refactor: 首次运行为空列表并简化存储初始化

- 移除 seed-data 模块，首次运行改为持久化空任务列表
- 简化 initializeStore()，将 tasksInitialized 处理集中到 store 层
- 移除 loadTasksData() 写入 tasksInitialized 的副作用
- 已归一化的任务数据跳过多余的 localStorage 回写
- 为旧版安装补写 tasksInitialized；首次写入失败时下次访问重试
- 补充存储兼容性测试并更新 README

test/core.test.js

@@ -32,7 +32,6 @@ import {
   setSortOrder,
   updateTask,
 } from '../src/js/store.js';
-import { createSeedTasks } from '../src/js/seed-data.js';
 
 const base = (id, title, extra = {}) => ({
   id,
@@ -46,7 +45,10 @@ const base = (id, title, extra = {}) => ({
   ...extra,
 });
 
-beforeEach(() => localStorage.clear());
+beforeEach(() => {
+  localStorage.clear();
+  consumeStorageWriteFailure();
+});
 afterEach(() => vi.restoreAllMocks());
 
 describe('task model', () => {
@@ -153,28 +155,62 @@ describe('due dates', () => {
   });
 });
 
-describe('seed data', () => {
-  it('creates five unique tasks at the initialization time', () => {
-    const now = new Date('2026-07-19T02:54:00.000Z');
-    const tasks = createSeedTasks(now);
-    expect(tasks).toHaveLength(5);
-    expect(new Set(tasks.map((task) => task.id)).size).toBe(5);
-    expect(tasks.every((task) => task.createdDate === now.toISOString())).toBe(true);
-  });
-});
-
 describe('storage and store compatibility', () => {
   it('distinguishes a missing task key from an intentionally empty task list', () => {
     expect(loadTasksData()).toMatchObject({ tasks: [], corrupted: false, exists: false });
     localStorage.setItem('tasks', '[]');
     expect(loadTasksData()).toMatchObject({ tasks: [], corrupted: false, exists: true });
   });
-  it('preserves corrupted raw data without replacing it with seed tasks', () => {
+  it('backfills tasksInitialized for legacy installs that already have tasks', () => {
+    localStorage.setItem('tasks', JSON.stringify([base(1, 'Legacy')]));
+    expect(isInitialized()).toBe(false);
+    initializeStore();
+    expect(isInitialized()).toBe(true);
+    expect(getTasks()).toMatchObject([{ id: 1, title: 'Legacy' }]);
+  });
+  it('starts with an empty task list on first use', () => {
+    initializeStore();
+    expect(getTasks()).toEqual([]);
+    expect(localStorage.getItem('tasks')).toBe('[]');
+    expect(isInitialized()).toBe(true);
+    expect(consumeStorageWriteFailure()).toBe(false);
+  });
+  it('skips the redundant rewrite when stored tasks are already normalized', () => {
+    initializeStore();
+    addTask(base(1, 'Kept'));
+    const setItem = vi.spyOn(Storage.prototype, 'setItem');
+    initializeStore();
+    const taskWrites = setItem.mock.calls.filter(([key]) => key === 'tasks');
+    expect(taskWrites).toHaveLength(0);
+    expect(getTasks()).toMatchObject([{ id: 1, title: 'Kept' }]);
+  });
+  it('does not mark initialized when first persist fails', () => {
+    vi.spyOn(Storage.prototype, 'setItem').mockImplementation(() => {
+      throw new DOMException('full', 'QuotaExceededError');
+    });
+    initializeStore();
+    expect(getTasks()).toEqual([]);
+    expect(localStorage.getItem('tasks')).toBeNull();
+    expect(isInitialized()).toBe(false);
+    expect(consumeStorageWriteFailure()).toBe(true);
+  });
+  it('attempts no write at all when storage is unavailable', () => {
+    vi.spyOn(Storage.prototype, 'getItem').mockImplementation(() => {
+      throw new DOMException('blocked', 'SecurityError');
+    });
+    const setItem = vi.spyOn(Storage.prototype, 'setItem');
+    initializeStore();
+    expect(getTasks()).toEqual([]);
+    expect(setItem).not.toHaveBeenCalled();
+    expect(consumeStorageWriteFailure()).toBe(false);
+  });
+  it('preserves corrupted raw data without replacing it', () => {
     localStorage.setItem('tasks', '{broken');
-    initializeStore([base(1, 'Seed')], false);
+    initializeStore();
     expect(getTasks()).toEqual([]);
     expect(localStorage.getItem('tasks')).toBe('{broken');
     expect(localStorage.getItem('tasksCorruptedBackup')).toBe('{broken');
+    expect(isInitialized()).toBe(false);
   });
   it('restores all legacy preferences and task fields', () => {
     localStorage.setItem('tasks', JSON.stringify(legacyBackup.data.tasks));
@@ -183,8 +219,9 @@ describe('storage and store compatibility', () => {
     localStorage.setItem('showHiddenTodoTasks', 'false');
     localStorage.setItem('tasksInitialized', 'true');
     localStorage.setItem('tasksCorruptedBackup', '{historical backup');
-    initializeStore([], isInitialized());
+    initializeStore();
     expect(getTasks()).toMatchObject(legacyBackup.data.tasks);
+    expect(JSON.parse(localStorage.getItem('tasks'))).toEqual(getTasks());
     expect(getSortOrders()).toEqual(legacyBackup.data.sortOrders);
     expect(getShowHidden('completed')).toBe(true);
     expect(getShowHidden('todo')).toBe(false);
@@ -193,7 +230,7 @@ describe('storage and store compatibility', () => {
     expect(localStorage.getItem('tasksCorruptedBackup')).toBe('{historical backup');
   });
   it('maintains store ids and rejects invalid preference mutations', () => {
-    initializeStore([], true);
+    initializeStore();
     const first = addTask(base(1, 'First'));
     const duplicate = addTask(base(1, 'Second'));
     const [appended] = appendTasks([base(first.id, 'Third')]);
@@ -213,7 +250,7 @@ describe('storage and store compatibility', () => {
     vi.spyOn(Storage.prototype, 'setItem').mockImplementation(() => {
       throw new DOMException('full', 'QuotaExceededError');
     });
-    expect(() => initializeStore([base(1, 'Seed')], false)).not.toThrow();
+    expect(() => initializeStore()).not.toThrow();
     expect(consumeStorageWriteFailure()).toBe(true);
     expect(consumeStorageWriteFailure()).toBe(false);
   });
@@ -237,7 +274,7 @@ describe('imports', () => {
       Modal: { getOrCreateInstance: () => ({ hide: vi.fn(), show: vi.fn() }) },
     };
     document.body.innerHTML = '<div id="importModal"></div>';
-    initializeStore([], true);
+    initializeStore();
   });
   it('validates the legacy export fixture', () => {
     expect(validateImportData(legacyBackup)).toBe(true);
@@ -296,7 +333,7 @@ describe('imports', () => {
 });
 
 describe('timeline entries', () => {
-  beforeEach(() => initializeStore([], true));
+  beforeEach(() => initializeStore());
 
   it('ignores fields that the change set omits', () => {
     const task = addTask(base(1, 'Untouched', { assignee: 'Ada', dueDate: '2025-01-01' }));
@@ -367,7 +404,7 @@ describe('board rendering', () => {
 
   beforeEach(() => {
     document.body.innerHTML = fixture();
-    initializeStore([], true);
+    initializeStore();
   });
 
   it('lists timeline entries newest first within a single day', () => {
@@ -474,7 +511,7 @@ describe('export', () => {
     original.createObjectURL = URL.createObjectURL;
     original.revokeObjectURL = URL.revokeObjectURL;
     document.body.innerHTML = '';
-    initializeStore([], true);
+    initializeStore();
   });
   afterEach(() => {
     URL.createObjectURL = original.createObjectURL;