diff --git a/crates/focus-core/src/agent.rs b/crates/focus-core/src/agent.rs
index 5dbc1ae..95d47e7 100644
--- a/crates/focus-core/src/agent.rs
+++ b/crates/focus-core/src/agent.rs
@@ -14,7 +14,7 @@ use crate::error::{CoreError, CoreResult};
 use crate::event::{AgentEvent, EventSink};
 use crate::model::*;
 use crate::provider::{ProviderRequest, StreamEvent, StreamProvider};
-use crate::tool::{ToolEffects, ToolRegistry, ToolResult};
+use crate::tool::{ToolEffects, ToolRegistry, ToolResult, ToolUpdate};
 
 /// 一次 [`Agent`] 运行的配置。
 /// Configuration for an [`Agent`] run.
@@ -385,7 +385,35 @@ impl Agent {
             .tools
             .get(&tc.name)
             .ok_or_else(|| CoreError::ToolNotFound(tc.name.clone()))?;
-        let result = tool.execute(&tc.id, &tc.arguments, None)?;
+        // 把工具的增量更新（如 shell 流式输出）转发为 ToolExecutionUpdate 事件，
+        // 让 UI 实时显示输出，而不是等工具结束。
+        // Forward the tool's incremental updates (e.g. shell streaming output)
+        // as ToolExecutionUpdate events so the UI shows output live instead of
+        // waiting for the tool to finish.
+        let tc_id = tc.id.clone();
+        let tc_name = tc.name.clone();
+        // `Fn` 闭包不能可变借用 sink，用 Mutex 提供内部可变性（满足
+        // ToolUpdateSink 的 Send + Sync 约束）；闭包在 execute 返回后被丢弃，
+        // 随后把 sink 取回供 ToolExecutionEnd 使用。
+        // An `Fn` closure cannot mutably borrow the sink, so a Mutex provides
+        // interior mutability (satisfying ToolUpdateSink's Send + Sync bound);
+        // the closure is dropped when execute returns, then the sink is
+        // recovered for ToolExecutionEnd.
+        let sink_mutex = std::sync::Mutex::new(sink);
+        let on_update = |update: ToolUpdate| {
+            if let Ok(mut sink) = sink_mutex.lock() {
+                sink.emit(AgentEvent::ToolExecutionUpdate {
+                    tool_call_id: tc_id.clone(),
+                    tool_name: tc_name.clone(),
+                    partial_result: update,
+                });
+            }
+        };
+        let result = tool.execute(&tc.id, &tc.arguments, Some(&on_update))?;
+        // NLL 在最后使用后结束闭包对 sink_mutex 的借用，随后取回 sink。
+        // NLL ends the closure's borrow of sink_mutex after its last use;
+        // the sink is then recovered.
+        let sink = sink_mutex.into_inner().expect("sink mutex not poisoned");
         sink.emit(AgentEvent::ToolExecutionEnd {
             tool_call_id: tc.id.clone(),
             tool_name: tc.name.clone(),
diff --git a/crates/focus-core/src/event.rs b/crates/focus-core/src/event.rs
index 4da2f0d..3c4d558 100644
--- a/crates/focus-core/src/event.rs
+++ b/crates/focus-core/src/event.rs
@@ -61,7 +61,12 @@ pub enum AgentEvent {
 
 /// [`AgentEvent`] 的接收端。
 /// A sink for [`AgentEvent`]s.
-pub trait EventSink: Send {
+///
+/// `Sync` 是必需的：工具增量更新转发为事件时，闭包要满足
+/// [`ToolUpdateSink`](crate::tool::ToolUpdateSink)（`Fn + Send + Sync`）约束。
+/// `Sync` is required: forwarding tool updates as events needs a closure that
+/// satisfies [`ToolUpdateSink`](crate::tool::ToolUpdateSink) (`Fn + Send + Sync`).
+pub trait EventSink: Send + Sync {
     /// 接收一个事件。
     /// Receive one event.
     fn emit(&mut self, event: AgentEvent);
diff --git a/crates/focus-core/src/tool.rs b/crates/focus-core/src/tool.rs
index ee9c51a..068c7ae 100644
--- a/crates/focus-core/src/tool.rs
+++ b/crates/focus-core/src/tool.rs
@@ -182,13 +182,19 @@ pub trait Tool: Send + Sync + fmt::Debug {
         &self,
         tool_call_id: &str,
         arguments: &JsonValue,
-        on_update: Option<&ToolUpdateSink>,
+        on_update: Option<&ToolUpdateSink<'_>>,
     ) -> CoreResult<ToolResult>;
 }
 
-/// 工具用来推送增量更新的 channel 式 sink。
-/// A channel-style sink a tool uses to push incremental updates.
-pub type ToolUpdateSink = dyn Fn(ToolUpdate) + Send + Sync;
+/// 工具用来推送增量更新的回调。
+/// A callback a tool uses to push incremental updates.
+///
+/// 带生命周期参数：裸 trait object 别名的默认对象生命周期是 `'static`，
+/// 会导致增量回调无法借用调用方的局部状态；`'_` 允许短生命周期对象。
+/// Lifetime-parameterized: a bare trait-object alias defaults to `'static`,
+/// which would forbid callbacks borrowing caller-local state; `'_` admits
+/// short-lived objects.
+pub type ToolUpdateSink<'a> = dyn Fn(ToolUpdate) + Send + Sync + 'a;
 
 /// 可用工具的注册表，按名查找。
 /// A registry of available tools, looked up by name.
diff --git a/crates/focus-core/tests/agent_loop.rs b/crates/focus-core/tests/agent_loop.rs
index 8a2c017..ce57df2 100644
--- a/crates/focus-core/tests/agent_loop.rs
+++ b/crates/focus-core/tests/agent_loop.rs
@@ -33,7 +33,7 @@ impl Tool for EchoTool {
         &self,
         _id: &str,
         args: &JsonValue,
-        _on_update: Option<&ToolUpdateSink>,
+        _on_update: Option<&ToolUpdateSink<'_>>,
     ) -> Result<ToolResult, focus_core::CoreError> {
         let text = args.get_str("text").unwrap_or("(none)").to_string();
         Ok(ToolResult::text(format!("echo: {}", text)))
diff --git a/crates/focus-core/tests/tool_tests.rs b/crates/focus-core/tests/tool_tests.rs
index cbe6807..e05658e 100644
--- a/crates/focus-core/tests/tool_tests.rs
+++ b/crates/focus-core/tests/tool_tests.rs
@@ -25,7 +25,7 @@ impl Tool for EchoTool {
         &self,
         _id: &str,
         args: &JsonValue,
-        _on_update: Option<&ToolUpdateSink>,
+        _on_update: Option<&ToolUpdateSink<'_>>,
     ) -> CoreResult<ToolResult> {
         let text = focus_json::to_string(args);
         Ok(ToolResult::text(text))
@@ -64,3 +64,131 @@ fn read_effects_compatible() {
     assert!(!ToolEffects::NETWORK.compatible_with(ToolEffects::NONE));
     assert!(!ToolEffects::PROCESS.compatible_with(ToolEffects::NONE));
 }
+
+/// 工具的增量更新（on_update）必须被 agent 转发为 ToolExecutionUpdate 事件，
+/// 而不是等工具结束才一次性出现（回归：此前 agent 把 on_update 传成 None）。
+/// A tool's incremental updates (on_update) must be forwarded by the agent as
+/// ToolExecutionUpdate events, not appear only when the tool finishes
+/// (regression: the agent used to pass None for on_update).
+#[test]
+fn tool_updates_stream_to_agent_events() {
+    use focus_core::event::{AgentEvent, VecSink};
+    use focus_core::model::ContentBlock;
+    use focus_core::provider::{
+        ProviderRequest, StreamEvent, StreamIterator, StreamProvider, StreamResult,
+    };
+    use focus_core::{Agent, AgentConfig};
+    use std::sync::{Arc, Mutex};
+
+    /// 在 execute 期间通过 on_update 推送两段增量文本的工具。
+    /// A tool that pushes two incremental texts via on_update during execute.
+    #[derive(Debug)]
+    struct StreamingTool;
+    impl Tool for StreamingTool {
+        fn name(&self) -> &str {
+            "stream"
+        }
+        fn description(&self) -> &str {
+            "streams updates"
+        }
+        fn parameters(&self) -> JsonValue {
+            JsonValue::obj()
+        }
+        fn effects(&self) -> ToolEffects {
+            ToolEffects::READ
+        }
+        fn execute(
+            &self,
+            _id: &str,
+            _args: &JsonValue,
+            on_update: Option<&ToolUpdateSink<'_>>,
+        ) -> CoreResult<ToolResult> {
+            let cb = on_update.expect("agent must pass on_update");
+            cb(focus_core::tool::ToolUpdate {
+                content: vec![ContentBlock::text("line one")],
+                details: JsonValue::obj(),
+            });
+            cb(focus_core::tool::ToolUpdate {
+                content: vec![ContentBlock::text("line two")],
+                details: JsonValue::obj(),
+            });
+            Ok(ToolResult::text("done"))
+        }
+    }
+
+    /// 回放固定事件序列的 mock provider：第一段模型调用 stream 工具，
+    /// 第二段给出最终文本。
+    /// A mock provider replaying fixed event sequences: turn 1 calls the
+    /// stream tool, turn 2 gives the final text.
+    #[derive(Debug, Clone, Default)]
+    struct StaticProvider {
+        responses: Arc<Mutex<Vec<Vec<StreamEvent>>>>,
+    }
+    impl StaticProvider {
+        fn tool_turn(model: &str) -> Vec<StreamEvent> {
+            let mut reducer = focus_core::provider::ProviderEventReducer::new(model);
+            let mut events = reducer.tool_call_start(0, "stream");
+            events.extend(reducer.finalize_events());
+            let message = reducer.finish().expect("final message");
+            events.push(StreamEvent::Done { message });
+            events
+        }
+        fn text_turn(model: &str) -> Vec<StreamEvent> {
+            let mut reducer = focus_core::provider::ProviderEventReducer::new(model);
+            let mut events = reducer.text_delta("final text");
+            events.extend(reducer.finalize_events());
+            let message = reducer.finish().expect("final message");
+            events.push(StreamEvent::Done { message });
+            events
+        }
+    }
+    impl StreamProvider for StaticProvider {
+        fn stream(&self, _request: &ProviderRequest) -> StreamResult {
+            let mut queue = self.responses.lock().expect("not poisoned");
+            if queue.is_empty() {
+                return Err(focus_core::CoreError::Provider("mock exhausted".into()));
+            }
+            let events = queue.remove(0);
+            Ok(Box::new(Replay { events }))
+        }
+    }
+    struct Replay {
+        events: Vec<StreamEvent>,
+    }
+    impl StreamIterator for Replay {
+        fn next_event(&mut self) -> Option<StreamEvent> {
+            if self.events.is_empty() {
+                None
+            } else {
+                Some(self.events.remove(0))
+            }
+        }
+    }
+
+    let provider = StaticProvider {
+        responses: Arc::new(Mutex::new(vec![
+            StaticProvider::tool_turn("m"),
+            StaticProvider::text_turn("m"),
+        ])),
+    };
+    let config = AgentConfig {
+        model: "m".into(),
+        ..Default::default()
+    };
+    let tools = ToolRegistry::with(Box::new(StreamingTool));
+    let mut agent = Agent::new(config, Box::new(provider), tools);
+    let mut sink = VecSink::new();
+    agent.prompt("go", &mut sink).expect("run failed");
+
+    let updates: Vec<&String> = sink
+        .events
+        .iter()
+        .filter_map(|e| match e {
+            AgentEvent::ToolExecutionUpdate { partial_result, .. } => {
+                partial_result.content[0].as_text().map(|t| &t.text)
+            }
+            _ => None,
+        })
+        .collect();
+    assert_eq!(updates, vec!["line one", "line two"]);
+}
diff --git a/crates/focus-providers/tests/agent_integration.rs b/crates/focus-providers/tests/agent_integration.rs
index 6a20599..c59a99d 100644
--- a/crates/focus-providers/tests/agent_integration.rs
+++ b/crates/focus-providers/tests/agent_integration.rs
@@ -50,7 +50,7 @@ impl Tool for EchoTool {
         &self,
         _id: &str,
         args: &JsonValue,
-        _u: Option<&ToolUpdateSink>,
+        _u: Option<&ToolUpdateSink<'_>>,
     ) -> Result<ToolResult, CoreError> {
         self.calls.lock().unwrap().push(args.clone());
         Ok(ToolResult::text(format!(
diff --git a/crates/focus-providers/tests/anthropic_tests.rs b/crates/focus-providers/tests/anthropic_tests.rs
index bc735ea..e7297b7 100644
--- a/crates/focus-providers/tests/anthropic_tests.rs
+++ b/crates/focus-providers/tests/anthropic_tests.rs
@@ -271,7 +271,7 @@ fn request_body_carries_full_transcript() {
             &self,
             _id: &str,
             _args: &focus_json::JsonValue,
-            _u: Option<&ToolUpdateSink>,
+            _u: Option<&ToolUpdateSink<'_>>,
         ) -> Result<ToolResult, focus_core::CoreError> {
             Ok(ToolResult::text("ok"))
         }
diff --git a/crates/focus-providers/tests/compaction_integration.rs b/crates/focus-providers/tests/compaction_integration.rs
index 9eae6d7..5922461 100644
--- a/crates/focus-providers/tests/compaction_integration.rs
+++ b/crates/focus-providers/tests/compaction_integration.rs
@@ -43,7 +43,7 @@ impl focus_core::Tool for NoopTool {
         &self,
         _id: &str,
         _args: &JsonValue,
-        _u: Option<&focus_core::tool::ToolUpdateSink>,
+        _u: Option<&focus_core::tool::ToolUpdateSink<'_>>,
     ) -> Result<ToolResult, CoreError> {
         Ok(ToolResult::text("ok"))
     }
diff --git a/crates/focus-providers/tests/openai_tests.rs b/crates/focus-providers/tests/openai_tests.rs
index 83edd9a..b072cd6 100644
--- a/crates/focus-providers/tests/openai_tests.rs
+++ b/crates/focus-providers/tests/openai_tests.rs
@@ -309,7 +309,7 @@ fn rich_request() -> ProviderRequest {
             &self,
             _id: &str,
             _args: &focus_json::JsonValue,
-            _u: Option<&ToolUpdateSink>,
+            _u: Option<&ToolUpdateSink<'_>>,
         ) -> Result<ToolResult, focus_core::CoreError> {
             Ok(ToolResult::text("ok"))
         }
@@ -373,7 +373,7 @@ fn chat_replays_reasoning_content() {
             &self,
             _id: &str,
             _args: &focus_json::JsonValue,
-            _u: Option<&ToolUpdateSink>,
+            _u: Option<&ToolUpdateSink<'_>>,
         ) -> Result<ToolResult, focus_core::CoreError> {
             Ok(ToolResult::text("ok"))
         }
@@ -496,7 +496,7 @@ fn chat_replays_both_reasoning_field_names() {
             &self,
             _id: &str,
             _args: &focus_json::JsonValue,
-            _u: Option<&ToolUpdateSink>,
+            _u: Option<&ToolUpdateSink<'_>>,
         ) -> Result<ToolResult, focus_core::CoreError> {
             Ok(ToolResult::text("ok"))
         }
@@ -729,7 +729,7 @@ fn agent_multi_turn_replays_reasoning() {
             &self,
             _id: &str,
             _args: &focus_json::JsonValue,
-            _u: Option<&ToolUpdateSink>,
+            _u: Option<&ToolUpdateSink<'_>>,
         ) -> Result<ToolResult, CoreError> {
             Ok(ToolResult::text("ok"))
         }
diff --git a/crates/focus-tools/src/edit.rs b/crates/focus-tools/src/edit.rs
index e86ca8f..94441bc 100644
--- a/crates/focus-tools/src/edit.rs
+++ b/crates/focus-tools/src/edit.rs
@@ -84,7 +84,7 @@ impl Tool for EditTool {
         &self,
         _id: &str,
         args: &JsonValue,
-        _on_update: Option<&ToolUpdateSink>,
+        _on_update: Option<&ToolUpdateSink<'_>>,
     ) -> CoreResult<ToolResult> {
         let path = args
             .get_str("path")
diff --git a/crates/focus-tools/src/read.rs b/crates/focus-tools/src/read.rs
index 76952b5..5a0f0c4 100644
--- a/crates/focus-tools/src/read.rs
+++ b/crates/focus-tools/src/read.rs
@@ -66,7 +66,7 @@ impl Tool for ReadTool {
         &self,
         _id: &str,
         args: &JsonValue,
-        _on_update: Option<&ToolUpdateSink>,
+        _on_update: Option<&ToolUpdateSink<'_>>,
     ) -> CoreResult<ToolResult> {
         let path = args
             .get_str("path")
diff --git a/crates/focus-tools/src/shell.rs b/crates/focus-tools/src/shell.rs
index 63d11ed..4507e8b 100644
--- a/crates/focus-tools/src/shell.rs
+++ b/crates/focus-tools/src/shell.rs
@@ -81,7 +81,7 @@ impl Tool for ShellTool {
         &self,
         _id: &str,
         args: &JsonValue,
-        on_update: Option<&ToolUpdateSink>,
+        on_update: Option<&ToolUpdateSink<'_>>,
     ) -> CoreResult<ToolResult> {
         let command = args
             .get_str("command")
@@ -189,7 +189,7 @@ enum StreamMsg {
 fn run_child(
     child: &mut Child,
     timeout: Duration,
-    on_update: Option<&ToolUpdateSink>,
+    on_update: Option<&ToolUpdateSink<'_>>,
 ) -> CoreResult<(String, String, i32, bool)> {
     let stdout = child
         .stdout
diff --git a/crates/focus-tools/src/write.rs b/crates/focus-tools/src/write.rs
index 8f221f9..babcbd1 100644
--- a/crates/focus-tools/src/write.rs
+++ b/crates/focus-tools/src/write.rs
@@ -59,7 +59,7 @@ impl Tool for WriteTool {
         &self,
         _id: &str,
         args: &JsonValue,
-        _on_update: Option<&ToolUpdateSink>,
+        _on_update: Option<&ToolUpdateSink<'_>>,
     ) -> CoreResult<ToolResult> {
         let path = args
             .get_str("path")
diff --git a/crates/focus-tui/src/ui.rs b/crates/focus-tui/src/ui.rs
index 4e37475..80fdecd 100644
--- a/crates/focus-tui/src/ui.rs
+++ b/crates/focus-tui/src/ui.rs
@@ -327,9 +327,14 @@ fn block_lines(block: &UiBlock, width: usize) -> Vec<Line<'static>> {
                         "  ── 结果 ──",
                         Style::new().fg(Color::DarkGray),
                     )));
-                    // 结果：部分/全部（在那返回）。
-                    // Result: partial/full (the return).
-                    out.extend(preview_lines(output, *full, width, "  ", dim));
+                    // 运行中：实时显示最新的输出（尾部）；结束后：头部 + 剩余提示。
+                    // Running: show the newest output live (the tail); done:
+                    // head plus a remaining-line hint.
+                    if running {
+                        out.extend(tail_preview(output, width, "  ", dim));
+                    } else {
+                        out.extend(preview_lines(output, *full, width, "  ", dim));
+                    }
                 }
                 if !running && *is_error {
                     out.push(Line::from(Span::styled(
@@ -671,3 +676,27 @@ fn preview_lines(
     }
     out
 }
+
+/// 运行中输出的实时预览：只显示最后若干行（最新的内容）。
+/// Live preview of running output: only the last few lines (the newest).
+fn tail_preview(text: &str, width: usize, indent: &str, style: Style) -> Vec<Line<'static>> {
+    const TAIL_MAX_LINES: usize = 15;
+    let lines: Vec<&str> = text.lines().collect();
+    let tail = lines.len().saturating_sub(TAIL_MAX_LINES);
+    let mut out: Vec<Line<'static>> = Vec::new();
+    if tail > 0 {
+        out.push(Line::from(Span::styled(
+            format!("{}… （以上 {} 行已折叠，运行中仅显示最新）", indent, tail),
+            style,
+        )));
+    }
+    for line in lines.into_iter().skip(tail) {
+        for wrapped in wrap_text(line, width.saturating_sub(2)) {
+            out.push(Line::from(Span::styled(
+                format!("{}{}", indent, wrapped),
+                style,
+            )));
+        }
+    }
+    out
+}