refactor(LocalDataSource, PostRepository, ChatScreen): enhance database handling and message loading

- Introduced a promise-based initialization mechanism in LocalDataSource to prevent concurrent initialization issues.
- Updated PostRepository to utilize an enqueueWrite method for database operations, ensuring thread-safe writes.
- Refactored ChatScreen to improve message loading logic, including preloading history and managing scroll behavior more effectively.
- Enhanced message rendering logic to maintain correct indices in inverted lists and optimize user experience during scrolling.

src/screens/message/ChatScreen.tsx

@@ -22,12 +22,11 @@
 import React, { useState, useEffect, useMemo, useCallback, useRef } from 'react';
 import {
   View,
-  TouchableWithoutFeedback,
+  FlatList,
   ActivityIndicator,
   KeyboardAvoidingView,
   Platform,
 } from 'react-native';
-import { FlashList } from "@shopify/flash-list";
 import { useNavigation } from '@react-navigation/native';
 import { StatusBar } from 'expo-status-bar';
 import { useSafeAreaInsets } from 'react-native-safe-area-context';
@@ -78,6 +77,15 @@ export const ChatScreen: React.FC = () => {
   
   // 输入框区域高度（用于定位浮动 mention 面板）
   const [inputWrapperHeight, setInputWrapperHeight] = useState(60);
+  const isPreloadingRef = useRef(false);
+  const lastScrollYRef = useRef(0);
+  const isUserDraggingRef = useRef(false);
+  const historyAnchorRef = useRef<{ active: boolean; beforeY: number; beforeHeight: number }>({
+    active: false,
+    beforeY: 0,
+    beforeHeight: 0,
+  });
+  const preloadCooldownTimerRef = useRef<ReturnType<typeof setTimeout> | null>(null);
 
   const containerStyle = useMemo(() => ([
     styles.container,
@@ -194,8 +202,17 @@ export const ChatScreen: React.FC = () => {
     navigateToChatSettings,
     loadMoreHistory,
     handleMessageListContentSizeChange,
+    handleReachLatestEdge,
   } = useChatScreen();
 
+  useEffect(() => {
+    return () => {
+      if (preloadCooldownTimerRef.current) {
+        clearTimeout(preloadCooldownTimerRef.current);
+      }
+    };
+  }, []);
+
   // 监听返回事件，刷新会话列表
   useEffect(() => {
     const unsubscribe = navigation.addListener('beforeRemove', () => {
@@ -206,38 +223,92 @@ export const ChatScreen: React.FC = () => {
   }, [navigation]);
 
   // 渲染消息气泡
-  const renderMessage = ({ item, index }: { item: any; index: number }) => (
-    <MessageBubble
-      message={item}
-      index={index}
-      currentUserId={currentUserId}
-      currentUser={currentUser}
-      otherUser={otherUser}
-      isGroupChat={isGroupChat}
-      groupMembers={groupMembers}
-      otherUserLastReadSeq={otherUserLastReadSeq}
-      selectedMessageId={selectedMessageId}
-      messageMap={messageMap}
-      onLongPress={handleLongPressMessage}
-      onAvatarPress={handleAvatarPress}
-      onAvatarLongPress={handleAvatarLongPress}
-      formatTime={formatTime}
-      shouldShowTime={shouldShowTime}
-      onImagePress={handleImagePress}
-      onReply={handleReplyMessage}
-    />
-  );
+  const messageIndexMap = useMemo(() => {
+    const map = new Map<string, number>();
+    messages.forEach((msg, idx) => {
+      map.set(String(msg.id), idx);
+    });
+    return map;
+  }, [messages]);
+
+  const renderMessage = ({ item, index }: { item: any; index: number }) => {
+    // inverted 下 renderItem 的 index 与时间顺序不一致，需回查原始序索引
+    const logicalIndex = messageIndexMap.get(String(item.id)) ?? index;
+    return (
+      <MessageBubble
+        message={item}
+        index={logicalIndex}
+        currentUserId={currentUserId}
+        currentUser={currentUser}
+        otherUser={otherUser}
+        isGroupChat={isGroupChat}
+        groupMembers={groupMembers}
+        otherUserLastReadSeq={otherUserLastReadSeq}
+        selectedMessageId={selectedMessageId}
+        messageMap={messageMap}
+        onLongPress={handleLongPressMessage}
+        onAvatarPress={handleAvatarPress}
+        onAvatarLongPress={handleAvatarLongPress}
+        formatTime={formatTime}
+        shouldShowTime={shouldShowTime}
+        onImagePress={handleImagePress}
+        onReply={handleReplyMessage}
+      />
+    );
+  };
 
   // 获取正在输入提示
   const typingHint = getTypingHint();
+  const displayMessages = useMemo(() => [...messages].reverse(), [messages]);
 
   const handleMessageListScroll = useCallback((event: any) => {
-    const { contentSize, contentOffset } = event.nativeEvent;
+    const { contentSize, contentOffset, layoutMeasurement } = event.nativeEvent;
     scrollPositionRef.current = {
       contentHeight: contentSize.height,
       scrollY: contentOffset.y,
+      viewportHeight: layoutMeasurement.height,
     };
-  }, [scrollPositionRef]);
+
+    // 仅用户手势主动回到底部时才解除历史阅读锁（避免加载阶段误解锁）
+    const isScrollingTowardLatest = contentOffset.y < lastScrollYRef.current;
+    if (
+      isUserDraggingRef.current &&
+      !loadingMore &&
+      isScrollingTowardLatest &&
+      contentOffset.y <= 40
+    ) {
+      handleReachLatestEdge();
+    }
+
+    // inverted 下历史端在“列表尾部”，对应 offset 增大且距离尾部变小
+    const distanceToHistoryEdge = contentSize.height - (contentOffset.y + layoutMeasurement.height);
+    const isScrollingTowardHistory = contentOffset.y > lastScrollYRef.current;
+    lastScrollYRef.current = contentOffset.y;
+
+    const PRELOAD_HISTORY_THRESHOLD = 120;
+    if (
+      distanceToHistoryEdge <= PRELOAD_HISTORY_THRESHOLD &&
+      isScrollingTowardHistory &&
+      hasMoreHistory &&
+      !loadingMore &&
+      !loading &&
+      !isPreloadingRef.current
+    ) {
+      isPreloadingRef.current = true;
+      loadMoreHistory().finally(() => {
+        if (preloadCooldownTimerRef.current) {
+          clearTimeout(preloadCooldownTimerRef.current);
+        }
+        preloadCooldownTimerRef.current = setTimeout(() => {
+          isPreloadingRef.current = false;
+        }, 350);
+      });
+    }
+  }, [scrollPositionRef, hasMoreHistory, loadingMore, loading, loadMoreHistory, handleReachLatestEdge]);
+
+  const handleContentSizeChange = useCallback((contentWidth: number, contentHeight: number) => {
+    handleMessageListContentSizeChange(contentWidth, contentHeight);
+  }, [handleMessageListContentSizeChange]);
 
   return (
     <KeyboardAvoidingView
@@ -262,34 +333,65 @@ export const ChatScreen: React.FC = () => {
       />
 
       {/* 消息列表 */}
-      <TouchableWithoutFeedback onPress={handleDismiss}>
-        <View style={styles.messageListContainer}>
-          {loading ? (
-            <View style={styles.loadingContainer}>
-              <ActivityIndicator size="large" color={colors.primary.main} />
+      <View
+        style={styles.messageListContainer}
+        onLayout={e => {
+          scrollPositionRef.current.viewportHeight = e.nativeEvent.layout.height;
+        }}
+      >
+        {loading ? (
+          <View style={styles.loadingContainer}>
+            <ActivityIndicator size="large" color={colors.primary.main} />
+          </View>
+        ) : (
+          <FlatList
+            ref={flatListRef}
+            inverted
+            data={displayMessages}
+            renderItem={renderMessage}
+            keyExtractor={(item: any) => String(item.id)}
+            contentContainerStyle={listContentStyle as any}
+            showsVerticalScrollIndicator={false}
+            keyboardShouldPersistTaps="handled"
+            onScroll={handleMessageListScroll}
+            onScrollBeginDrag={() => {
+              isUserDraggingRef.current = true;
+              handleDismiss();
+            }}
+            onScrollEndDrag={() => {
+              isUserDraggingRef.current = false;
+            }}
+            onMomentumScrollEnd={() => {
+              isUserDraggingRef.current = false;
+            }}
+            scrollEventThrottle={16}
+            onContentSizeChange={handleContentSizeChange}
+          />
+        )}
+        {loadingMore && (
+          <View
+            pointerEvents="none"
+            style={{
+              position: 'absolute',
+              top: 8,
+              left: 0,
+              right: 0,
+              alignItems: 'center',
+            }}
+          >
+            <View
+              style={{
+                backgroundColor: 'rgba(255,255,255,0.9)',
+                borderRadius: 12,
+                paddingHorizontal: 10,
+                paddingVertical: 6,
+              }}
+            >
+              <ActivityIndicator size="small" color={colors.primary.main} />
             </View>
-          ) : (
-            <FlashList
-              ref={flatListRef}
-              data={messages}
-              renderItem={renderMessage}
-              keyExtractor={(item: any) => String(item.id)}
-              contentContainerStyle={listContentStyle as any}
-              showsVerticalScrollIndicator={false}
-              keyboardShouldPersistTaps="handled"
-              refreshing={loadingMore}
-              onRefresh={hasMoreHistory ? loadMoreHistory : undefined}
-              // @ts-ignore FlashList 类型定义问题：estimatedItemSize 是必需属性但类型定义缺失
-              estimatedItemSize={80}
-              maintainVisibleContentPosition={{
-                minIndexForVisible: 0,
-                autoscrollToTopThreshold: undefined,
-              } as any}
-              onScroll={handleMessageListScroll}
-            />
-          )}
-        </View>
-      </TouchableWithoutFeedback>
+          </View>
+        )}
+      </View>
 
       {/* 底部区域：输入框 + 面板 */}
       <View style={{ marginBottom: keyboardHeight > 0 ? keyboardHeight : 0 }}>