Reduce message cloning and gate scroll work on load

packages/ui/src/components/message-stream-v2.tsx

@@ -332,6 +332,8 @@ export default function MessageStreamV2(props: MessageStreamV2Props) {
   let pendingScrollFrame: number | null = null
   let userScrollIntentUntil = 0
   let detachScrollIntentListeners: (() => void) | undefined
+  let hasRestoredScroll = false
+  let hasInitialScroll = false
 
   function markUserScrollIntent() {
     const now = typeof performance !== "undefined" ? performance.now() : Date.now()
@@ -405,7 +407,11 @@ export default function MessageStreamV2(props: MessageStreamV2Props) {
  
   function scrollToBottomAndClamp(immediate = false) {
     scrollToBottom(immediate)
-    requestAnimationFrame(() => clampScrollAfterShrink())
+    if (hasInitialScroll) {
+      requestAnimationFrame(() => clampScrollAfterShrink())
+    } else {
+      hasInitialScroll = true
+    }
   }
  
   function scrollToTop(immediate = false) {
@@ -476,9 +482,13 @@ export default function MessageStreamV2(props: MessageStreamV2Props) {
  
   createEffect(() => {
     const target = containerRef
+    const loading = props.loading
+
     if (!target) return
+    if (loading) return
+    if (hasRestoredScroll) return
+
     scrollCache.restore(target, {
-      fallback: () => scrollToBottom(true),
       onApplied: (snapshot) => {
         if (snapshot) {
           setAutoScroll(snapshot.atBottom)
@@ -490,12 +500,17 @@ export default function MessageStreamV2(props: MessageStreamV2Props) {
         updateScrollIndicators(target)
       },
     })
+
+    hasRestoredScroll = true
   })
  
   let previousToken: string | undefined
  
   createEffect(() => {
     const token = changeToken()
+    const loading = props.loading
+
+    if (loading) return
     if (!token || token === previousToken) {
       return
     }
@@ -507,6 +522,7 @@ export default function MessageStreamV2(props: MessageStreamV2Props) {
  
   createEffect(() => {
     preferenceSignature()
+    if (props.loading) return
     if (!autoScroll()) {
       return
     }

packages/ui/src/stores/message-v2/instance-store.ts

@@ -46,36 +46,13 @@ function ensurePartId(messageId: string, part: ClientPart, index: number): strin
 const PENDING_PART_MAX_AGE_MS = 30_000
 
 function clonePart(part: ClientPart): ClientPart {
-  if (!part || typeof part !== "object") {
-    return part
-  }
-  const cloned: Record<string, any> = { ...part }
-  if ("renderCache" in cloned) {
-    cloned.renderCache = undefined
-  }
-  if ("text" in cloned) {
-    cloned.text = cloneStructuredValue(cloned.text)
-  }
-  if ("thinking" in cloned && typeof cloned.thinking === "object") {
-    cloned.thinking = cloneStructuredValue(cloned.thinking)
-  }
-  if ("content" in cloned && Array.isArray(cloned.content)) {
-    cloned.content = cloneStructuredValue(cloned.content)
-  }
-  return cloned as ClientPart
+  // Cloning is intentionally disabled; message parts
+  // are stored as received from the backend.
+  return part
 }
 
 function cloneStructuredValue<T>(value: T): T {
-  if (Array.isArray(value)) {
-    return value.map((item) => cloneStructuredValue(item)) as T
-  }
-  if (value && typeof value === "object") {
-    const next: Record<string, any> = {}
-    Object.entries(value as Record<string, any>).forEach(([key, nested]) => {
-      next[key] = cloneStructuredValue(nested)
-    })
-    return next as T
-  }
+  // Legacy helper kept as a no-op to avoid deep copies.
   return value
 }