feat(kernel): Agent 导入/导出 + message_count 跟踪

Sprint 3.1 message_count 修复:
- AgentRegistry 新增 message_counts 字段跟踪每个 agent 的消息数
- increment_message_count() 在 send_message 和 send_message_stream 中调用
- get_info() 返回实际计数值

Sprint 3.3 Agent 导入/导出:
- Kernel 新增 get_agent_config() 方法返回原始 AgentConfig
- 新增 agent_export Tauri 命令，导出配置为 JSON
- 新增 agent_import Tauri 命令，从 JSON 导入并自动生成新 ID
- 注册到 Tauri invoke_handler

desktop/src-tauri/src/kernel_commands.rs

@@ -378,6 +378,54 @@ pub async fn agent_delete(
         .map_err(|e| format!("Failed to delete agent: {}", e))
 }
 
+/// Export an agent configuration as JSON
+#[tauri::command]
+pub async fn agent_export(
+    state: State<'_, KernelState>,
+    agent_id: String,
+) -> Result<String, String> {
+    let agent_id = validate_agent_id(&agent_id)?;
+
+    let kernel_lock = state.lock().await;
+    let kernel = kernel_lock.as_ref()
+        .ok_or_else(|| "Kernel not initialized. Call kernel_init first.".to_string())?;
+
+    let id: AgentId = agent_id.parse()
+        .map_err(|_| "Invalid agent ID format".to_string())?;
+
+    let config = kernel.get_agent_config(&id)
+        .ok_or_else(|| format!("Agent not found: {}", agent_id))?;
+
+    serde_json::to_string_pretty(&config)
+        .map_err(|e| format!("Failed to serialize agent config: {}", e))
+}
+
+/// Import an agent from JSON configuration
+#[tauri::command]
+pub async fn agent_import(
+    state: State<'_, KernelState>,
+    config_json: String,
+) -> Result<AgentInfo, String> {
+    validate_string_length(&config_json, "config_json", 1_000_000)
+        .map_err(|e| format!("{}", e))?;
+
+    let mut config: AgentConfig = serde_json::from_str(&config_json)
+        .map_err(|e| format!("Invalid agent config JSON: {}", e))?;
+
+    // Regenerate ID to avoid collisions
+    config.id = AgentId::new();
+
+    let kernel_lock = state.lock().await;
+    let kernel = kernel_lock.as_ref()
+        .ok_or_else(|| "Kernel not initialized. Call kernel_init first.".to_string())?;
+
+    let new_id = kernel.spawn_agent(config).await
+        .map_err(|e| format!("Failed to import agent: {}", e))?;
+
+    kernel.get_agent(&new_id)
+        .ok_or_else(|| "Agent was created but could not be retrieved".to_string())
+}
+
 /// Send a message to an agent
 #[tauri::command]
 pub async fn agent_chat(

desktop/src-tauri/src/lib.rs

@@ -1331,6 +1331,8 @@ pub fn run() {
             kernel_commands::agent_list,
             kernel_commands::agent_get,
             kernel_commands::agent_delete,
+            kernel_commands::agent_export,
+            kernel_commands::agent_import,
             kernel_commands::agent_chat,
             kernel_commands::agent_chat_stream,
             // Skills commands (dynamic discovery)