Add copy button for assistant turns in agent stream

- Add TurnCopyButton component that copies all assistant messages from a turn
- Detect turn boundaries (before user message or end of stream when not running)
- Lazily compute turn content on click to avoid render-time overhead
- Ghost icon style with hover effect (color lightens)

packages/app/src/components/agent-stream-view.tsx

@@ -37,6 +37,7 @@ import {
   ToolCall,
   AgentThoughtMessage,
   TodoListCard,
+  TurnCopyButton,
   MessageOuterSpacingProvider,
   type InlinePathTarget,
 } from "./message";
@@ -382,6 +383,26 @@ export function AgentStreamView({
     [handleInlinePathPress, agent.cwd, flatListData]
   );
 
+  const collectTurnContent = useCallback(
+    (index: number) => {
+      const messages: string[] = [];
+      // Walk backwards (older items) from current index
+      // In inverted list: index+1 is the item above (older in time)
+      for (let i = index; i < flatListData.length; i++) {
+        const currentItem = flatListData[i];
+        if (currentItem.kind === "user_message") {
+          break;
+        }
+        if (currentItem.kind === "assistant_message") {
+          messages.push(currentItem.text);
+        }
+      }
+      // Messages are collected newest-first, reverse for chronological order
+      return messages.reverse().join("\n\n");
+    },
+    [flatListData]
+  );
+
   const renderStreamItem = useCallback(
     ({ item, index }: ListRenderItemInfo<StreamItem>) => {
       const content = renderStreamItemContent(item, index);
@@ -391,6 +412,16 @@ export function AgentStreamView({
 
       const gap = getGapAbove(item, index);
 
+      // Check if this is the end of a turn (before a user message or end of stream when not running)
+      // In inverted list: index-1 is the next item (newer in time)
+      const nextItem = flatListData[index - 1];
+      const isEndOfTurn =
+        item.kind !== "user_message" &&
+        (nextItem?.kind === "user_message" ||
+          (nextItem === undefined && agent.status !== "running"));
+
+      const getContent = () => collectTurnContent(index);
+
       return (
         <View
           style={[
@@ -399,10 +430,11 @@ export function AgentStreamView({
           ]}
         >
           {content}
+          {isEndOfTurn ? <TurnCopyButton getContent={getContent} /> : null}
         </View>
       );
     },
-    [getGapAbove, renderStreamItemContent]
+    [getGapAbove, renderStreamItemContent, flatListData, agent.status, collectTurnContent]
   );
 
   const pendingPermissionItems = useMemo(

packages/app/src/components/message.tsx

@@ -30,6 +30,7 @@ import {
   SquareTerminal,
   Search,
   Brain,
+  Copy,
 } from "lucide-react-native";
 import {
   StyleSheet,
@@ -254,6 +255,78 @@ export const assistantMessageStylesheet = StyleSheet.create((theme) => ({
   },
 }));
 
+const turnCopyButtonStylesheet = StyleSheet.create((theme) => ({
+  container: {
+    alignSelf: "flex-start",
+    padding: theme.spacing[2],
+    marginLeft: theme.spacing[4],
+  },
+  iconColor: {
+    color: theme.colors.mutedForeground,
+  },
+  iconHoveredColor: {
+    color: theme.colors.foreground,
+  },
+}));
+
+interface TurnCopyButtonProps {
+  getContent: () => string;
+}
+
+export const TurnCopyButton = memo(function TurnCopyButton({
+  getContent,
+}: TurnCopyButtonProps) {
+  const [copied, setCopied] = useState(false);
+  const copyTimeoutRef = useRef<ReturnType<typeof setTimeout> | null>(null);
+
+  const handleCopy = useCallback(async () => {
+    const content = getContent();
+    if (!content) {
+      return;
+    }
+
+    await Clipboard.setStringAsync(content);
+    setCopied(true);
+
+    if (copyTimeoutRef.current) {
+      clearTimeout(copyTimeoutRef.current);
+    }
+
+    copyTimeoutRef.current = setTimeout(() => {
+      setCopied(false);
+      copyTimeoutRef.current = null;
+    }, 1500);
+  }, [getContent]);
+
+  useEffect(() => {
+    return () => {
+      if (copyTimeoutRef.current) {
+        clearTimeout(copyTimeoutRef.current);
+      }
+    };
+  }, []);
+
+  return (
+    <Pressable
+      onPress={handleCopy}
+      style={turnCopyButtonStylesheet.container}
+      accessibilityRole="button"
+      accessibilityLabel={copied ? "Copied" : "Copy turn"}
+    >
+      {({ hovered }) => {
+        const iconColor = hovered
+          ? turnCopyButtonStylesheet.iconHoveredColor.color
+          : turnCopyButtonStylesheet.iconColor.color;
+        return copied ? (
+          <Check size={18} color={iconColor} />
+        ) : (
+          <Copy size={18} color={iconColor} />
+        );
+      }}
+    </Pressable>
+  );
+});
+
 const expandableBadgeStylesheet = StyleSheet.create((theme) => ({
   container: {
     marginHorizontal: theme.spacing[2],