feat(ui): add scroll-to-latest button in assistant feed

Track the assistant feed scroll position and footer height, and show a
floating button to jump back to the newest message when scrolled up.

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

frontend/src/i18n/locales/en-US.json

@@ -117,6 +117,7 @@
   "conversation": "Chat",
   "newChat": "New chat",
   "conversationHistory": "History",
+  "scrollToLatest": "Scroll to latest",
   "searchConversationPlaceholder": "Search conversations",
   "deleteConversation": "Delete conversation",
   "noConversationHistory": "No history yet",

frontend/src/i18n/locales/zh-CN.json

@@ -117,6 +117,7 @@
   "conversation": "对话",
   "newChat": "新对话",
   "conversationHistory": "历史对话",
+  "scrollToLatest": "回到底部",
   "searchConversationPlaceholder": "请输入搜索关键词",
   "deleteConversation": "删除对话",
   "noConversationHistory": "暂无历史对话",

frontend/src/ui/pages/CanvasWorkspace/index.tsx

@@ -1,6 +1,6 @@
 "use client";
 
-import { BookOpen, ChevronDown, Circle, Folder, Frame, Globe2, Image as ImageIcon, Layers, Lock, LogOut, Map as MapIcon, Loader2, MessageCircle, MessageSquarePlus, PanelRightClose, PenLine, Search, Share2, Trash2, Type, User, Zap } from "lucide-react";
+import { ArrowDown, BookOpen, ChevronDown, Circle, Folder, Frame, Globe2, Image as ImageIcon, Layers, Lock, LogOut, Map as MapIcon, Loader2, MessageCircle, MessageSquarePlus, PanelRightClose, PenLine, Search, Share2, Trash2, Type, User, Zap } from "lucide-react";
 import { useCallback, useEffect, useMemo, useRef, useState, type CSSProperties } from "react";
 import { openHome } from "@/application/route";
 import { ContextMenu, ContextMenuTrigger } from "@/components/ui/context-menu";
@@ -550,6 +550,9 @@ export function CanvasWorkspace({ projectId }: { projectId: string }) {
   const containerRef = useRef<HTMLDivElement | null>(null);
   const canvasImageInputRef = useRef<HTMLInputElement | null>(null);
   const agentComposerRef = useRef<PromptComposerHandle | null>(null);
+  const assistantFeedRef = useRef<HTMLDivElement | null>(null);
+  const assistantFooterRef = useRef<HTMLDivElement | null>(null);
+  const autoScrollAgentFeedRef = useRef(false);
   const referenceImagesRef = useRef<UploadedReferenceImage[]>([]);
   const annotationsRef = useRef<CanvasAnnotation[]>([]);
   const imageGeneratorThreadIdsRef = useRef<Set<string>>(new Set());
@@ -572,6 +575,8 @@ export function CanvasWorkspace({ projectId }: { projectId: string }) {
   const [agentHistoryOpen, setAgentHistoryOpen] = useState(false);
   const [agentHistorySearch, setAgentHistorySearch] = useState("");
   const [selectedAgentThreadId, setSelectedAgentThreadId] = useState<string | null>(null);
+  const [assistantFooterHeight, setAssistantFooterHeight] = useState(0);
+  const [showAssistantScrollButton, setShowAssistantScrollButton] = useState(false);
   const [referenceImages, setReferenceImages] = useState<UploadedReferenceImage[]>([]);
   const [annotations, setAnnotations] = useState<CanvasAnnotation[]>([]);
   const [annotationPreview, setAnnotationPreview] = useState<AnnotationPreviewRequest | null>(null);
@@ -650,6 +655,29 @@ export function CanvasWorkspace({ projectId }: { projectId: string }) {
   const agentTimelineActive = agentGenerating || Boolean(project && !projectHasCanvasActionGeneration(project) && nodes.some(isAgentVisibleGeneratingNode));
   const mockupPreparing = Boolean(mockupPendingTargetId);
   const anyGenerating = agentGenerating || imageGeneratorGenerating || canvasActionWorkActive || mockupPreparing;
+  const updateAssistantScrollButton = useCallback(() => {
+    const feed = assistantFeedRef.current;
+    if (!feed || feed.scrollHeight <= feed.clientHeight) {
+      setShowAssistantScrollButton(false);
+      return;
+    }
+    const distanceToEnd = feed.scrollHeight - feed.scrollTop - feed.clientHeight;
+    const shouldShow = distanceToEnd > 24;
+    setShowAssistantScrollButton((current) => (current === shouldShow ? current : shouldShow));
+  }, []);
+  const scrollAssistantFeedToEnd = useCallback((behavior: ScrollBehavior = "auto") => {
+    window.requestAnimationFrame(() => {
+      const feed = assistantFeedRef.current;
+      if (!feed) return;
+      if (behavior === "auto") {
+        feed.scrollTop = feed.scrollHeight;
+        updateAssistantScrollButton();
+        return;
+      }
+      feed.scrollTo({ top: feed.scrollHeight, behavior });
+      window.setTimeout(updateAssistantScrollButton, 220);
+    });
+  }, [updateAssistantScrollButton]);
 
   useEffect(() => {
     window.localStorage.setItem("fluxo:show-minimap", showMinimap ? "true" : "false");
@@ -754,12 +782,47 @@ export function CanvasWorkspace({ projectId }: { projectId: string }) {
     }
   }, [agentGenerating]);
 
+  useEffect(() => {
+    if (!assistantPanelOpen || !autoScrollAgentFeedRef.current) return;
+    scrollAssistantFeedToEnd("auto");
+    if (agentTimelineActive) return;
+    const timer = window.setTimeout(() => {
+      autoScrollAgentFeedRef.current = false;
+    }, 250);
+    return () => window.clearTimeout(timer);
+  }, [agentTimelineActive, assistantPanelOpen, messages, scrollAssistantFeedToEnd]);
+
+  useEffect(() => {
+    if (!assistantPanelOpen) {
+      setShowAssistantScrollButton(false);
+      return;
+    }
+    const frame = window.requestAnimationFrame(updateAssistantScrollButton);
+    return () => window.cancelAnimationFrame(frame);
+  }, [agentTimelineActive, assistantPanelOpen, messages, updateAssistantScrollButton]);
+
+  useEffect(() => {
+    if (!assistantPanelOpen) return;
+    const footer = assistantFooterRef.current;
+    if (!footer) return;
+    const updateFooterHeight = () => {
+      setAssistantFooterHeight(Math.ceil(footer.getBoundingClientRect().height));
+      updateAssistantScrollButton();
+    };
+    updateFooterHeight();
+    if (typeof ResizeObserver === "undefined") return;
+    const observer = new ResizeObserver(updateFooterHeight);
+    observer.observe(footer);
+    return () => observer.disconnect();
+  }, [assistantPanelOpen, error, updateAssistantScrollButton]);
+
   useEffect(() => {
     selectedAgentThreadIdRef.current = null;
     setSelectedAgentThreadId(null);
     setAgentThreads([]);
     setAgentHistorySearch("");
     setAgentHistoryOpen(false);
+    autoScrollAgentFeedRef.current = false;
   }, [projectId]);
 
   useEffect(() => {
@@ -2435,6 +2498,7 @@ export function CanvasWorkspace({ projectId }: { projectId: string }) {
   };
 
   const beginNewAgentConversation = () => {
+    autoScrollAgentFeedRef.current = false;
     selectedAgentThreadIdRef.current = newAgentConversationId;
     setSelectedAgentThreadId(newAgentConversationId);
     setAgentHistoryOpen(false);
@@ -2446,6 +2510,7 @@ export function CanvasWorkspace({ projectId }: { projectId: string }) {
   };
 
   const selectAgentThread = (threadId: string) => {
+    autoScrollAgentFeedRef.current = false;
     selectedAgentThreadIdRef.current = threadId;
     setSelectedAgentThreadId(threadId);
     setAgentHistoryOpen(false);
@@ -2500,6 +2565,7 @@ export function CanvasWorkspace({ projectId }: { projectId: string }) {
       selectedAgentThreadIdRef.current = threadId;
       setSelectedAgentThreadId(threadId);
       setAgentGenerating(true);
+      autoScrollAgentFeedRef.current = true;
     }
     setError("");
     if (source === "image-generator") {
@@ -2551,6 +2617,7 @@ export function CanvasWorkspace({ projectId }: { projectId: string }) {
   const stopAgentTask = async () => {
     if (!project) return;
     const threadId = activeAgentThreadIdRef.current || project.lastThreadId;
+    autoScrollAgentFeedRef.current = false;
     stopGenerationStream("agent");
     activeAgentThreadIdRef.current = null;
     setAgentGenerating(false);
@@ -3858,37 +3925,52 @@ export function CanvasWorkspace({ projectId }: { projectId: string }) {
             </div>
           </div>
 
-          <div className="assistant-feed">
+          <div className="assistant-feed" ref={assistantFeedRef} onScroll={updateAssistantScrollButton}>
             <CanvasAgentTimeline messages={messages} nodes={nodes} active={agentTimelineActive} />
           </div>
 
-          {error && <p className="panel-error">{error}</p>}
+          {showAssistantScrollButton && (
+            <div className="assistant-scroll-to-end" style={{ bottom: assistantFooterHeight > 0 ? assistantFooterHeight + 12 : 178 }}>
+              <button
+                type="button"
+                aria-label={t("scrollToLatest")}
+                title={t("scrollToLatest")}
+                onClick={() => scrollAssistantFeedToEnd("smooth")}
+              >
+                <ArrowDown size={18} />
+              </button>
+            </div>
+          )}
 
-          <CanvasAgentComposer
-            ref={agentComposerRef}
-            text={prompt}
-            mode={composerMode}
-            models={imageModels}
-            selectedModel={selectedCanvasModel}
-            settings={composerImageSettings}
-            references={referenceImages}
-            annotations={annotations}
-            webSearchEnabled={useAgentWebSearch}
-            generating={agentGenerating}
-            previewSlot={<CanvasAnnotationPreview preview={annotationPreview} nodes={nodes} />}
-            onTextChange={setPrompt}
-            onModeChange={setComposerMode}
-            onSettingsChange={updateComposerImageSettings}
-            onModelChange={setSelectedCanvasModelId}
-            onWebSearchChange={setUseAgentWebSearch}
-            onUploadFile={attachImage}
-            onReferencesChange={syncReferenceImages}
-            onReferenceRemoved={handleReferenceRemoved}
-            onAnnotationsChange={syncAnnotations}
-            onAnnotationPreviewChange={setAnnotationPreview}
-            onSubmit={() => void generate("agent")}
-            onStop={() => void stopAgentTask()}
-          />
+          <div className="assistant-footer-dock" ref={assistantFooterRef}>
+            {error && <p className="panel-error">{error}</p>}
+
+            <CanvasAgentComposer
+              ref={agentComposerRef}
+              text={prompt}
+              mode={composerMode}
+              models={imageModels}
+              selectedModel={selectedCanvasModel}
+              settings={composerImageSettings}
+              references={referenceImages}
+              annotations={annotations}
+              webSearchEnabled={useAgentWebSearch}
+              generating={agentGenerating}
+              previewSlot={<CanvasAnnotationPreview preview={annotationPreview} nodes={nodes} />}
+              onTextChange={setPrompt}
+              onModeChange={setComposerMode}
+              onSettingsChange={updateComposerImageSettings}
+              onModelChange={setSelectedCanvasModelId}
+              onWebSearchChange={setUseAgentWebSearch}
+              onUploadFile={attachImage}
+              onReferencesChange={syncReferenceImages}
+              onReferenceRemoved={handleReferenceRemoved}
+              onAnnotationsChange={syncAnnotations}
+              onAnnotationPreviewChange={setAnnotationPreview}
+              onSubmit={() => void generate("agent")}
+              onStop={() => void stopAgentTask()}
+            />
+          </div>
           </aside>
         )}
       </main>

frontend/src/ui/styles.css

@@ -3602,6 +3602,11 @@ button:disabled {
   font-size: 13px;
 }
 
+.assistant-footer-dock {
+  width: 100%;
+  flex: 0 0 auto;
+}
+
 .assistant-feed {
   position: relative;
   width: 100%;
@@ -3637,6 +3642,40 @@ button:disabled {
   background: #dfe0e2;
 }
 
+.assistant-scroll-to-end {
+  position: absolute;
+  inset-inline: 0;
+  z-index: 12;
+  display: flex;
+  justify-content: center;
+  pointer-events: none;
+}
+
+.assistant-scroll-to-end button {
+  width: 40px;
+  height: 40px;
+  display: grid;
+  place-items: center;
+  border: 1px solid #e1e3e8;
+  border-radius: 999px;
+  color: #373b42;
+  background: #fff;
+  box-shadow: 0 8px 24px rgba(17, 24, 39, 0.12);
+  pointer-events: auto;
+  transition: background 0.15s ease, border-color 0.15s ease, transform 0.15s ease;
+}
+
+.assistant-scroll-to-end button:hover {
+  border-color: #d4d8df;
+  background: #f8f9fa;
+  transform: translateY(-1px);
+}
+
+.assistant-scroll-to-end button:active {
+  background: #eef0f3;
+  transform: translateY(0);
+}
+
 .generated-preview-card {
   display: grid;
   gap: 10px;