diff --git a/crates/agent-gateway/web/src/pages/StatusDashboardPage.tsx b/crates/agent-gateway/web/src/pages/StatusDashboardPage.tsx
index 9b6855646..629b2c63a 100644
--- a/crates/agent-gateway/web/src/pages/StatusDashboardPage.tsx
+++ b/crates/agent-gateway/web/src/pages/StatusDashboardPage.tsx
@@ -28,6 +28,7 @@ import {
 import { Button } from "@liveagent/ui/components/ui/button";
 import { useAutomation } from "@liveagent/ui/lib/automation/index";
 import type { GatewaySettingsSyncPayload } from "@liveagent/ui/lib/settings/sync";
+import { cachedDateTimeFormat, cachedNumberFormat } from "@liveagent/ui/lib/shared/intlFormatters";
 import { cn } from "@liveagent/ui/lib/shared/utils";
 import type { TerminalSession } from "@liveagent/ui/lib/terminal/types";
 import { useEffect, useMemo, useRef, useState } from "react";
@@ -192,7 +193,7 @@ function formatClock(ms: number) {
   if (!ms) {
     return "--:--:--";
   }
-  return new Intl.DateTimeFormat("zh-CN", {
+  return cachedDateTimeFormat("zh-CN", "status-dashboard-clock", {
     hour: "2-digit",
     minute: "2-digit",
     second: "2-digit",
@@ -201,9 +202,10 @@ function formatClock(ms: number) {
 }
 
 function compactNumber(value: number) {
-  return new Intl.NumberFormat("zh-CN", { notation: "compact", maximumFractionDigits: 1 }).format(
-    Math.max(0, value),
-  );
+  return cachedNumberFormat("zh-CN", "status-dashboard-compact", {
+    notation: "compact",
+    maximumFractionDigits: 1,
+  }).format(Math.max(0, value));
 }
 
 function percentage(value: number) {
diff --git a/crates/agent-gui/test/chat/rendering-perf-locks.test.mjs b/crates/agent-gui/test/chat/rendering-perf-locks.test.mjs
new file mode 100644
index 000000000..a9c781405
--- /dev/null
+++ b/crates/agent-gui/test/chat/rendering-perf-locks.test.mjs
@@ -0,0 +1,135 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+import { createTsModuleLoader } from "../helpers/load-ts-module.mjs";
+
+// 渲染进程长会话性能的反漂移锁（见 issue：3.7 小时会话把 WebContent 顶到 88~124% CPU）。
+//
+// 1. Intl formatter 必须按 (variant, locale) 复用：`sample` 抓到的热点栈是
+//    timerFired → JSEventListener::handleEvent → constructIntlDateTimeFormat →
+//    udat_open，即渲染/tick 路径里反复新建 formatter（每次一次 ICU 初始化）。
+// 2. 可见性判定必须同时认 `document.hidden` 与 `visibilityState`：Tauri/WKWebView
+//    后台启动出现过两者不同步；据此收敛的定时器不能在隐藏时继续跑。
+const loader = createTsModuleLoader();
+const intl = loader.loadModule("@liveagent/ui/lib/shared/intlFormatters.ts");
+const visibility = loader.loadModule("@liveagent/ui/lib/shared/documentVisibility.ts");
+const stats = loader.loadModule("@liveagent/ui/lib/trajectory/stats.ts");
+const presentation = loader.loadModule("@liveagent/ui/lib/trajectory/presentation.ts");
+
+/** 统计期间构造了多少个 Intl 实例。 */
+function countConstructions(kind, run) {
+  const Original = Intl[kind];
+  let built = 0;
+  class Counting extends Original {
+    constructor(...args) {
+      super(...args);
+      built += 1;
+    }
+  }
+  Intl[kind] = Counting;
+  try {
+    const result = run();
+    return { built, result };
+  } finally {
+    Intl[kind] = Original;
+  }
+}
+
+test("cachedNumberFormat constructs once per variant and locale", () => {
+  intl.clearIntlFormatterCaches();
+  const { built } = countConstructions("NumberFormat", () => {
+    for (let index = 0; index < 25; index += 1) {
+      intl.cachedNumberFormat("zh-CN", "integer-0", { maximumFractionDigits: 0 }).format(index);
+    }
+    // 同一个 variant 换 locale 是新的一档。
+    intl.cachedNumberFormat("en-US", "integer-0", { maximumFractionDigits: 0 }).format(1);
+    // 同一个 locale 换 variant 也是新的一档。
+    intl.cachedNumberFormat("zh-CN", "decimal-2", { maximumFractionDigits: 2 }).format(1);
+  });
+  assert.equal(built, 3);
+});
+
+test("cachedNumberFormat returns the same instance for repeated lookups", () => {
+  intl.clearIntlFormatterCaches();
+  const first = intl.cachedNumberFormat("zh-CN", "count");
+  const second = intl.cachedNumberFormat("zh-CN", "count");
+  assert.equal(first, second);
+});
+
+test("cached formatters keep the uncached formatting output", () => {
+  intl.clearIntlFormatterCaches();
+  const cases = [
+    { locale: "zh-CN", variant: "integer-0", options: { maximumFractionDigits: 0 }, value: 12345.678 },
+    { locale: "en-US", variant: "decimal-2", options: { maximumFractionDigits: 2 }, value: 1.239 },
+  ];
+  for (const item of cases) {
+    const expected = new Intl.NumberFormat(item.locale, item.options).format(item.value);
+    assert.equal(intl.cachedNumberFormat(item.locale, item.variant, item.options).format(item.value), expected);
+  }
+
+  const stamp = Date.UTC(2026, 8, 12, 3, 4, 5);
+  const expectedClock = new Intl.DateTimeFormat("zh-CN", {
+    hour: "2-digit",
+    minute: "2-digit",
+    second: "2-digit",
+    fractionalSecondDigits: 3,
+  }).format(new Date(stamp));
+  assert.equal(
+    intl
+      .cachedDateTimeFormat("zh-CN", "clock-ms", {
+        hour: "2-digit",
+        minute: "2-digit",
+        second: "2-digit",
+        fractionalSecondDigits: 3,
+      })
+      .format(new Date(stamp)),
+    expectedClock,
+  );
+});
+
+test("trajectory stats formatters reuse one formatter per locale", () => {
+  intl.clearIntlFormatterCaches();
+  const { built, result } = countConstructions("NumberFormat", () => {
+    const values = [];
+    for (let index = 0; index < 20; index += 1) {
+      values.push(stats.formatStatTokens(index * 900, "zh-CN"));
+      values.push(stats.formatStatCount(index, "zh-CN"));
+    }
+    return values;
+  });
+  // compact-whole / compact-1 / count —— 三档，与调用次数无关。
+  assert.equal(built, 3);
+  assert.equal(result.length, 40);
+});
+
+test("trajectory presentation formatters reuse one formatter per locale", () => {
+  intl.clearIntlFormatterCaches();
+  const { built } = countConstructions("NumberFormat", () => {
+    for (let index = 0; index < 30; index += 1) {
+      presentation.formatTrajectoryDuration(index * 120, "zh-CN");
+      presentation.formatTrajectoryCount(index, "zh-CN");
+    }
+  });
+  assert.equal(built, 2);
+});
+
+test("isDocumentHidden treats both hidden signals as hidden", () => {
+  const original = Object.getOwnPropertyDescriptor(globalThis, "document");
+  try {
+    assert.equal(visibility.isDocumentHidden(), false, "no document (plain node) is not hidden");
+
+    globalThis.document = { hidden: true, visibilityState: "visible" };
+    assert.equal(visibility.isDocumentHidden(), true, "hidden=true wins over a stale visibilityState");
+
+    globalThis.document = { hidden: false, visibilityState: "hidden" };
+    assert.equal(visibility.isDocumentHidden(), true, "visibilityState=hidden counts too");
+
+    globalThis.document = { hidden: false, visibilityState: "visible" };
+    assert.equal(visibility.isDocumentHidden(), false);
+  } finally {
+    if (original) {
+      Object.defineProperty(globalThis, "document", original);
+    } else {
+      delete globalThis.document;
+    }
+  }
+});
diff --git a/crates/agent-ui/src/components/Markdown.tsx b/crates/agent-ui/src/components/Markdown.tsx
index c150a163f..99d5abf82 100644
--- a/crates/agent-ui/src/components/Markdown.tsx
+++ b/crates/agent-ui/src/components/Markdown.tsx
@@ -682,7 +682,7 @@ const MARKDOWN_EMBED_CLASSNAME = cn(
   "[&_[data-streamdown='mermaid-block-actions']]:gap-2 [&_[data-streamdown='mermaid-block-actions']]:rounded-none [&_[data-streamdown='mermaid-block-actions']]:border-0 [&_[data-streamdown='mermaid-block-actions']]:bg-transparent [&_[data-streamdown='mermaid-block-actions']]:p-0 [&_[data-streamdown='mermaid-block-actions']]:shadow-none [&_[data-streamdown='mermaid-block-actions']]:backdrop-blur-none",
   "[&_[data-streamdown='mermaid-block-actions']_svg]:size-3 [&_[data-streamdown='mermaid-block']_button>svg]:size-3",
   "[&_[data-streamdown='table-wrapper']]:my-4 [&_[data-streamdown='table-wrapper']]:!w-full [&_[data-streamdown='table-wrapper']]:min-w-0 [&_[data-streamdown='table-wrapper']]:gap-0 [&_[data-streamdown='table-wrapper']]:rounded-none [&_[data-streamdown='table-wrapper']]:border-0 [&_[data-streamdown='table-wrapper']]:bg-transparent [&_[data-streamdown='table-wrapper']]:p-0 [&_[data-streamdown='table-wrapper']]:shadow-none [&_[data-streamdown='table-wrapper']]:outline-none [&_[data-streamdown='table-wrapper']]:ring-0",
-  "[&_[data-streamdown='table-wrapper']>div:last-child]:!w-full [&_[data-streamdown='table-wrapper']>div:last-child]:min-w-0 [&_[data-streamdown='table-wrapper']>div:last-child]:overflow-x-auto [&_[data-streamdown='table-wrapper']>div:last-child]:overflow-y-hidden [&_[data-streamdown='table-wrapper']>div:last-child]:rounded-none [&_[data-streamdown='table-wrapper']>div:last-child]:border-0 [&_[data-streamdown='table-wrapper']>div:last-child]:bg-transparent [&_[data-streamdown='table-wrapper']>div:last-child]:p-0 [&_[data-streamdown='table-wrapper']>div:last-child]:shadow-none [&_[data-streamdown='table-wrapper']>div:last-child]:outline-none [&_[data-streamdown='table-wrapper']>div:last-child]:ring-0",
+  "[&_[data-streamdown='table-wrapper']>div:last-child]:!w-full [&_[data-streamdown='table-wrapper']>div:last-child]:min-w-0 [&_[data-streamdown='table-wrapper']>div:last-child]:overflow-x-auto [&_[data-streamdown='table-wrapper']>div:last-child]:overflow-y-hidden [&_[data-streamdown='table-wrapper']>div:last-child]:[contain:layout_paint_style] [&_[data-streamdown='table-wrapper']>div:last-child]:rounded-none [&_[data-streamdown='table-wrapper']>div:last-child]:border-0 [&_[data-streamdown='table-wrapper']>div:last-child]:bg-transparent [&_[data-streamdown='table-wrapper']>div:last-child]:p-0 [&_[data-streamdown='table-wrapper']>div:last-child]:shadow-none [&_[data-streamdown='table-wrapper']>div:last-child]:outline-none [&_[data-streamdown='table-wrapper']>div:last-child]:ring-0",
   "[&_table]:my-2 [&_table]:!w-full [&_table]:!min-w-full [&_table]:max-w-none [&_table]:table-auto [&_table]:border-collapse [&_table]:rounded-none [&_table]:border-0 [&_table]:bg-transparent [&_table]:shadow-none [&_table]:outline-none [&_table]:ring-0",
   "[&_thead]:bg-transparent [&_tbody]:bg-transparent [&_tr]:border-b [&_tr]:border-border/50 [&_tr]:bg-transparent [&_tbody_tr:last-child]:border-b-0",
   "[&_th]:border-0 [&_th]:px-0 [&_th]:py-2 [&_th]:pr-8 [&_th]:text-left [&_th]:align-bottom [&_th]:font-semibold [&_th]:tracking-[-0.01em] [&_th]:text-foreground",
diff --git a/crates/agent-ui/src/components/chat/AssistantWorkTrace.tsx b/crates/agent-ui/src/components/chat/AssistantWorkTrace.tsx
index 6cfe498c5..2a01fe3d6 100644
--- a/crates/agent-ui/src/components/chat/AssistantWorkTrace.tsx
+++ b/crates/agent-ui/src/components/chat/AssistantWorkTrace.tsx
@@ -1,5 +1,6 @@
 import { ChevronDown } from "@liveagent/ui/components/IconSet";
 import { useLocale } from "@liveagent/ui/i18n/index";
+import { isDocumentHidden } from "@liveagent/ui/lib/shared/documentVisibility";
 import { cn } from "@liveagent/ui/lib/shared/utils";
 import { type CSSProperties, type ReactNode, useEffect, useRef, useState } from "react";
 import { LazyCollapse } from "./LazyCollapse";
@@ -120,7 +121,12 @@ export function AssistantWorkTrace({
       if (startedAt !== null) setElapsedMs(Math.max(0, Date.now() - startedAt));
     };
     updateElapsed();
-    const timer = window.setInterval(updateElapsed, 1_000);
+    // 不可见时停表：work trace 的秒表只服务于"看着它跑"的观感，隐藏窗口里的
+    // 每秒重渲染纯属白烧 CPU；重新可见时 effect 重跑，读数立即补上。
+    const timer = window.setInterval(() => {
+      if (isDocumentHidden()) return;
+      updateElapsed();
+    }, 1_000);
     return () => window.clearInterval(timer);
   }, [durationMs, running]);
 
diff --git a/crates/agent-ui/src/components/chat/ConversationSearchDialog.tsx b/crates/agent-ui/src/components/chat/ConversationSearchDialog.tsx
index 09c866cd2..96e5c1adc 100644
--- a/crates/agent-ui/src/components/chat/ConversationSearchDialog.tsx
+++ b/crates/agent-ui/src/components/chat/ConversationSearchDialog.tsx
@@ -11,6 +11,7 @@ import {
   type PersistedConversationSearchResult,
   searchPersistedConversations,
 } from "@liveagent/ui/lib/chat/conversationSearch";
+import { cachedDateTimeFormat } from "@liveagent/ui/lib/shared/intlFormatters";
 import { cn } from "@liveagent/ui/lib/shared/utils";
 import { Fragment, type ReactNode, useCallback, useEffect, useMemo, useRef, useState } from "react";
 import type { ConversationOpenOptions } from "../../lib/sidebar/openController";
@@ -47,7 +48,7 @@ function toSearchResult(item: SidebarConversation): PersistedConversationSearchR
 
 function formatUpdatedAt(value: number | undefined, locale: string) {
   if (!value || !Number.isFinite(value)) return "";
-  return new Intl.DateTimeFormat(locale, {
+  return cachedDateTimeFormat(locale, "search-updated-at", {
     month: "short",
     day: "numeric",
     hour: "2-digit",
diff --git a/crates/agent-ui/src/components/chat/ConversationStatsBar.tsx b/crates/agent-ui/src/components/chat/ConversationStatsBar.tsx
index cf8845287..251259149 100644
--- a/crates/agent-ui/src/components/chat/ConversationStatsBar.tsx
+++ b/crates/agent-ui/src/components/chat/ConversationStatsBar.tsx
@@ -1,4 +1,5 @@
 import { useLocale } from "@liveagent/ui/i18n/index";
+import { useDocumentHidden } from "@liveagent/ui/lib/shared/documentVisibility";
 import { cn } from "@liveagent/ui/lib/shared/utils";
 import { useEffect, useState } from "react";
 import { canManualCompact, contextUsageRatio } from "../../lib/chat/contextUsage";
@@ -28,12 +29,16 @@ type StatGroup = {
 
 /** 运行中每秒重渲染一次，把 *RunningSinceAt 折算进显示值；空闲时零定时器。 */
 function useRunningHeartbeat(running: boolean): number {
+  const hidden = useDocumentHidden();
   const [, setBeat] = useState(0);
   useEffect(() => {
-    if (!running) return;
+    // 窗口不可见时不起心跳：这些帧用户看不到，代价却是每秒重渲染一次统计条
+    // （连带重建其中的 formatter、以及在长会话里重排可见行邻域）。重新可见时
+    // hidden 翻转会重启 effect，读数立刻回到当前值。
+    if (!running || hidden) return;
     const timer = setInterval(() => setBeat((beat) => beat + 1), HEARTBEAT_MS);
     return () => clearInterval(timer);
-  }, [running]);
+  }, [hidden, running]);
   return Date.now();
 }
 
diff --git a/crates/agent-ui/src/components/chat/SharedHistoryManagerModal.tsx b/crates/agent-ui/src/components/chat/SharedHistoryManagerModal.tsx
index b7aa98034..683840765 100644
--- a/crates/agent-ui/src/components/chat/SharedHistoryManagerModal.tsx
+++ b/crates/agent-ui/src/components/chat/SharedHistoryManagerModal.tsx
@@ -22,6 +22,7 @@ import {
 } from "@liveagent/ui/components/ui/dialog";
 import { useLocale } from "@liveagent/ui/i18n/index";
 import { buildShareUrl, resolveShareOrigin } from "@liveagent/ui/lib/chat/historyShareOrigin";
+import { cachedDateTimeFormat } from "@liveagent/ui/lib/shared/intlFormatters";
 import { cn } from "@liveagent/ui/lib/shared/utils";
 import { useMemo, useState } from "react";
 
@@ -65,7 +66,7 @@ function formatConversationTime(timestamp: number | undefined, locale: string, f
   if (typeof timestamp !== "number" || !Number.isFinite(timestamp) || timestamp <= 0) {
     return fallback;
   }
-  return new Intl.DateTimeFormat(locale, {
+  return cachedDateTimeFormat(locale, "shared-history-time", {
     month: "2-digit",
     day: "2-digit",
     hour: "2-digit",
diff --git a/crates/agent-ui/src/components/project-tools/BackgroundTasksPanel.tsx b/crates/agent-ui/src/components/project-tools/BackgroundTasksPanel.tsx
index f1213d326..0dc3f0715 100644
--- a/crates/agent-ui/src/components/project-tools/BackgroundTasksPanel.tsx
+++ b/crates/agent-ui/src/components/project-tools/BackgroundTasksPanel.tsx
@@ -9,6 +9,7 @@ import {
   Trash2,
 } from "@liveagent/ui/components/IconSet";
 import { useLocale } from "@liveagent/ui/i18n/index";
+import { isDocumentHidden } from "@liveagent/ui/lib/shared/documentVisibility";
 import {
   memo,
   type MouseEvent as ReactMouseEvent,
@@ -494,7 +495,11 @@ export const BackgroundTasksPanel = memo(function BackgroundTasksPanel(
 
   useEffect(() => {
     if (!active || !hasRunning) return;
-    const timer = window.setInterval(() => setNow(Date.now()), 1000);
+    // 与面板的 30s reconcile 同一口径：窗口不可见时这一秒一跳只是白烧 CPU。
+    const timer = window.setInterval(() => {
+      if (isDocumentHidden()) return;
+      setNow(Date.now());
+    }, 1000);
     setNow(Date.now());
     return () => window.clearInterval(timer);
   }, [active, hasRunning]);
diff --git a/crates/agent-ui/src/lib/chat/uiMessages.ts b/crates/agent-ui/src/lib/chat/uiMessages.ts
index 7cdd6b676..88813551f 100644
--- a/crates/agent-ui/src/lib/chat/uiMessages.ts
+++ b/crates/agent-ui/src/lib/chat/uiMessages.ts
@@ -859,6 +859,9 @@ export function appendThinkingBlockFromAssistant(
 }
 
 function rebalanceHostedSearchTextBoundaries(blocks: UiRoundContentBlock[]): UiRoundContentBlock[] {
+  // 绝大多数回复里没有任何 hosted-search 块：直接返回同一数组。否则每次文本增量
+  // 都会重建整个块数组（长会话里等价于每 delta 一次全量分配 + 数组拷贝）。
+  if (!blocks.some((block) => block.kind === "hostedSearch")) return blocks;
   const out: UiRoundContentBlock[] = [];
   for (let index = 0; index < blocks.length; index += 1) {
     const current = blocks[index];
diff --git a/crates/agent-ui/src/lib/chat/userMessageContent.tsx b/crates/agent-ui/src/lib/chat/userMessageContent.tsx
index 7a206c415..505dcb098 100644
--- a/crates/agent-ui/src/lib/chat/userMessageContent.tsx
+++ b/crates/agent-ui/src/lib/chat/userMessageContent.tsx
@@ -28,6 +28,11 @@ import {
   type PendingUploadedFile,
   parsePastedTextDisplayReferences,
 } from "@liveagent/ui/lib/chat/uploadedFiles";
+import {
+  cachedDateTimeFormat,
+  cachedNumberFormat,
+  cachedRelativeTimeFormat,
+} from "@liveagent/ui/lib/shared/intlFormatters";
 import {
   type FocusEvent,
   type MouseEvent,
@@ -548,20 +553,20 @@ export function tokenizeUserMessage(
 }
 
 function formatPastedTextCount(value: number) {
-  return new Intl.NumberFormat().format(value);
+  return cachedNumberFormat(undefined, "count").format(value);
 }
 
 function formatCommitTooltipDate(value: string | undefined, locale: string) {
   if (!value) return null;
   const date = new Date(value);
   if (Number.isNaN(date.getTime())) return null;
-  const absolute = date.toLocaleString(locale, {
+  const absolute = cachedDateTimeFormat(locale, "commit-date", {
     year: "numeric",
     month: "long",
     day: "numeric",
     hour: "2-digit",
     minute: "2-digit",
-  });
+  }).format(date);
   const deltaSeconds = Math.round((date.getTime() - Date.now()) / 1000);
   const units: Array<{
     unit: "year" | "month" | "day" | "hour" | "minute" | "second";
@@ -578,10 +583,9 @@ function formatCommitTooltipDate(value: string | undefined, locale: string) {
     unit: "second",
     seconds: 1,
   };
-  const relative = new Intl.RelativeTimeFormat(locale, { numeric: "auto" }).format(
-    Math.round(deltaSeconds / selected.seconds),
-    selected.unit,
-  );
+  const relative = cachedRelativeTimeFormat(locale, "commit-relative", {
+    numeric: "auto",
+  }).format(Math.round(deltaSeconds / selected.seconds), selected.unit);
   return { relative, absolute };
 }
 
diff --git a/crates/agent-ui/src/lib/shared/documentVisibility.ts b/crates/agent-ui/src/lib/shared/documentVisibility.ts
new file mode 100644
index 000000000..c44f9ea41
--- /dev/null
+++ b/crates/agent-ui/src/lib/shared/documentVisibility.ts
@@ -0,0 +1,36 @@
+import { useEffect, useState } from "react";
+
+/**
+ * 文档是否隐藏。
+ *
+ * 两个信号都当作隐藏：`document.hidden` 与 `document.visibilityState` 本该同步，
+ * 但 Tauri/WKWebView 的后台启动状态下出现过 `hidden=true` 而 `visibilityState`
+ * 仍是 `"visible"` 的组合（原实现见设置页的 section-enter 兜底）。
+ *
+ * 退出后台时 `visibilitychange` 只会触发一次，因此以隐藏期间的定时器一律用
+ * 「重新订阅 + 重算」而不是「暂停后继续累加」的方式恢复。
+ */
+export function isDocumentHidden(): boolean {
+  if (typeof document === "undefined") return false;
+  return document.hidden || document.visibilityState === "hidden";
+}
+
+/**
+ * 订阅文档可见性。渲染进程在窗口不可见时不该继续跑每秒心跳、重建账本或重绘
+ * 长列表——这些工作产生的帧用户看不到，却照样烧 CPU（长会话下表现为渲染进程
+ * 持续 80%+ 与整机热限流）。
+ */
+export function useDocumentHidden(): boolean {
+  const [hidden, setHidden] = useState(isDocumentHidden);
+
+  useEffect(() => {
+    const sync = () => setHidden(isDocumentHidden());
+    sync();
+    document.addEventListener("visibilitychange", sync);
+    return () => {
+      document.removeEventListener("visibilitychange", sync);
+    };
+  }, []);
+
+  return hidden;
+}
diff --git a/crates/agent-ui/src/lib/shared/intlFormatters.ts b/crates/agent-ui/src/lib/shared/intlFormatters.ts
new file mode 100644
index 000000000..2852d9076
--- /dev/null
+++ b/crates/agent-ui/src/lib/shared/intlFormatters.ts
@@ -0,0 +1,75 @@
+/**
+ * Intl formatter 缓存。
+ *
+ * 构造一个 `Intl.*Format` 会走 ICU 初始化（`udat_open` →
+ * `icu::SimpleDateFormat`），是公认的昂贵操作。在渲染体或定时器回调里每次
+ * `new` 一次，等价于每个 tick 做一次 ICU 初始化：实测长会话下这条路径把渲染
+ * 进程 CPU 顶到 100%+，`sample` 抓到的热点栈正是
+ * `timerFired → JSEventListener::handleEvent → constructIntlDateTimeFormat →
+ * udat_open`。同一个 formatter 的生命周期应当是进程级的——locale 集合极小，
+ * 选项形状在调用点都是字面量常量。
+ *
+ * 缓存键是 `${variant}|${locale}`，而不是把 options 序列化进去：调用方为每处
+ * 调用点给一个稳定的 variant 名，这样键只是短字符串拼接；若用
+ * `JSON.stringify(options)` 作键，每次调用都要付一次序列化成本，等于把省下来的
+ * ICU 开销换成字符串开销——而那正是同一份 sample 里 `WTF::findCommon` 那类
+ * 热点的由来。
+ *
+ * 用法：同一处调用点必须始终使用同一个 variant 名，并始终传同一套 options。
+ * variant 与 options 不一致会让缓存返回错误的格式化结果，因此这里不做运行时
+ * 校验——调用点相邻书写，评审时一眼可见。
+ */
+
+const numberFormats = new Map<string, Intl.NumberFormat>();
+const dateTimeFormats = new Map<string, Intl.DateTimeFormat>();
+const relativeTimeFormats = new Map<string, Intl.RelativeTimeFormat>();
+
+function cacheKey(variant: string, locale: string | undefined): string {
+  return `${variant}|${locale ?? ""}`;
+}
+
+export function cachedNumberFormat(
+  locale: string | undefined,
+  variant: string,
+  options?: Intl.NumberFormatOptions,
+): Intl.NumberFormat {
+  const key = cacheKey(variant, locale);
+  const cached = numberFormats.get(key);
+  if (cached) return cached;
+  const formatter = new Intl.NumberFormat(locale, options);
+  numberFormats.set(key, formatter);
+  return formatter;
+}
+
+export function cachedDateTimeFormat(
+  locale: string | undefined,
+  variant: string,
+  options?: Intl.DateTimeFormatOptions,
+): Intl.DateTimeFormat {
+  const key = cacheKey(variant, locale);
+  const cached = dateTimeFormats.get(key);
+  if (cached) return cached;
+  const formatter = new Intl.DateTimeFormat(locale, options);
+  dateTimeFormats.set(key, formatter);
+  return formatter;
+}
+
+export function cachedRelativeTimeFormat(
+  locale: string | undefined,
+  variant: string,
+  options?: Intl.RelativeTimeFormatOptions,
+): Intl.RelativeTimeFormat {
+  const key = cacheKey(variant, locale);
+  const cached = relativeTimeFormats.get(key);
+  if (cached) return cached;
+  const formatter = new Intl.RelativeTimeFormat(locale, options);
+  relativeTimeFormats.set(key, formatter);
+  return formatter;
+}
+
+/** 测试用：清空缓存（省略参数则全清）。 */
+export function clearIntlFormatterCaches(kind?: "number" | "dateTime" | "relativeTime"): void {
+  if (kind === undefined || kind === "number") numberFormats.clear();
+  if (kind === undefined || kind === "dateTime") dateTimeFormats.clear();
+  if (kind === undefined || kind === "relativeTime") relativeTimeFormats.clear();
+}
diff --git a/crates/agent-ui/src/lib/trajectory/presentation.ts b/crates/agent-ui/src/lib/trajectory/presentation.ts
index cf9fbfe26..b8799b83a 100644
--- a/crates/agent-ui/src/lib/trajectory/presentation.ts
+++ b/crates/agent-ui/src/lib/trajectory/presentation.ts
@@ -5,6 +5,7 @@
  * 记录翻译成 i18n key 与格式化数值，真正的取词留给组件。
  */
 
+import { cachedDateTimeFormat, cachedNumberFormat } from "../shared/intlFormatters";
 import type {
   TrajectoryHeaderChange,
   TrajectoryLedger,
@@ -81,9 +82,9 @@ export function formatTrajectoryDuration(milliseconds: number | null, locale: st
   if (milliseconds === null || !Number.isFinite(milliseconds)) return "—";
   const rounded = Math.max(0, milliseconds);
   if (rounded < 1000) {
-    return `${new Intl.NumberFormat(locale, { maximumFractionDigits: 0 }).format(rounded)} ms`;
+    return `${cachedNumberFormat(locale, "integer-0", { maximumFractionDigits: 0 }).format(rounded)} ms`;
   }
-  return `${new Intl.NumberFormat(locale, { maximumFractionDigits: 2 }).format(rounded / 1000)} s`;
+  return `${cachedNumberFormat(locale, "decimal-2", { maximumFractionDigits: 2 }).format(rounded / 1000)} s`;
 }
 
 export function formatTrajectorySeconds(seconds: number | null, locale: string): string {
@@ -92,17 +93,17 @@ export function formatTrajectorySeconds(seconds: number | null, locale: string):
 
 export function formatTrajectoryCount(value: number | undefined, locale: string): string {
   if (value === undefined || !Number.isFinite(value)) return "—";
-  return new Intl.NumberFormat(locale, { maximumFractionDigits: 0 }).format(value);
+  return cachedNumberFormat(locale, "integer-0", { maximumFractionDigits: 0 }).format(value);
 }
 
 export function formatTrajectoryClock(timestamp: number | null, locale: string): string {
   if (timestamp === null || !Number.isFinite(timestamp)) return "—";
-  return new Date(timestamp).toLocaleTimeString(locale, {
+  return cachedDateTimeFormat(locale, "clock-ms", {
     hour: "2-digit",
     minute: "2-digit",
     second: "2-digit",
     fractionalSecondDigits: 3,
-  });
+  }).format(new Date(timestamp));
 }
 
 /** 解码吞吐；缺少任一时序事实时返回 null 而不是估算。 */
diff --git a/crates/agent-ui/src/lib/trajectory/stats.ts b/crates/agent-ui/src/lib/trajectory/stats.ts
index a35fb0472..7c2c37c3a 100644
--- a/crates/agent-ui/src/lib/trajectory/stats.ts
+++ b/crates/agent-ui/src/lib/trajectory/stats.ts
@@ -6,6 +6,7 @@
  * `*RunningSinceAt` 让展示层用心跳补齐，聚合结果因此保持纯函数、可缓存。
  */
 
+import { cachedNumberFormat } from "../shared/intlFormatters";
 import type { TrajectoryLedger } from "./types";
 
 export type ConversationStats = {
@@ -189,15 +190,19 @@ export function formatStatLatency(ms: number): string {
 
 export function formatStatTokens(value: number, locale: string): string {
   if (!Number.isFinite(value) || value <= 0) return "0";
-  return new Intl.NumberFormat(locale, {
+  // 两个档位各自成键：<1000 不留小数位（892 → "892"，而不是 compact 的 "0.9K"）。
+  // formatter 按 (variant, locale) 缓存——这一族函数在状态栏渲染体里被逐个调用，
+  // 而状态栏运行中每秒重渲染一次（see ConversationStatsBar 心跳）。
+  const formatter = cachedNumberFormat(locale, value < 1000 ? "compact-whole" : "compact-1", {
     notation: "compact",
     maximumFractionDigits: value < 1000 ? 0 : 1,
-  }).format(Math.round(value));
+  });
+  return formatter.format(Math.round(value));
 }
 
 export function formatStatCount(value: number, locale: string): string {
   if (!Number.isFinite(value) || value <= 0) return "0";
-  return new Intl.NumberFormat(locale).format(Math.round(value));
+  return cachedNumberFormat(locale, "count").format(Math.round(value));
 }
 
 export function formatStatThroughput(tokPerSec: number): string {
diff --git a/crates/agent-ui/src/pages/settings/SettingsShell.tsx b/crates/agent-ui/src/pages/settings/SettingsShell.tsx
index 8cef4763c..fe23c9927 100644
--- a/crates/agent-ui/src/pages/settings/SettingsShell.tsx
+++ b/crates/agent-ui/src/pages/settings/SettingsShell.tsx
@@ -2,6 +2,7 @@ import { ArrowLeft, Search } from "@liveagent/ui/components/IconSet";
 import { useEffect, useMemo, useState } from "react";
 import type { SettingsSaveState, UiExtensionRegistry } from "../../contracts/registry";
 import { useLocale } from "../../i18n";
+import { useDocumentHidden } from "../../lib/shared/documentVisibility";
 import { cn } from "../../lib/shared/utils";
 
 type SettingsShellProps<Context> = {
@@ -16,28 +17,8 @@ type SettingsShellProps<Context> = {
 // 文档隐藏时 WebKit/Chromium 会暂停 CSS keyframe 动画，`.settings-section-enter`
 // 与 `.settings-section-title-enter` 因此停在 from 态（opacity:0 + 位移缩放），
 // 整个设置页看起来是空白。useSettingsOverlay 只兜底了外层浮层容器，内层区块
-// 需要这一份。
-//
-// 两个信号都当作隐藏：`document.hidden` 与 `document.visibilityState` 本该同步，
-// 但 Tauri/WKWebView 的后台启动状态下出现过 hidden=true 而 visibilityState 仍是
-// "visible" 的组合。
-function isDocumentHidden() {
-  if (typeof document === "undefined") return false;
-  return document.hidden || document.visibilityState === "hidden";
-}
-
-function useIsDocumentHidden() {
-  const [hidden, setHidden] = useState(isDocumentHidden);
-  useEffect(() => {
-    const sync = () => setHidden(isDocumentHidden());
-    sync();
-    document.addEventListener("visibilitychange", sync);
-    return () => {
-      document.removeEventListener("visibilitychange", sync);
-    };
-  }, []);
-  return hidden;
-}
+// 需要这一份。可见性判定（含 Tauri/WKWebView 的 hidden/visibilityState 不同步
+// 组合）与其它按可见性收敛的定时器共用 lib/shared/documentVisibility。
 
 function getSaveIndicator(state: SettingsSaveState, t: (key: string) => string) {
   switch (state.status) {
@@ -75,7 +56,7 @@ export function SettingsShell<Context>(props: SettingsShellProps<Context>) {
   const { t } = useLocale();
   const [section, setSection] = useState(initialSection);
   const [navQuery, setNavQuery] = useState("");
-  const isDocumentHidden = useIsDocumentHidden();
+  const isDocumentHidden = useDocumentHidden();
   const hiddenSectionSet = useMemo(() => new Set(hiddenSections), [hiddenSections]);
   const sections = useMemo(
     () =>
diff --git a/crates/agent-ui/src/pages/settings/memory/panelModel.ts b/crates/agent-ui/src/pages/settings/memory/panelModel.ts
index 553be1991..230b0aa0b 100644
--- a/crates/agent-ui/src/pages/settings/memory/panelModel.ts
+++ b/crates/agent-ui/src/pages/settings/memory/panelModel.ts
@@ -24,6 +24,7 @@ import type {
   OrganizerSafeDecision,
 } from "../../../lib/memory/organizer/runRecord";
 import { REJECTION_BUCKET_KEYS, type RejectionBucketKey } from "../../../lib/memory/schema";
+import { cachedDateTimeFormat } from "../../../lib/shared/intlFormatters";
 
 export type MemoryTab = "global" | "project" | "journal";
 
@@ -68,7 +69,9 @@ export function formatTime(value: number) {
   if (!value) return "";
   const date = new Date(value);
   if (Number.isNaN(date.getTime())) return String(value);
-  return date.toLocaleString();
+  // 默认 locale 的时间戳（`toLocaleString()` 每次调用都会新建一个
+  // DateTimeFormat，即一次 ICU 初始化）；面板里每行都会调一次。
+  return cachedDateTimeFormat(undefined, "memory-panel-time").format(date);
 }
 
 function dailyTitle(entry: { slug: string; dateLocal?: string | null }) {