feat(chat): add virtual scrolling for large message lists

- Integrate react-window v2 List component for messages > 100
- Add VirtualizedMessageList and VirtualizedMessageRow components
- Use useVirtualizedMessages hook for dynamic height measurement
- Preserve smooth animations for small message counts (< 100)
- Auto-scroll to bottom for both virtualized and non-virtualized modes

Performance improvements:
- Only render visible messages in viewport
- Dynamic height measurement for accurate positioning
- LRU cache for message content

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

desktop/src/components/ChatArea.tsx

@@ -1,5 +1,6 @@
-import { useState, useEffect, useRef, useCallback, useMemo } from 'react';
+import { useState, useEffect, useRef, useCallback, useMemo, type CSSProperties, type RefObject, type MutableRefObject } from 'react';
 import { motion, AnimatePresence } from 'framer-motion';
+import { List, type ListImperativeAPI } from 'react-window';
 import { useChatStore, Message } from '../store/chatStore';
 import { useConnectionStore } from '../store/connectionStore';
 import { useAgentStore } from '../store/agentStore';
@@ -9,6 +10,23 @@ import { Button, EmptyState } from './ui';
 import { listItemVariants, defaultTransition, fadeInVariants } from '../lib/animations';
 import { FirstConversationPrompt } from './FirstConversationPrompt';
 import { MessageSearch } from './MessageSearch';
+import {
+  useVirtualizedMessages,
+  type VirtualizedMessageItem,
+} from '../lib/message-virtualization';
+
+// Default heights for virtualized messages
+const DEFAULT_MESSAGE_HEIGHTS: Record<string, number> = {
+  user: 80,
+  assistant: 150,
+  tool: 120,
+  hand: 120,
+  workflow: 100,
+  system: 60,
+};
+
+// Threshold for enabling virtualization (messages count)
+const VIRTUALIZATION_THRESHOLD = 100;
 
 export function ChatArea() {
   const {
@@ -26,6 +44,27 @@ export function ChatArea() {
   const textareaRef = useRef<HTMLTextAreaElement>(null);
   const messageRefs = useRef<Map<string, HTMLDivElement>>(new Map());
 
+  // Convert messages to virtualization format
+  const virtualizedMessages: VirtualizedMessageItem[] = useMemo(
+    () => messages.map((msg) => ({
+      id: msg.id,
+      height: DEFAULT_MESSAGE_HEIGHTS[msg.role] ?? 100,
+      role: msg.role,
+    })),
+    [messages]
+  );
+
+  // Use virtualization hook
+  const {
+    listRef,
+    getHeight,
+    setHeight,
+    scrollToBottom,
+  } = useVirtualizedMessages(virtualizedMessages, DEFAULT_MESSAGE_HEIGHTS);
+
+  // Whether to use virtualization
+  const useVirtualization = messages.length >= VIRTUALIZATION_THRESHOLD;
+
   // Get current clone for first conversation prompt
   const currentClone = useMemo(() => {
     if (!currentAgent) return null;
@@ -58,10 +97,12 @@ export function ChatArea() {
 
   // Auto-scroll to bottom on new messages
   useEffect(() => {
-    if (scrollRef.current) {
+    if (scrollRef.current && !useVirtualization) {
       scrollRef.current.scrollTop = scrollRef.current.scrollHeight;
+    } else if (useVirtualization && messages.length > 0) {
+      scrollToBottom();
     }
-  }, [messages]);
+  }, [messages, useVirtualization, scrollToBottom]);
 
   const handleSend = () => {
     if (!input.trim() || isStreaming || !connected) return;
@@ -155,7 +196,17 @@ export function ChatArea() {
             </motion.div>
           )}
 
-          {messages.map((message) => (
+          {/* Virtualized list for large message counts, smooth scroll for small counts */}
+          {useVirtualization && messages.length > 0 ? (
+            <VirtualizedMessageList
+              messages={messages}
+              listRef={listRef}
+              getHeight={getHeight}
+              onHeightChange={setHeight}
+              messageRefs={messageRefs}
+            />
+          ) : (
+            messages.map((message) => (
               <motion.div
                 key={message.id}
                 ref={(el) => { if (el) messageRefs.current.set(message.id, el); }}
@@ -167,7 +218,8 @@ export function ChatArea() {
               >
                 <MessageBubble message={message} />
               </motion.div>
-          ))}
+            ))
+          )}
         </AnimatePresence>
       </div>
 
@@ -354,6 +406,20 @@ function CodeBlock({ code, language, index }: { code: string; language: string;
 }
 
 /** Lightweight markdown renderer — handles code blocks, inline code, bold, italic, links */
+
+function sanitizeUrl(url: string): string {
+  const safeProtocols = ['http:', 'https:', 'mailto:'];
+  try {
+    const parsed = new URL(url, window.location.origin);
+    if (safeProtocols.includes(parsed.protocol)) {
+      return parsed.href;
+    }
+  } catch {
+    // Invalid URL
+  }
+  return '#';
+}
+
 function renderMarkdown(text: string): React.ReactNode[] {
   const nodes: React.ReactNode[] = [];
   const lines = text.split('\n');
@@ -418,9 +484,9 @@ function renderInline(text: string): React.ReactNode[] {
         </code>
       );
     } else if (match[7]) {
-      // [text](url)
+      // [text](url) - 使用 sanitizeUrl 防止 XSS
       parts.push(
-        <a key={parts.length} href={match[9]} target="_blank" rel="noopener noreferrer"
+        <a key={parts.length} href={sanitizeUrl(match[9])} target="_blank" rel="noopener noreferrer"
           className="text-orange-600 dark:text-orange-400 underline hover:text-orange-700 dark:hover:text-orange-300">{match[8]}</a>
       );
     }
@@ -519,3 +585,110 @@ function MessageBubble({ message }: { message: Message }) {
     </div>
   );
 }
+
+// === Virtualized Message Components ===
+
+interface VirtualizedMessageRowProps {
+  message: Message;
+  onHeightChange: (height: number) => void;
+  messageRefs: MutableRefObject<Map<string, HTMLDivElement>>;
+}
+
+/**
+ * Single row in the virtualized list.
+ * Measures actual height after render and reports back.
+ */
+function VirtualizedMessageRow({
+  message,
+  onHeightChange,
+  messageRefs,
+  style,
+  ariaAttributes,
+}: VirtualizedMessageRowProps & {
+  style: CSSProperties;
+  ariaAttributes: {
+    'aria-posinset': number;
+    'aria-setsize': number;
+    role: 'listitem';
+  };
+}) {
+  const rowRef = useRef<HTMLDivElement>(null);
+
+  // Measure height after mount
+  useEffect(() => {
+    if (rowRef.current) {
+      const height = rowRef.current.getBoundingClientRect().height;
+      if (height > 0) {
+        onHeightChange(height);
+      }
+    }
+  }, [message.content, message.streaming, onHeightChange]);
+
+  return (
+    <div
+      ref={(el) => {
+        if (el) {
+          (rowRef as MutableRefObject<HTMLDivElement | null>).current = el;
+          messageRefs.current.set(message.id, el);
+        }
+      }}
+      style={style}
+      className="py-3"
+      {...ariaAttributes}
+    >
+      <MessageBubble message={message} />
+    </div>
+  );
+}
+
+interface VirtualizedMessageListProps {
+  messages: Message[];
+  listRef: RefObject<ListImperativeAPI | null>;
+  getHeight: (id: string, role: string) => number;
+  onHeightChange: (id: string, height: number) => void;
+  messageRefs: MutableRefObject<Map<string, HTMLDivElement>>;
+}
+
+/**
+ * Virtualized message list for efficient rendering of large message counts.
+ * Uses react-window's List with dynamic height measurement.
+ */
+function VirtualizedMessageList({
+  messages,
+  listRef,
+  getHeight,
+  onHeightChange,
+  messageRefs,
+}: VirtualizedMessageListProps) {
+  // Row component for react-window v2
+  const RowComponent = (props: {
+    ariaAttributes: {
+      'aria-posinset': number;
+      'aria-setsize': number;
+      role: 'listitem';
+    };
+    index: number;
+    style: CSSProperties;
+  }) => (
+    <VirtualizedMessageRow
+      message={messages[props.index]}
+      onHeightChange={(h) => onHeightChange(messages[props.index].id, h)}
+      messageRefs={messageRefs}
+      style={props.style}
+      ariaAttributes={props.ariaAttributes}
+    />
+  );
+
+  return (
+    <List
+      listRef={listRef}
+      rowComponent={RowComponent}
+      rowProps={{}}
+      rowHeight={(index: number) => getHeight(messages[index].id, messages[index].role)}
+      rowCount={messages.length}
+      defaultHeight={500}
+      overscanCount={5}
+      className="focus:outline-none"
+    />
+  );
+}