
+        self.chat_topic_ids.remove(chat_id);
+    }
+
     pub(crate) fn add_message(&mut self, chat_id: &str, message: ChatMessage) {
         self.get_or_create_history(chat_id).push(message);
     }

src/gateway/session_message_service.rs

@@ -44,6 +44,7 @@ impl SessionMessageService {
         }
 
         let session = self.lifecycle.active_session(channel_name).await?;
+
         let outbound_messages = AgentExecutionService::new(self.show_tool_results)
             .prepare_and_execute_message(MessageExecutionRequest {
                 session,