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/EmptyState.tsx

@@ -0,0 +1,99 @@
+import { useThemeColor } from '@/hooks/useThemeColor';
+import { MessageSquare, Sparkles } from 'lucide-react-native';
+import React from 'react';
+import { StyleSheet, Text, TouchableOpacity, View } from 'react-native';
+
+export const PROMPT_SUGGESTIONS = [
+    'Explain recursion in simple terms',
+    'Write a short poem about coding',
+    'What are the best practices for React Native?',
+    'Help me debug a JavaScript error',
+];
+
+interface EmptyStateProps {
+    onSelectPrompt: (prompt: string) => void;
+}
+
+export function EmptyState({ onSelectPrompt }: EmptyStateProps) {
+    const colors = useThemeColor();
+
+    return (
+        <View style={[styles.emptyState, { backgroundColor: colors.backgroundColor }]}>
+            <View style={[styles.emptyIconWrap, { backgroundColor: colors.cardBackground, shadowColor: colors.shadow }]}>
+                <MessageSquare size={40} color={colors.textMuted} />
+            </View>
+            <Text style={[styles.emptyTitle, { color: colors.text }]}>Start a conversation</Text>
+            <Text style={[styles.emptySubtitle, { color: colors.textMuted }]}>
+                Send a message to begin chatting with your local AI model.
+            </Text>
+
+            <View style={styles.suggestionsWrap}>
+                {PROMPT_SUGGESTIONS.map((prompt) => (
+                    <TouchableOpacity
+                        key={prompt}
+                        style={[styles.suggestionChip, { backgroundColor: colors.cardBackground, borderColor: colors.border }]}
+                        onPress={() => onSelectPrompt(prompt)}
+                        activeOpacity={0.7}
+                        accessibilityRole="button"
+                        accessibilityLabel={prompt}
+                    >
+                        <Sparkles size={14} color={colors.textMuted} />
+                        <Text style={[styles.suggestionText, { color: colors.text }]} numberOfLines={1}>{prompt}</Text>
+                    </TouchableOpacity>
+                ))}
+            </View>
+        </View>
+    );
+}
+
+const styles = StyleSheet.create({
+    emptyState: {
+        flex: 1,
+        alignItems: 'center',
+        justifyContent: 'center',
+        paddingHorizontal: 32,
+        paddingBottom: 80,
+    },
+    emptyIconWrap: {
+        width: 80,
+        height: 80,
+        borderRadius: 40,
+        alignItems: 'center',
+        justifyContent: 'center',
+        marginBottom: 20,
+        shadowOffset: { width: 0, height: 4 },
+        shadowOpacity: 0.05,
+        shadowRadius: 10,
+        elevation: 2,
+    },
+    emptyTitle: {
+        fontSize: 22,
+        fontWeight: '700',
+        marginBottom: 8,
+    },
+    emptySubtitle: {
+        fontSize: 15,
+        textAlign: 'center',
+        lineHeight: 22,
+        marginBottom: 32,
+    },
+    suggestionsWrap: {
+        width: '100%',
+        maxWidth: 400,
+        gap: 12,
+    },
+    suggestionChip: {
+        flexDirection: 'row',
+        alignItems: 'center',
+        gap: 12,
+        borderWidth: 1,
+        borderRadius: 16,
+        paddingHorizontal: 16,
+        paddingVertical: 14,
+    },
+    suggestionText: {
+        fontSize: 15,
+        flex: 1,
+        fontWeight: '500',
+    },
+});

components/chat/MessageList.tsx

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+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,
+    },
+});

components/chat/OfflineBanner.tsx

@@ -0,0 +1,31 @@
+import { useThemeColor } from '@/hooks/useThemeColor';
+import React from 'react';
+import { StyleSheet, Text, View } from 'react-native';
+
+export function OfflineBanner() {
+    const colors = useThemeColor();
+
+    return (
+        <View
+            accessibilityRole="alert"
+            style={[styles.banner, { backgroundColor: colors.bannerBg, borderBottomColor: colors.bannerBg }]}
+        >
+            <Text style={[styles.bannerText, { color: colors.bannerText }]}>
+                ⚠️ Server offline. Check Settings → Server Connection.
+            </Text>
+        </View>
+    );
+}
+
+const styles = StyleSheet.create({
+    banner: {
+        paddingHorizontal: 16,
+        paddingVertical: 10,
+        borderBottomWidth: 1,
+    },
+    bannerText: {
+        fontSize: 13,
+        textAlign: 'center',
+        fontWeight: '500',
+    },
+});