feat(task): 增加子代理最大嵌套深度支持，更新相关文档和提示

src/config/mod.rs

@@ -242,7 +242,7 @@ fn default_task_ttl_hours() -> u64 {
 }
 
 fn default_task_max_nesting_depth() -> u32 {
-    1
+    2
 }
 
 fn default_task_allowed_tools() -> Vec<String> {

src/gateway/runtime.rs

@@ -17,7 +17,7 @@ use crate::storage::{
 };
 use crate::tools::{
     DefaultSubAgentRuntime, InMemoryTaskRepository, NoopSessionMessageSender,
-    SessionMessageSender, SubAgentRuntimeConfig, SubagentCatalog, ToolRegistry,
+    SessionMessageSender, SubAgentRuntimeConfig, SubagentCatalog, TaskTool, ToolRegistry,
 };
 use crate::tools::task::repository::TaskRepository;
 use crate::tools::todo_write::TodoItem;
@@ -173,7 +173,7 @@ pub(crate) fn build_session_manager_with_sender(
     // Create SubAgentRuntime (if task tool is enabled)
     let (factory, task_repository): (_, Arc<dyn TaskRepository>) = if task_config.enabled {
         let task_repository = Arc::new(InMemoryTaskRepository::new());
-        // Build subagent tools with MCP tools
+        // Build subagent tools with MCP tools (task tool registered separately below)
         let subagent_tools = Arc::new(
             factory.build_subagent_tools(
                 if mcp_tools_for_subagents.is_empty() {
@@ -200,20 +200,28 @@ pub(crate) fn build_session_manager_with_sender(
             runtime_config,
             task_repository.clone(),
             conversations.clone(),
-            subagent_tools,
+            subagent_tools.clone(),
             provider_config.clone(),
             catalog,
             bus.clone(),
             store.clone(),
         ));
 
+        // 注册 task 工具到子代理工具集（需在 runtime 创建之后，打破循环依赖）
+        if factory.is_enabled("task") {
+            subagent_tools.register(TaskTool::new_with_depth(
+                subagent_runtime.clone(),
+                task_config.max_nesting_depth,
+            ));
+        }
+
         (factory.with_subagent_runtime(subagent_runtime), task_repository)
     } else {
         (factory, Arc::new(InMemoryTaskRepository::new()))
     };
 
     // Build base tools
-    let mut tools = factory.build();
+    let tools = factory.build();
 
     // Register MCP tools to main agent (async)
     // Note: MCP tools for subagents are already collected above

src/gateway/tool_registry_factory.rs

@@ -88,7 +88,7 @@ impl ToolRegistryFactory {
         self
     }
 
-    fn is_enabled(&self, tool_name: &str) -> bool {
+    pub(crate) fn is_enabled(&self, tool_name: &str) -> bool {
         !self.disabled_tools.contains(tool_name)
     }
 
@@ -99,7 +99,7 @@ impl ToolRegistryFactory {
     }
 
     pub(crate) fn build(&self) -> ToolRegistry {
-        let mut registry = ToolRegistry::new();
+        let registry = ToolRegistry::new();
 
         if self.is_enabled("calculator") {
             registry.register(CalculatorTool::new());
@@ -171,13 +171,14 @@ impl ToolRegistryFactory {
         registry
     }
 
-    /// 构建子代理专用工具集（不包含 task 工具防止递归）
+    /// 构建子代理专用工具集
     /// 可选地包含 MCP 工具（通过 mcp_tools 参数传递）
+    /// 注意：task 工具由调用方在 runtime 就绪后通过 registry.register() 单独注册
     pub(crate) fn build_subagent_tools(
         &self,
         mcp_tools: Option<Vec<crate::mcp::tool_adapter::McpToolWrapper>>,
     ) -> ToolRegistry {
-        let mut registry = ToolRegistry::new();
+        let registry = ToolRegistry::new();
 
         // 基础工具
         if self.is_enabled("calculator") {
@@ -243,16 +244,6 @@ impl ToolRegistryFactory {
             }
         }
 
-        // 注册 task 工具，允许子代理创建孙代理（深度由 TaskTool 运行时控制）
-        if self.is_enabled("task") && self.task_config.enabled {
-            if let Some(runtime) = &self.subagent_runtime {
-                registry.register(TaskTool::new_with_depth(
-                    runtime.clone(),
-                    self.task_config.max_nesting_depth,
-                ));
-            }
-        }
-
         registry
     }
 }

src/tools/registry.rs

@@ -1,36 +1,51 @@
 use std::collections::HashMap;
+use std::sync::{Arc, RwLock};
 
 use crate::domain::tools::{Tool, ToolFunction};
 
 use super::traits::Tool as ToolTrait;
 
 pub struct ToolRegistry {
-    tools: HashMap<String, Box<dyn ToolTrait>>,
+    tools: RwLock<HashMap<String, Arc<dyn ToolTrait>>>,
 }
 
 impl ToolRegistry {
     pub fn new() -> Self {
         Self {
-            tools: HashMap::new(),
+            tools: RwLock::new(HashMap::new()),
         }
     }
 
-    pub fn register<T: ToolTrait + 'static>(&mut self, tool: T) {
+    pub fn register<T: ToolTrait + 'static>(&self, tool: T) {
-        self.tools.insert(tool.name().to_string(), Box::new(tool));
+        self.tools
+            .write()
+            .expect("ToolRegistry lock poisoned")
+            .insert(tool.name().to_string(), Arc::new(tool));
     }
 
-    pub fn get(&self, name: &str) -> Option<&Box<dyn ToolTrait>> {
+    pub fn get(&self, name: &str) -> Option<Arc<dyn ToolTrait>> {
-        self.tools.get(name)
+        self.tools
+            .read()
+            .expect("ToolRegistry lock poisoned")
+            .get(name)
+            .cloned()
     }
 
     /// Get all registered tools.
     /// Used for concurrent tool execution when we need to look up tools by name.
-    pub fn get_all(&self) -> Vec<&Box<dyn ToolTrait>> {
+    pub fn get_all(&self) -> Vec<Arc<dyn ToolTrait>> {
-        self.tools.values().collect()
+        self.tools
+            .read()
+            .expect("ToolRegistry lock poisoned")
+            .values()
+            .cloned()
+            .collect()
     }
 
     pub fn get_definitions(&self) -> Vec<Tool> {
         self.tools
+            .read()
+            .expect("ToolRegistry lock poisoned")
             .values()
             .map(|tool| Tool {
                 tool_type: "function".to_string(),
@@ -44,11 +59,19 @@ impl ToolRegistry {
     }
 
     pub fn has_tools(&self) -> bool {
-        !self.tools.is_empty()
+        !self.tools
+            .read()
+            .expect("ToolRegistry lock poisoned")
+            .is_empty()
     }
 
     pub fn tool_names(&self) -> Vec<String> {
-        self.tools.keys().cloned().collect()
+        self.tools
+            .read()
+            .expect("ToolRegistry lock poisoned")
+            .keys()
+            .cloned()
+            .collect()
     }
 }
 

src/tools/task/prompt.rs

@@ -51,7 +51,7 @@ impl SubagentPromptBuilder {
              1. 专注于完成任务，不要偏离目标\n\
              2. 使用可用的工具进行必要操作\n\
              3. 完成后给出简洁的总结\n\
-             4. 不要尝试创建新的子代理任务\n\n\
+             4. 当任务复杂度较高时，可以使用 `task` 工具创建子代理来处理独立子任务\n\n\
              任务追踪:\n\
              你可以使用 `todo_write` 工具追踪子任务进度。规则：同一时间只有一个 in_progress，完成后再标记下一个，3步以上才使用。\n\n\
              注意: 你没有访问主对话历史的权限，这是一个独立的执行上下文。"

src/tools/task/tool.rs

@@ -10,7 +10,7 @@ use super::types::{TaskDefinition, TaskToolArgs};
 /// Task 工具 - 创建和管理子代理
 pub struct TaskTool {
     runtime: Arc<dyn SubAgentRuntime>,
-    /// 最大嵌套深度（0 = 主 agent 不允许创建子代理，1 = 子 agent 可创建 1 层孙 agent）
+    /// 最大嵌套深度（0 = 无限制用于主 agent，>0 = 限制子代理最大嵌套层级）
     max_nesting_depth: u32,
 }