fix: improve desktop chat performance

src/components/chat/hooks/useChatComposerState.ts

@@ -204,6 +204,8 @@ export function useChatComposerState({
 
   const textareaRef = useRef<HTMLTextAreaElement>(null);
   const inputHighlightRef = useRef<HTMLDivElement>(null);
+  const textareaLineHeightRef = useRef<number | null>(null);
+  const lastAutosizedInputRef = useRef<string | null>(null);
   const handleSubmitRef = useRef<
     ((event: FormEvent<HTMLFormElement> | MouseEvent | TouchEvent | KeyboardEvent<HTMLTextAreaElement>) => Promise<void>) | null
   >(null);
@@ -457,6 +459,22 @@ export function useChatComposerState({
     inputHighlightRef.current.scrollLeft = target.scrollLeft;
   }, []);
 
+  const resizeTextarea = useCallback((target: HTMLTextAreaElement) => {
+    target.style.height = 'auto';
+    const nextHeight = Math.max(22, target.scrollHeight);
+    target.style.height = `${nextHeight}px`;
+
+    let lineHeight = textareaLineHeightRef.current;
+    if (!lineHeight) {
+      lineHeight = parseInt(window.getComputedStyle(target).lineHeight);
+      textareaLineHeightRef.current = Number.isFinite(lineHeight) ? lineHeight : 24;
+    }
+
+    const expanded = nextHeight > (textareaLineHeightRef.current || 24) * 2;
+    setIsTextareaExpanded((previous) => previous === expanded ? previous : expanded);
+    lastAutosizedInputRef.current = target.value;
+  }, []);
+
   const handleImageFiles = useCallback((files: File[]) => {
     const validFiles = files.filter((file) => {
       try {
@@ -806,13 +824,13 @@ export function useChatComposerState({
     if (!textareaRef.current) {
       return;
     }
-    // Re-run when input changes so restored drafts get the same autosize behavior as typed text.
-    textareaRef.current.style.height = 'auto';
-    textareaRef.current.style.height = `${Math.max(22, textareaRef.current.scrollHeight)}px`;
-    const lineHeight = parseInt(window.getComputedStyle(textareaRef.current).lineHeight);
-    const expanded = textareaRef.current.scrollHeight > lineHeight * 2;
-    setIsTextareaExpanded(expanded);
-  }, [input]);
+    if (lastAutosizedInputRef.current === input) {
+      return;
+    }
+    // Re-run for restored drafts and programmatic input changes. User typing is
+    // already resized in onInput, so this avoids doing the same forced layout twice.
+    resizeTextarea(textareaRef.current);
+  }, [input, resizeTextarea]);
 
   useEffect(() => {
     if (!textareaRef.current || input.trim()) {
@@ -894,15 +912,11 @@ export function useChatComposerState({
   const handleTextareaInput = useCallback(
     (event: FormEvent<HTMLTextAreaElement>) => {
       const target = event.currentTarget;
-      target.style.height = 'auto';
-      target.style.height = `${Math.max(22, target.scrollHeight)}px`;
+      resizeTextarea(target);
       setCursorPosition(target.selectionStart);
       syncInputOverlayScroll(target);
-
-      const lineHeight = parseInt(window.getComputedStyle(target).lineHeight);
-      setIsTextareaExpanded(target.scrollHeight > lineHeight * 2);
     },
-    [setCursorPosition, syncInputOverlayScroll],
+    [resizeTextarea, setCursorPosition, syncInputOverlayScroll],
   );
 
   const handleClearInput = useCallback(() => {

src/components/chat/view/ChatInterface.tsx

@@ -309,7 +309,7 @@ function ChatInterface({
 
   return (
     <PermissionContext.Provider value={permissionContextValue}>
-      <div className="flex h-full flex-col">
+      <div className="flex h-full min-h-0 flex-col">
         <ChatMessagesPane
           scrollContainerRef={scrollContainerRef}
           onWheel={handleScroll}

src/components/chat/view/subcomponents/ChatComposer.tsx

@@ -1,4 +1,5 @@
 import { useTranslation } from 'react-i18next';
+import { useMemo } from 'react';
 import type {
   ChangeEvent,
   ClipboardEvent,
@@ -154,12 +155,17 @@ export default function ChatComposer({
   sendByCtrlEnter,
 }: ChatComposerProps) {
   const { t } = useTranslation('chat');
-  const textareaRect = textareaRef.current?.getBoundingClientRect();
-  const commandMenuPosition = {
-    top: textareaRect ? Math.max(16, textareaRect.top - 316) : 0,
-    left: textareaRect ? textareaRect.left : 16,
-    bottom: textareaRect ? window.innerHeight - textareaRect.top + 8 : 90,
-  };
+  const commandMenuPosition = useMemo(() => {
+    if (!isCommandMenuOpen) {
+      return { top: 0, left: 16, bottom: 90 };
+    }
+    const textareaRect = textareaRef.current?.getBoundingClientRect();
+    return {
+      top: textareaRect ? Math.max(16, textareaRect.top - 316) : 0,
+      left: textareaRect ? textareaRect.left : 16,
+      bottom: textareaRect ? window.innerHeight - textareaRect.top + 8 : 90,
+    };
+  }, [input, isCommandMenuOpen, textareaRef]);
 
   // Detect if the AskUserQuestion interactive panel is active
   const hasQuestionPanel = pendingPermissionRequests.some(
@@ -170,7 +176,7 @@ export default function ChatComposer({
   const hasPendingPermissions = pendingPermissionRequests.length > 0;
 
   return (
-    <div className="flex-shrink-0 p-2 pb-2 sm:p-4 sm:pb-4 md:p-4 md:pb-6">
+    <div className="chat-composer-shell flex-shrink-0 p-2 pb-2 sm:p-4 sm:pb-4 md:p-4 md:pb-6">
       {!hasPendingPermissions && (
         <ActivityIndicator activity={activity} onAbort={onAbortSession} />
       )}

src/components/chat/view/subcomponents/ChatMessagesPane.tsx

@@ -1,5 +1,5 @@
 import { useTranslation } from 'react-i18next';
-import { useCallback, useMemo, useRef } from 'react';
+import { memo, useCallback, useMemo, useRef } from 'react';
 import type { Dispatch, RefObject, SetStateAction } from 'react';
 
 import type { ChatMessage } from '../../types/types';
@@ -67,7 +67,7 @@ interface ChatMessagesPaneProps {
   selectedProject: Project;
 }
 
-export default function ChatMessagesPane({
+function ChatMessagesPane({
   scrollContainerRef,
   onWheel,
   onTouchMove,
@@ -151,7 +151,7 @@ export default function ChatMessagesPane({
       ref={scrollContainerRef}
       onWheel={onWheel}
       onTouchMove={onTouchMove}
-      className="relative flex-1 space-y-3 overflow-y-auto overflow-x-hidden px-0 py-3 sm:space-y-4 sm:p-4"
+      className="chat-messages-pane relative min-h-0 flex-1 space-y-3 overflow-y-auto overflow-x-hidden px-0 py-3 sm:space-y-4 sm:p-4"
     >
       {(isLoadingSessionMessages || isProcessing) && chatMessages.length === 0 ? (
         <div className="mt-8 text-center text-gray-500 dark:text-gray-400">
@@ -308,3 +308,5 @@ export default function ChatMessagesPane({
     </div>
   );
 }
+
+export default memo(ChatMessagesPane);