feat(stage4): 自动保存/崩溃恢复/外部修改检测/工作区管理（含合并验收清单）

tests/stage4.test.ts

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+// 阶段 4 验收：恢复记录纯逻辑（键/提供与清理划分）与标签 reducer 的重载/改路径动作。
+import { describe, it, expect } from 'vitest'
+import { recoveryKey, planRecovery } from '../src/utils/recovery'
+import { tabsReducer, createTab, isDirty, type TabsState } from '../src/stores/tabs'
+import type { RecoveryEntry } from '../src/services/platform'
+
+describe('recoveryKey', () => {
+  it('文件文档按路径键，未命名按标签 id', () => {
+    expect(recoveryKey({ id: 't1', path: 'D:\\a.md' })).toBe('path:D:\\a.md')
+    expect(recoveryKey({ id: 't2', path: null })).toBe('untitled:t2')
+  })
+})
+
+describe('planRecovery', () => {
+  const fileRecord: RecoveryEntry = {
+    docKey: 'path:D:\\a.md', path: 'D:\\a.md', title: 'a', content: '新草稿', updatedAt: 2,
+  }
+  const savedRecord: RecoveryEntry = {
+    docKey: 'path:D:\\b.md', path: 'D:\\b.md', title: 'b', content: '已存内容', updatedAt: 1,
+  }
+  const untitledRecord: RecoveryEntry = {
+    docKey: 'untitled:t9', path: null, title: '未命名', content: '临时', updatedAt: 3,
+  }
+
+  it('与磁盘一致的记录清理、不一致与未命名的提供恢复、文件已删的也提供', () => {
+    const plan = planRecovery([fileRecord, savedRecord, untitledRecord], (path) =>
+      path === 'D:\\b.md' ? '已存内容' : '磁盘旧内容',
+    )
+    expect(plan.purgeKeys).toEqual(['path:D:\\b.md'])
+    expect(plan.offer.map((r) => r.docKey)).toEqual(['path:D:\\a.md', 'untitled:t9'])
+
+    const gonePlan = planRecovery([fileRecord], () => null)
+    expect(gonePlan.offer).toHaveLength(1)
+    expect(gonePlan.purgeKeys).toEqual([])
+  })
+})
+
+describe('tabs reducer 阶段 4 动作', () => {
+  it('loadContent 整表替换并变干净，setPath 改路径与标题', () => {
+    const tab = createTab({ path: 'D:\\a.md', title: 'a', content: '旧' })
+    let state: TabsState = { tabs: [tab], activeId: tab.id }
+    state = tabsReducer(state, { type: 'updateContent', id: tab.id, content: '我的修改' })
+    expect(isDirty(state.tabs[0])).toBe(true)
+    state = tabsReducer(state, { type: 'loadContent', id: tab.id, content: '磁盘新内容', encoding: 'GBK' })
+    expect(state.tabs[0].content).toBe('磁盘新内容')
+    expect(isDirty(state.tabs[0])).toBe(false)
+    expect(state.tabs[0].encoding).toBe('GBK')
+    state = tabsReducer(state, { type: 'setPath', id: tab.id, path: 'D:\\b.md', title: 'b' })
+    expect(state.tabs[0].path).toBe('D:\\b.md')
+    expect(state.tabs[0].title).toBe('b')
+  })
+})