fix(frontend): fallback Streamdown clipboard copy (#3397)

* fix(frontend): fallback streamdown clipboard copy

* fix(frontend): address clipboard fallback review

* fix(frontend): normalize clipboard fallback rejection

* fix(frontend): harden clipboard fallback install

* fix(frontend): clarify clipboard fallback errors

* fix(frontend): cover clipboard fallback edge cases

* fix(frontend): tighten clipboard fallback cleanup

* fix(frontend): reduce clipboard fallback copy window

* fix(frontend): guard clipboard item fallback install

* fix(frontend): clean up clipboard fallback on selection errors

* Address clipboard fallback review feedback

* fix(frontend): guard clipboard fallback install during SSR

frontend/src/components/ai-elements/message.tsx

@@ -18,7 +18,8 @@ import {
 } from "lucide-react";
 import type { ComponentProps, HTMLAttributes, ReactElement } from "react";
 import { createContext, memo, useContext, useEffect, useState } from "react";
-import { Streamdown } from "streamdown";
+
+import { ClipboardSafeStreamdown } from "./streamdown";
 
 export type MessageProps = HTMLAttributes<HTMLDivElement> & {
   from: UIMessage["role"];
@@ -302,11 +303,13 @@ export const MessageBranchPage = ({
   );
 };
 
-export type MessageResponseProps = ComponentProps<typeof Streamdown>;
+export type MessageResponseProps = ComponentProps<
+  typeof ClipboardSafeStreamdown
+>;
 
 export const MessageResponse = memo(
   ({ className, ...props }: MessageResponseProps) => (
-    <Streamdown
+    <ClipboardSafeStreamdown
       className={cn(
         "size-full [&>*:first-child]:mt-0 [&>*:last-child]:mb-0",
         className,

frontend/src/components/ai-elements/reasoning.tsx

@@ -10,9 +10,9 @@ import { cn } from "@/lib/utils";
 import { BrainIcon, ChevronDownIcon } from "lucide-react";
 import type { ComponentProps, ReactNode } from "react";
 import { createContext, memo, useContext, useEffect, useState } from "react";
-import { Streamdown } from "streamdown";
 import { reasoningPlugins } from "@/core/streamdown/plugins";
 import { Shimmer } from "./shimmer";
+import { ClipboardSafeStreamdown } from "./streamdown";
 
 type ReasoningContextValue = {
   isStreaming: boolean;
@@ -178,7 +178,9 @@ export const ReasoningContent = memo(
       )}
       {...props}
     >
-      <Streamdown {...reasoningPlugins}>{children}</Streamdown>
+      <ClipboardSafeStreamdown {...reasoningPlugins}>
+        {children}
+      </ClipboardSafeStreamdown>
     </CollapsibleContent>
   ),
 );

frontend/src/components/ai-elements/streamdown.tsx

@@ -0,0 +1,17 @@
+"use client";
+
+import { type ComponentProps } from "react";
+import { Streamdown } from "streamdown";
+
+import { installClipboardFallback } from "@/core/clipboard";
+
+export type ClipboardSafeStreamdownProps = ComponentProps<typeof Streamdown>;
+
+// Only patch browser globals in client context; skip during SSR
+if (typeof document !== "undefined") {
+  installClipboardFallback();
+}
+
+export function ClipboardSafeStreamdown(props: ClipboardSafeStreamdownProps) {
+  return <Streamdown {...props} />;
+}