feat(assets): add chat typing indicator lottie animation

src/data/storage/chat/local_chat_storage.ts

@@ -0,0 +1,163 @@
+"use client";
+
+/**
+ * LocalChatStorage 完整实现（示范 2：IndexedDB via Dexie）
+ *
+ * 对齐 Dart 端 `LocalChatStorage`（lib/data/services/storage/chat/local_chat_storage.dart）：
+ *   - init / saveMessage / saveMessages / getAllMessages / clearAll / deleteMessage / close
+ *   - 额外提供 `getMessageCount`（异步）替代 Dart 的同步 `messageCount` getter
+ *   - 额外提供 `getAllMessagesBySession(sessionId)`（filter 模拟，等下一轮加索引后再用 where）
+ *
+ * 单例挂在 class 静态字段。
+ * Dexie 实例可注入，便于测试用 fake-indexeddb 跑真 Dexie。
+ *
+ * 注意：当前表无次级索引，所有过滤（sessionId）都是 `toArray().then(filter)`，O(n)。
+ * 数据量大时考虑升级 schema 加索引。
+ */
+
+import { Result, type Result as ResultT } from "../result";
+import { LocalChatDB } from "./local_chat_db";
+import { LocalMessage } from "./local_message";
+
+export class LocalChatStorage {
+  private readonly db: LocalChatDB;
+  private static _instance: LocalChatStorage | null = null;
+
+  constructor(db?: LocalChatDB) {
+    this.db = db ?? new LocalChatDB();
+  }
+
+  static getInstance(): LocalChatStorage {
+    if (!LocalChatStorage._instance) {
+      LocalChatStorage._instance = new LocalChatStorage();
+    }
+    return LocalChatStorage._instance;
+  }
+
+  /** @internal */
+  static _resetForTests(): void {
+    LocalChatStorage._instance = null;
+  }
+
+  /**
+   * 触发 Dexie 打开数据库。
+   * 幂等：Dexie.open() 多次调用无副作用。
+   * 在 bootstrap 中 await 此方法可保证后续操作不会因连接未开而延迟。
+   */
+  async init(): Promise<ResultT<void>> {
+    try {
+      await this.db.open();
+      return Result.success(undefined);
+    } catch (e) {
+      return Result.failure(e);
+    }
+  }
+
+  // ---- create / append ----
+
+  async saveMessage(message: LocalMessage): Promise<ResultT<void>> {
+    try {
+      await this.db.messages.add(message.toRow());
+      return Result.success(undefined);
+    } catch (e) {
+      return Result.failure(e);
+    }
+  }
+
+  async saveMessages(messages: readonly LocalMessage[]): Promise<ResultT<void>> {
+    try {
+      await this.db.transaction(
+        "rw",
+        this.db.messages,
+        async () => {
+          for (const m of messages) {
+            await this.db.messages.add(m.toRow());
+          }
+        },
+      );
+      return Result.success(undefined);
+    } catch (e) {
+      return Result.failure(e);
+    }
+  }
+
+  // ---- read ----
+
+  async getAllMessages(): Promise<ResultT<LocalMessage[]>> {
+    try {
+      const rows = await this.db.messages.toArray();
+      // 按 dbId 升序（与 Dart `box.values.toList()` 插入序语义一致）
+      rows.sort((a, b) => (a.dbId ?? 0) - (b.dbId ?? 0));
+      return Result.success(rows.map((r) => LocalMessage.fromRow(r)));
+    } catch (e) {
+      return Result.failure(e);
+    }
+  }
+
+  async getMessageCount(): Promise<ResultT<number>> {
+    try {
+      return Result.success(await this.db.messages.count());
+    } catch (e) {
+      return Result.failure(e);
+    }
+  }
+
+  async getAllMessagesBySession(
+    sessionId: string,
+  ): Promise<ResultT<LocalMessage[]>> {
+    try {
+      const rows = await this.db.messages
+        .filter((r) => r.sessionId === sessionId)
+        .toArray();
+      rows.sort((a, b) => (a.dbId ?? 0) - (b.dbId ?? 0));
+      return Result.success(rows.map((r) => LocalMessage.fromRow(r)));
+    } catch (e) {
+      return Result.failure(e);
+    }
+  }
+
+  // ---- delete ----
+
+  async clearAll(): Promise<ResultT<void>> {
+    try {
+      await this.db.messages.clear();
+      return Result.success(undefined);
+    } catch (e) {
+      return Result.failure(e);
+    }
+  }
+
+  /**
+   * 按数组下标删除（保持 Dart 端语义：`box.values.toList()[index].delete()`）。
+   * O(n) 取下标后单条 delete，与 Dart 行为一致。
+   */
+  async deleteMessage(index: number): Promise<ResultT<void>> {
+    try {
+      if (!Number.isInteger(index) || index < 0) {
+        return Result.failure(
+          new RangeError(`deleteMessage: index ${index} out of range`),
+        );
+      }
+      const rows = await this.db.messages.toArray();
+      if (index >= rows.length) {
+        return Result.failure(
+          new RangeError(`deleteMessage: index ${index} out of range`),
+        );
+      }
+      const target = rows[index]!;
+      await this.db.messages.delete(target.dbId!);
+      return Result.success(undefined);
+    } catch (e) {
+      return Result.failure(e);
+    }
+  }
+
+  async close(): Promise<ResultT<void>> {
+    try {
+      this.db.close();
+      return Result.success(undefined);
+    } catch (e) {
+      return Result.failure(e);
+    }
+  }
+}