feat: 聊天增加回到最新悬浮钮,智能体面板生成即收起

- 复用 ConversationScrollButton 接入 MessageList,滚离底部时显示一键回到最新问答的悬浮按钮;新增 scrollButtonClassName 以适配各页输入框高度
- 智能体详情面板改用 open+selectedArtifact 判定收起,流式写文件开始即收起让位预览,不再等生成结束

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend-web/src/components/workspace/agents/agent-detail-panel.tsx

@@ -187,23 +187,30 @@ export function AgentDetailPanel({
   const isSaving = updateAgent.isPending || setFeatured.isPending;
 
   // 对话生成文件（md/txt 等 artifact）并在右侧展开预览时，自动收起智能体
-  // 信息面板给预览让位；新文件落地时同样收起。编辑中不打断用户，用户随时
+  // 信息面板给预览让位；切换到新文件时同样收起。编辑中不打断用户，用户随时
   // 可手动重新展开。
+  //
+  // 关键：判定用 open + selectedArtifact，而非 artifacts.length。流式写文件时
+  // message-group 一开始就调用 select()+setOpen(true) 打开预览并选中该文件，但
+  // 该文件要等生成结束、artifact 入库后才会进 thread.values.artifacts。若按
+  // 数量判定就只能等生成结束才收起——正是之前「生成完才收起」的 bug 根因。
   const artifactsCtx = useArtifactsOptional();
   const artifactCount = artifactsCtx?.artifacts.length ?? 0;
-  const artifactPanelVisible = !!artifactsCtx?.open && artifactCount > 0;
+  const selectedArtifact = artifactsCtx?.selectedArtifact ?? null;
+  const artifactPanelVisible =
+    !!artifactsCtx?.open && (!!selectedArtifact || artifactCount > 0);
   const prevArtifactPanelVisible = useRef(false);
-  const prevArtifactCount = useRef(0);
+  const prevSelectedArtifact = useRef<string | null>(null);
   useEffect(() => {
     const opened = artifactPanelVisible && !prevArtifactPanelVisible.current;
-    const grew =
-      artifactPanelVisible && artifactCount > prevArtifactCount.current;
+    const switched =
+      artifactPanelVisible && selectedArtifact !== prevSelectedArtifact.current;
     prevArtifactPanelVisible.current = artifactPanelVisible;
-    prevArtifactCount.current = artifactCount;
-    if ((opened || grew) && !editing) {
+    prevSelectedArtifact.current = selectedArtifact;
+    if ((opened || switched) && !editing) {
       setCollapsed(true);
     }
-  }, [artifactPanelVisible, artifactCount, editing]);
+  }, [artifactPanelVisible, selectedArtifact, editing]);
 
   const displayName = desensitize(agent?.name ?? agentName);
   const questions = useMemo(

frontend-web/src/components/workspace/messages/message-list.tsx

@@ -6,6 +6,7 @@ import { useCallback, useContext, useEffect, useMemo, useState } from "react";
 import {
   Conversation,
   ConversationContent,
+  ConversationScrollButton,
 } from "@/components/ai-elements/conversation";
 import { Button } from "@/components/ui/button";
 import { Textarea } from "@/components/ui/textarea";
@@ -61,6 +62,7 @@ export function MessageList({
   paddingBottom = MESSAGE_LIST_DEFAULT_PADDING_BOTTOM,
   tokenUsageEnabled = false,
   extraRehypePlugins,
+  scrollButtonClassName,
   onClarificationSubmit,
   onEditResubmit,
   onSetupAgentApprove,
@@ -75,6 +77,8 @@ export function MessageList({
   thread: BaseStream<AgentThreadState>;
   paddingBottom?: number;
   tokenUsageEnabled?: boolean;
+  /** 额外定位「回到最新」悬浮按钮——不同页面输入框高度不同，需上移让位。 */
+  scrollButtonClassName?: string;
   extraRehypePlugins?: ReturnType<typeof useRehypeSplitWordsIntoSpans>;
   onClarificationSubmit?: (answer: string) => void | Promise<void>;
   onEditResubmit?: (text: string) => void;
@@ -543,6 +547,16 @@ export function MessageList({
         <div style={{ height: `${paddingBottom}px` }} />
         </MessageMetricsProvider>
       </ConversationContent>
+      {/* ChatGPT 式「回到最新」悬浮钮：仅在向上滚离底部时出现，点击平滑回到
+          最新问答。默认贴底，调用方可用 scrollButtonClassName 上移避开输入框。 */}
+      <ConversationScrollButton
+        className={cn(
+          "pointer-events-auto z-20 size-9 shadow-md",
+          scrollButtonClassName,
+        )}
+        aria-label="回到最新"
+        title="回到最新"
+      />
     </Conversation>
   );
 }

frontend-web/src/pages/AgentChatPage.tsx

@@ -285,6 +285,8 @@ export default function AgentChatPage() {
                     thread={thread}
                     paddingBottom={showFollowups ? 96 : 24}
                     tokenUsageEnabled={tokenUsageEnabled}
+                    // 输入框在流内（MessageList 下方），按钮贴对话区底部即可。
+                    scrollButtonClassName="bottom-2"
                     onClarificationSubmit={handleClarificationSubmit}
                     onEditResubmit={(text) => handleSubmit({ text, files: [] })}
                   />

frontend-web/src/pages/ChatPage.tsx

@@ -493,6 +493,8 @@ export default function ChatPage() {
                   thread={thread}
                   paddingBottom={messageListPaddingBottom}
                   tokenUsageEnabled={tokenUsageEnabled}
+                  // 输入框为底部绝对浮层（约 160px 高），按钮上移到其上方居中。
+                  scrollButtonClassName="bottom-40"
                   onClarificationSubmit={handleClarificationSubmit}
                   onEditResubmit={(text) =>
                     handleSubmit({ text, files: [] })