添加 /dump 命令，导出 session 为 markdown 文档

/dump 命令会输出当前 session 的完整信息：
- Session 元信息 (ID, channel, chat_id, model 等)
- 所有对话历史 (system, user, assistant, tool)
- 每条消息包含角色、时间戳、内容、工具调用等

src/session/session.rs

@@ -142,6 +142,71 @@ impl Session {
             format!("{}\n\n## Skills\n\n{}\n\nUse the `get_skill` tool to load a skill's full content when needed.", base_prompt, skills_prompt)
         }
     }
+
+    /// 将当前 session 导出为 markdown 文档
+    pub fn dump_as_markdown(&self) -> String {
+        use chrono::{DateTime, Local};
+
+        let now = Local::now().format("%Y-%m-%d %H:%M:%S");
+
+        let mut md = String::new();
+        md.push_str(&format!("# Session Dump\n\n"));
+        md.push_str(&format!("- **Session ID**: `{}`\n", self.id));
+        md.push_str(&format!("- **Channel**: `{}`\n", self.id.channel));
+        md.push_str(&format!("- **Chat ID**: `{}`\n", self.id.chat_id));
+        md.push_str(&format!("- **Dialog ID**: `{}`\n", self.id.dialog_id));
+        md.push_str(&format!("- **Message Count**: {}\n", self.messages.len()));
+        md.push_str(&format!("- **Model**: `{}`\n", self.provider_config.model_id));
+        md.push_str(&format!("- **Exported At**: {}\n", now));
+        md.push_str("\n---\n\n");
+
+        md.push_str("## Conversation History\n\n");
+
+        for (i, msg) in self.messages.iter().enumerate() {
+            let role = match msg.role.as_str() {
+                "system" => "System",
+                "user" => "User",
+                "assistant" => "Assistant",
+                "tool" => "Tool",
+                r => r,
+            };
+
+            let timestamp = if msg.timestamp > 0 {
+                DateTime::from_timestamp_millis(msg.timestamp)
+                    .map(|dt| dt.format("%Y-%m-%d %H:%M:%S").to_string())
+                    .unwrap_or_default()
+            } else {
+                String::new()
+            };
+
+            md.push_str(&format!("### [{:03}] {} {}\n\n", i + 1, role, timestamp));
+            md.push_str("```\n");
+
+            if let Some(ref tool_calls) = msg.tool_calls {
+                md.push_str(&format!("[Tool Calls]\n"));
+                for tc in tool_calls {
+                    md.push_str(&format!("- {}: {:?}\n", tc.name, tc.arguments));
+                }
+            }
+
+            if let Some(ref tool_name) = msg.tool_name {
+                md.push_str(&format!("[Tool: {}]\n", tool_name));
+            }
+
+            if let Some(ref tool_call_id) = msg.tool_call_id {
+                md.push_str(&format!("[Tool Call ID: {}]\n", tool_call_id));
+            }
+
+            md.push_str(&msg.content);
+            md.push_str("\n```\n\n");
+
+            if !msg.media_refs.is_empty() {
+                md.push_str(&format!("**Media**: {:?}\n\n", msg.media_refs));
+            }
+        }
+
+        md
+    }
 }
 
 /// SessionManager 管理所有 Session，按 channel_name 路由
@@ -219,6 +284,11 @@ pub static SLASH_COMMANDS: &[SlashCommand] = &[
         description: "Print current session information",
         aliases: &["/info"],
     },
+    SlashCommand {
+        name: "dump",
+        description: "Save current session as markdown document",
+        aliases: &["/dump"],
+    },
 ];
 
 impl SessionManager {
@@ -313,6 +383,16 @@ impl SessionManager {
                     Ok((None, "No active session.".to_string()))
                 }
             }
+            "dump" => {
+                if let Some(sid) = current_session_id {
+                    let session = self.get_or_create_session(sid).await?;
+                    let session_guard = session.lock().await;
+                    let md = session_guard.dump_as_markdown();
+                    Ok((None, md))
+                } else {
+                    Ok((None, "No active session.".to_string()))
+                }
+            }
             _ => Err(AgentError::Other(format!("Command not implemented: {}", cmd.name))),
         }
     }