refactor(chat): split ChatScreen and reuse regenerateResponse after editing a message

The edit path duplicated the streaming flow with inline require() calls; it now reuses regenerateResponse, which also fixes:
- edited conversations were never saved to History
- the answer generated after an edit could not be stopped (no abort handle kept)
Stopping a stream now saves the partial conversation, like finishing or failing does.
Adds characterization tests for ChatScreen and useLMStudio.

components/chat/MessageList.tsx

@@ -0,0 +1,60 @@
+import { MessageBubble } from '@/components/chat/MessageBubble';
+import { TypingIndicator } from '@/components/chat/TypingIndicator';
+import { ChatMessage } from '@/store/useAppStore';
+import { findLastAssistantId, shouldShowTypingIndicator } from '@/utils/chatSelectors';
+import React, { useEffect, useRef } from 'react';
+import { FlatList, StyleSheet } from 'react-native';
+import Animated, { FadeInDown } from 'react-native-reanimated';
+
+interface MessageListProps {
+    messages: ChatMessage[];
+    isStreaming: boolean;
+    onEdit: (id: string) => void;
+    onDelete: (id: string) => void;
+    onRegenerate: () => void;
+}
+
+export function MessageList({ messages, isStreaming, onEdit, onDelete, onRegenerate }: MessageListProps) {
+    const flatListRef = useRef<FlatList>(null);
+    const lastAssistantId = findLastAssistantId(messages);
+    const lastContentLength = messages[messages.length - 1]?.content?.length;
+
+    useEffect(() => {
+        if (messages.length > 0 && flatListRef.current) {
+            setTimeout(() => {
+                flatListRef.current?.scrollToEnd({ animated: !isStreaming });
+            }, 100);
+        }
+    }, [messages.length, lastContentLength, isStreaming]);
+
+    return (
+        <>
+            <FlatList
+                ref={flatListRef}
+                data={messages}
+                keyExtractor={(item) => item.id}
+                renderItem={({ item, index }) => (
+                    <Animated.View entering={FadeInDown.duration(300).delay(index > messages.length - 4 ? 100 : 0)}>
+                        <MessageBubble
+                            message={item}
+                            onEdit={() => onEdit(item.id)}
+                            onRegenerate={onRegenerate}
+                            onDelete={() => onDelete(item.id)}
+                            isStreaming={isStreaming}
+                            isLastAssistant={item.id === lastAssistantId}
+                        />
+                    </Animated.View>
+                )}
+                contentContainerStyle={styles.listContent}
+            />
+            {shouldShowTypingIndicator(messages, isStreaming) && <TypingIndicator />}
+        </>
+    );
+}
+
+const styles = StyleSheet.create({
+    listContent: {
+        paddingTop: 16,
+        paddingBottom: 24,
+    },
+});