diff --git a/vscode/webview-ui/src/codeReader/App.tsx b/vscode/webview-ui/src/codeReader/App.tsx
index 8ea4c17..6bdee0a 100644
--- a/vscode/webview-ui/src/codeReader/App.tsx
+++ b/vscode/webview-ui/src/codeReader/App.tsx
@@ -5,7 +5,7 @@ import type { TextMarks } from './SegmentText'
 import type { BlockView, DocumentMessage } from './types'
 import type { OccurrencePage } from './useOccurrences'
 import { TriangleAlert } from 'lucide-react'
-import { useCallback, useEffect, useMemo, useRef, useState } from 'react'
+import { useCallback, useEffect, useLayoutEffect, useMemo, useRef, useState } from 'react'
 import { AskThread, FEATURE_THREAD } from './AskThread'
 import { BlockTree } from './BlockTree'
 import { CallTreeDialog } from './CallTreeDialog'
@@ -17,6 +17,7 @@ import { startEditing } from './editing'
 import { keptWhileEditing } from './filter'
 import { FilterBar } from './FilterBar'
 import { OverviewRuler } from './OverviewRuler'
+import { pageLayout } from './pageLayout'
 import { createPageStore } from './pageState'
 import { chatOf, PATH_ASK_ANCHOR, sameChat } from './qa'
 import { TextMarksContext } from './SegmentText'
@@ -75,6 +76,13 @@ export function App(): ReactElement | null {
   const restoreCall = useRef(viewState.get().callTree)
   /** 块树所在的页面内容：钉住卡片时在这里面量 */
   const content = useRef<HTMLDivElement>(null)
+  /** 页面内容挂上时，卡片的位置从它量（pageLayout）：筛选栏和它在同一次提交里画出来 */
+  const attachContent = useCallback((el: HTMLDivElement | null) => {
+    content.current = el
+    return el ? pageLayout.attach(el, document.querySelector<HTMLElement>('.cr-filter-bar')) : undefined
+  }, [])
+  // 这一层重画了：同一段脚本里接着要量位置的（滚到某一行、跳到改动、滚到当前那一处）不能用重画前量的，先作废；放在它们前面
+  useLayoutEffect(() => pageLayout.invalidate())
   const { doc, editing, folds, reveal, excluded, diff, onlyChanges, openCall, changes, collapsed, filter, covered, unshown, stops } = useStore(page, current => current)
   const pathChat = useStore(qa.store, state => chatOf(state, PATH_ASK_ANCHOR), sameChat)
   const qaAvailable = useStore(qa.store, state => state.available)
@@ -236,7 +244,7 @@ export function App(): ReactElement | null {
         )}
       />
       {changes && diff && <OverviewRuler stops={stops} lineCount={diff.lineCount} onPick={nav.goTo} />}
-      <div ref={content} className="mx-auto box-content max-w-[880px] px-6 py-5">
+      <div ref={attachContent} className="mx-auto box-content max-w-[880px] px-6 py-5">
         {qaAvailable && (
           <div className="mb-4">
             <AskThread
@@ -273,7 +281,7 @@ export function App(): ReactElement | null {
         {doc.blocks.length === 0
           ? doc.error === undefined && qaSubject === 'file' && <div className="text-[var(--vscode-descriptionForeground)]">这个文件里没有代码。</div>
           : doc.blocks.some(block => !filter.hidden.has(block.id))
-            ? <BlockTree blocks={doc.blocks} tree={tree} />
+            ? <BlockTree blocks={doc.blocks} tree={tree} items />
             : <div className="text-[var(--vscode-descriptionForeground)]">所有块都被筛选隐藏了。</div>}
       </div>
       {sticky?.enabled && <StickyLines content={content} blocks={doc.blocks} settings={sticky} />}
diff --git a/vscode/webview-ui/src/codeReader/BlockTree.tsx b/vscode/webview-ui/src/codeReader/BlockTree.tsx
index ce5c2f1..e113066 100644
--- a/vscode/webview-ui/src/codeReader/BlockTree.tsx
+++ b/vscode/webview-ui/src/codeReader/BlockTree.tsx
@@ -1,4 +1,4 @@
-import type { CSSProperties, ReactElement } from 'react'
+import type { CSSProperties, ReactElement, ReactNode } from 'react'
 import type { RewriteTool } from './BlockTools'
 import type { DiffTree, FoldedRuns, PlacedRemoved } from './diffView'
 import type { GridSlots } from './PropertyGrid'
@@ -117,11 +117,14 @@ function useBlockTree(): BlockTreeHandle {
   return tree
 }
 
-/** 一棵块树：blocks 是顶层的块，tree 是它的状态和动作（见 BlockTreeHandle）。 */
-export function BlockTree({ blocks, tree }: { blocks: BlockView[], tree: BlockTreeHandle }): ReactElement {
+/**
+ * 一棵块树：blocks 是顶层的块，tree 是它的状态和动作（见 BlockTreeHandle）。
+ * items：顶层每块（连同它的问答区、子块）套一层 .cr-item，页面上按它分段量位置（见 pageLayout）；定义卡片浮窗里只有一块，不套。
+ */
+export function BlockTree({ blocks, tree, items = false }: { blocks: BlockView[], tree: BlockTreeHandle, items?: boolean }): ReactElement {
   return (
     <BlockTreeContext value={tree}>
-      <BlockLevel blocks={blocks} />
+      <BlockLevel blocks={blocks} items={items} />
     </BlockTreeContext>
   )
 }
@@ -287,8 +290,9 @@ function sameRewrite(a: RewriteShape, b: RewriteShape): boolean {
 /**
  * 一块：「只看改动」折起来的一段、卡片、下面的问答区和重写记录、子块那一层。块树、问 AI、重写注释三份状态里只订阅这一块自己的，
  * 都没变就不重画；子块那一层的各块、卡片的内容各自 memo，这一块重画了它们也不跟着重画。
+ * item：画出来的卡片、问答区、子块那一层套一层 .cr-item（记着起始行），见 BlockTree。
  */
-const BlockItem = memo(({ block }: { block: BlockView }): ReactElement => {
+const BlockItem = memo(({ block, item }: { block: BlockView, item: boolean }): ReactElement => {
   const tree = useBlockTree()
   const { qa, rewrite } = tree
   const shape = useStore(tree.state, state => shapeOf(block, state), shallowEqual)
@@ -299,7 +303,7 @@ const BlockItem = memo(({ block }: { block: BlockView }): ReactElement => {
     <>
       {shape.run !== undefined && <UnchangedStrip count={shape.run} onOpen={() => tree.onOpenRun(block.id)} />}
       {shape.shown && (
-        <>
+        <Item item={item} line={block.startLine}>
           <BlockCard block={block} shape={shape} ask={ask} rewrite={rewriting} />
           {/* 输入框、展开状态跟着块的记号走，文档刷新块 id 变了也不丢 */}
           {qa && ask.chat && (
@@ -333,20 +337,27 @@ const BlockItem = memo(({ block }: { block: BlockView }): ReactElement => {
             />
           )}
           {shape.open && <BlockLevel blocks={block.children} owner={block} />}
-        </>
+        </Item>
       )}
     </>
   )
 })
 BlockItem.displayName = 'BlockItem'
 
+/** 顶层一块的外层（见 BlockTree 的 items）；不套时原样 */
+function Item({ item, line, children }: { item: boolean, line: number, children: ReactNode }): ReactElement {
+  if (!item)
+    return <>{children}</>
+  return <div className="cr-item flex flex-col gap-2" data-line={line}>{children}</div>
+}
+
 /**
  * 一层代码块：左边一条竖线标出这一层，每块的子块紧跟在它下面、再往右缩进一层。被筛掉、被盖住的块不画，不留空位，竖线跟着变短。
  * owner 是这一层所属的块（顶层没有，记在 data-owner 上，钉住卡片时按它算卡片连同子块管到哪、套着几层），悬停它时竖线换成它的种类色。
  * 标差异时每张卡片左边外侧一条改动色条，删掉的块收成一行放回原来的位置（见 RemovedCard）；「只看改动」时连着没变的块折成一条（UnchangedStrip）。
- * slotted：这一层是画在卡片属性表某一行下面的子块（BlockSlot），blocks 只有那几块。
+ * slotted：这一层是画在卡片属性表某一行下面的子块（BlockSlot），blocks 只有那几块。items：这一层每块套一层 .cr-item（只有页面上的顶层）。
  */
-export function BlockLevel({ blocks, owner, slotted = false }: { blocks: BlockView[], owner?: BlockView, slotted?: boolean }): ReactElement {
+export function BlockLevel({ blocks, owner, slotted = false, items = false }: { blocks: BlockView[], owner?: BlockView, slotted?: boolean, items?: boolean }): ReactElement {
   const tree = useBlockTree()
   // 挂在卡片子行上的子块画在卡片属性表里（slotted 的那一层），这一层不画；删掉的块都放回卡片后面这一层
   const listed = useMemo(() => slotted ? blocks : blocks.filter(block => !block.slot), [blocks, slotted])
@@ -371,7 +382,7 @@ export function BlockLevel({ blocks, owner, slotted = false }: { blocks: BlockVi
         {removedAfter(undefined)}
         {listed.map(block => (
           <Fragment key={block.id}>
-            <BlockItem block={block} />
+            <BlockItem block={block} item={items} />
             {removedAfter(block.id)}
           </Fragment>
         ))}
diff --git a/vscode/webview-ui/src/codeReader/StickyLines.tsx b/vscode/webview-ui/src/codeReader/StickyLines.tsx
index ce9bde2..e0255ec 100644
--- a/vscode/webview-ui/src/codeReader/StickyLines.tsx
+++ b/vscode/webview-ui/src/codeReader/StickyLines.tsx
@@ -2,10 +2,11 @@ import type { ReactElement, RefObject } from 'react'
 import type { BlockView, StickyScrollSettings } from './types'
 import { useContext, useLayoutEffect, useMemo } from 'react'
 import { KindIcon } from './kindIcons'
+import { pageLayout } from './pageLayout'
 import { SegmentText, TextMarksContext } from './SegmentText'
 import { selectStore } from './store'
 import { flash } from './useReveal'
-import { pinnedHeight, usePinnedHeight } from './useScrollPosition'
+import { usePinnedHeight } from './useScrollPosition'
 import { STICKY_LINE_HEIGHT, stickyInset, useStickyLines } from './useStickyScroll'
 
 /** 块 id → 块，连同各层子块 */
@@ -74,7 +75,7 @@ export function StickyLines({ content, blocks, settings }: { content: RefObject<
     const card = content.current?.querySelector<HTMLElement>(`.cr-block[data-id="${id}"]`)
     if (!card)
       return
-    window.scrollTo(0, card.getBoundingClientRect().top + window.scrollY - pinnedHeight() - stickyInset(card, settings))
+    window.scrollTo(0, card.getBoundingClientRect().top + window.scrollY - pageLayout.pinnedHeight() - stickyInset(card, settings))
     flash(card)
   }
 
diff --git a/vscode/webview-ui/src/codeReader/codeReader.css b/vscode/webview-ui/src/codeReader/codeReader.css
index facebc8..060a0db 100644
--- a/vscode/webview-ui/src/codeReader/codeReader.css
+++ b/vscode/webview-ui/src/codeReader/codeReader.css
@@ -963,7 +963,8 @@ body {
  * 卡片左边外侧的改动色条：3px 宽、和卡片等高，空 5px 再是卡片；没变的卡片留一条透明的，同一层的卡片照样对齐。
  * 色条画在卡片里（标不标差异卡片都是同一个元素），标差异的那一层（data-diff）卡片、折起来的一段、问答区都往右让出 8px，色条挪进这 8px 里
  */
-.cr-level[data-diff] > div > :is(.cr-block, .cr-unchanged, .cr-qa) {
+.cr-level[data-diff] > div > :is(.cr-block, .cr-unchanged, .cr-qa),
+.cr-level[data-diff] > div > .cr-item > :is(.cr-block, .cr-qa) {
   margin-left: 8px;
 }
 .cr-change-bar {
diff --git a/vscode/webview-ui/src/codeReader/occurrences.test.ts b/vscode/webview-ui/src/codeReader/occurrences.test.ts
index 0b2db0f..fbff43b 100644
--- a/vscode/webview-ui/src/codeReader/occurrences.test.ts
+++ b/vscode/webview-ui/src/codeReader/occurrences.test.ts
@@ -1,6 +1,6 @@
 import type { Click, Highlight } from './occurrences'
 import type { BlockView, Inline, Occurrence, PreviewText, PropertyItem, Segment, WebviewToExtension } from './types'
-import { describe, expect, it } from 'vitest'
+import { describe, expect, it, vi } from 'vitest'
 import { toBlockViews } from '../../../src/codeReader/blockView'
 import { createPythonAdapter } from '../../../src/codeReader/languages/python'
 import { WASM_DIR, withBlocks } from '../../../src/codeReader/testSupport'
@@ -359,26 +359,38 @@ describe('occurrences：用键盘在各处出现之间跳', () => {
     scroll.press({ x: 0, y: 40 }, 1000)
     scroll.take(1012)
     // 刚回到按键那一刻、还没跳完：守住按键那一刻的位置
-    expect(scroll.scrolled({ x: 0, y: 300 }, 1020)).toEqual({ x: 0, y: 40 })
+    expect(scroll.scrolled(1020, () => ({ x: 0, y: 300 }))).toEqual({ x: 0, y: 40 })
     scroll.hold({ x: 0, y: 900 })
-    expect(scroll.scrolled({ x: 0, y: 900 }, 1030)).toBeUndefined()
-    expect(scroll.scrolled({ x: 0, y: 1200 }, 1040)).toEqual({ x: 0, y: 900 })
-    expect(scroll.scrolled({ x: 0, y: 1200 }, 1000 + KEY_SCROLL_MS + 1)).toBeUndefined()
-    expect(scroll.scrolled({ x: 0, y: 1300 }, 1000 + KEY_SCROLL_MS + 2)).toBeUndefined()
+    expect(scroll.scrolled(1030, () => ({ x: 0, y: 900 }))).toBeUndefined()
+    expect(scroll.scrolled(1040, () => ({ x: 0, y: 1200 }))).toEqual({ x: 0, y: 900 })
+    expect(scroll.scrolled(1000 + KEY_SCROLL_MS + 1, () => ({ x: 0, y: 1200 }))).toBeUndefined()
+    expect(scroll.scrolled(1000 + KEY_SCROLL_MS + 2, () => ({ x: 0, y: 1300 }))).toBeUndefined()
   })
 
   it('不是按键触发的跳转、又按了键、点了鼠标：不守', () => {
     const scroll = new KeyScroll()
     scroll.take(10)
     scroll.hold({ x: 0, y: 900 })
-    expect(scroll.scrolled({ x: 0, y: 0 }, 20)).toBeUndefined()
+    expect(scroll.scrolled(20, () => ({ x: 0, y: 0 }))).toBeUndefined()
     scroll.press({ x: 0, y: 40 }, 1000)
     scroll.take(1010)
     scroll.press({ x: 0, y: 40 }, 1100)
-    expect(scroll.scrolled({ x: 0, y: 300 }, 1110)).toBeUndefined()
+    expect(scroll.scrolled(1110, () => ({ x: 0, y: 300 }))).toBeUndefined()
     scroll.take(1120)
     scroll.forget()
-    expect(scroll.scrolled({ x: 0, y: 300 }, 1130)).toBeUndefined()
+    expect(scroll.scrolled(1130, () => ({ x: 0, y: 300 }))).toBeUndefined()
+  })
+
+  it('不守着时滚动不读滚动位置（读它会逼浏览器先排版）', () => {
+    const scroll = new KeyScroll()
+    const read = vi.fn(() => ({ x: 0, y: 300 }))
+    expect(scroll.scrolled(10, read)).toBeUndefined()
+    scroll.press({ x: 0, y: 40 }, 1000)
+    expect(scroll.scrolled(1005, read)).toBeUndefined()
+    expect(read).not.toHaveBeenCalled()
+    scroll.take(1010)
+    expect(scroll.scrolled(1020, read)).toEqual({ x: 0, y: 40 })
+    expect(read).toHaveBeenCalledTimes(1)
   })
 
   it('我们自己滚过的位置不算浏览器滚走：差 1 像素、滚进视口都不再拉一次，真被滚走仍拉回', () => {
@@ -389,12 +401,12 @@ describe('occurrences：用键盘在各处出现之间跳', () => {
     scroll.own({ x: 0, y: 39 })
     scroll.own({ x: 0, y: 40 })
     scroll.own({ x: 0, y: 800 })
-    expect(scroll.scrolled({ x: 0, y: 39 }, 1020)).toBeUndefined()
-    expect(scroll.scrolled({ x: 0, y: 39 }, 1021)).toBeUndefined()
-    expect(scroll.scrolled({ x: 0, y: 800 }, 1022)).toBeUndefined()
+    expect(scroll.scrolled(1020, () => ({ x: 0, y: 39 }))).toBeUndefined()
+    expect(scroll.scrolled(1021, () => ({ x: 0, y: 39 }))).toBeUndefined()
+    expect(scroll.scrolled(1022, () => ({ x: 0, y: 800 }))).toBeUndefined()
     scroll.hold({ x: 0, y: 800 })
-    expect(scroll.scrolled({ x: 0, y: 39 }, 1030)).toBeUndefined()
-    expect(scroll.scrolled({ x: 0, y: 300 }, 1040)).toEqual({ x: 0, y: 800 })
+    expect(scroll.scrolled(1030, () => ({ x: 0, y: 39 }))).toBeUndefined()
+    expect(scroll.scrolled(1040, () => ({ x: 0, y: 300 }))).toEqual({ x: 0, y: 800 })
   })
 
   it('默认快捷键：mac 是 ⌘↓ / ⌘↑，别的系统是 ctrl；带了别的修饰键不算', () => {
diff --git a/vscode/webview-ui/src/codeReader/occurrences.ts b/vscode/webview-ui/src/codeReader/occurrences.ts
index d2b57e4..9227634 100644
--- a/vscode/webview-ui/src/codeReader/occurrences.ts
+++ b/vscode/webview-ui/src/codeReader/occurrences.ts
@@ -229,14 +229,15 @@ export class KeyScroll {
       this.held = { ...this.held, position }
   }
 
-  /** 页面滚动了：还在守着、又被浏览器滚走了，给出要拉回的位置。我们自己滚到的位置不算。 */
-  scrolled(position: ScrollPosition, now: number): ScrollPosition | undefined {
+  /** 页面滚动了：还在守着、又被浏览器滚走了，给出要拉回的位置。我们自己滚到的位置不算。守着时才读滚动位置（read）：读它会逼浏览器先排版，平常滚动不读。 */
+  scrolled(now: number, read: () => ScrollPosition): ScrollPosition | undefined {
     const held = this.held
     if (!held || now > held.until) {
       this.held = undefined
       this.owned = []
       return undefined
     }
+    const position = read()
     if (this.owned.some(item => item.x === position.x && item.y === position.y))
       return undefined
     return held.position.x === position.x && held.position.y === position.y ? undefined : held.position
diff --git a/vscode/webview-ui/src/codeReader/pageLayout.test.ts b/vscode/webview-ui/src/codeReader/pageLayout.test.ts
new file mode 100644
index 0000000..658ceeb
--- /dev/null
+++ b/vscode/webview-ui/src/codeReader/pageLayout.test.ts
@@ -0,0 +1,100 @@
+// @vitest-environment happy-dom
+
+import type { BlockBox } from './scrollPosition'
+import { afterEach, describe, expect, it } from 'vitest'
+import { PageLayout } from './pageLayout'
+import { anchorAt, blockForLine } from './scrollPosition'
+
+/** 量过几次位置 */
+let reads = 0
+
+/** 元素的位置写死（happy-dom 不排版），每量一次记一次 */
+function place<T extends HTMLElement>(el: T, top: number, bottom: number, left = 0, right = 800): T {
+  el.getBoundingClientRect = () => {
+    reads++
+    return { top, bottom, left, right, width: right - left, height: bottom - top, x: left, y: top, toJSON: () => ({}) } as DOMRect
+  }
+  return el
+}
+
+function div(className: string, attrs: Record<string, string> = {}, ...children: HTMLElement[]): HTMLElement {
+  const el = document.createElement('div')
+  el.className = className
+  for (const [name, value] of Object.entries(attrs))
+    el.setAttribute(name, value)
+  el.append(...children)
+  return el
+}
+
+/** 一层：左边竖线那格、右边一栏 */
+function level(owner: string | undefined, ...children: HTMLElement[]): HTMLElement {
+  return div('cr-level', owner === undefined ? {} : { 'data-owner': owner }, div('guide'), div('column', {}, ...children))
+}
+
+function card(id: string, line: number, top: number, bottom: number, editing = false): HTMLElement {
+  return place(div('cr-block', { 'data-id': id, 'data-line': String(line), ...(editing && { 'data-editing': '' }) }), top, bottom)
+}
+
+/**
+ * 三段顶层块，每段 1000px：第 0 段一张卡片和它的两张子卡片（子层到 900 结束），第 1 段一张卡片（在编辑），第 2 段一张卡片。
+ */
+function page(): { root: HTMLElement, cards: BlockBox[] } {
+  const root = document.createElement('div')
+  root.append(level(
+    undefined,
+    place(div('cr-item', { 'data-line': '0' }, card('0', 0, 0, 100), place(level('0', card('0.0', 2, 120, 300), card('0.1', 8, 320, 500)), 110, 900)), 0, 1000),
+    place(div('cr-item', { 'data-line': '20' }, card('1', 20, 1010, 1500, true)), 1010, 1500),
+    place(div('cr-item', { 'data-line': '40' }, card('2', 40, 1510, 2000)), 1510, 2000),
+  ))
+  document.body.append(root)
+  const cards = [[0, 0, 100], [2, 120, 300], [8, 320, 500], [20, 1010, 1500], [40, 1510, 2000]].map(([line, top, bottom]) => ({ line, top, bottom }))
+  return { root, cards }
+}
+
+afterEach(() => {
+  document.body.innerHTML = ''
+  reads = 0
+})
+
+describe('卡片位置量过就记着', () => {
+  it('滚动位置、包含某一行的块：和把全部卡片量一遍算出来的一样', () => {
+    const { root, cards } = page()
+    const layout = new PageLayout()
+    layout.attach(root, null)
+    for (const y of [0, 50, 100, 310, 950, 1200, 1999, 2500]) {
+      const found = layout.anchorAt(y)
+      expect(found && { line: found.line, offset: found.offset }, `y ${y}`).toEqual((({ line, offset }) => ({ line, offset }))(anchorAt(cards, y)!))
+    }
+    for (const line of [0, 1, 5, 9, 25, 100])
+      expect(layout.cardForLine(line)?.line, `line ${line}`).toBe(blockForLine(cards, line)?.line)
+    expect(layout.topFor({ line: 8, offset: 5, scrollTop: 9999 })).toBe(325)
+    expect(layout.topFor({ line: 9, offset: 5, scrollTop: 9999 })).toBe(9999)
+  })
+
+  it('钉住的卡片：只算和顶上那一段相交的顶层块，在编辑的不钉；外层卡片的下沿算到它的子层', () => {
+    const { root } = page()
+    const layout = new PageLayout()
+    layout.attach(root, null)
+    window.scrollTo(0, 0)
+    const scopes = layout.stickyScopes(48)
+    expect(scopes.map(scope => [scope.id, scope.depth, scope.top, scope.bottom])).toEqual([['0', 0, 0, 900]])
+  })
+
+  it('滚动时不再量：同一份内容问几次都只量一次；只量用到的那几段；内容变了才重量', async () => {
+    const { root } = page()
+    const layout = new PageLayout()
+    layout.attach(root, null)
+    layout.anchorAt(0)
+    // 三段顶层块的外框 + 第 0、1 段里的卡片和子层
+    const first = reads
+    expect(first).toBe(3 + 4 + 1)
+    for (const y of [0, 10, 20, 300, 600])
+      layout.anchorAt(y)
+    layout.stickyScopes(48)
+    expect(reads).toBe(first)
+    root.querySelector('.cr-item')!.append(div('cr-qa'))
+    await Promise.resolve()
+    layout.anchorAt(0)
+    expect(reads).toBe(first * 2)
+  })
+})
diff --git a/vscode/webview-ui/src/codeReader/pageLayout.ts b/vscode/webview-ui/src/codeReader/pageLayout.ts
new file mode 100644
index 0000000..fc9ceaf
--- /dev/null
+++ b/vscode/webview-ui/src/codeReader/pageLayout.ts
@@ -0,0 +1,191 @@
+import type { BlockBox, ScrollAnchor } from './scrollPosition'
+import type { StickyScope } from './stickyScroll'
+import { anchorAt, blockForLine, scrollTopFor } from './scrollPosition'
+
+/** 一张卡片量出来的位置（文档坐标）：BlockBox 之外，块 id、外面套着几张卡片、连同画出来的子块的下沿、左右边，在不在编辑。 */
+interface CardBox extends BlockBox {
+  id: string
+  depth: number
+  scopeBottom: number
+  left: number
+  right: number
+  editing: boolean
+}
+
+/** 顶层的一块（.cr-item，块树按它分段）：上下边（文档坐标）和起始行。 */
+interface ItemBox {
+  el: HTMLElement
+  top: number
+  bottom: number
+  line: number
+}
+
+/** 卡片外面套着几张卡片：它所在的各层子层（BlockLevel 画的、带 data-owner 的）一层算一张 */
+export function depthOf(card: Element): number {
+  let depth = 0
+  for (let level = card.closest('.cr-level[data-owner]'); level; level = level.parentElement?.closest('.cr-level[data-owner]') ?? null)
+    depth++
+  return depth
+}
+
+/** 一段顶层块里的卡片（BlockCard 带 data-line；删掉的块那张没有），按页面先后；下沿算到它名下画出来的子层（带 data-owner）的最后 */
+function measureCards(item: HTMLElement): CardBox[] {
+  const x = window.scrollX
+  const y = window.scrollY
+  const bottoms = new Map<string, number>()
+  for (const level of item.querySelectorAll<HTMLElement>('.cr-level[data-owner]')) {
+    const owner = level.dataset.owner ?? ''
+    bottoms.set(owner, Math.max(bottoms.get(owner) ?? Number.NEGATIVE_INFINITY, level.getBoundingClientRect().bottom + y))
+  }
+  return Array.from(item.querySelectorAll<HTMLElement>('.cr-block[data-line]'), (card) => {
+    const id = card.dataset.id ?? ''
+    const rect = card.getBoundingClientRect()
+    const bottom = rect.bottom + y
+    return {
+      id,
+      line: Number(card.dataset.line),
+      top: rect.top + y,
+      bottom,
+      scopeBottom: Math.max(bottom, bottoms.get(id) ?? bottom),
+      left: rect.left + x,
+      right: rect.right + x,
+      depth: depthOf(card),
+      editing: card.hasAttribute('data-editing'),
+    }
+  })
+}
+
+/** 第一个满足 test 的序号，没有时是总数；test 按先后是先不满足、后满足（顶层块按页面先后排，上下边、起始行都是递增的） */
+function firstWhere(items: readonly ItemBox[], test: (item: ItemBox) => boolean): number {
+  let low = 0
+  let high = items.length
+  while (low < high) {
+    const middle = (low + high) >> 1
+    if (test(items[middle]))
+      high = middle
+    else
+      low = middle + 1
+  }
+  return low
+}
+
+/** 起始行不超过 line 的最后一段顶层块的序号；line 在所有块之前时是 0 */
+function itemOfLine(items: readonly ItemBox[], line: number): number {
+  return Math.max(0, firstWhere(items, item => item.line > line) - 1)
+}
+
+/**
+ * 页面上卡片的位置和筛选栏的高度，量过就记着，滚动时只在记着的里面按顶层块二分找，不再每帧量全部卡片（量位置会逼浏览器先排版）。
+ * 顶层的块（.cr-item）先整段量，里面的卡片用到哪段才量哪段（屏幕外的段可能没排版，量它要先排一次）。坐标都是文档坐标（视口坐标 + 滚动位置），滚动不改它。
+ * 页面内容的结构变了（MutationObserver）、大小变了（ResizeObserver）、窗口大小变了，或页面重画了（invalidate，同一段脚本里改完马上要量的）才作废，下次用时重量。
+ */
+export class PageLayout {
+  private root: HTMLElement | null = null
+  private bar: HTMLElement | null = null
+  private items: ItemBox[] | undefined
+  private cards = new Map<HTMLElement, CardBox[]>()
+  private barHeight: number | undefined
+
+  /** 量 root（块树所在的页面内容）里的卡片，筛选栏是 bar；返回停止观察的函数 */
+  attach(root: HTMLElement, bar: HTMLElement | null): () => void {
+    this.root = root
+    this.bar = bar
+    this.invalidate()
+    const invalidate = (): void => this.invalidate()
+    const mutations = new MutationObserver(invalidate)
+    mutations.observe(root, { childList: true, subtree: true, attributes: true, attributeFilter: ['data-line', 'data-editing', 'data-id'] })
+    const sizes = new ResizeObserver(invalidate)
+    sizes.observe(root)
+    if (bar)
+      sizes.observe(bar)
+    window.addEventListener('resize', invalidate)
+    return () => {
+      mutations.disconnect()
+      sizes.disconnect()
+      window.removeEventListener('resize', invalidate)
+      if (this.root === root) {
+        this.root = null
+        this.bar = null
+        this.invalidate()
+      }
+    }
+  }
+
+  invalidate(): void {
+    this.items = undefined
+    this.cards.clear()
+    this.barHeight = undefined
+  }
+
+  /** 顶部钉住的筛选栏的高度：视口里露出块的部分从它下面开始，记位置、滚过去都按这部分算。 */
+  pinnedHeight(): number {
+    this.barHeight ??= this.bar?.offsetHeight ?? 0
+    return this.barHeight
+  }
+
+  private itemBoxes(): ItemBox[] {
+    if (!this.items) {
+      // 顶层那一层：块树最外面的 .cr-level 的右栏，里面的 .cr-item 一块一段
+      const column = this.root?.querySelector(':scope > .cr-level > :last-child')
+      const y = window.scrollY
+      this.items = Array.from(column?.children ?? []).flatMap((el) => {
+        if (!(el instanceof HTMLElement) || !el.classList.contains('cr-item'))
+          return []
+        const rect = el.getBoundingClientRect()
+        return [{ el, top: rect.top + y, bottom: rect.bottom + y, line: Number(el.dataset.line) }]
+      })
+    }
+    return this.items
+  }
+
+  private cardsOf(item: ItemBox): CardBox[] {
+    let cards = this.cards.get(item.el)
+    if (!cards) {
+      cards = measureCards(item.el)
+      this.cards.set(item.el, cards)
+    }
+    return cards
+  }
+
+  /** 视口顶部（scrollTop，见 ScrollAnchor）那块（同 anchorAt）：只量它所在的那段和下一段（那段里的卡片都在 scrollTop 之上结束时是下一段的第一张）。 */
+  anchorAt(scrollTop: number): ScrollAnchor | undefined {
+    const items = this.itemBoxes()
+    if (items.length === 0)
+      return undefined
+    const index = Math.min(firstWhere(items, item => item.bottom > scrollTop), items.length - 1)
+    return anchorAt(items.slice(index, index + 2).flatMap(item => this.cardsOf(item)), scrollTop)
+  }
+
+  /** 包含这一行的块（同 blockForLine）：顶层块按起始行排，先找到它所在的那段，只量那一段。 */
+  cardForLine(line: number): BlockBox | undefined {
+    const items = this.itemBoxes()
+    return items.length === 0 ? undefined : blockForLine(this.cardsOf(items[itemOfLine(items, line)]), line)
+  }
+
+  /** 恢复时视口顶部要在的位置（同 scrollTopFor）：起始行是 anchor.line 的块只会在它所在的那段里。 */
+  topFor(anchor: ScrollAnchor): number {
+    const items = this.itemBoxes()
+    return items.length === 0 ? anchor.scrollTop : scrollTopFor(this.cardsOf(items[itemOfLine(items, anchor.line)]), anchor)
+  }
+
+  /**
+   * 能钉住的卡片，按页面先后，竖直坐标以筛选栏下沿为 0：画出来了、不在编辑的（折叠着的、没有子块的也算）。
+   * 只留可能钉住的：上沿在钉住的那几行（高 band）以内或更高、下沿（连同子块）还在筛选栏下沿以下。只看和这一段相交的顶层块。
+   */
+  stickyScopes(band: number): StickyScope[] {
+    const items = this.itemBoxes()
+    const top = window.scrollY + this.pinnedHeight()
+    const x = window.scrollX
+    const scopes: StickyScope[] = []
+    for (let index = firstWhere(items, item => item.bottom >= top); index < items.length && items[index].top < top + band; index++) {
+      for (const card of this.cardsOf(items[index])) {
+        if (!card.editing && card.top - top < band && card.scopeBottom - top >= 0)
+          scopes.push({ id: card.id, depth: card.depth, top: card.top - top, bottom: card.scopeBottom - top, left: card.left - x, right: card.right - x })
+      }
+    }
+    return scopes
+  }
+}
+
+/** 预览页只有一份页面内容：App 挂上它，滚动位置、钉住的卡片、跳转都从这里取位置。 */
+export const pageLayout = new PageLayout()
diff --git a/vscode/webview-ui/src/codeReader/useChangeNav.ts b/vscode/webview-ui/src/codeReader/useChangeNav.ts
index bd192db..2e6d78e 100644
--- a/vscode/webview-ui/src/codeReader/useChangeNav.ts
+++ b/vscode/webview-ui/src/codeReader/useChangeNav.ts
@@ -2,9 +2,8 @@ import type { ChangeStop } from './diffView'
 import type { StickyScrollSettings } from './types'
 import { useCallback, useLayoutEffect, useRef, useState } from 'react'
 import { nextStop } from './diffView'
-import { anchorAt } from './scrollPosition'
+import { pageLayout } from './pageLayout'
 import { flash } from './useReveal'
-import { measureBlocks, pinnedHeight } from './useScrollPosition'
 import { stickyInset } from './useStickyScroll'
 
 /** 跳到的那处离筛选栏下沿留多少像素。 */
@@ -33,7 +32,7 @@ export function useChangeNav(stops: readonly ChangeStop[], collapsed: ReadonlySe
     }
     const card = document.querySelector<HTMLElement>(`.cr-block[data-id="${target.id}"]`)
     if (card) {
-      window.scrollTo(0, card.getBoundingClientRect().top + window.scrollY - pinnedHeight() - stickyInset(card, sticky) - MARGIN)
+      window.scrollTo(0, card.getBoundingClientRect().top + window.scrollY - pageLayout.pinnedHeight() - stickyInset(card, sticky) - MARGIN)
       flash(card)
     }
     jumped.current = { id: target.id, scrollY: window.scrollY }
@@ -45,7 +44,7 @@ export function useChangeNav(stops: readonly ChangeStop[], collapsed: ReadonlySe
       return
     const from = jumped.current && Math.abs(window.scrollY - jumped.current.scrollY) < 2 ? jumped.current.id : undefined
     const index = from === undefined ? -1 : stops.findIndex(stop => stop.id === from)
-    const at = index >= 0 ? { index } : { line: anchorAt(measureBlocks(), window.scrollY + pinnedHeight())?.line }
+    const at = index >= 0 ? { index } : { line: pageLayout.anchorAt(window.scrollY + pageLayout.pinnedHeight())?.line }
     setTarget(stops[nextStop(stops, at, step)])
   }, [stops])
 
diff --git a/vscode/webview-ui/src/codeReader/useOccurrences.ts b/vscode/webview-ui/src/codeReader/useOccurrences.ts
index cd48b1e..18fa9aa 100644
--- a/vscode/webview-ui/src/codeReader/useOccurrences.ts
+++ b/vscode/webview-ui/src/codeReader/useOccurrences.ts
@@ -145,7 +145,7 @@ export function useOccurrences(version: number | undefined, translatorId: string
     }
     const onPointer = (): void => keyScroll.forget()
     const onScroll = (event: Event): void => {
-      const back = keyScroll.scrolled(scrollPosition(), event.timeStamp)
+      const back = keyScroll.scrolled(event.timeStamp, scrollPosition)
       if (back)
         scrollBack(back, position => keyScroll.own(position))
     }
diff --git a/vscode/webview-ui/src/codeReader/useReveal.ts b/vscode/webview-ui/src/codeReader/useReveal.ts
index 13613a6..89e0917 100644
--- a/vscode/webview-ui/src/codeReader/useReveal.ts
+++ b/vscode/webview-ui/src/codeReader/useReveal.ts
@@ -2,9 +2,8 @@ import type { ScrollPosition } from './occurrences'
 import type { DocumentMessage, Reveal } from './types'
 import { useLayoutEffect } from 'react'
 import { blockPath } from './filter'
+import { pageLayout } from './pageLayout'
 import { revealPlan, scrollTopToShow, uncoveredPlan } from './reveal'
-import { blockForLine } from './scrollPosition'
-import { measureBlocks, pinnedHeight } from './useScrollPosition'
 import { stickyHeight } from './useStickyScroll'
 
 /** 让一块或属性表里的一行闪几下（codeReader.css 的 [data-flash]）；正在闪的同一处再跳一次时从头闪。 */
@@ -28,7 +27,7 @@ export function flash(el: HTMLElement): void {
 /** 把 el 滚进钉住的筛选栏和卡片下面的视口。已经整个看得见就不滚。beforeScroll 在真正滚动前拿到将要落到的位置。 */
 export function showInViewport(el: HTMLElement, beforeScroll?: (position: ScrollPosition) => void): void {
   const rect = el.getBoundingClientRect()
-  const pinned = pinnedHeight() + stickyHeight()
+  const pinned = pageLayout.pinnedHeight() + stickyHeight()
   const top = scrollTopToShow(
     { top: rect.top + window.scrollY, bottom: rect.bottom + window.scrollY },
     window.scrollY,
@@ -75,9 +74,9 @@ export function useReveal(
     if (!doc || !reveal)
       return
     if (reveal.definition === undefined) {
-      const top = blockForLine(measureBlocks(), reveal.line)?.top
+      const top = pageLayout.cardForLine(reveal.line)?.top
       if (top !== undefined)
-        window.scrollTo(0, top - pinnedHeight())
+        window.scrollTo(0, top - pageLayout.pinnedHeight())
       done()
       return
     }
diff --git a/vscode/webview-ui/src/codeReader/useScrollPosition.ts b/vscode/webview-ui/src/codeReader/useScrollPosition.ts
index 9e283c7..7c2cd1c 100644
--- a/vscode/webview-ui/src/codeReader/useScrollPosition.ts
+++ b/vscode/webview-ui/src/codeReader/useScrollPosition.ts
@@ -1,18 +1,15 @@
-import type { BlockBox } from './scrollPosition'
 import type { DocumentMessage } from './types'
 import { useEffect, useLayoutEffect, useRef, useState } from 'react'
-import { anchorAt, scrollTopFor } from './scrollPosition'
+import { pageLayout } from './pageLayout'
 import { postMessage, viewState } from './vscode'
 
 /** 滚动时最多这么久记一次位置 */
 const RECORD_INTERVAL_MS = 100
 
-/** 顶部钉住的筛选栏的高度：视口里露出块的部分从它下面开始，记位置、滚过去都按这部分算。 */
-export function pinnedHeight(): number {
-  return document.querySelector<HTMLElement>('.cr-filter-bar')?.offsetHeight ?? 0
-}
-
-/** 筛选栏有多高，跟着它变（换行、多出第二行时）：钉在它下面的东西（总览条、钉住的卡片）从这儿开始。 */
+/**
+ * 筛选栏有多高，跟着它变（换行、多出第二行时）：钉在它下面的东西（总览条、钉住的卡片）从这儿开始。
+ * 大小变了从 ResizeObserver 报来的尺寸里取，不回头读它的 offsetHeight（那要先排版）。
+ */
 export function usePinnedHeight(): number {
   const [height, setHeight] = useState(0)
   useLayoutEffect(() => {
@@ -20,25 +17,16 @@ export function usePinnedHeight(): number {
     if (!bar)
       return
     setHeight(bar.offsetHeight)
-    const observer = new ResizeObserver(() => setHeight(bar.offsetHeight))
+    const observer = new ResizeObserver(([entry]) => setHeight(entry.borderBoxSize[0]?.blockSize ?? bar.offsetHeight))
     observer.observe(bar)
     return () => observer.disconnect()
   }, [])
   return height
 }
 
-/** 页面上每块（BlockCard 带 data-line）的位置，按页面上的先后；被筛掉的块不在页面上，不算。 */
-export function measureBlocks(): BlockBox[] {
-  const y = window.scrollY
-  return Array.from(document.querySelectorAll<HTMLElement>('.cr-block[data-line]'), (el) => {
-    const rect = el.getBoundingClientRect()
-    return { line: Number(el.dataset.line), top: rect.top + y, bottom: rect.bottom + y }
-  })
-}
-
 /** 记下视口顶部那块；它的起始行变了才报给扩展端。 */
 function record(reportedLine: { current: number | undefined }): void {
-  const anchor = anchorAt(measureBlocks(), window.scrollY + pinnedHeight())
+  const anchor = pageLayout.anchorAt(window.scrollY + pageLayout.pinnedHeight())
   if (!anchor)
     return
   viewState.update({ scroll: anchor })
@@ -53,6 +41,7 @@ function record(reportedLine: { current: number | undefined }): void {
  * ① 滚动时把视口顶部那块记进 webview 状态，页面重新加载后（VS Code 重启后恢复标签页、webview 进程崩了重建）照着滚回去；
  * ② 同时把那块的起始行报给扩展端，切回文本编辑器时把这行放到顶部。
  * 第一份文档带 reveal（刚从文本编辑器切过来、跳到定义）时不恢复，交给 useReveal 滚。
+ * 块的位置从 pageLayout 取：滚动时用量过的，不每次量全部卡片。
  */
 export function useScrollPosition(doc: DocumentMessage | null): void {
   const restored = useRef(false)
@@ -64,9 +53,8 @@ export function useScrollPosition(doc: DocumentMessage | null): void {
       return
     restored.current = true
     const saved = viewState.get().scroll
-    const top = doc.reveal === undefined && saved ? scrollTopFor(measureBlocks(), saved) : undefined
-    if (top !== undefined)
-      window.scrollTo(0, top - pinnedHeight())
+    if (doc.reveal === undefined && saved)
+      window.scrollTo(0, pageLayout.topFor(saved) - pageLayout.pinnedHeight())
     record(reportedLine)
   }, [doc])
 
diff --git a/vscode/webview-ui/src/codeReader/useStickyScroll.ts b/vscode/webview-ui/src/codeReader/useStickyScroll.ts
index 3571020..71b1262 100644
--- a/vscode/webview-ui/src/codeReader/useStickyScroll.ts
+++ b/vscode/webview-ui/src/codeReader/useStickyScroll.ts
@@ -1,49 +1,17 @@
 import type { RefObject } from 'react'
-import type { PinnedLines, StickyScope } from './stickyScroll'
+import type { PinnedLines } from './stickyScroll'
 import type { StickyScrollSettings } from './types'
 import { useEffect, useLayoutEffect, useRef, useState } from 'react'
+import { depthOf, pageLayout } from './pageLayout'
 import { insetAbove, lineLimit, NO_PINNED, pinnedLines, samePinned } from './stickyScroll'
-import { pinnedHeight } from './useScrollPosition'
 import { onMessage } from './vscode'
 
 /** 钉在顶上的一行多高（像素） */
 export const STICKY_LINE_HEIGHT = 24
 
-/** 卡片外面套着几张卡片：它所在的各层子层（BlockLevel 画的、带 data-owner 的）一层算一张 */
-function depthOf(card: Element): number {
-  let depth = 0
-  for (let level = card.closest('.cr-level[data-owner]'); level; level = level.parentElement?.closest('.cr-level[data-owner]') ?? null)
-    depth++
-  return depth
-}
-
 /** 筛选栏下面的可视区域里最多钉几行 */
 function limitOf(maxLineCount: number): number {
-  return lineLimit(window.innerHeight - pinnedHeight(), STICKY_LINE_HEIGHT, maxLineCount)
-}
-
-/**
- * root 里能钉住的卡片，按页面先后，竖直坐标以筛选栏下沿为 0：画出来了、不在编辑的每一张（BlockCard 带 data-line；删掉的块那张没有），
- * 折叠着的、没有子块的也算，卡片自己就是一层。下沿算到它画出来的子块的最后（它名下的子层带 data-owner，挂在子行上的子块那层在卡片里面）。
- * 只留可能钉住的：上沿在钉住的那几行（高 band）以内或更高、下沿还在筛选栏下沿以下
- */
-function measureScopes(root: HTMLElement, band: number): StickyScope[] {
-  const bottoms = new Map<string, number>()
-  for (const level of root.querySelectorAll<HTMLElement>('.cr-level[data-owner]')) {
-    const owner = level.dataset.owner ?? ''
-    bottoms.set(owner, Math.max(bottoms.get(owner) ?? Number.NEGATIVE_INFINITY, level.getBoundingClientRect().bottom))
-  }
-  const base = pinnedHeight()
-  const scopes: StickyScope[] = []
-  for (const card of root.querySelectorAll<HTMLElement>('.cr-block[data-line]:not([data-editing])')) {
-    const id = card.dataset.id ?? ''
-    const rect = card.getBoundingClientRect()
-    const top = rect.top - base
-    const bottom = Math.max(rect.bottom, bottoms.get(id) ?? rect.bottom) - base
-    if (top < band && bottom >= 0)
-      scopes.push({ id, depth: depthOf(card), top, bottom, left: rect.left, right: rect.right })
-  }
-  return scopes
+  return lineLimit(window.innerHeight - pageLayout.pinnedHeight(), STICKY_LINE_HEIGHT, maxLineCount)
 }
 
 /** VS Code 的 Sticky Scroll 设置：扩展端 ready 后先于第一份文档发来，设置改了再发；收到之前不钉。 */
@@ -58,7 +26,7 @@ export function useStickySettings(): StickyScrollSettings | undefined {
 
 /**
  * 眼下 content 里钉着哪几张卡片（见 pinnedLines），最多 maxLineCount 行（窗口矮时更少，见 lineLimit）。滚动、窗口大小变了、内容的大小变了、用它的组件重画了（页面状态变了）时排一次，
- * 每帧最多量一次、算一次（requestAnimationFrame）；钉的没变不更新。只有用它的组件跟着重画，块树不动。
+ * 每帧最多算一次（requestAnimationFrame），卡片的位置用 pageLayout 量过记着的，滚动时不重量；钉的没变不更新。只有用它的组件跟着重画，块树不动。
  */
 export function useStickyLines(content: RefObject<HTMLElement | null>, maxLineCount: number): PinnedLines {
   const [lines, setLines] = useState(NO_PINNED)
@@ -68,9 +36,8 @@ export function useStickyLines(content: RefObject<HTMLElement | null>, maxLineCo
     let frame = 0
     const update = (): void => {
       frame = 0
-      const root = content.current
       const limit = limitOf(maxLineCount)
-      const next = root ? pinnedLines(measureScopes(root, limit * STICKY_LINE_HEIGHT), STICKY_LINE_HEIGHT, limit) : NO_PINNED
+      const next = content.current ? pinnedLines(pageLayout.stickyScopes(limit * STICKY_LINE_HEIGHT), STICKY_LINE_HEIGHT, limit) : NO_PINNED
       setLines(prev => samePinned(prev, next) ? prev : next)
     }
     schedule.current = () => {