feat: implement lazy singleton pattern for repository instances and update related imports

src/stores/chat/chat-machine.actors.ts

@@ -6,11 +6,11 @@ import { fromPromise, fromCallback } from "xstate";
 
 import { MessageQueue } from "@/core/net/message-queue";
 import type { ChatSendResponse } from "@/data/dto/chat";
+import { getChatRepository } from "@/data/repositories/chat_repository";
 import { Result, Logger } from "@/utils";
 
 import {
   PAGE_SIZE,
-  chatRepo,
   localMessagesToUi,
   readAndSyncHistory,
   sendResponseToUiMessage,
@@ -60,6 +60,7 @@ export const loadMoreHistoryActor = fromPromise<
   { messages: UiMessage[]; hasMore: boolean; newOffset: number },
   { offset: number }
 >(async ({ input }) => {
+  const chatRepo = getChatRepository();
   const result = await chatRepo.getHistory(PAGE_SIZE, input.offset);
   if (Result.isErr(result)) {
     log.error("[chat-machine] loadMoreHistoryActor failed", { error: result.error });
@@ -81,6 +82,7 @@ export const unlockHistoryActor = fromPromise<{
   hasMore: boolean;
   newOffset: number;
 }>(async () => {
+  const chatRepo = getChatRepository();
   const unlockResult = await chatRepo.unlockHistory();
   if (Result.isErr(unlockResult)) {
     log.error("[chat-machine] unlockHistoryActor failed", {
@@ -148,6 +150,7 @@ async function sendMessageViaHttp(content: string): Promise<{
   response: ChatSendResponse;
   reply: UiMessage | null;
 }> {
+  const chatRepo = getChatRepository();
   const result = await chatRepo.sendMessage(content);
   if (Result.isErr(result)) {
     log.error("[chat-machine] sendMessageHttpActor failed", { error: result.error });

src/stores/chat/chat-machine.helpers.ts

@@ -1,6 +1,5 @@
 import type { UiMessage } from "@/data/dto/chat";
-import { chatRepository } from "@/data/repositories/chat_repository";
-import type { IChatRepository } from "@/data/repositories/interfaces";
+import { getChatRepository } from "@/data/repositories/chat_repository";
 import { ChatSendResponse } from "@/data/dto/chat/chat_send_response";
 import { todayString, Result, Logger } from "@/utils";
 
@@ -14,12 +13,6 @@ const log = new Logger("StoresChatChatMachineHelpers");
 /** 翻历史每页大小（仅 `loadMoreHistoryActor` 用） */
 export const PAGE_SIZE = 50;
 
-// ============================================================
-// Repository injection
-// ============================================================
-// 仓库以接口类型注入：调用面只看接口，运行时仍是同一单例
-export const chatRepo: IChatRepository = chatRepository;
-
 // ============================================================
 // DTO ↔ UiMessage 映射
 // ============================================================
@@ -279,6 +272,7 @@ export async function readAndSyncHistory(): Promise<{
    *   - 用户从未发过消息就关掉 app 再开，仍然没 network 消息 → 会再次显示本条
    *     （"每次冷启动给个温暖的起点" —— 若要"只显示一次"，需额外存 local）
    */
+  const chatRepo = getChatRepository();
   const greetingMessage: UiMessage = {
     content:
       "You're here! Facebook is so restrictive, " +