fix(web): keep onboarding and mobile natal board on one aligned overlay

Put the compact board trigger in the chat header, keep the sheet above the composer on iOS, and align onboarding messages with the intake card on the session column.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/components/rectification-agentic-chat.tsx

@@ -2,6 +2,7 @@
 
 import { ArrowUp, Square } from "lucide-react";
 import { useCallback, useEffect, useId, useLayoutEffect, useRef, useState } from "react";
+import { createPortal } from "react-dom";
 import { parseAgentReply } from "@/lib/agent-reply";
 import type { ChatMessage, ChatMessageView } from "@/lib/chat-message-view";
 import {
@@ -262,9 +263,14 @@ export function RectificationAgenticChat(props: RectificationAgenticChatProps) {
   const [compactBoard, setCompactBoard] = useState(false);
   const [boardOpen, setBoardOpen] = useState(false);
   const [boardDiff, setBoardDiff] = useState(() => diffRectificationBoard(null, null));
+  const [headerSlot, setHeaderSlot] = useState<HTMLElement | null>(null);
   const boardId = useId();
   const boardTitleId = useId();
 
+  useLayoutEffect(() => {
+    setHeaderSlot(document.querySelector("[data-rectification-header-slot]"));
+  }, []);
+
   useLayoutEffect(() => {
     const query = window.matchMedia(`(max-width: ${RECTIFICATION_BOARD_SPLIT_MIN_PX - 1}px)`);
     const update = () => {
@@ -682,11 +688,21 @@ export function RectificationAgenticChat(props: RectificationAgenticChatProps) {
     : undefined;
   const canSend = !busy && !readonly && !regeneratingMessageKey;
 
+  const boardPeek = compactBoard && !boardOpen ? (
+    <RectificationBoardPeek
+      result={candidateResult}
+      expanded={boardOpen}
+      boardId={boardId}
+      onOpen={toggleBoard}
+    />
+  ) : null;
+
   return (
     <div
       ref={workspace}
       className={`rectification-workspace${compactBoard ? " is-compact" : ""}${boardOpen ? " is-board-open" : ""}`}
     >
+      {headerSlot && boardPeek ? createPortal(boardPeek, headerSlot) : null}
       <div className="rectification-workspace__chat" inert={compactBoard && boardOpen ? true : undefined}>
         <section ref={conversation} className="conversation is-rectification" aria-label="生时校正对话" aria-busy={busy || regeneratingMessageKey !== null}>
           <div className="message-list">
@@ -777,14 +793,6 @@ export function RectificationAgenticChat(props: RectificationAgenticChatProps) {
       </section>
 
         <div className="composer-wrap">
-          {compactBoard && (
-            <RectificationBoardPeek
-              result={candidateResult}
-              expanded={boardOpen}
-              boardId={boardId}
-              onOpen={toggleBoard}
-            />
-          )}
           <form className="composer" onSubmit={submit}>
           <Textarea
             ref={composer}

frontend/src/components/rectification-board.tsx

@@ -271,6 +271,7 @@ export function RectificationBoardPeek({
     <button
       className="rectification-board-peek"
       type="button"
+      aria-label={peek.detail ? `${peek.title}，${peek.detail}` : peek.title}
       aria-expanded={expanded}
       aria-controls={boardId}
       onClick={onOpen}