diff --git a/src/core/op.ts b/src/core/op.ts
index 5574e6a..bfb10f3 100644
--- a/src/core/op.ts
+++ b/src/core/op.ts
@@ -40,6 +40,8 @@ export interface Op {
 export interface HistoryEntry {
   forward: Op
   backward: Op
+  /** 批次标记：同批多条（如一次导入 N 张图）undo/redo 时整组一起回滚 */
+  group?: string
 }
 
 /* ---------- 工具 ---------- */
@@ -107,8 +109,12 @@ export function applyOp(inputDeck: Deck, op: Op): Deck {
     case 'add_element': {
       const slideIdx = op.slideIdx as number
       const element = op.element as SlideElement
+      const atIndex = op.atIndex as number | undefined
       const s = deck.slides[slideIdx]
-      if (s) s.elements.push(element)
+      if (s) {
+        if (atIndex != null) s.elements.splice(atIndex, 0, element)  // 指定位置插入（撤销删除时回到原 z 序）
+        else s.elements.push(element)
+      }
       break
     }
 
@@ -244,18 +250,34 @@ export function invertOp(inputDeck: Deck, op: Op): Op {
     }
 
     case 'del_element': {
-      // 逆：把删掉的元素加回去
+      // 逆：把删掉的元素加回原位置（保持 z 序）
       const slideIdx = op.slideIdx as number
       const deletedElement = op.deletedElement as SlideElement | undefined
       if (deletedElement) {
-        return { type: 'add_element', slideIdx, element: deletedElement }
+        const s = deck.slides[slideIdx]
+        const at = s ? s.elements.findIndex(e => e.id === deletedElement.id) : -1
+        // 已删状态里找不到 → 原位置 = 删除后第一个"本应在其后"的元素处；用 indexOf 拿不到，
+        // 所以在执行前由 invertOp 拿到 index：这里 s.elements 已无该元素，取其后继位置
+        const insertAt = at >= 0 ? at : (s ? s.elements.length : 0)
+        return { type: 'add_element', slideIdx, element: deletedElement, atIndex: insertAt }
       }
       return { type: 'replace_deck', deck: clone(deck) }
     }
 
     case 'move_element_z': {
-      // 逆：方向反过来
-      return { type: 'move_element_z', slideIdx: op.slideIdx, elementId: op.elementId, dir: -(op.dir as number) }
+      // 逆：方向反过来。正向若越界是 no-op（applyOp break），
+      // 此时逆必须也是 no-op（空 patch 的 update_element 无副作用）——
+      // 否则撤销会移动一个从未移动过的元素
+      const slideIdx = op.slideIdx as number
+      const elementId = op.elementId as string
+      const s = deck.slides[slideIdx]
+      const i = s ? s.elements.findIndex(e => e.id === elementId) : -1
+      const j = i >= 0 ? ((op.dir as number) > 0 ? i + 1 : i - 1) : -1
+      const outOfRange = i < 0 || j < 0 || j >= (s ? s.elements.length : 0)
+      if (outOfRange) {
+        return { type: 'update_element', slideIdx, elementId, patch: {} }
+      }
+      return { type: 'move_element_z', slideIdx, elementId, dir: -(op.dir as number) }
     }
 
     case 'set_theme': {
diff --git a/tests/op.test.ts b/tests/op.test.ts
new file mode 100644
index 0000000..7f414d4
--- /dev/null
+++ b/tests/op.test.ts
@@ -0,0 +1,114 @@
+/* =====================================================================
+ * op.test.ts — Op 引擎核心语义测试
+ * 保护对象：applyOp 正向应用 / invertOp 逆操作 / undo 往返一致性
+ * 这些是 undo/redo 正确性的地基，任何改动必须保持以下断言成立
+ * ===================================================================== */
+import { describe, it, expect } from 'vitest'
+import { applyOp, invertOp, type Op } from '../src/core/op'
+import type { Deck, Slide, SlideElement } from '../src/core/types'
+
+/* ---------- 测试数据工厂 ---------- */
+function el(id: string, over: Partial<SlideElement> = {}): SlideElement {
+  return {
+    id, type: 'text', x: 10, y: 10, w: 40, h: 15,
+    content: id, style: { fontSize: 24 },
+    ...over
+  }
+}
+function slide(id: string, elements: SlideElement[] = []): Slide {
+  return { id, background: 'bg', elements }
+}
+function deck(slides: Slide[]): Deck {
+  return { v: 3, theme: 'indigo', slides, chatId: 'test' } as Deck
+}
+
+const D1 = deck([slide('s1', [el('a'), el('b')]), slide('s2', [el('c')])])
+
+/* ---------- applyOp 正向 ---------- */
+describe('applyOp', () => {
+  it('add_element 在目标页追加元素', () => {
+    const op: Op = { type: 'add_element', slideIdx: 0, element: el('new') }
+    const d = applyOp(D1, op)
+    expect(d.slides[0].elements.map(e => e.id)).toEqual(['a', 'b', 'new'])
+    expect(d.slides[1].elements).toHaveLength(1)  // 其他页不受影响
+  })
+
+  it('del_element 删除指定元素', () => {
+    const op: Op = { type: 'del_element', slideIdx: 0, elementId: 'a' }
+    const d = applyOp(D1, op)
+    expect(d.slides[0].elements.map(e => e.id)).toEqual(['b'])
+  })
+
+  it('update_element 只改 patch 覆盖的字段', () => {
+    const op: Op = { type: 'update_element', slideIdx: 0, elementId: 'a', patch: { content: '改后', style: { fontSize: 32 } } }
+    const d = applyOp(D1, op)
+    const target = d.slides[0].elements[0]
+    expect(target.content).toBe('改后')
+    expect(target.style.fontSize).toBe(32)
+    expect(target.x).toBe(10)  // 未覆盖字段保持
+  })
+
+  it('move_slide 调整页序', () => {
+    const op: Op = { type: 'move_slide', from: 0, to: 1 }
+    const d = applyOp(D1, op)
+    expect(d.slides.map(s => s.id)).toEqual(['s2', 's1'])
+  })
+
+  it('不 mutate 输入 deck（纯函数）', () => {
+    const snapshot = JSON.stringify(D1)
+    applyOp(D1, { type: 'add_element', slideIdx: 0, element: el('x') })
+    applyOp(D1, { type: 'del_element', slideIdx: 0, elementId: 'a' })
+    expect(JSON.stringify(D1)).toBe(snapshot)
+  })
+})
+
+/* ---------- invertOp + undo 往返 ---------- */
+describe('invertOp 往返一致性', () => {
+  const cases: Array<{ name: string; op: Op }> = [
+    { name: 'add_element', op: { type: 'add_element', slideIdx: 0, element: el('new') } },
+    { name: 'del_element', op: { type: 'del_element', slideIdx: 0, elementId: 'a', deletedElement: el('a') } },
+    { name: 'update_element', op: { type: 'update_element', slideIdx: 0, elementId: 'a', patch: { content: '改', style: { bold: true } } } },
+    { name: 'add_slide', op: { type: 'add_slide', atIndex: 1, slide: slide('s3') } },
+    { name: 'move_slide', op: { type: 'move_slide', from: 0, to: 1 } },
+    { name: 'set_slide_bg', op: { type: 'set_slide_bg', index: 0, bg: 'primary' } },
+    { name: 'move_element_z', op: { type: 'move_element_z', slideIdx: 0, elementId: 'b', dir: 1 } },
+  ]
+
+  for (const { name, op } of cases) {
+    it(`${name}：执行后撤销回到原状`, () => {
+      const after = applyOp(D1, op)
+      const back = invertOp(D1, op)
+      const restored = applyOp(after, back)
+      expect(JSON.stringify(restored)).toBe(JSON.stringify(D1))
+    })
+  }
+
+  it('update_element 无 style patch 也往返一致', () => {
+    const op: Op = { type: 'update_element', slideIdx: 1, elementId: 'c', patch: { x: 55, y: 60 } }
+    const after = applyOp(D1, op)
+    const restored = applyOp(after, invertOp(D1, op))
+    expect(JSON.stringify(restored)).toBe(JSON.stringify(D1))
+  })
+})
+
+/* ---------- 连续操作链撤销 ---------- */
+describe('多步操作链撤销', () => {
+  it('三条操作逐步回滚最终回到初始', () => {
+    let d = D1
+    const trail: Array<{ forward: Op; backward: Op }> = []
+    const ops: Op[] = [
+      { type: 'add_element', slideIdx: 0, element: el('n1') },
+      { type: 'update_element', slideIdx: 0, elementId: 'n1', patch: { content: '更新' } },
+      { type: 'del_element', slideIdx: 0, elementId: 'b' },
+    ]
+    for (const op of ops) {
+      trail.push({ forward: op, backward: invertOp(d, op) })
+      d = applyOp(d, op)
+    }
+    // 逆序回滚
+    for (let i = trail.length - 1; i >= 0; i--) {
+      d = applyOp(d, trail[i].backward)
+    }
+    expect(JSON.stringify(d)).toBe(JSON.stringify(D1))
+  })
+})