diff --git a/docs/external-plugin-guide.md b/docs/external-plugin-guide.md
index ca4c5ee..7a9903d 100644
--- a/docs/external-plugin-guide.md
+++ b/docs/external-plugin-guide.md
@@ -752,7 +752,7 @@ ctx.effect(() =>
 - **面板表面**：右/底面板背景 = `var(--dsw-alias-bg-layer-1)`。**绝不消费 `--dsw-specific-sidebar-fill`**（宿主左导航专属，皮肤按左导航语义覆盖它，面板消费会失去填充）。换面板表面 = 覆写 `--dsw-alias-bg-layer-1`。
 - **终端/编辑器表面**：`effectiveTokenValue` 读 `--dsw-alias-bg-base`——`transparent` 与 alpha < 0.9 的半透明值回退不透明底色（文字不叠背景画，issue #90）；≥ 0.9 放行。
 - **根锚点**：宿主 div 带 `data-dsh-better-sidebar`（append 到 body）；其内**面板宿主层** `[data-dsh-panel-host]`（`fixed; inset:0; z-25; pointer-events:none`，v0.13.1+），面板/开关簇 absolute 定位，免疫中间层 transform 劫持；页面级 transform 触发 `data-dsh-panel-host-degraded` 降级。皮肤作用域覆盖限定在 `[data-dsh-better-sidebar]` 内。
-- **布局变量**（`<html>` 上，面板打开时有效）：`--dsh-sidebar-width` / `--dsh-sidebar-height`。宿主推挤 = `#root` margin/width calc + centerCol `margin-bottom`；锚点用**复合选择器双保险**（禁止 `nth-child`）：`#root [data-dsh-frame] > [data-pane="conversation"]` 与 `#root :has(> [data-slot="conversation"])`（两代命名同元素，`drag-layout.e2e.ts` 断言）。
+- **布局变量**（`<html>` 上，面板打开时有效）：`--dsh-sidebar-width` / `--dsh-sidebar-height`。宿主推挤 = `#root` margin/width calc + centerCol `margin-bottom`；锚点 = **JS 标注**（禁止 `nth-child`）：侧栏 shell 的定位器给测得的 centerCol 节点打 `[data-dsh-center-col]` 标签（`Sidebar.tsx` locate，节点更换/HMR 时随 ref 迁移），`layout.css` 用 `#root [data-dsh-center-col]` 选中（`drag-layout.e2e.ts` 断言恰一节点且为 `[data-slot="conversation"]` 的父级）。
 - **桌面信号与标题栏**（v0.14.1+ 四方案模型 `SidebarPrefs.titleBarScheme`，唯一决策点 `src/client/titlebar-strip.ts` 纯函数）：
   - 壳信号（只读，不自动触发修改）：URL `dsh-desktop-mode` / `dsh-desktop-platform` / 可选 `dsh-desktop-titlebar-inset`（0–120 clamp）。
   - **strip 取值链**：⓪ `web` 方案强制 0；① `navigator.windowControlsOverlay` 真实几何（`wco.ts` 订阅 `geometrychange`，**为 0 也权威**，`visible=false` 幽灵 API 视为缺失）；② URL inset；③ 壳预设 `stripFor`（仅 `preset`）；④ 手动 `titleBarStripPx`（仅 `custom`）；⑤ 0。驱动 `body[data-dsh-title-bar-compat]` + `--dsh-title-bar-strip`。
diff --git a/docs/plans/2026-08-31-perf-optimization.md b/docs/plans/2026-08-31-perf-optimization.md
new file mode 100644
index 0000000..bb61520
--- /dev/null
+++ b/docs/plans/2026-08-31-perf-optimization.md
@@ -0,0 +1,87 @@
+# 侧边栏性能优化 + 底栏拖拽布局突变修复
+
+**日期**：2026-08-31（2026-09-01 rebase 到 main c199212 并在 alpha.3 上复测）
+**状态**：已实施（分支 `feat/sidebar-perf`，单 PR 多 commit）
+**目标宿主**：DSH v0.1.2-alpha.2 起开发，宿主参考 `/Users/menghuan/Code/deepseek-harness`（只读）；main 已切 alpha.3（v0.18.1-alpha.0），rebase 后在 alpha.3 真机全量复测（§3.1）
+**测量环境**：macOS arm64 本机，真实 `dsh web`（npx 钉版）+ scratch profile 挂载 tarball，Playwright Chromium 无头，每指标 3 次取中位数（`tests/e2e/perf.e2e.ts` 输出 `PERF_JSON`）。
+
+## 1. 修复的 bug：底栏拖拽引发原生左侧边栏突变
+
+**症状**：右侧面板关闭时拖动底栏 resizer，DSH 原生左侧边栏突然折叠/跳动；松手后弹回。插件自己的右侧边栏不受影响。
+
+**根因**（源码级定位，`Sidebar.tsx`）：底栏拖拽的 `applyDrag` 把「持久化的右栏宽度偏好」（如 400px）无条件写进 `--dsh-sidebar-width`，不看 `panelOpen`；而静止时的 push effect 走 `layoutPushSize` 门控（面板关闭 → 0）。于是拖拽首帧该变量 0 → ~400px：
+
+1. `layout.css` 的 `#root { margin-right; width: calc(100% - …) }` 瞬间挤掉宿主 400px（拖拽期间 transition 被 `body[data-dsh-sidebar-dragging]` 关闭——瞬跳而非动画）；
+2. 宿主 `AppFrame` 的 ResizeObserver → `setViewport` → viewport 跌破 1024px 断点 → `computeColumns` 把原生左栏折叠成 56px rail（0.3s grid 轨道动画）；
+3. 松手 `commitDrag` → store 提交 → push effect 又写回 0 → `#root` 弹回 → 左栏再展开。
+
+插件右栏在 `#root` 之外的 `document.body` fixed 层（`[data-dsh-panel-host]`），几何上碰不到——这正是「左栏突变、右栏无恙」的不对称来源。底栏是**唯一**在 `panelOpen === false` 时可达的拖拽（宽度/角点拖拽都要求面板开着），所以只有它触发。`abortDrag` 路径此前已修过（走 `layoutPushSize` 门控），move/up 路径漏网。
+
+**修复**：`applyDrag` 里 `writeGeometry` 的 width 实参加上与 push effect 一致的门控（`!narrow && panelOpen ? min(width, vw) : 0`）；面板 DOM 写入（`panelRef`/`bottomRef`/`lastDragSize`）保持原始 width（底栏 `right` 定位派生自它）。
+
+**验证**：e2e 回归（`drag-layout.e2e.ts`）——右面板关闭 + 底栏打开拖 strip，逐帧断言 pushed width 恒 0、宿主 grid 模板 / 左栏渲染宽度 / `#root` 右边缘全程不变。旧代码上实测泄漏 504px（红），修复后通过（绿）。
+
+## 2. 性能改动清单
+
+| # | 改动 | 类别 | commit |
+|---|---|---|---|
+| 1 | boot 路径 `loadPrefs` + `loadExternalDisable` 合并为一次 `settingsGet`（原来同文档串行拉两次，第二个无超时——settings RPC 挂起则侧边栏永不出现） | 启动 | perf: cut the boot and poll overhead |
+| 2 | GitLens 2s silent 轮询不再每 tick 重列 worktrees（每 tick 少 spawn 1 个 git 进程；每 15 tick ≈30s 才重列+自动选择一次） | 运行时开销 | 同上 |
+| 3 | ChangesTab 的 `extractFileOps` fold 从「每 poll 两遍（badge 一遍 + render 一遍）」改为每 poll 一遍、结果进 ref 共享（4000 条事件 × 每条 JSON.parse） | CPU | 同上 |
+| 4 | SideChat 转录行引用复用：`transcriptRows` 接受上次结果，位置对齐内容相同的行复用旧对象——2s 轮询只重渲染变化的尾部（原来全部行连同 markdown 重解析每轮重渲染） | 渲染 | perf: stabilize renders |
+| 5 | FileTree `expanded`/`revealed` 数组 → Set（原来每行 `includes()` 线性扫描，整树 O(rows×expanded)） | 渲染 | 同上 |
+| 6 | `buildNewTabOptions` 从两处 JSX 内联调用改为共享 memo（原来每次 render 两个新数组，击穿 LeafView 的 props 比较） | 渲染 | 同上 |
+| 7 | DiffPane 高度拖拽、TerminalView ResizeObserver 走每帧批处理（原来每 pointer/resize 事件一次 setState / 一次含字形度量的 fit()）；SessionLens 的 `new Blob().size`（整段编辑内容的 UTF-8 编码）从每行每 render 移到每变化一次的 memo | 渲染 | 同上 |
+| 8 | 19 个非 zh/en 字典移入 lazy `locale` chunk（`lib/client-locale.js`，仅安装 better-locale 时按需拉取；核心包只留 zh/en——`t()` 本来也只查 zh/en + override store） | 启动体积 | perf: move the 19 dictionaries |
+| 9 | 底栏推挤锚点从 `:has(> [data-slot=conversation])` 换成 shell 定位器打的 `[data-dsh-center-col]` 标注（`:has()` 匹配缓存随流式聊天的 #root 子树变动不断失效，每次布局推挤帧全文档重估） | 拖拽帧成本 | perf: tag the center column |
+| 10 | TextEditor 不再每键 `doc.toString()` 全文字符串化进 React state（O(docLength)/键）；listener 只翻 dirty，进预览/换文件时从 live view 快照一次；保存本就现读 | 编辑 | 同上 |
+
+## 3. Before / After 对比
+
+测量说明：`mount-sweep` = 冷导航 → 插件挂载 → 展开面板 → 依次打开全部 6 个内置 tab；`bottom-drag` = 面板关闭 + 底栏打开时拖 12 步的 rAF 帧间隔。同机同夜连续跑，数字用于相对比较而非绝对承诺。
+
+| 指标 | before（main d70db8f） | after（本分支） | 变化 |
+|---|---|---|---|
+| 挂载时延（navigationStart → host attach，中位） | 376.9 ms | 272.9 ms | **-28%** |
+| 挂载+扫 tab 期间 longtask 数 / 总时长 / 最长 | 2 / 161 ms / 96 ms | 2 / 146 ms / 84 ms | 总时长 -9%，最长 -13% |
+| 核心 client.js 体积（未压缩） | 1.46 MB | 0.80 MB | **-45%** |
+| 宿主聚合 client bundle 传输量（含全部插件，gzip） | 1,436,478 B | 1,233,778 B | **-203 KB / -14%** |
+| 宿主聚合 client bundle 解码体积 | 5,136,894 B | 4,497,363 B | -640 KB（即字典总量，吻合） |
+| 侧栏 shape 的资源请求数 / 其中 settings.get | 20 / ×4 | 18 / ×2 | boot 合并生效 |
+| 底栏拖拽帧间隔 p50 / p95 / max | 8 / 10 / 11 ms | 8 / 10 / 11 ms | 持平（本就不掉帧；修复的是布局突变） |
+| 底栏拖拽 pushed width 泄漏（右面板关闭时） | **504 px**（bug） | **0 px** | 修复 |
+
+### 结构性收益（不随单次测量波动）
+
+- **核心 bundle**：19 个字典（源码 ~640KB）出核心包，`client.js` 1.46MB → 822KB（构建产物实测）。绝大多数会话（未装 better-locale）永远不拉 `client-locale.js`（gzip 171KB）；装了的用户按需拉一次（HTTP 缓存 + ETag 复用）。
+- **boot RPC**：settings 文档从 2 次串行 → 1 次；`loadExternalDisable` 有了 2s 超时兜底。
+- **GitLens 轮询的 git 进程 spawn**：每分钟 60 个（2 个/tick × 30 tick）→ ~34 个（1 个/tick + 每 15 tick 多 1 个），-43%。
+- **ChangesTab fold**：每 2.5s poll 的 fold 次数 2 → 1（每次 fold 对至多 4000 条事件逐条处理、tool/call 还要 `JSON.parse`）。
+- **SideChat 转录**：内容未变的行不再重建对象 → 下游 React reconcile + markdown 解析 + DOMPurify 全部跳过（引用稳定性由 `sidechat-transcript.spec.ts` 契约钉住）。
+- **TextEditor**：每次按键的 O(文档长度) 字符串化 + shell 重渲染 → 0（仅 dirty 布尔）。
+
+### 3.1 alpha.3 复测（rebase 到 main c199212 之后）
+
+main 在本分支开发期间合入了 alpha.3 适配（peer `^0.1.2-alpha.3`，v0.18.1-alpha.0）与 sidechat 渲染升级（新增 `turnSummary` 行 kind 与 tool `card`——`rowsEqual` 已补齐两者，card 只在 tool/result 落地时变化、被 `executing`/`failed`/`resultText` 的比较覆盖，无需值比较）。rebase 后在 alpha.3 真机重测（同法 3 次中位，before 侧 = main c199212 代码 + 本分支的测量工具）：
+
+| 指标 | before（main c199212） | after（本分支） | 变化 |
+|---|---|---|---|
+| 挂载时延（中位） | 372.3 ms | 316.5 ms | **-15%** |
+| longtask 总时长 / 最长 | 170 / 100 ms | 165 / 96 ms | -3% / -4% |
+| 宿主聚合 bundle 传输 | 1,456,668 B | 1,246,595 B | **-210 KB / -14%** |
+| boot settings.get | ×4 | ×2 | 合并生效 |
+| 底栏拖拽 pushed width 泄漏 | **504 px**（复现） | **0 px** | 修复 |
+
+全部收益在新 main 基线上成立；完整 mount lane（17 测试）在 alpha.3 真机全绿。§3 主表为 alpha.2 上的原始测量记录（两端同宿主，对比自洽），保留作历史基线。
+
+## 4. 守护
+
+- e2e：`drag-layout.e2e.ts` 新增底栏回归（宿主布局全程静止）与 center-col 标注断言（恰一节点、为 conversation slot 的父级）；`perf.e2e.ts` 的 width-leak 断言在每次测量 lane 里复检。
+- 单测：`prefs.spec.ts`（boot 决策单次 fetch）、`sidechat-transcript.spec.ts`（行引用复用契约）、`locales.spec.ts`（chunk 内全部字典 key-set 与 zh 一致）、`layout-css.spec.ts`（锚点选择器契约，禁 `:has` 回潮）、`bundle-route.spec.ts`（chunk 清单含 locale）。
+- 完整 mount lane（17 测试）在本分支全绿（alpha.2 与 alpha.3 真机各跑一轮）。
+
+## 5. 明确不做（取舍）
+
+- `pinnedEntries` 的 store 版本号改造、连续 `store.reduce` 合并：侵入 store API，收益不明确，KISS 取舍。
+- FileTree / SideChat 列表虚拟化：Set 化 + 引用复用后若真实负载仍不达标再立项。
+- `e2e-mount.sh` 的 `command -v "$DSH_CMD"` 对带空格命令失效（回退未钉版本的 npx）是**宿主侧脚本的既有行为**，本地以 `DSH_CMD=/tmp/dsh-alpha2.sh` 包装脚本绕过，不改脚本（CI 全局安装钉版本，不受影响）。
diff --git a/src/bundle-route.ts b/src/bundle-route.ts
index 3c404f3..4f098ec 100644
--- a/src/bundle-route.ts
+++ b/src/bundle-route.ts
@@ -19,7 +19,7 @@ import { fileURLToPath } from 'node:url'
 import type { Context, SidebarHttpRequest, SidebarHttpResponse } from './context-types.ts'
 
 /** The chunk names the client may request (mirror of src/client/chunk-loader.ts). */
-export const CHUNK_NAMES = ['terminal', 'editor', 'mermaid'] as const
+export const CHUNK_NAMES = ['terminal', 'editor', 'mermaid', 'locale'] as const
 export type ChunkName = (typeof CHUNK_NAMES)[number]
 
 /** Directory of this host-half module (lib/ — the chunk scripts live next to it). */
diff --git a/src/client/FileTree.tsx b/src/client/FileTree.tsx
index 942a06f..684ceb4 100644
--- a/src/client/FileTree.tsx
+++ b/src/client/FileTree.tsx
@@ -20,7 +20,7 @@
  * (VSCode semantics — a drop on a file row targets its parent directory),
  * and `busy` gates new drags while one upload is in flight.
  */
-import { useCallback, useEffect, useRef, useState, type DragEvent, type MouseEvent, type ReactNode } from 'react'
+import { useCallback, useEffect, useMemo, useRef, useState, type DragEvent, type MouseEvent, type ReactNode } from 'react'
 import { createPortal } from 'react-dom'
 import clsx from 'clsx'
 import {
@@ -441,6 +441,12 @@ export function FileTree(props: {
 
   const root = cwd
 
+  // Membership is tested per rendered row (deep trees run this thousands of
+  // times per render): includes() made every row O(expanded), the whole tree
+  // O(rows × expanded). One Set per render keeps it O(1) per row.
+  const expandedSet = useMemo(() => new Set(expanded), [expanded])
+  const revealedSet = useMemo(() => new Set(revealed), [revealed])
+
   const renderLevel = (dir: string, depth: number): ReactNode => {
     const level = data[dir]
     if (level === undefined) {
@@ -466,7 +472,7 @@ export function FileTree(props: {
     const entries = level.entries ?? []
     return entries.map(entry => {
       if (entry.isDir) {
-        const isOpen = expanded.includes(entry.path)
+        const isOpen = expandedSet.has(entry.path)
         return (
           <div key={entry.path}>
             <div
@@ -475,9 +481,9 @@ export function FileTree(props: {
               className={clsx(
                 css.explorerRow, css.explorerDir, entry.hidden && css.explorerHidden,
                 dropTarget === entry.path && css.explorerRowDropTarget,
-                revealed.includes(entry.path) && css.explorerRowRevealed,
+                revealedSet.has(entry.path) && css.explorerRowRevealed,
               )}
-              data-dsh-revealed={revealed.includes(entry.path) ? 'true' : undefined}
+              data-dsh-revealed={revealedSet.has(entry.path) ? 'true' : undefined}
               style={{ paddingLeft: depth * 22 + 6 }}
               onClick={() => { onToggle(entry.path) }}
               onKeyDown={(event) => {
@@ -507,9 +513,9 @@ export function FileTree(props: {
           className={clsx(
             css.explorerRow, entry.hidden && css.explorerHidden, entry.broken && css.explorerBroken,
             dropTarget === parentOf(entry.path) && css.explorerRowDropTarget,
-            revealed.includes(entry.path) && css.explorerRowRevealed,
+            revealedSet.has(entry.path) && css.explorerRowRevealed,
           )}
-          data-dsh-revealed={revealed.includes(entry.path) ? 'true' : undefined}
+          data-dsh-revealed={revealedSet.has(entry.path) ? 'true' : undefined}
           style={{ paddingLeft: depth * 22 + 6 }}
           title={entry.broken ? `${entry.path} — ${t('brokenSymlink')}` : entry.path}
           onClick={() => { onOpenFile(entry.path) }}
diff --git a/src/client/SideChatView.tsx b/src/client/SideChatView.tsx
index e409c1a..f6ed825 100644
--- a/src/client/SideChatView.tsx
+++ b/src/client/SideChatView.tsx
@@ -383,6 +383,8 @@ export function SideChatView(props: {
   const [menuOpen, setMenuOpen] = useState(false)
 
   const cacheRef = useRef<ThreadCache>({ entries: [] })
+  // The previous poll's rows (see the mapping's reuse pass below).
+  const prevRowsRef = useRef<SidechatTranscriptRow[]>([])
   const controllerRef = useRef<AbortController | null>(null)
   const scrollRef = useRef<HTMLDivElement | null>(null)
   const composerRef = useRef<HTMLTextAreaElement | null>(null)
@@ -480,6 +482,7 @@ export function SideChatView(props: {
   // the composer — it owns the first message of a fresh thread.
   useEffect(() => {
     cacheRef.current = { entries: [] }
+    prevRowsRef.current = []
     controllerRef.current?.abort()
     setError(null)
     setSaved(false)
@@ -517,8 +520,14 @@ export function SideChatView(props: {
     }
   }, [connectionState, threadId, fetchThread, fetchInfo])
 
-  const rows = useMemo(
-    () => (threadId === undefined ? [] : transcriptRows(cacheRef.current.entries)),
+  // The previous poll's rows ride into the mapping so unchanged rows keep
+  // their object identity (see reuseRows): the 2s poll re-renders only the
+  // changed tail instead of re-parsing markdown for the whole transcript.
+  const rows = useMemo(() => {
+    const next = threadId === undefined ? [] : transcriptRows(cacheRef.current.entries, prevRowsRef.current)
+    prevRowsRef.current = next
+    return next
+  },
     // The cache is a ref; revision bumps on every successful pull.
     // eslint-disable-next-line react-hooks/exhaustive-deps
     [threadId, revision],
diff --git a/src/client/Sidebar.tsx b/src/client/Sidebar.tsx
index 8897571..4b6c538 100644
--- a/src/client/Sidebar.tsx
+++ b/src/client/Sidebar.tsx
@@ -407,6 +407,20 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
   }, [sessionId, summaryCwd])
   const cwd = summaryCwd ?? fetchedCwd
 
+  // The + menu options ride a memo so the two Workbenches share ONE array
+  // identity across renders that did not change the store (drag state,
+  // viewport resize): fresh arrays per render re-rendered every LeafView's
+  // + affordance whether or not anything tab-related moved.
+  const newTabOptions = useMemo(
+    () => (state === undefined || sessionId === undefined ? [] : buildNewTabOptions(state, ctx, { sessionId, cwd })),
+    // state is the whole session state — every field it wraps is fair game
+    // for the descriptors' available() callbacks. (The render's own guard
+    // sits below every hook; this memo must handle the no-session case
+    // itself.)
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+    [state, ctx, sessionId, cwd],
+  )
+
   /**
    * Agent terminals push: subscribe to the host's live list of agent-owned
    * terminals for this session (created by the model through the
@@ -742,6 +756,7 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
         ?.parentElement as HTMLElement | undefined
       if (col === undefined || !col.isConnected) {
         if (centerColRef.current !== null) {
+          centerColRef.current.removeAttribute('data-dsh-center-col')
           centerColRef.current = null
           observer?.disconnect()
           observer = undefined
@@ -754,8 +769,13 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
         // measure it once. Same-node size changes are the ResizeObserver's
         // job — no forced measurement here, because a forced
         // getBoundingClientRect per mutation would reflow the shell at
-        // mutation cadence.
+        // mutation cadence. The tag retargets with the ref: layout.css's
+        // bottom-push rule anchors on [data-dsh-center-col], so exactly the
+        // measured node carries it (a stale tag on a swapped-out node would
+        // leave the push rule anchorless or doubled).
+        centerColRef.current?.removeAttribute('data-dsh-center-col')
         centerColRef.current = col
+        col.setAttribute('data-dsh-center-col', '')
         observer?.disconnect()
         observer = new ResizeObserver(measureCenter)
         observer.observe(col)
@@ -808,6 +828,7 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
       observer?.disconnect()
       watcher.disconnect()
       htmlStyleWatcher.disconnect()
+      centerColRef.current?.removeAttribute('data-dsh-center-col')
       centerColRef.current = null
     }
     // Opening the bottom panel re-runs the whole locate/measure chain: a
@@ -993,7 +1014,14 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
     // drag write-only (no React re-render mid-drag).
     bottomRef.current?.style.setProperty('right', `${(window.innerWidth - centerRectRef.current.right) + (width - (state?.width ?? 0))}px`)
     const bottomPush = !narrow && state?.bottomOpen === true ? height + keyboardInset : 0
-    writeGeometry(width, bottomPush)
+    // The pushed width must ride the same gate as the committed push effect
+    // (layoutPushSize): a collapsed right panel pushes 0. The bottom strip is
+    // the only drag reachable with the panel closed — writing the panel's
+    // persisted width preference here squeezed #root mid-drag, dropped the
+    // host viewport across its 1024px auto-collapse breakpoint, and the
+    // native left sidebar snapped to its 56px rail (and back on release).
+    const pushWidth = !narrow && state?.panelOpen === true ? Math.min(width, window.innerWidth) : 0
+    writeGeometry(pushWidth, bottomPush)
   }
 
   // Drags write at most once per frame: pointer events fire several times
@@ -1574,7 +1602,7 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
           <Workbench
             state={state}
             tree={augmentedTree}
-            newTabOptions={buildNewTabOptions(state, ctx, { sessionId, cwd })}
+            newTabOptions={newTabOptions}
             actions={wrappedActions}
             onNewTab={onNewTab}
             renderTab={renderTab}
@@ -1729,7 +1757,7 @@ export function Sidebar(props: { ctx: Context; store: SidebarStore }) {
           <Workbench
             state={state}
             tree={state.bottomSplits}
-            newTabOptions={buildNewTabOptions(state, ctx, { sessionId, cwd })}
+            newTabOptions={newTabOptions}
             actions={actions}
             onNewTab={onNewTab}
             renderTab={(tab, active, paneId) => renderTab(tab, active, paneId, 'bottom')}
diff --git a/src/client/TerminalView.tsx b/src/client/TerminalView.tsx
index eba3d93..ffaee8a 100644
--- a/src/client/TerminalView.tsx
+++ b/src/client/TerminalView.tsx
@@ -268,13 +268,23 @@ export function TerminalView(props: { scope: SessionScope; tabId: string; store:
     const inputSub = term.onData((data) => {
       if (socket !== null && socket.readyState === WebSocket.OPEN) socket.send(data)
     })
+    // Resize streams fire per layout frame during panel open/close
+    // animations; fit() measures glyphs, so coalesce to one fit per
+    // animation frame (same pattern as the core's frame-batcher, kept
+    // local — this view lives in the lazy terminal chunk and does not
+    // import core-bundle modules).
+    let resizeFrame: number | null = null
     const observer = new ResizeObserver(() => {
-      try {
-        fit.fit()
-        sendResize()
-      } catch {
-        // The terminal may be mid-dispose; ignore.
-      }
+      if (resizeFrame !== null) return
+      resizeFrame = requestAnimationFrame(() => {
+        resizeFrame = null
+        try {
+          fit.fit()
+          sendResize()
+        } catch {
+          // The terminal may be mid-dispose; ignore.
+        }
+      })
     })
     observer.observe(host)
 
@@ -323,6 +333,7 @@ export function TerminalView(props: { scope: SessionScope; tabId: string; store:
       cancelOpen()
       window.clearTimeout(retry)
       observer.disconnect()
+      if (resizeFrame !== null) cancelAnimationFrame(resizeFrame)
       fontSub()
       schemeSub()
       inputSub.dispose()
diff --git a/src/client/TextEditor.tsx b/src/client/TextEditor.tsx
index 25114c9..66b0fd7 100644
--- a/src/client/TextEditor.tsx
+++ b/src/client/TextEditor.tsx
@@ -114,11 +114,13 @@ export function TextEditor(props: FileViewerProps) {
   }, [content])
 
   // Create the CodeMirror editor once the content is loaded. The view owns
-  // the document; React only tracks dirty/draft state through the update
-  // listener. For markdown the view stays mounted while previewing (hidden),
-  // so unsaved edits survive the preview/edit toggle. The theme + syntax
-  // colors live in a compartment so a scheme flip reconfigures only that
-  // part — the document, undo history and scroll position survive.
+  // the document; React only tracks dirty state through the update listener
+  // (the draft — the preview's text — is snapshotted from the live view on
+  // entering preview, not re-stringified per keystroke). For markdown the
+  // view stays mounted while previewing (hidden), so unsaved edits survive
+  // the preview/edit toggle. The theme + syntax colors live in a compartment
+  // so a scheme flip reconfigures only that part — the document, undo
+  // history and scroll position survive.
   useEffect(() => {
     if (content === undefined) return
     const host = hostRef.current
@@ -139,7 +141,6 @@ export function TextEditor(props: FileViewerProps) {
         ...(language !== null ? [language] : []),
         CodeMirrorView.updateListener.of((update) => {
           if (update.docChanged) {
-            setDraft(update.state.doc.toString())
             setDirty(true)
           }
         }),
@@ -226,6 +227,17 @@ export function TextEditor(props: FileViewerProps) {
     if (mode === 'edit') viewRef.current?.requestMeasure()
   }, [mode])
 
+  // Snapshot the live document into the draft whenever the preview needs
+  // it: entering preview (the markdown preview renders `draft ?? content`)
+  // and a content swap (the view was just re-created above, so the read is
+  // the new document — matching the reset-to-null of a clean tab). The
+  // updateListener used to re-stringify the WHOLE document on every
+  // keystroke (O(docLength) per key) for a draft only preview reads.
+  useEffect(() => {
+    const view = viewRef.current
+    setDraft(view === null ? null : view.state.doc.toString())
+  }, [mode, content])
+
   const save = (): void => {
     const view = viewRef.current
     if (view === null || savingRef.current) return
diff --git a/src/client/changes/ChangesTab.tsx b/src/client/changes/ChangesTab.tsx
index ae7aa22..7726065 100644
--- a/src/client/changes/ChangesTab.tsx
+++ b/src/client/changes/ChangesTab.tsx
@@ -63,6 +63,12 @@ export function ChangesTab({ ctx, store, scope, tab, visible, onOpenFile, onOpen
   //    up). The cursor is the last delivered seq, so each poll ships only
   //    what the accumulator lacks. ────────────────────────────────────────
   const eventsRef = useRef<readonly SidebarSessionEvent[]>([])
+  // The fold of eventsRef as of the last poll. extractFileOps parses every
+  // accumulated tool/call (up to EVENTS_CAP events); running it once per
+  // poll and REUSING the result across renders (the render used to re-fold
+  // the whole window, twice per tick, and the fresh array defeated the
+  // downstream memo on every poll) keeps the 2.5s tick at one fold.
+  const opsRef = useRef<readonly FileOp[]>([])
   const seqRef = useRef(0)
   const pollGen = useRef(0)
   const [opsError, setOpsError] = useState(false)
@@ -77,7 +83,9 @@ export function ChangesTab({ ctx, store, scope, tab, visible, onOpenFile, onOpen
         eventsRef.current = merged.length > EVENTS_CAP ? merged.slice(merged.length - EVENTS_CAP) : merged
       }
       if (lastSeq > seqRef.current) seqRef.current = lastSeq
-      opCounts.set(scope.sessionId, extractFileOps(eventsRef.current).length)
+      const folded = extractFileOps(eventsRef.current)
+      opsRef.current = folded
+      opCounts.set(scope.sessionId, folded.length)
       setOpsError(false)
       setTick(value => value + 1)
     } catch {
@@ -89,6 +97,7 @@ export function ChangesTab({ ctx, store, scope, tab, visible, onOpenFile, onOpen
   useEffect(() => {
     pollGen.current += 1
     eventsRef.current = []
+    opsRef.current = []
     seqRef.current = 0
     setOpsError(false)
   }, [scope.sessionId])
@@ -100,7 +109,7 @@ export function ChangesTab({ ctx, store, scope, tab, visible, onOpenFile, onOpen
   }, [visible, pull])
   // tick only forces the re-render; the fold reads the ref directly.
   void tick
-  const ops = extractFileOps(eventsRef.current)
+  const ops = opsRef.current
 
   /** Persist a meta patch onto the tab (lens choice, pane height). */
   const patchMeta = (patch: ChangesMeta): void => {
diff --git a/src/client/changes/DiffPane.tsx b/src/client/changes/DiffPane.tsx
index c8ff841..436cb53 100644
--- a/src/client/changes/DiffPane.tsx
+++ b/src/client/changes/DiffPane.tsx
@@ -21,6 +21,7 @@ import { DiffFiles } from '../diff/DiffFiles.tsx'
 import { langOfPath } from '../diff/highlight.ts'
 import { buildDiffSegments, diffLines, diffStats, parseUnifiedDiff, unifiedSegments, type DiffRow } from '../diff/rows.ts'
 import { parseReadLines, type FileOp } from './ops.ts'
+import { createFrameBatcher } from '../frame-batcher.ts'
 import css from './changes.module.css'
 import diffCss from '../diff/diff.module.css'
 
@@ -176,17 +177,23 @@ export function DiffPane({ target, scope, height, onHeightCommit, onClose, onExp
   const paneHeight = dragHeight ?? height
   const clamp = (value: number): number => Math.min(Math.max(value, HEIGHT_MIN), Math.round(window.innerHeight * 0.7))
   const dragOrigin = useRef<{ y: number; h: number } | null>(null)
+  // Pointer streams fire several times per frame; one setState per event
+  // re-rendered the whole pane at event cadence (see frame-batcher).
+  const dragBatcher = useRef(createFrameBatcher()).current
+  useEffect(() => () => dragBatcher.dispose(), [dragBatcher])
   const onHandleDown = (event: ReactPointerEvent<HTMLDivElement>): void => {
     event.preventDefault()
     dragOrigin.current = { y: event.clientY, h: paneHeight }
     const onMove = (ev: PointerEvent): void => {
       if (dragOrigin.current === null) return
-      setDragHeight(clamp(dragOrigin.current.h + (dragOrigin.current.y - ev.clientY)))
+      const next = clamp(dragOrigin.current.h + (dragOrigin.current.y - ev.clientY))
+      dragBatcher.schedule(() => { setDragHeight(next) })
     }
     const onUp = (): void => {
       window.removeEventListener('pointermove', onMove)
       window.removeEventListener('pointerup', onUp)
       dragOrigin.current = null
+      dragBatcher.flushNow()
       setDragHeight(current => {
         if (current !== null) onHeightCommit(current)
         return null
diff --git a/src/client/changes/GitLens.tsx b/src/client/changes/GitLens.tsx
index afec62b..71b7324 100644
--- a/src/client/changes/GitLens.tsx
+++ b/src/client/changes/GitLens.tsx
@@ -76,6 +76,13 @@ interface ConfirmState {
  *  floods the panel at once (the end of the log is reached by paging). */
 const LOG_BATCH = 20
 
+/** Every Nth silent poll re-lists worktrees (and re-runs auto-selection): the
+ *  2s tick only needs the selected checkout's STATUS, and re-listing spawned
+ *  a second git process per tick for a list that almost never changes — a
+ *  linked checkout the agent creates mid-session is picked up within ~30s
+ *  instead of 2s. */
+const WORKTREE_RECHECK_TICKS = 15
+
 export interface GitLensProps {
   scope: SessionScope
   /** The sidebar store: reads the `workspaceFence` pref (see the open guard below). */
@@ -123,6 +130,8 @@ export function GitLens(props: GitLensProps) {
    *  callback and re-trigger the mount effect — an N→N+1 fetch loop). */
   const chosenPathRef = useRef<string | undefined>(undefined)
   useEffect(() => { chosenPathRef.current = selectedWorktree }, [selectedWorktree])
+  /** Silent polls since the last worktree re-list (see WORKTREE_RECHECK_TICKS). */
+  const silentTickCount = useRef(0)
 
   const gitScope: SessionScope = repoRoot === undefined ? scope : { ...scope, repoRoot }
 
@@ -160,6 +169,15 @@ export function GitLens(props: GitLensProps) {
     refreshInFlight.current = true
     let generation = refreshGeneration.current
     try {
+      // Fast path for the ordinary silent tick: the selected checkout's
+      // STATUS is all that changes between worktree re-lists (see
+      // WORKTREE_RECHECK_TICKS) — one git process instead of two.
+      if (silent && chosenPathRef.current !== undefined && (silentTickCount.current += 1) % WORKTREE_RECHECK_TICKS !== 0) {
+        const statusResult = await api.gitStatus(gitScope, chosenPathRef.current)
+        if (generation === refreshGeneration.current) setStatus(statusResult)
+        return
+      }
+      silentTickCount.current = 0
       const listed = await api.gitWorktrees(scope)
       if (generation !== refreshGeneration.current) return
       setWorktrees(listed)
@@ -214,6 +232,7 @@ export function GitLens(props: GitLensProps) {
     refreshInFlight.current = false
     worktreeChosenByUser.current = false
     chosenPathRef.current = undefined
+    silentTickCount.current = 0
     setSelectedWorktree(undefined)
   }, [scope.sessionId, scope.cwd])
   useEffect(() => { void refresh() }, [refresh])
diff --git a/src/client/changes/SessionLens.tsx b/src/client/changes/SessionLens.tsx
index 8b8e6a1..8e33319 100644
--- a/src/client/changes/SessionLens.tsx
+++ b/src/client/changes/SessionLens.tsx
@@ -54,6 +54,20 @@ export function SessionLens({ ops, loadError, onPreview, selectedCallId }: Sessi
     </button>
   )
 
+  // Sizing a row's content constructs a Blob (a UTF-8 encode of the whole
+  // edit) — that was per row PER RENDER, re-encoding every field on every
+  // poll tick. ops keeps its identity between unchanged polls (see the
+  // tab's opsRef), so one pass per changed fold covers every render.
+  const opSizes = useMemo(() => {
+    const sizes = new Map<string, string>()
+    for (const op of ops) {
+      if (op.kind !== 'read' && !op.isError) {
+        sizes.set(op.callId, formatBytes(new Blob([op.edit?.newString ?? op.content ?? '']).size))
+      }
+    }
+    return sizes
+  }, [ops])
+
   return (
     <div className={css.session}>
       <div className={css.filterRow} role="group" aria-label={t('changesSessionLens')}>
@@ -85,9 +99,9 @@ export function SessionLens({ ops, loadError, onPreview, selectedCallId }: Sessi
                 {op.running && <span className={css.opFlag}>{t('changesRunning')}</span>}
                 {op.isError && <span className={css.opFlagError}>{t('changesError')}</span>}
                 <span className={css.opMeta}>
-                  {op.kind !== 'read' && !op.isError && (
+                  {opSizes.get(op.callId) !== undefined && (
                     <span className={css.opSize}>
-                      {formatBytes(new Blob([op.edit?.newString ?? op.content ?? '']).size)}
+                      {opSizes.get(op.callId)}
                     </span>
                   )}
                   <span className={css.opTime}>{relativeTime(new Date(op.time).toISOString())}</span>
diff --git a/src/client/chunk-loader.ts b/src/client/chunk-loader.ts
index 76c90e1..169da7c 100644
--- a/src/client/chunk-loader.ts
+++ b/src/client/chunk-loader.ts
@@ -49,7 +49,7 @@
  * client.js); an edit that does land while a core HMR happens is caught by
  * the ETag comparison on the next activation.
  */
-export type ChunkName = 'terminal' | 'editor' | 'mermaid'
+export type ChunkName = 'terminal' | 'editor' | 'mermaid' | 'locale'
 
 /** The module exports a chunk factory provides (namespace-ish record). */
 export type ChunkExports = Record<string, unknown>
diff --git a/src/client/chunks/locale.tsx b/src/client/chunks/locale.tsx
new file mode 100644
index 0000000..b2a439e
--- /dev/null
+++ b/src/client/chunks/locale.tsx
@@ -0,0 +1,60 @@
+/**
+ * Lazy chunk entry: the 19 non-zh/en dictionaries (ja/de/fr/…/zh-HK/MO/TW —
+ * ~640KB of source). The sidebar's own `t()` only ever consults zh/en plus
+ * the better-locale override store, so these dicts are needed ONLY when
+ * @huanlin/dsh-plugin-better-locale is installed: they register into its
+ * override store from there (see the client apply's better-locale
+ * integration). Built as `lib/client-locale.js` and fetched from the
+ * plugin's /sidebar/bundle route on first need — never import this module
+ * from the core bundle: it would drag every language back into the startup
+ * path (see docs/plans/2026-08-31-perf-optimization.md).
+ */
+import { ja } from '../locales-ja.ts'
+import { de } from '../locales-de.ts'
+import { fr } from '../locales-fr.ts'
+import { pt } from '../locales-pt.ts'
+import { ko } from '../locales-ko.ts'
+import { ar } from '../locales-ar.ts'
+import { hi } from '../locales-hi.ts'
+import { id } from '../locales-id.ts'
+import { tr } from '../locales-tr.ts'
+import { vi } from '../locales-vi.ts'
+import { th } from '../locales-th.ts'
+import { ru } from '../locales-ru.ts'
+import { it } from '../locales-it.ts'
+import { nl } from '../locales-nl.ts'
+import { sv } from '../locales-sv.ts'
+import { pl } from '../locales-pl.ts'
+import { zhHK } from '../locales-zh-HK.ts'
+import { zhTW } from '../locales-zh-TW.ts'
+import { zhMO } from '../locales-zh-MO.ts'
+import type { CopyKey } from '../locales.ts'
+
+/** Key-set check against zh (type-only import — erased before bundling, so
+ *  this adds no runtime tie to the core bundle): a dictionary missing or
+ *  adding a key fails the build instead of silently falling back to en. */
+const checked = (dict: Record<CopyKey, string>): Record<string, string> => dict
+
+/** Every non-zh/en dictionary keyed by its override id, ready for the
+ *  better-locale store's `register(ns, dicts)`. */
+export const localeDicts: Record<string, Record<string, string>> = {
+  ja: checked(ja),
+  de: checked(de),
+  fr: checked(fr),
+  pt: checked(pt),
+  ko: checked(ko),
+  ar: checked(ar),
+  hi: checked(hi),
+  id: checked(id),
+  tr: checked(tr),
+  vi: checked(vi),
+  th: checked(th),
+  ru: checked(ru),
+  it: checked(it),
+  nl: checked(nl),
+  sv: checked(sv),
+  pl: checked(pl),
+  'zh-HK': checked(zhHK),
+  'zh-TW': checked(zhTW),
+  'zh-MO': checked(zhMO),
+}
diff --git a/src/client/index.tsx b/src/client/index.tsx
index 30033f9..ff25c8a 100644
--- a/src/client/index.tsx
+++ b/src/client/index.tsx
@@ -21,13 +21,11 @@ import { registerOpenPathInterception, registerTurnTailInterception } from './in
 import { registerLinkInterception } from './link-intercept.ts'
 import { registerImeGuard } from './ime-guard.ts'
 import { registerSettingsNavIcon } from './settings-nav-icon.ts'
-import { loadExternalDisable, loadPrefs } from './prefs.ts'
+import { loadBootDecision } from './prefs.ts'
 import { SideCardSection } from './SideCardSection.tsx'
 import { api } from './api.ts'
-import { LOCALE_NS, attachLocale, attachBetterLocale, t, zh, en,
-  ja, de, fr, pt, ko, ar, hi, id, tr, vi, th, ru, it, nl, sv, pl,
-  zhHK, zhTW, zhMO,
-} from './locales.ts'
+import { LOCALE_NS, attachLocale, attachBetterLocale, t, zh, en } from './locales.ts'
+import { loadChunk } from './chunk-loader.ts'
 import css from './sidebar.module.css'
 import './layout.css'
 
@@ -82,7 +80,12 @@ export function apply(ctx: Context): void {
   // the ja dict once the store becomes available.
   ctx.effect(() => {
     let dispose: (() => void) | undefined
+    // Guards the async chunk registration below: a sync() re-run (or fiber
+    // disposal) that lands while the chunk is still in flight must render
+    // that registration moot.
+    let generation = 0
     const sync = (): void => {
+      generation += 1
       dispose?.()
       dispose = undefined
       const store = ctx.get('betterLocale') as
@@ -96,10 +99,17 @@ export function apply(ctx: Context): void {
         | undefined
       attachBetterLocale(store)
       if (store !== undefined) {
-        dispose = store.register(LOCALE_NS, {
-          ja, de, fr, pt, ko, ar, hi, id, tr, vi, th, ru, it, nl, sv, pl,
-          'zh-HK': zhHK, 'zh-TW': zhTW, 'zh-MO': zhMO,
-        })
+        // The 19 override dictionaries ride the lazy `locale` chunk: until
+        // it lands, the store has no betterSidebar entries and t() keeps
+        // the zh/en chain; the store's own revision bump on register
+        // re-renders the chrome once the dicts arrive.
+        const myGeneration = generation
+        void loadChunk('locale')
+          .then(mod => {
+            if (myGeneration !== generation) return
+            dispose = store.register(LOCALE_NS, mod.localeDicts as Record<string, Record<string, string>>)
+          })
+          .catch(() => { /* the dicts stay unregistered; the zh/en chain runs */ })
       }
     }
     // Initial check (picks up the store if better-locale activated first).
@@ -108,6 +118,7 @@ export function apply(ctx: Context): void {
     // activates with a persisted override, and when the user switches).
     const unsubscribe = ctx.locale.subscribe(sync)
     return () => {
+      generation += 1
       unsubscribe()
       dispose?.()
       attachBetterLocale(undefined)
@@ -275,24 +286,26 @@ export function apply(ctx: Context): void {
       }
       const sync = async (): Promise<void> => {
         if (disposed) return
-        // Resolve the user's side card prefs BEFORE the first session seeds,
-        // so a brand-new conversation opens (or stays closed) at the chosen
-        // width from first paint. A settings route failure falls back to the
-        // schema defaults; the sidebar still mounts (a stalled wire gives up
-        // after the timeout and mounts on the defaults).
-        const prefs = await Promise.race([
-          loadPrefs(api),
+        // Resolve the user's side card prefs and the external-disable flag
+        // from ONE settings fetch BEFORE the first session seeds, so a
+        // brand-new conversation opens (or stays closed) at the chosen width
+        // from first paint. A settings route failure falls back to the schema
+        // defaults; the sidebar still mounts (a stalled wire gives up after
+        // the timeout and mounts on the defaults — the external-disable check
+        // rides the same fetch, so one round trip covers both decisions).
+        const decision = await Promise.race([
+          loadBootDecision(api),
           new Promise<null>(resolve => { const timer = window.setTimeout(() => resolve(null), 2000) }),
         ])
-        if (prefs !== null) sidebarStore.setPrefs(prefs)
         if (disposed) return
-        // Mutual exclusion with the dsh-web-ui family right panel: while the
-        // aionui-panel provider is selected, the sidebar must not mount at
-        // all. Re-evaluated on every settings-document update (live switch).
-        const suspended = await loadExternalDisable(api)
-        if (disposed) return
-        sidebarStore.setSuspended(suspended)
-        if (suspended) unmount()
+        if (decision !== null) {
+          sidebarStore.setPrefs(decision.prefs)
+          // Mutual exclusion with the dsh-web-ui family right panel: while the
+          // aionui-panel provider is selected, the sidebar must not mount at
+          // all. Re-evaluated on every settings-document update (live switch).
+          sidebarStore.setSuspended(decision.suspended)
+        }
+        if (decision?.suspended) unmount()
         else mount()
       }
       void sync()
diff --git a/src/client/layout.css b/src/client/layout.css
index 17075c6..c31a94a 100644
--- a/src/client/layout.css
+++ b/src/client/layout.css
@@ -35,14 +35,16 @@
     width var(--ds-transition-duration-slow) var(--ds-ease-in-out);
 }
 
-/* The AppFrame's center column, anchored by data attributes (see above).
-   Composite selector: DSH 0.1.x versions name the center grid item
-   `[data-pane="conversation"]`, while rc.8-era shells put a
-   `[data-slot="conversation"]` child inside it — both selectors resolve to
-   the SAME element on live pages (verified), and keeping both future-proofs
-   the rule against a host rename without touching shell-specific markup. */
-#root [data-dsh-frame] > [data-pane="conversation"],
-#root :has(> [data-slot="conversation"]) {
+/* The AppFrame's center column. The Sidebar shell's locator (Sidebar.tsx
+   locate/measureCenter) tags the measured column node with
+   [data-dsh-center-col] — one attribute write per node lifetime. The rule
+   used to anchor on a structural has()-selector over the conversation slot
+   wrapper, whose match cache invalidates on every #root subtree mutation
+   (the streaming chat mutates it constantly), re-evaluating the selector
+   against the whole document; the tag is evaluated once per node instead.
+   A stretched grid item shrinks by its margins, so the conversation
+   content (output + input bar) lifts without touching the sidebars. */
+#root [data-dsh-center-col] {
   margin-bottom: var(--dsh-sidebar-height, 0px);
   /* Grid/flex items default to min-height:auto. A long unbreakable token
      (OAuth URL) then grows this column past the viewport and clips the
@@ -68,8 +70,7 @@ body[data-dsh-sidebar-collapsed] [data-slot="conversation.session.header"] > hea
 }
 
 body[data-dsh-sidebar-dragging] #root,
-body[data-dsh-sidebar-dragging] #root [data-dsh-frame] > [data-pane="conversation"],
-body[data-dsh-sidebar-dragging] #root :has(> [data-slot="conversation"]) {
+body[data-dsh-sidebar-dragging] #root [data-dsh-center-col] {
   transition: none;
 }
 
@@ -94,8 +95,7 @@ body[data-dsh-sidebar-dragging] #root :has(> [data-slot="conversation"]) {
 
 @media (prefers-reduced-motion: reduce) {
   #root,
-  #root [data-dsh-frame] > [data-pane="conversation"],
-  #root :has(> [data-slot="conversation"]) {
+  #root [data-dsh-center-col] {
     transition: none;
   }
 }
diff --git a/src/client/locales.ts b/src/client/locales.ts
index 584a7b7..4177b6b 100644
--- a/src/client/locales.ts
+++ b/src/client/locales.ts
@@ -845,49 +845,13 @@ export const en: Record<keyof typeof zh, string> = {
  */
 export const LOCALE_NS = 'betterSidebar'
 
-// The ja dictionary lives in a sibling file (326 keys) so this module
-// stays readable. Type-checked against the zh key set: a missing or extra
-// ja key is a compile error.
-import { ja as jaDict } from './locales-ja.ts'
-import { de as deDict } from './locales-de.ts'
-import { fr as frDict } from './locales-fr.ts'
-import { pt as ptDict } from './locales-pt.ts'
-import { ko as koDict } from './locales-ko.ts'
-import { ar as arDict } from './locales-ar.ts'
-import { hi as hiDict } from './locales-hi.ts'
-import { id as idDict } from './locales-id.ts'
-import { tr as trDict } from './locales-tr.ts'
-import { vi as viDict } from './locales-vi.ts'
-import { th as thDict } from './locales-th.ts'
-import { ru as ruDict } from './locales-ru.ts'
-import { it as itDict } from './locales-it.ts'
-import { nl as nlDict } from './locales-nl.ts'
-import { sv as svDict } from './locales-sv.ts'
-import { pl as plDict } from './locales-pl.ts'
-import { zhHK as zhHKDict } from './locales-zh-HK.ts'
-import { zhTW as zhTWDict } from './locales-zh-TW.ts'
-import { zhMO as zhMODict } from './locales-zh-MO.ts'
-
-/** The ja dictionary (key-set-equal to zh, enforced by the type annotation). */
-export const ja: Record<keyof typeof zh, string> = jaDict as Record<keyof typeof zh, string>
-export const de: Record<keyof typeof zh, string> = deDict as Record<keyof typeof zh, string>
-export const fr: Record<keyof typeof zh, string> = frDict as Record<keyof typeof zh, string>
-export const pt: Record<keyof typeof zh, string> = ptDict as Record<keyof typeof zh, string>
-export const ko: Record<keyof typeof zh, string> = koDict as Record<keyof typeof zh, string>
-export const ar: Record<keyof typeof zh, string> = arDict as Record<keyof typeof zh, string>
-export const hi: Record<keyof typeof zh, string> = hiDict as Record<keyof typeof zh, string>
-export const id: Record<keyof typeof zh, string> = idDict as Record<keyof typeof zh, string>
-export const tr: Record<keyof typeof zh, string> = trDict as Record<keyof typeof zh, string>
-export const vi: Record<keyof typeof zh, string> = viDict as Record<keyof typeof zh, string>
-export const th: Record<keyof typeof zh, string> = thDict as Record<keyof typeof zh, string>
-export const ru: Record<keyof typeof zh, string> = ruDict as Record<keyof typeof zh, string>
-export const it: Record<keyof typeof zh, string> = itDict as Record<keyof typeof zh, string>
-export const nl: Record<keyof typeof zh, string> = nlDict as Record<keyof typeof zh, string>
-export const sv: Record<keyof typeof zh, string> = svDict as Record<keyof typeof zh, string>
-export const pl: Record<keyof typeof zh, string> = plDict as Record<keyof typeof zh, string>
-export const zhHK: Record<keyof typeof zh, string> = zhHKDict as Record<keyof typeof zh, string>
-export const zhTW: Record<keyof typeof zh, string> = zhTWDict as Record<keyof typeof zh, string>
-export const zhMO: Record<keyof typeof zh, string> = zhMODict as Record<keyof typeof zh, string>
+// The 19 non-zh/en dictionaries live in the LAZY `locale` chunk
+// (src/client/chunks/locale.tsx → lib/client-locale.js): `t()` only ever
+// consults zh/en plus the better-locale override store, so those dicts are
+// needed only when better-locale is installed — the client apply fetches the
+// chunk there and registers its `localeDicts` into the override store. They
+// used to sit statically in the core bundle (≈ half its weight) for a code
+// path most sessions never enter.
 
 /** The DSH locale service attached by the client apply (absent → browser detection). */
 let localeService: { getSnapshot(): { active: string } } | undefined
diff --git a/src/client/prefs.ts b/src/client/prefs.ts
index be4d482..082523a 100644
--- a/src/client/prefs.ts
+++ b/src/client/prefs.ts
@@ -217,3 +217,22 @@ export async function loadExternalDisable(settings: SidebarSettingsClient): Prom
     return false
   }
 }
+
+/** The boot decision both the prefs and the external-disable flag need:
+ *  ONE settings fetch answers both (the boot path used to await
+ *  {@link loadPrefs} and {@link loadExternalDisable} serially — two round
+ *  trips of the same document before the first paint, and the second had no
+ *  timeout, so a stalled wire could keep the sidebar unmounted forever). */
+export interface BootDecision {
+  prefs: SidebarPrefs
+  suspended: boolean
+}
+
+export async function loadBootDecision(settings: SidebarSettingsClient): Promise<BootDecision> {
+  try {
+    const view = await settings.settingsGet()
+    return { prefs: parsePrefs(view.value), suspended: view.externalDisable === true }
+  } catch {
+    return { prefs: { ...SIDEBAR_PREFS_DEFAULTS }, suspended: false }
+  }
+}
diff --git a/src/client/sidechat-transcript.ts b/src/client/sidechat-transcript.ts
index 61dde7a..0c9e400 100644
--- a/src/client/sidechat-transcript.ts
+++ b/src/client/sidechat-transcript.ts
@@ -307,7 +307,7 @@ function resultCard(
  * @param entries - history rows (event + host-computed view) in seq order.
  * @returns display rows in log order.
  */
-export function transcriptRows(entries: readonly SidebarHistoryEntry[]): SidechatTranscriptRow[] {
+export function transcriptRows(entries: readonly SidebarHistoryEntry[], prev?: readonly SidechatTranscriptRow[]): SidechatTranscriptRow[] {
   const events = entries.map(entry => entry.event)
   const seedEnd = lastSeedEnd(events)
   const rows: SidechatTranscriptRow[] = []
@@ -484,5 +484,59 @@ export function transcriptRows(entries: readonly SidebarHistoryEntry[]): Sidecha
       }
     }
   }
+  return reuseRows(rows, prev)
+}
+
+/** Whether two rows carry identical display content (identity fields plus
+ *  every rendered field of their kind). */
+function rowsEqual(a: SidechatTranscriptRow, b: SidechatTranscriptRow): boolean {
+  if (a.kind !== b.kind || a.seq !== b.seq) return false
+  switch (a.kind) {
+    case 'user':
+    case 'injection': {
+      const other = b as typeof a
+      return a.text === other.text
+    }
+    case 'assistant':
+    case 'reasoning': {
+      const other = b as typeof a
+      return a.text === other.text && a.settled === other.settled
+    }
+    case 'tool': {
+      // The card is NOT compared by value: its content is a pure function of
+      // the call-time args and the tool/result landing, and every transition
+      // (output/exit arriving) flips `executing`/`failed`/`resultText` —
+      // compared here — so a card whose content changed never slips through
+      // an equal compare, and an equal compare re-adopting the OLD card
+      // object (identical content, stale reference) only helps React skip.
+      const other = b as typeof a
+      return a.name === other.name && a.failed === other.failed && a.args === other.args
+        && a.resultText === other.resultText && a.executing === other.executing
+    }
+    case 'turnSummary': {
+      const other = b as typeof a
+      return a.inputTokens === other.inputTokens && a.outputTokens === other.outputTokens
+        && a.durationMs === other.durationMs
+    }
+  }
+}
+
+/** Re-adopt the PREVIOUS poll's row objects wherever the content is
+ *  unchanged (position-aligned, append-mostly): settled rows keep their
+ *  object identity across the 2s polls, so React's reconciler and the
+ *  markdown/DOMPurify caches downstream skip them instead of re-rendering
+ *  the whole transcript every poll. Comparing the strings is far cheaper
+ *  than what a fresh reference costs the row below. Rows past the first
+ *  mismatch (an inserted/superseded streaming row) rebuild as usual — that
+ *  is exactly the changed tail. */
+function reuseRows(rows: SidechatTranscriptRow[], prev: readonly SidechatTranscriptRow[] | undefined): SidechatTranscriptRow[] {
+  if (prev === undefined) return rows
+  const shared = Math.min(rows.length, prev.length)
+  for (let index = 0; index < shared; index++) {
+    const before = prev[index]
+    const after = rows[index]
+    if (before === undefined || after === undefined) continue
+    if (rowsEqual(before, after)) rows[index] = before
+  }
   return rows
 }
diff --git a/tests/bundle-route.spec.ts b/tests/bundle-route.spec.ts
index faf4400..1585cd5 100644
--- a/tests/bundle-route.spec.ts
+++ b/tests/bundle-route.spec.ts
@@ -145,6 +145,6 @@ describe('/sidebar/bundle route', () => {
   })
 
   it('exports the chunk allowlist (mirror of src/client/chunk-loader.ts)', () => {
-    expect([...CHUNK_NAMES]).toEqual(['terminal', 'editor', 'mermaid'])
+    expect([...CHUNK_NAMES]).toEqual(['terminal', 'editor', 'mermaid', 'locale'])
   })
 })
diff --git a/tests/e2e/drag-layout.e2e.ts b/tests/e2e/drag-layout.e2e.ts
index a3ce7fb..9f131d7 100644
--- a/tests/e2e/drag-layout.e2e.ts
+++ b/tests/e2e/drag-layout.e2e.ts
@@ -612,33 +612,163 @@ test('bottom panel never flashes full-width after a width drag release (issue #2
   }
 })
 
-test('the bottom-push anchor resolves through the composite selectors (at least one; same element when both)', async ({ page }) => {
-  // layout.css pushes the bottom panel via the center column. The selector
-  // is COMPOSITE on purpose: `[data-pane="conversation"]` (0.1.x naming)
-  // and `:has(> [data-slot="conversation"])` (rc.8-era naming) — HOST
-  // VERSIONS MAY RENAME THE ATTRIBUTE (issue #208 comment / PR #226), so
-  // the contract is "at least one resolves", and when both resolve they
-  // must hit the SAME element (otherwise the push would land twice).
+test('the bottom-push anchor resolves through the shell-written center-column tag', async ({ page }) => {
+  // layout.css pushes the bottom panel via the center column, anchored on
+  // the [data-dsh-center-col] tag the Sidebar shell's locator writes onto
+  // the measured column node (Sidebar.tsx locate — the slot wrapper
+  // [data-slot="conversation"]'s parent). The tag must sit on exactly ONE
+  // node: a stale tag on a swapped-out node (boot swap / HMR) would leave
+  // the push rule anchorless or doubled.
   await page.goto(PAGE_URL, { waitUntil: 'domcontentloaded' })
   await expect(page.locator('[data-dsh-better-sidebar]')).toBeAttached({ timeout: 90_000 })
+  await expect
+    .poll(async () => page.evaluate(() => document.querySelectorAll('#root [data-dsh-center-col]').length), { timeout: 90_000 })
+    .toBe(1)
   const anchors = await page.evaluate(() => {
-    const a = document.querySelector('#root [data-dsh-frame] > [data-pane="conversation"]')
-    const b = document.querySelector('#root :has(> [data-slot="conversation"])')
-    const frame = document.querySelector('#root [data-dsh-frame]')
+    const tagged = document.querySelector('#root [data-dsh-center-col]')
+    const slotParent = document.querySelector('#root [data-slot="conversation"]')?.parentElement ?? null
     return {
-      a: a !== null,
-      b: b !== null,
-      same: a !== null && b !== null && a === b,
-      frameChildren: frame !== null
-        ? [...frame.children].map(el => `${el.tagName}[${[...el.attributes].map(attr => attr.name).filter(name => name.startsWith('data-')).join(',')}]`)
-        : [],
+      tagged: tagged !== null,
+      same: tagged !== null && slotParent !== null && tagged === slotParent,
     }
   })
-  expect(
-    anchors.a || anchors.b,
-    `at least one bottom-push anchor must resolve on this host (frame children: ${anchors.frameChildren.join(' / ') || 'no [data-dsh-frame]'})`,
-  ).toBe(true)
-  if (anchors.a && anchors.b) {
-    expect(anchors.same, 'both selectors must hit the SAME center-column element').toBe(true)
+  expect(anchors.tagged, 'the tagged center column must resolve').toBe(true)
+  expect(anchors.same, 'the tag must sit on the conversation slot wrapper\'s parent (the measured column)').toBe(true)
+})
+
+/* ── bottom-strip drag with the right panel CLOSED must not touch the host
+      layout — the regression test for the width-gate fix ───────────────── */
+
+test('dragging the bottom strip while the right panel is closed keeps the host layout still', async ({ page }) => {
+  // The bottom drag used to write the panel's persisted width preference into
+  // `--dsh-sidebar-width` regardless of `panelOpen` (only the idle push
+  // effect gated it): with the panel closed the variable jumped 0 → ~400px on the
+  // first drag frame, #root lost 400px instantly, the host frame's viewport
+  // dropped across its 1024px auto-collapse breakpoint, and the NATIVE left
+  // sidebar snapped to its 56px rail — then snapped back on release. The
+  // panel-side DOM writes keep the raw width (the bottom panel's `right`
+  // derives from it); only the PUSHED width must ride the panelOpen gate.
+  await page.goto(PAGE_URL, { waitUntil: 'domcontentloaded' })
+  await expect(page.locator('#root > *')).not.toHaveCount(0, { timeout: 90_000 })
+  const sidebar = page.locator('[data-dsh-better-sidebar]')
+  await expect(sidebar).toBeAttached({ timeout: 90_000 })
+  await dismissOnboarding(page)
+
+  // The right panel stays CLOSED (openByDefault off): the width variable
+  // must read as the collapsed push before anything happens.
+  const readPushWidth = (): Promise<number> => page.evaluate(() => {
+    const value = parseFloat(document.documentElement.style.getPropertyValue('--dsh-sidebar-width'))
+    return Number.isNaN(value) ? 0 : value
+  })
+  await expect
+    .poll(async () => {
+      const height = await page.evaluate(() => parseFloat(document.documentElement.style.getPropertyValue('--dsh-sidebar-height')) || 0)
+      return height
+    }, { timeout: 90_000 })
+    .toBe(0)
+
+  const bottomExpand = sidebar.getByRole('button', { name: 'Expand bottom panel' })
+  await expect(bottomExpand, 'the toggle cluster must offer the bottom-panel expand button').toHaveCount(1)
+  await bottomExpand.click()
+  await expect
+    .poll(async () => {
+      const value = await page.evaluate(() => parseFloat(document.documentElement.style.getPropertyValue('--dsh-sidebar-height')) || 0)
+      return value
+    }, { timeout: 90_000 })
+    .toBeGreaterThan(0)
+  expect(await readPushWidth(), 'the closed right panel must push 0 width').toBe(0)
+
+  // Per-frame sampler on the HOST side: the pushed width variable, the host
+  // frame's inline grid template (its first track is the native left
+  // sidebar's width), the rendered left-column width (the grid transition
+  // animates mid-states, so this catches even a transient snap), and #root's
+  // right edge (where the width push lands).
+  await page.evaluate(() => {
+    const samples: Array<{ t: number; varW: number; gridCols: string; leftColW: number; rootRight: number; dragging: boolean }> = []
+    const center = document.querySelector('#root [data-slot="conversation"]')?.parentElement ?? null
+    const frame = center?.parentElement ?? null
+    const leftCol = frame?.firstElementChild ?? null
+    const root = document.querySelector('#root') as HTMLElement
+    const loop = (): void => {
+      const varW = parseFloat(document.documentElement.style.getPropertyValue('--dsh-sidebar-width'))
+      samples.push({
+        t: performance.now(),
+        varW: Number.isNaN(varW) ? 0 : varW,
+        gridCols: frame instanceof HTMLElement ? frame.style.gridTemplateColumns : '',
+        leftColW: leftCol?.getBoundingClientRect().width ?? -1,
+        rootRight: root.getBoundingClientRect().right,
+        dragging: document.body.hasAttribute('data-dsh-sidebar-dragging'),
+      })
+      requestAnimationFrame(loop)
+    }
+    requestAnimationFrame(loop)
+    ;(window as unknown as { __bottomDragSamples: typeof samples }).__bottomDragSamples = samples
+  })
+
+  // The bottom strip is the panel's top-edge row-resize hit strip. The panel
+  // SLIDES DOWN into place on expand: a box read mid-animation sits above the
+  // settled geometry and the pointerdown lands off-strip (the drag never
+  // starts). Wait until the strip's center sits at innerHeight - the pushed
+  // height (the panel's final top edge).
+  await expect
+    .poll(async () => {
+      const probe = await page.evaluate(() => {
+        const bottom = document.querySelector('[data-dsh-better-sidebar] [data-dsh-bottom-panel]')
+        if (bottom === null) return null
+        const strip = [...bottom.querySelectorAll<HTMLElement>('*')].find(el => getComputedStyle(el).cursor === 'row-resize')
+        if (strip === undefined) return null
+        const r = strip.getBoundingClientRect()
+        const heightVar = parseFloat(document.documentElement.style.getPropertyValue('--dsh-sidebar-height')) || 0
+        return Math.abs((r.y + r.height / 2) - (window.innerHeight - heightVar))
+      })
+      return probe === null ? Number.NaN : probe
+    }, { timeout: 30_000 })
+    .toBeLessThanOrEqual(8)
+  const stripBox = await page.evaluate(() => {
+    const bottom = document.querySelector('[data-dsh-better-sidebar] [data-dsh-bottom-panel]')
+    if (bottom === null) return null
+    const strip = [...bottom.querySelectorAll<HTMLElement>('*')].find(el => getComputedStyle(el).cursor === 'row-resize')
+    if (strip === undefined) return null
+    const r = strip.getBoundingClientRect()
+    return { x: r.x + r.width / 2, y: r.y + r.height / 2 }
+  })
+  expect(stripBox, 'the bottom drag strip must be present (cursor: row-resize)').not.toBeNull()
+
+  // Drag the strip UP (grow the bottom panel) in steps, like a real resize.
+  await page.mouse.move(stripBox!.x, stripBox!.y)
+  await page.mouse.down()
+  for (let i = 1; i <= 12; i++) {
+    await page.mouse.move(stripBox!.x, stripBox!.y - i * 8, { steps: 2 })
+    await page.waitForTimeout(40)
+  }
+  await page.mouse.up()
+  await page.waitForTimeout(500)
+
+  const samples = await page.evaluate(
+    () => (window as unknown as { __bottomDragSamples: Array<{ t: number; varW: number; gridCols: string; leftColW: number; rootRight: number; dragging: boolean }> }).__bottomDragSamples,
+  )
+  expect(samples.length, 'the frame sampler must have collected frames').toBeGreaterThan(20)
+  const dragging = samples.filter(s => s.dragging)
+  expect(dragging.length, 'the dragging attribute must appear during the drag').toBeGreaterThan(5)
+
+  // The drag must actually have resized the bottom panel (sanity: the height
+  // push committed to a bigger value than where it started).
+  const heightAfter = await page.evaluate(() => parseFloat(document.documentElement.style.getPropertyValue('--dsh-sidebar-height')) || 0)
+  expect(heightAfter).toBeGreaterThan(0)
+
+  // Contract: the pushed width stays 0 for EVERY frame — mid-drag AND after
+  // release. The old code let the panel's persisted preference (~400px)
+  // through on the first drag frame and the release commit.
+  for (const s of samples) {
+    expect(s.varW, `pushed width leaked during the bottom drag at t=${Math.round(s.t)} (got ${s.varW}px)`).toBe(0)
+  }
+  // Contract: the host layout never moves — same inline grid template, same
+  // rendered left-column width (the native sidebar would snap to its 56px
+  // rail when #root loses 400px on a 1280px viewport), same #root right edge.
+  const first = samples[0]!
+  for (const s of samples) {
+    expect(s.gridCols, `host grid template changed at t=${Math.round(s.t)}: ${first.gridCols} -> ${s.gridCols}`).toBe(first.gridCols)
+    expect(Math.abs(s.leftColW - first.leftColW), `native left column width changed at t=${Math.round(s.t)}: ${first.leftColW} -> ${s.leftColW}`).toBeLessThanOrEqual(1)
+    expect(Math.abs(s.rootRight - first.rootRight), `#root right edge changed at t=${Math.round(s.t)}: ${first.rootRight} -> ${s.rootRight}`).toBeLessThanOrEqual(1)
   }
 })
diff --git a/tests/e2e/perf.e2e.ts b/tests/e2e/perf.e2e.ts
new file mode 100644
index 0000000..0e90493
--- /dev/null
+++ b/tests/e2e/perf.e2e.ts
@@ -0,0 +1,278 @@
+/**
+ * Perf lane: a MEASUREMENT harness, not a pass/fail gate (beyond the mount
+ * sanity it shares with the other lanes).
+ *
+ * It exists to put NUMBERS on the sidebar's client-side cost in a real
+ * mounted `dsh web` (the same scratch-profile boot as scripts/e2e-mount.sh):
+ *
+ *   1. mount latency  — navigationStart → `[data-dsh-better-sidebar]`
+ *      attached, sampled by an init-script probe (rAF loop, so it catches
+ *      the attach even before Playwright's first poll);
+ *   2. longtasks      — every >50ms main-thread task from first paint
+ *      through the full built-in tab sweep (the heaviest mount surface);
+ *   3. bundle cost    — per-resource transferSize/decodedBodySize/duration
+ *      for everything sidebar-shaped the page fetched;
+ *   4. bottom-drag frames — rAF frame-interval p95/max while dragging the
+ *      bottom strip (the layout-push hot path), plus the width-leak guard
+ *      from the drag lane (a closed right panel must push 0).
+ *
+ * Results print as single-line `PERF_JSON` records (plus a `PERF_SUMMARY`
+ * aggregate) so a shell run can `tee` the log and grep them out; the
+ * before/after comparison lives in docs/plans/2026-08-31-perf-optimization.md.
+ * Run it 3× and take the median of each metric — single-run numbers on a
+ * developer machine are noise, not baselines.
+ */
+import { mkdirSync, writeFileSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { test, expect, type APIRequestContext, type Page } from '@playwright/test'
+import { PAGE_URL, createHostApi, hostRpc } from './host'
+
+/** This lane's own workspace (lanes run serially against one server — never
+ *  share seed paths with mount/drag). */
+const WORKSPACE_PATH = process.env.DSH_E2E_PERF_WORKSPACE ?? join(tmpdir(), 'dsh-e2e-perf-workspace')
+
+/** Built-in tab titles the sweep drives (en-US copy; follows DSH locale). */
+const BUILTIN_TABS = ['Files', 'Changes', 'Tasks', 'Side Chat (beta)', 'Terminal', 'Browser']
+
+let api: APIRequestContext
+
+async function seedSession(): Promise<void> {
+  mkdirSync(WORKSPACE_PATH, { recursive: true })
+  writeFileSync(join(WORKSPACE_PATH, 'seed.txt'), 'perf lane\n')
+  const workspace = await hostRpc<{ workspace: { workspaceId: string } }>(api, 'workspace.create', { path: WORKSPACE_PATH })
+  await hostRpc(api, 'session.create', { workspaceId: workspace.value.workspace.workspaceId })
+}
+
+test.beforeAll(async () => {
+  api = await createHostApi()
+  await seedSession()
+})
+
+test.afterAll(async () => {
+  await api?.dispose()
+})
+
+/** The longtask collector + mount-attach probe, injected before ANY page
+ *  script runs (longtasks observed late are gone forever). */
+const PERF_PROBE = `(() => {
+  const perf = { mountAt: null, longtasks: [] }
+  window.__perfProbe = perf
+  new PerformanceObserver(list => {
+    for (const entry of list.getEntries()) perf.longtasks.push({ start: entry.startTime, duration: entry.duration })
+  }).observe({ entryTypes: ['longtask'] })
+  const check = () => {
+    if (document.querySelector('[data-dsh-better-sidebar]') !== null) { perf.mountAt = performance.now(); return }
+    requestAnimationFrame(check)
+  }
+  requestAnimationFrame(check)
+})()`
+
+function percentile(values: number[], p: number): number {
+  if (values.length === 0) return 0
+  const sorted = [...values].sort((a, b) => a - b)
+  const index = Math.min(sorted.length - 1, Math.max(0, Math.ceil((p / 100) * sorted.length) - 1))
+  return sorted[index]!
+}
+
+interface ResourceStat {
+  name: string
+  transferSize: number
+  decodedBodySize: number
+  duration: number
+}
+
+/** Dismiss whatever onboarding takeover is present (same dance as the other
+ *  lanes) so the pointer can reach the sidebar's controls. */
+async function dismissOnboarding(page: Page): Promise<void> {
+  try {
+    await expect
+      .poll(() => page.getByRole('button', { name: /^(Continue|Configure later)$/ }).count(), { timeout: 60_000 })
+      .toBeGreaterThan(0)
+  } catch {
+    console.warn('[e2e-perf] no onboarding takeover appeared; proceeding')
+  }
+  for (let round = 0; round < 8; round++) {
+    let dismissed = false
+    for (const name of ['Continue', 'Configure later']) {
+      const button = page.getByRole('button', { name, exact: true }).first()
+      if ((await button.count()) === 0) continue
+      try {
+        await button.click({ timeout: 4_000 })
+        dismissed = true
+        await page.waitForTimeout(1_000)
+      } catch {
+        // Masked by a takeover stacked above; retry in the next round.
+      }
+    }
+    if (!dismissed) break
+  }
+}
+
+test('measure: mount latency, longtasks and bundle cost through a full tab sweep', async ({ page }) => {
+  await page.addInitScript(PERF_PROBE)
+  await page.goto(PAGE_URL, { waitUntil: 'domcontentloaded' })
+  await expect(page.locator('#root > *')).not.toHaveCount(0, { timeout: 90_000 })
+  const sidebar = page.locator('[data-dsh-better-sidebar]')
+  await expect(sidebar).toBeAttached({ timeout: 90_000 })
+
+  const mountLatency = await page.evaluate(() =>
+    (window as unknown as { __perfProbe: { mountAt: number | null } }).__perfProbe.mountAt)
+  expect(mountLatency, 'the mount probe must have caught the attach').not.toBeNull()
+
+  await dismissOnboarding(page)
+
+  // Open the panel, then sweep every built-in tab through the "+" menu — the
+  // same crash-sweep surface as mount.e2e.ts, reused here as the workload.
+  const expandButton = sidebar.getByRole('button', { name: 'Expand sidebar' })
+  await expect(expandButton).toHaveCount(1)
+  await expandButton.click()
+  await expect
+    .poll(async () => {
+      const value = await page.evaluate(() => document.documentElement.style.getPropertyValue('--dsh-sidebar-width'))
+      return value !== '' && value !== '0px'
+    }, { timeout: 90_000 })
+    .toBe(true)
+
+  const newTabButton = sidebar.getByRole('button', { name: 'New tab' }).first()
+  for (const title of BUILTIN_TABS) {
+    await newTabButton.click()
+    const item = page.getByRole('menuitem', { name: title }).first()
+    await expect(item, `built-in tab "${title}" must be offered by the + menu`).toHaveCount(1)
+    await item.click()
+    await page.waitForTimeout(1_500)
+  }
+
+  // Let the last tab settle (lazy chunks + first render) before reading.
+  await page.waitForTimeout(2_000)
+  const probe = await page.evaluate(() => (window as unknown as { __perfProbe: { mountAt: number | null; longtasks: Array<{ start: number; duration: number }> } }).__perfProbe)
+  const resources = await page.evaluate(() =>
+    performance.getEntriesByType('resource')
+      .filter(entry => /sidebar/.test(entry.name))
+      .map(entry => {
+        const resource = entry as PerformanceResourceTiming
+        return {
+          name: entry.name.replace(/^https?:\/\/[^/]+/, ''),
+          transferSize: resource.transferSize,
+          decodedBodySize: resource.decodedBodySize,
+          duration: entry.duration,
+        }
+      }) as ResourceStat[],
+  )
+
+  const longtasks = probe.longtasks ?? []
+  const record = {
+    metric: 'mount-sweep',
+    mountLatencyMs: mountLatency,
+    longtaskCount: longtasks.length,
+    longtaskTotalMs: Math.round(longtasks.reduce((sum, task) => sum + task.duration, 0)),
+    longtaskMaxMs: longtasks.reduce((max, task) => Math.max(max, task.duration), 0),
+    resourceCount: resources.length,
+    resourceTransferTotal: resources.reduce((sum, r) => sum + r.transferSize, 0),
+    resourceDecodedTotal: resources.reduce((sum, r) => sum + r.decodedBodySize, 0),
+    resources,
+  }
+  console.log(`PERF_JSON ${JSON.stringify(record)}`)
+  console.log(
+    `PERF_SUMMARY mount=${Math.round(mountLatency!)}ms longtasks=${record.longtaskCount}/${record.longtaskTotalMs}ms `
+    + `resources=${record.resourceCount}/${(record.resourceTransferTotal / 1024).toFixed(0)}KiB`,
+  )
+})
+
+test('measure: bottom-strip drag frame pacing', async ({ page }) => {
+  await page.addInitScript(PERF_PROBE)
+  await page.goto(PAGE_URL, { waitUntil: 'domcontentloaded' })
+  await expect(page.locator('#root > *')).not.toHaveCount(0, { timeout: 90_000 })
+  const sidebar = page.locator('[data-dsh-better-sidebar]')
+  await expect(sidebar).toBeAttached({ timeout: 90_000 })
+  await dismissOnboarding(page)
+
+  // The right panel stays CLOSED on purpose: the bottom drag must not push
+  // the host layout in that pose (the width-leak regression the drag lane
+  // locks; recorded here as a number-adjacent guard for the perf story).
+  const bottomExpand = sidebar.getByRole('button', { name: 'Expand bottom panel' })
+  await expect(bottomExpand).toHaveCount(1)
+  await bottomExpand.click()
+  await expect
+    .poll(async () => {
+      const value = await page.evaluate(() => parseFloat(document.documentElement.style.getPropertyValue('--dsh-sidebar-height')) || 0)
+      return value
+    }, { timeout: 90_000 })
+    .toBeGreaterThan(0)
+
+  // Frame-pacing sampler: rAF timestamps during the drag only.
+  await page.evaluate(() => {
+    const frames: number[] = []
+    const pushWidths: number[] = []
+    const loop = (): void => {
+      frames.push(performance.now())
+      const width = parseFloat(document.documentElement.style.getPropertyValue('--dsh-sidebar-width'))
+      pushWidths.push(Number.isNaN(width) ? 0 : width)
+      requestAnimationFrame(loop)
+    }
+    requestAnimationFrame(loop)
+    ;(window as unknown as { __dragFrames: number[]; __dragPushWidths: number[] }).__dragFrames = frames
+    ;(window as unknown as { __dragPushWidths: number[] }).__dragPushWidths = pushWidths
+  })
+
+  // The panel slides down into place on expand: read the strip only after it
+  // settles at innerHeight - the pushed height (a mid-animation box makes the
+  // pointerdown land off-strip and the drag never starts).
+  await expect
+    .poll(async () => {
+      const probe = await page.evaluate(() => {
+        const bottom = document.querySelector('[data-dsh-better-sidebar] [data-dsh-bottom-panel]')
+        if (bottom === null) return null
+        const strip = [...bottom.querySelectorAll<HTMLElement>('*')].find(el => getComputedStyle(el).cursor === 'row-resize')
+        if (strip === undefined) return null
+        const r = strip.getBoundingClientRect()
+        const heightVar = parseFloat(document.documentElement.style.getPropertyValue('--dsh-sidebar-height')) || 0
+        return Math.abs((r.y + r.height / 2) - (window.innerHeight - heightVar))
+      })
+      return probe === null ? Number.NaN : probe
+    }, { timeout: 30_000 })
+    .toBeLessThanOrEqual(8)
+  const stripPoint = await page.evaluate(() => {
+    const bottom = document.querySelector('[data-dsh-better-sidebar] [data-dsh-bottom-panel]')
+    if (bottom === null) return null
+    const strip = [...bottom.querySelectorAll<HTMLElement>('*')].find(el => getComputedStyle(el).cursor === 'row-resize')
+    if (strip === undefined) return null
+    const r = strip.getBoundingClientRect()
+    return { x: r.x + r.width / 2, y: r.y + r.height / 2 }
+  })
+  expect(stripPoint, 'the bottom drag strip must be present').not.toBeNull()
+
+  const t0 = await page.evaluate(() => performance.now())
+  await page.mouse.move(stripPoint!.x, stripPoint!.y)
+  await page.mouse.down()
+  for (let i = 1; i <= 12; i++) {
+    await page.mouse.move(stripPoint!.x, stripPoint!.y - i * 8, { steps: 2 })
+    await page.waitForTimeout(40)
+  }
+  await page.mouse.up()
+  const t1 = await page.evaluate(() => performance.now())
+  await page.waitForTimeout(300)
+
+  const { frames, widths } = await page.evaluate(() => ({
+    frames: (window as unknown as { __dragFrames: number[] }).__dragFrames,
+    widths: (window as unknown as { __dragPushWidths: number[] }).__dragPushWidths,
+  }))
+  const dragFrames = frames.filter(t => t >= t0 && t <= t1)
+  const intervals: number[] = []
+  for (let i = 1; i < dragFrames.length; i++) intervals.push(dragFrames[i]! - dragFrames[i - 1]!)
+  const dragWidths = widths.slice(Math.max(0, frames.indexOf(dragFrames[0] ?? frames[0]!)))
+  const record = {
+    metric: 'bottom-drag',
+    frames: dragFrames.length,
+    intervalMedianMs: Math.round(percentile(intervals, 50)),
+    intervalP95Ms: Math.round(percentile(intervals, 95)),
+    intervalMaxMs: Math.round(Math.max(0, ...intervals)),
+    pushWidthLeakMax: Math.max(0, ...dragWidths),
+  }
+  console.log(`PERF_JSON ${JSON.stringify(record)}`)
+  console.log(
+    `PERF_SUMMARY drag-frames=${record.frames} p50=${record.intervalMedianMs}ms p95=${record.intervalP95Ms}ms `
+    + `max=${record.intervalMaxMs}ms widthLeak=${record.pushWidthLeakMax}px`,
+  )
+  expect(record.pushWidthLeakMax, 'the closed right panel must push 0 width during the bottom drag').toBe(0)
+})
diff --git a/tests/layout-css.spec.ts b/tests/layout-css.spec.ts
index c90d889..6613607 100644
--- a/tests/layout-css.spec.ts
+++ b/tests/layout-css.spec.ts
@@ -9,9 +9,13 @@ import { describe, expect, it } from 'vitest'
 const css = readFileSync('src/client/layout.css', 'utf8')
 
 describe('layout.css conversation column', () => {
-  it('targets the AppFrame center column', () => {
-    expect(css).toContain('[data-pane="conversation"]')
-    expect(css).toContain('[data-slot="conversation"]')
+  it('targets the AppFrame center column through the shell-written tag', () => {
+    // The bottom-push rule anchors on the [data-dsh-center-col] tag the
+    // Sidebar shell's locator writes onto the measured column node (see
+    // Sidebar.tsx locate) — not on a `:has()` selector, whose cache
+    // invalidates on every #root subtree mutation (the streaming chat).
+    expect(css).toContain('[data-dsh-center-col]')
+    expect(css).not.toContain(':has(')
   })
 
   it('allows the center column to shrink and wrap long tokens', () => {
@@ -21,7 +25,7 @@ describe('layout.css conversation column', () => {
 
   it('leaves overflow ownership to the host conversation descendants', () => {
     const conversationRule = css.match(
-      /#root \[data-dsh-frame\][\s\S]*?\{([\s\S]*?)\n\}/,
+      /#root \[data-dsh-center-col\][\s\S]*?\{([\s\S]*?)\n\}/,
     )?.[1]
     expect(conversationRule).toBeDefined()
     expect(conversationRule).not.toMatch(/(?:^|[;\s])overflow\s*:/)
diff --git a/tests/locales.spec.ts b/tests/locales.spec.ts
index 4e12ffe..e2e6cab 100644
--- a/tests/locales.spec.ts
+++ b/tests/locales.spec.ts
@@ -6,7 +6,8 @@
  * interpolation.
  */
 import { afterEach, describe, expect, it } from 'vitest'
-import { LOCALE_NS, attachBetterLocale, attachLocale, en, isZh, ja, relativeTime, t, zh, de, fr, pt, ko, ar, hi, id as idDict, tr, vi, th, ru, it as itDict, nl, sv, pl, zhHK, zhTW, zhMO } from '../src/client/locales.ts'
+import { LOCALE_NS, attachBetterLocale, attachLocale, en, isZh, relativeTime, t, zh } from '../src/client/locales.ts'
+import { localeDicts } from '../src/client/chunks/locale.tsx'
 
 /** Minimal structural fake of the DSH LocaleService face the sidebar uses. */
 class FakeLocale {
@@ -108,20 +109,15 @@ describe('locales (DSH i18n following)', () => {
     expect(Object.keys(en).sort()).toEqual(Object.keys(zh).sort())
   })
 
-  it('keeps the ja dictionary key-set-equal to zh', () => {
-    expect(Object.keys(ja).sort()).toEqual(Object.keys(zh).sort())
-  })
-
   it('keeps every shipped third-language dictionary key-set-equal to zh', () => {
-    // The third-language dicts are typed `Record<keyof typeof zh, string>` via
-    // an `as` cast (unchecked by tsc). This test catches missing/extra keys
-    // introduced when a zh key is added without updating every language.
-    const thirdLangs = {
-      de, fr, pt, ko, ar, hi, idDict, tr, vi, th, ru, itDict, nl, sv, pl, zhHK, zhTW, zhMO,
-    }
-    for (const [lang, dict] of Object.entries(thirdLangs)) {
-      expect(Object.keys(dict as Record<string, string>).sort(), lang).toEqual(Object.keys(zh).sort())
+    // The third-language dicts live in the lazy locale chunk typed as plain
+    // records (the chunk boundary has no key-set type tie to zh). This test
+    // catches missing/extra keys introduced when a zh key is added without
+    // updating every language — a missing key silently falls back to en.
+    for (const [lang, dict] of Object.entries(localeDicts)) {
+      expect(Object.keys(dict).sort(), lang).toEqual(Object.keys(zh).sort())
     }
+    expect(Object.keys(localeDicts), 'every shipped third language rides the locale chunk').toContain('ja')
   })
 })
 
@@ -247,7 +243,7 @@ describe('locales (better-locale override)', () => {
     locale.switchTo('en')
     attachLocale(locale)
 
-    const betterLocale = new FakeBetterLocale({ [LOCALE_NS]: { ja } })
+    const betterLocale = new FakeBetterLocale({ [LOCALE_NS]: { ja: localeDicts.ja! } })
     betterLocale.active = 'ja'
     attachBetterLocale(betterLocale)
 
diff --git a/tests/prefs.spec.ts b/tests/prefs.spec.ts
index 449f55b..fe48adb 100644
--- a/tests/prefs.spec.ts
+++ b/tests/prefs.spec.ts
@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vitest'
-import { loadExternalDisable, loadPrefs, type SidebarSettingsClient } from '../src/client/prefs.ts'
+import { loadBootDecision, loadExternalDisable, loadPrefs, type SidebarSettingsClient } from '../src/client/prefs.ts'
 import { allLeaves, createSidebarStore, defaultWidthFor, makeDefaultState, setWidth } from '../src/client/state.ts'
 import { SIDEBAR_PREFS_DEFAULTS } from '../src/prefs-shared.ts'
 
@@ -416,3 +416,28 @@ describe('external disable (aionui-panel provider choice)', () => {
     expect(await loadExternalDisable(rejecting())).toBe(false)
   })
 })
+
+describe('boot decision (one fetch for prefs + external disable)', () => {
+  it('answers both decisions from a single settingsGet call', async () => {
+    let calls = 0
+    const counting = (): SidebarSettingsClient => ({
+      settingsGet: async () => { calls += 1; return { value: { openByDefault: true, defaultWidthPercent: 40 }, revision: 1, externalDisable: true } },
+      settingsUpdate: async () => ({ value: {}, revision: 2 }),
+    })
+    const decision = await loadBootDecision(counting())
+    expect(calls, 'the boot path must fetch the settings document exactly once').toBe(1)
+    expect(decision.suspended).toBe(true)
+    expect(decision.prefs.openByDefault).toBe(true)
+  })
+
+  it('falls back to the defaults + not suspended on any failure', async () => {
+    const decision = await loadBootDecision(rejecting())
+    expect(decision).toEqual({ prefs: SIDEBAR_PREFS_DEFAULTS, suspended: false })
+  })
+
+  it('reads suspended false when the flag is absent', async () => {
+    const decision = await loadBootDecision(wire({ defaultWidthPercent: 50 }))
+    expect(decision.suspended).toBe(false)
+    expect(decision.prefs.defaultWidthPercent).toBe(50)
+  })
+})
diff --git a/tests/sidechat-transcript.spec.ts b/tests/sidechat-transcript.spec.ts
index fbe5a6a..6c8e532 100644
--- a/tests/sidechat-transcript.spec.ts
+++ b/tests/sidechat-transcript.spec.ts
@@ -371,3 +371,75 @@ describe('toolArgsSummary', () => {
     expect(toolArgsSummary('{"command":"   "}')).toBe('{"command":" "}')
   })
 })
+
+describe('transcriptRows row reuse (the poll-to-poll identity pass)', () => {
+  it('re-adopts the previous poll\'s row objects wherever content is unchanged', () => {
+    const entries = [
+      entry(ev('session/end-seed', 0)),
+      entry(ev('user/message', 1, { content: textBlocks('the side question'), source: { kind: 'user' } })),
+      entry(ev('assistant/message', 2, { message: { content: textBlocks('the answer') } })),
+    ]
+    const first = transcriptRows(entries)
+    const second = transcriptRows(entries, first)
+    expect(second).toEqual(first)
+    // Settled rows keep their object identity (fresh references defeat the
+    // downstream memo and re-render the whole transcript every 2s poll).
+    expect(second[1]).toBe(first[1])
+    expect(second[2]).toBe(first[2])
+  })
+
+  it('rebuilds changed rows and everything past the change', () => {
+    const before = transcriptRows([
+      entry(ev('session/end-seed', 0)),
+      entry(ev('user/message', 1, { content: textBlocks('q'), source: { kind: 'user' } })),
+    ])
+    const after = transcriptRows([
+      entry(ev('session/end-seed', 0)),
+      entry(ev('user/message', 1, { content: textBlocks('q'), source: { kind: 'user' } })),
+      entry(ev('user/message', 2, { content: textBlocks('q2'), source: { kind: 'user' } })),
+    ], before)
+    expect(after).toHaveLength(2)
+    expect(after[0]).toBe(before[0])
+    expect(after[1]).not.toBe(before[1])
+    expect(after[1]).toMatchObject({ kind: 'user', seq: 2, text: 'q2' })
+  })
+
+  it('never re-adopts a row whose rendered fields changed (tool result lands)', () => {
+    const call = entry(ev('tool/call', 1, { callId: 'c1', name: 'bash', arguments: '{"command":"ls"}' }))
+    const before = transcriptRows([entry(ev('session/end-seed', 0)), call])
+    expect(before[0]).toMatchObject({ kind: 'tool', executing: true })
+    const result = entry(ev('tool/result', 2, {
+      message: { source: { callId: 'c1' }, content: [{ type: 'tool-result', content: [{ type: 'text', text: 'out' }] }] },
+    }))
+    const after = transcriptRows([entry(ev('session/end-seed', 0)), call, result], before)
+    expect(after[0]).not.toBe(before[0])
+    expect(after[0]).toMatchObject({ kind: 'tool', executing: false, resultText: 'out' })
+  })
+})
+
+describe('transcriptRows row reuse (newer row kinds)', () => {
+  it('re-adopts settled turnSummary rows (token usage tail)', () => {
+    const entries = [
+      entry(ev('session/end-seed', 0)),
+      entry(ev('turn/start', 1, { turn: 1 })),
+      entry(ev('turn/end', 2, { turn: 1, reason: 'completed' })),
+    ]
+    const first = transcriptRows(entries)
+    const summary = first.find(row => row.kind === 'turnSummary')
+    expect(summary).toBeDefined()
+    const second = transcriptRows(entries, first)
+    expect(second[second.length - 1]).toBe(summary)
+  })
+
+  it('re-adopts a tool row whose card landed (executing flip forces the rebuild)', () => {
+    const call = entry(ev('tool/call', 1, { callId: 'c1', name: 'bash', arguments: '{"command":"ls"}' }))
+    const before = transcriptRows([entry(ev('session/end-seed', 0)), call])
+    expect(before[0]).toMatchObject({ kind: 'tool', executing: true })
+    const result = entry(ev('tool/result', 2, {
+      message: { source: { callId: 'c1' }, content: [{ type: 'tool-result', content: [{ type: 'text', text: 'out\n[exit 0]' }] }] },
+    }))
+    const after = transcriptRows([entry(ev('session/end-seed', 0)), call, result], before)
+    expect(after[0]).not.toBe(before[0])
+    expect(after[0]).toMatchObject({ kind: 'tool', executing: false })
+  })
+})
diff --git a/tsdown.config.ts b/tsdown.config.ts
index 2183fd9..881a45d 100644
--- a/tsdown.config.ts
+++ b/tsdown.config.ts
@@ -324,7 +324,7 @@ function makeCssPlugin(pluginId: string): BuildPlugin {
 }
 
 /** The lazy chunk names (keep in sync with src/bundle-route.ts CHUNK_NAMES). */
-const CHUNKS = ['terminal', 'editor', 'mermaid']
+const CHUNKS = ['terminal', 'editor', 'mermaid', 'locale']
 
 export default [
   {