diff --git a/src/gateway/agent_factory.rs b/src/gateway/agent_factory.rs
index d7abd4b..3a4fb2c 100644
--- a/src/gateway/agent_factory.rs
+++ b/src/gateway/agent_factory.rs
@@ -80,6 +80,7 @@ impl AgentFactory {
                 message_seq: None,
                 subagent_description: None,
                 nesting_depth: 0,
+                parent_task_id: None,
             });
             // 如果有取消信号接收端，注入 Agent
             if let Some(token) = request.cancel_token {
diff --git a/src/protocol/mod.rs b/src/protocol/mod.rs
index 3ac298e..a640957 100644
--- a/src/protocol/mod.rs
+++ b/src/protocol/mod.rs
@@ -212,6 +212,8 @@ pub enum WsOutbound {
         subagent_type: String,
         #[serde(default, skip_serializing_if = "Option::is_none")]
         topic_id: Option<String>,
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        parent_task_id: Option<String>,
     },
     #[serde(rename = "session_established")]
     SessionEstablished { session_id: String },
diff --git a/src/protocol/ws_adapter.rs b/src/protocol/ws_adapter.rs
index 231bb04..043c9d4 100644
--- a/src/protocol/ws_adapter.rs
+++ b/src/protocol/ws_adapter.rs
@@ -173,6 +173,7 @@ pub(crate) fn ws_outbound_from_outbound_message(message: &OutboundMessage) -> Ve
             description: message.metadata.get("task_description").cloned().unwrap_or_default(),
             subagent_type: message.metadata.get("task_subagent_type").cloned().unwrap_or_default(),
             topic_id: message.metadata.get("topic_id").cloned(),
+            parent_task_id: message.metadata.get("parent_task_id").cloned(),
         }],
         OutboundEventKind::StreamDelta => vec![WsOutbound::StreamDelta {
             id: message.tool_call_id.clone().unwrap_or_default(),
diff --git a/src/tools/task/runtime.rs b/src/tools/task/runtime.rs
index 8e3192f..bdf1dda 100644
--- a/src/tools/task/runtime.rs
+++ b/src/tools/task/runtime.rs
@@ -262,6 +262,14 @@ impl SystemPromptProvider for StaticSystemPromptProvider {
     }
 }
 
+/// 从 session_id 中提取 task_id 部分
+/// session_id 格式: "sub:{...}:task:{uuid}"，提取 "task:{uuid}" 部分
+fn extract_task_id_from_session_id(session_id: &str) -> Option<String> {
+    session_id
+        .rfind(":task:")
+        .map(|pos| session_id[pos + 1..].to_string())
+}
+
 /// 默认子代理运行时实现
 pub struct DefaultSubAgentRuntime {
     config: SubAgentRuntimeConfig,
@@ -337,6 +345,15 @@ impl DefaultSubAgentRuntime {
             None, // 子代理不需要 skill provider
         )
         .map(|agent| {
+            // 确定 parent_task_id：
+            // - 主 agent (depth=0) 创建子 agent → parent_task_id = None
+            // - 子 agent (depth>0) 创建孙 agent → parent_task_id = 父 agent 自身的 task_id
+            let parent_task_id = if parent_nesting_depth > 0 {
+                extract_task_id_from_session_id(&session.parent_session_id)
+            } else {
+                None
+            };
+
             let agent = agent.with_tool_context(ToolContext {
                 channel_name: Some(session.parent_channel_name.clone()),
                 sender_id: None,
@@ -347,6 +364,7 @@ impl DefaultSubAgentRuntime {
                 message_seq: None,
                 subagent_description: Some(session.description.clone()),
                 nesting_depth: parent_nesting_depth + 1,
+                parent_task_id,
             });
 
             // 如果有 MessageBus，附加实时广播 emitter
@@ -534,6 +552,17 @@ impl SubAgentRuntime for DefaultSubAgentRuntime {
             metadata.insert("task_subagent_type".to_string(), session.subagent_type.clone());
             metadata.insert("topic_id".to_string(), session.parent_topic_id.clone().unwrap_or_default());
 
+            // 如果是子智能体创建的孙智能体，传递父 task_id
+            if parent_context.nesting_depth > 0 {
+                if let Some(ref ptid) = parent_context.parent_task_id {
+                    metadata.insert("parent_task_id".to_string(), ptid.clone());
+                } else if let Some(ptid) = extract_task_id_from_session_id(
+                    parent_context.session_id.as_deref().unwrap_or(""),
+                ) {
+                    metadata.insert("parent_task_id".to_string(), ptid);
+                }
+            }
+
             let event = OutboundMessage {
                 channel: session.parent_channel_name.clone(),
                 chat_id: session.parent_chat_id.clone(),
diff --git a/src/tools/todo_read.rs b/src/tools/todo_read.rs
index d9cca0f..d0e8d8d 100644
--- a/src/tools/todo_read.rs
+++ b/src/tools/todo_read.rs
@@ -183,6 +183,7 @@ mod tests {
             message_seq: Some(1),
             subagent_description: None,
             nesting_depth: 0,
+            parent_task_id: None,
         }
     }
 
diff --git a/src/tools/todo_write.rs b/src/tools/todo_write.rs
index 6195e48..17c4616 100644
--- a/src/tools/todo_write.rs
+++ b/src/tools/todo_write.rs
@@ -409,6 +409,7 @@ mod tests {
             message_seq: Some(1),
             subagent_description: None,
             nesting_depth: 0,
+            parent_task_id: None,
         }
     }
 
diff --git a/src/tools/traits.rs b/src/tools/traits.rs
index 02960aa..52d6f2b 100644
--- a/src/tools/traits.rs
+++ b/src/tools/traits.rs
@@ -20,6 +20,8 @@ pub struct ToolContext {
     pub subagent_description: Option<String>,
     /// 当前嵌套深度（0 = 主 agent，1 = 子 agent，2 = 孙 agent...）
     pub nesting_depth: u32,
+    /// 父任务 ID（仅子/孙智能体有值，用于构建任务层级）
+    pub parent_task_id: Option<String>,
 }
 
 #[async_trait]
diff --git a/web/src/hooks/useChat.ts b/web/src/hooks/useChat.ts
index d7321d1..92d5075 100644
--- a/web/src/hooks/useChat.ts
+++ b/web/src/hooks/useChat.ts
@@ -431,6 +431,8 @@ export function useChat(): UseChatReturn {
         const msg = message as TaskStarted
         // 只 backfill 当前话题的 task tool_call，避免跨话题串扰
         if (msg.topic_id && msg.topic_id !== selectedTopicRef.current) break
+        // 孙智能体的 TaskStarted 不应 backfill 到主视图
+        if (msg.parent_task_id) break
 
         // 立即更新对应的 task tool_call，让用户可以点击查看实时进度
         setMessages((prev) => {
diff --git a/web/src/types/protocol.ts b/web/src/types/protocol.ts
index c34d5d0..1701900 100644
--- a/web/src/types/protocol.ts
+++ b/web/src/types/protocol.ts
@@ -101,6 +101,7 @@ export interface TaskStarted {
   description: string
   subagent_type: string
   topic_id?: string
+  parent_task_id?: string
 }
 
 export interface SessionEstablished {