diff --git a/docs/BUG_HISTORY.md b/docs/BUG_HISTORY.md
index 2007b7e4..058bfb68 100644
--- a/docs/BUG_HISTORY.md
+++ b/docs/BUG_HISTORY.md
@@ -3878,3 +3878,18 @@
 - 防复发：镜像构建日志里的 `EBADENGINE` 不得当作噪声跳过——它意味着依赖声明的运行环境与镜像实际提供的不一致，而 npm 不会阻止这种安装，因此它是少数「构建期唯一一次提示、之后只会在运行期爆发」的信号。基础镜像用浮动 tag（`node:22-alpine`）时，实际 Node 版本会随上游重建漂移，依赖的引擎下限也会随升级上移，两者相向移动，这类不匹配会反复出现。
 - 相关记录：BUG-262 无前序同类记录。与 BUG-261 同为首次本地构建 staging 镜像时暴露的构建期问题。
 - 修复版本：未修复
+
+## BUG-263 | “跳到最新”按钮悬在输入框上方约 160px，压住正文而不是贴着输入框
+
+- 状态：resolved（本地修复，待提交与发布）
+- 首次发现：2026-08-17
+- 最近更新：2026-08-17
+- 影响面：`/` 主对话页在用户向上翻阅历史时出现的“跳到最新”控件。
+- 用户现象：按钮既没有贴着下方输入框，也没有落在空白处，而是悬在正文中间挡住一整行回答文字；视觉上不像输入框的附属控件，更像漂在内容上的异物。
+- 触发条件：会话已有消息，用户向上滚动超过 96px 锚定阈值。桌面端偏移约 160px，移动端约 128px。
+- 根因：按钮此前是 `.conversation`（滚动容器）的 `position: sticky; bottom: 12px` 子元素，而 `.conversation` 带 `padding-bottom: var(--composer-reserve)`（桌面 148px / 移动 116px）。sticky 元素被钉在视口底部之前，会先被自己的包含块——也就是滚动容器的 **内容盒**——夹住，而内容盒底边正好比容器可视底边高出这一段 padding。于是 `bottom: 12px` 从未生效，按钮实际停在 padding + 12px 处。这段 padding 是早期输入框覆盖式布局的遗留：现在 `.chat-panel` 用 `grid-template-rows: 68px minmax(0,1fr) auto`，`.composer-wrap` 已是独立行、不再覆盖对话区。
+- 修复：把按钮从滚动容器移到 `.composer-wrap` 内部，改用 `absolute inset-x-0 bottom-full` + `pb-3`，让它挂在输入框区域自己的上边缘。`.composer-wrap` 本就是 `position: sticky`（定位元素）且 `z-index: 2`，可直接作为包含块，无需新增定位上下文。这样偏移不再依赖 `--composer-reserve`，输入框长高、推荐问题行出现或消失时按钮都跟着走。按钮自身的可访问性属性（真实 `<button>`、`aria-label`、焦点环、44×44 触控区、`pointer-events-auto`）原样保留。
+- 验证：新增合同测试固定新位置（断言控件位于 composer 块内、使用 `bottom-full`、不再出现 `sticky`），并把 BUG-218 / BUG-252 两个文件里按缩进切片的定位锚点改成与缩进无关；两文件 23 条断言全绿。几何结论这次经过浏览器实测：用一份复刻 `.chat-panel` / `.conversation` / `.composer-wrap` 真实规则的静态页面同时渲染新旧两种写法，量得旧写法距输入框 160px、新写法 11px，与线上截图相符；量完即删，未留在仓库。`tsc`、`eslint` 清洁。未做的验证：**没有在真实登录会话里目视确认**（需要长对话与账户），复刻页面只覆盖了本条涉及的布局规则。
+- 防复发：滚动容器留了 `padding-bottom` 时，它的 `position: sticky` 子元素永远无法贴到容器可视底边——sticky 受包含块内容盒夹持，调 `bottom` 偏移不解决问题。悬浮在输入框上方的控件应挂在输入框容器上（`bottom: 100%`），而不是挂在滚动容器里，这样才不依赖任何预留高度常量。另：BUG-218 当时已写明“浏览器内的视觉位置未经人工目视确认”，本条正是那句话对应的实际后果——纯源码合同测试能固定 DOM 与属性，固定不了几何位置，涉及定位的改动必须实测。
+- 相关记录：BUG-218（引入该按钮与锚定逻辑）、BUG-252（曾把它记作 BUG-217 新增，并留下焦点丢失的待跟进项，本轮未处理）
+- 修复版本：本地未提交候选
diff --git a/frontend/src/app/page.tsx b/frontend/src/app/page.tsx
index f6f4841e..6a2c2aa9 100644
--- a/frontend/src/app/page.tsx
+++ b/frontend/src/app/page.tsx
@@ -3466,19 +3466,6 @@ export default function Home() {
               {activeError && <p className="error-message" role="alert">{activeError}</p>}
             </div>
             )}
-            {jumpToLatestVisible && (
-              <div className="pointer-events-none sticky bottom-3 z-10 flex h-0 items-end justify-center">
-                <button
-                  className="pointer-events-auto inline-flex min-h-11 min-w-11 items-center gap-1.5 rounded-full border border-border bg-canvas px-4 text-sm text-ink shadow-md transition-colors outline-none hover:bg-canvas-muted focus-visible:border-ring focus-visible:ring-3 focus-visible:ring-ring/50"
-                  type="button"
-                  aria-label="跳到最新"
-                  onClick={conversationAnchor.anchorToLatest}
-                >
-                  <ArrowDown aria-hidden="true" className="size-4" />
-                  跳到最新
-                </button>
-              </div>
-            )}
           </div>
         )}
 
@@ -3504,6 +3491,19 @@ export default function Home() {
         )}
 
         {!rectificationSurfaceOpen && !onboardingFormActive && <div className={`composer-wrap ${starterHomeVisible ? "composer-wrap-starter" : ""}`}>
+          {jumpToLatestVisible && (
+            <div className="pointer-events-none absolute inset-x-0 bottom-full flex justify-center pb-3">
+              <button
+                className="pointer-events-auto inline-flex min-h-11 min-w-11 items-center gap-1.5 rounded-full border border-border bg-canvas px-4 text-sm text-ink shadow-md transition-colors outline-none hover:bg-canvas-muted focus-visible:border-ring focus-visible:ring-3 focus-visible:ring-ring/50"
+                type="button"
+                aria-label="跳到最新"
+                onClick={conversationAnchor.anchorToLatest}
+              >
+                <ArrowDown aria-hidden="true" className="size-4" />
+                跳到最新
+              </button>
+            </div>
+          )}
           {activeSuggestions.length > 0 && (
             <div className="composer-suggestions" aria-label="推荐继续提问">
               {activeSuggestions.map((question) => (
diff --git a/frontend/tests/chat-navigation-a11y-contract.test.ts b/frontend/tests/chat-navigation-a11y-contract.test.ts
index 88aea49b..51a5227c 100644
--- a/frontend/tests/chat-navigation-a11y-contract.test.ts
+++ b/frontend/tests/chat-navigation-a11y-contract.test.ts
@@ -199,7 +199,7 @@ test("aria-busy marks the updating message list without swallowing the status re
 });
 
 test("the jump-to-latest control stays keyboard reachable and labelled", () => {
-  const jumpControl = sourceBetween(pageSource, "{jumpToLatestVisible && (", "</div>\n            )}");
+  const jumpControl = sourceBetween(pageSource, "{jumpToLatestVisible && (", "</button>");
   const buttonTag = sourceBetween(jumpControl, "<button", ">");
 
   // Given: a real button in document order, never removed from the tab sequence.
diff --git a/frontend/tests/chat-notice-and-scroll-contract.test.ts b/frontend/tests/chat-notice-and-scroll-contract.test.ts
index f0c2aae0..6130b3f9 100644
--- a/frontend/tests/chat-notice-and-scroll-contract.test.ts
+++ b/frontend/tests/chat-notice-and-scroll-contract.test.ts
@@ -8,6 +8,7 @@ import { nextAnchorState } from "../src/hooks/use-conversation-scroll-anchor.ts"
 const pageSource = readFileSync(new URL("../src/app/page.tsx", import.meta.url), "utf8");
 const noticeSource = readFileSync(new URL("../src/lib/chat-notice.ts", import.meta.url), "utf8");
 const anchorSource = readFileSync(new URL("../src/hooks/use-conversation-scroll-anchor.ts", import.meta.url), "utf8");
+const globalsSource = readFileSync(new URL("../src/app/globals.css", import.meta.url), "utf8");
 
 function sourceBetween(source: string, startMarker: string, endMarker: string) {
   const start = source.indexOf(startMarker);
@@ -86,7 +87,7 @@ test("scrolls to the newest turn on intentional jumps", () => {
 });
 
 test("offers an accessible jump-to-latest control while reading history", () => {
-  const jumpControl = sourceBetween(pageSource, "{jumpToLatestVisible && (", "</div>\n            )}");
+  const jumpControl = sourceBetween(pageSource, "{jumpToLatestVisible && (", "</button>");
 
   assert.match(pageSource, /const jumpToLatestVisible = !rectificationSurfaceOpen[\s\S]*?&& !conversationAnchor\.anchored/);
   assert.match(jumpControl, /type="button"/);
@@ -97,6 +98,19 @@ test("offers an accessible jump-to-latest control while reading history", () =>
   assert.match(jumpControl, /onClick=\{conversationAnchor\.anchorToLatest\}/);
 });
 
+test("rests the jump-to-latest control on the composer instead of the padded scroller", () => {
+  // Given: the scroll container reserves composer-sized padding, which clamps any sticky child
+  // of it that far above the composer, on top of the transcript the reader is still reading.
+  assert.match(globalsSource, /\.conversation \{[^}]*padding-bottom: var\(--composer-reserve\)/);
+  assert.match(globalsSource, /\.composer-wrap \{[^}]*position: sticky/);
+
+  // Then: the control hangs off the composer's own top edge, whatever that reserve is.
+  const composerWrap = sourceBetween(pageSource, "className={`composer-wrap ", "<ChatComposer");
+  const jumpControl = sourceBetween(composerWrap, "{jumpToLatestVisible && (", "</button>");
+  assert.match(jumpControl, /absolute inset-x-0 bottom-full/);
+  assert.doesNotMatch(jumpControl, /sticky/);
+});
+
 test("keeps the scroll listener passive and reduced-motion aware", () => {
   assert.match(anchorSource, /addEventListener\("scroll", onScroll, \{ passive: true \}\)/);
   assert.match(anchorSource, /frame = window\.requestAnimationFrame\(measure\)/);