fix: copy button functionality in web browsers

- Add clipboard utility with fallback for non-secure contexts
- Implement modern Clipboard API with document.execCommand fallback
- Update copy buttons in code blocks, markdown, messages, and session list
- Add proper error handling and user feedback for copy operations

Fixes issue where copy buttons did not work in web browsers served over HTTP or without Clipboard API support

packages/ui/src/components/message-item.tsx

@@ -3,6 +3,7 @@ import type { MessageInfo, ClientPart } from "../types/message"
 import { partHasRenderableText } from "../types/message"
 import type { MessageRecord } from "../stores/message-v2/types"
 import MessagePart from "./message-part"
+import { copyToClipboard } from "../lib/clipboard"
 
 interface MessageItemProps {
   record: MessageRecord
@@ -15,9 +16,9 @@ interface MessageItemProps {
   onFork?: (messageId?: string) => void
   showAgentMeta?: boolean
   onContentRendered?: () => void
- }
+}
 
- export default function MessageItem(props: MessageItemProps) {
+export default function MessageItem(props: MessageItemProps) {
   const [copied, setCopied] = createSignal(false)
 
   const isUser = () => props.record.role === "user"
@@ -155,8 +156,8 @@ interface MessageItemProps {
   const handleCopy = async () => {
     const content = getRawContent()
     if (!content) return
-    await navigator.clipboard.writeText(content)
-    setCopied(true)
+    const success = await copyToClipboard(content)
+    setCopied(success)
     setTimeout(() => setCopied(false), 2000)
   }