diff --git a/tests/unit/domain/test_clip_operations.py b/tests/unit/domain/test_clip_operations.py
new file mode 100755
index 000000000..14c9d0dd2
--- /dev/null
+++ b/tests/unit/domain/test_clip_operations.py
@@ -0,0 +1,518 @@
+"""片段操作工具单测.
+
+纯函数模块，覆盖：分割校验/计算、合并校验/计算、
+order重排、order偏移。
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+from packages.domain.clip_operations import (
+    DEFAULT_SPLIT_DURATION,
+    MergeResult,
+    SplitResult,
+    calculate_merge,
+    calculate_reorder_new_orders,
+    calculate_shift_orders,
+    calculate_split,
+    validate_merge_clips,
+    validate_split_time,
+)
+
+
+class TestConstants:
+    def test_default_split_duration(self):
+        assert DEFAULT_SPLIT_DURATION == 5.0
+
+
+class TestValidateSplitTime:
+    def test_valid_middle(self):
+        validate_split_time(5.0, 10.0)  # 不抛异常就是通过
+
+    def test_valid_small(self):
+        validate_split_time(0.1, 10.0)
+
+    def test_valid_near_end(self):
+        validate_split_time(9.9, 10.0)
+
+    def test_zero_invalid(self):
+        try:
+            validate_split_time(0.0, 10.0)
+        except ValueError as e:
+            assert "分割时间" in str(e)
+        else:
+            raise AssertionError("expected ValueError")
+
+    def test_negative_invalid(self):
+        try:
+            validate_split_time(-1.0, 10.0)
+        except ValueError:
+            pass
+        else:
+            raise AssertionError("expected ValueError")
+
+    def test_equal_to_duration_invalid(self):
+        try:
+            validate_split_time(10.0, 10.0)
+        except ValueError:
+            pass
+        else:
+            raise AssertionError("expected ValueError")
+
+    def test_greater_than_duration_invalid(self):
+        try:
+            validate_split_time(15.0, 10.0)
+        except ValueError:
+            pass
+        else:
+            raise AssertionError("expected ValueError")
+
+
+class TestCalculateSplit:
+    def test_split_half(self):
+        result = calculate_split(10.0, 5.0)
+        assert isinstance(result, SplitResult)
+        assert result.left_duration == 5.0
+        assert result.right_duration == 5.0
+        assert result.right_start_time == 5.0
+        assert result.left_trim_end == 5.0
+        assert result.right_trim_start == 5.0
+
+    def test_split_one_third(self):
+        result = calculate_split(9.0, 3.0)
+        assert result.left_duration == 3.0
+        assert result.right_duration == 6.0
+        assert result.right_start_time == 3.0
+
+    def test_split_with_start_time(self):
+        result = calculate_split(10.0, 4.0, start_time=100.0)
+        assert result.left_duration == 4.0
+        assert result.right_duration == 6.0
+        assert result.right_start_time == 104.0
+
+    def test_split_precision_rounding(self):
+        result = calculate_split(1.0, 1 / 3, precision=3)
+        assert result.left_duration == round(1 / 3, 3)
+        assert result.right_duration == round(2 / 3, 3)
+
+    def test_split_default_precision_is_3(self):
+        result = calculate_split(1.0, 0.123456)
+        # 默认精度3位
+        assert result.left_duration == 0.123
+
+    def test_custom_precision(self):
+        result = calculate_split(1.0, 0.123456, precision=5)
+        assert result.left_duration == 0.12346  # 5位精度，四舍五入
+
+    def test_split_returns_frozen_dataclass(self):
+        result = calculate_split(10.0, 5.0)
+        try:
+            result.left_duration = 3.0  # type: ignore
+        except AttributeError:
+            pass  # frozen，应该抛异常
+        else:
+            raise AssertionError("SplitResult should be frozen")
+
+    def test_invalid_split_time_raises(self):
+        try:
+            calculate_split(10.0, 0.0)
+        except ValueError:
+            pass
+        else:
+            raise AssertionError("expected ValueError")
+
+
+@dataclass
+class FakeClip:
+    """模拟 EditPlanClip 的最小数据类."""
+
+    id: str = ""
+    plan_id: str = "plan_1"
+    order: int = 0
+    duration: float = 3.0
+    clip_type: str = "main"
+    text_content: str = ""
+    config: dict | None = None
+
+
+class TestValidateMergeClips:
+    def test_valid_two_clips(self):
+        clips = [
+            FakeClip(id="c1", order=0),
+            FakeClip(id="c2", order=1),
+        ]
+        plan_id, first_order = validate_merge_clips(clips)
+        assert plan_id == "plan_1"
+        assert first_order == 0
+
+    def test_valid_three_clips(self):
+        clips = [
+            FakeClip(id="c1", order=2),
+            FakeClip(id="c2", order=3),
+            FakeClip(id="c3", order=4),
+        ]
+        plan_id, first_order = validate_merge_clips(clips)
+        assert plan_id == "plan_1"
+        assert first_order == 2
+
+    def test_unordered_input_still_valid(self):
+        """输入顺序不影响，内部会排序."""
+        clips = [
+            FakeClip(id="c3", order=2),
+            FakeClip(id="c1", order=0),
+            FakeClip(id="c2", order=1),
+        ]
+        plan_id, first_order = validate_merge_clips(clips)
+        assert first_order == 0
+
+    def test_single_clip_invalid(self):
+        try:
+            validate_merge_clips([FakeClip()])
+        except ValueError as e:
+            assert "至少需要 2 个" in str(e)
+        else:
+            raise AssertionError("expected ValueError")
+
+    def test_empty_list_invalid(self):
+        try:
+            validate_merge_clips([])
+        except ValueError:
+            pass
+        else:
+            raise AssertionError("expected ValueError")
+
+    def test_different_plan_invalid(self):
+        clips = [
+            FakeClip(id="c1", plan_id="plan_a", order=0),
+            FakeClip(id="c2", plan_id="plan_b", order=1),
+        ]
+        try:
+            validate_merge_clips(clips)
+        except ValueError as e:
+            assert "同一计划" in str(e)
+        else:
+            raise AssertionError("expected ValueError")
+
+    def test_non_consecutive_order_invalid(self):
+        clips = [
+            FakeClip(id="c1", order=0),
+            FakeClip(id="c2", order=2),  # 跳过1
+        ]
+        try:
+            validate_merge_clips(clips)
+        except ValueError as e:
+            assert "不连续" in str(e)
+        else:
+            raise AssertionError("expected ValueError")
+
+    def test_different_clip_type_invalid(self):
+        clips = [
+            FakeClip(id="c1", order=0, clip_type="main"),
+            FakeClip(id="c2", order=1, clip_type="title"),
+        ]
+        try:
+            validate_merge_clips(clips)
+        except ValueError as e:
+            assert "相同类型" in str(e)
+        else:
+            raise AssertionError("expected ValueError")
+
+
+class TestCalculateMerge:
+    def test_merge_two_clips_duration(self):
+        clips = [
+            FakeClip(id="c1", order=0, duration=3.0),
+            FakeClip(id="c2", order=1, duration=5.0),
+        ]
+        result = calculate_merge(clips)
+        assert isinstance(result, MergeResult)
+        assert result.total_duration == 8.0
+
+    def test_merge_three_clips_duration(self):
+        clips = [
+            FakeClip(id="c1", order=0, duration=2.0),
+            FakeClip(id="c2", order=1, duration=3.0),
+            FakeClip(id="c3", order=2, duration=4.0),
+        ]
+        result = calculate_merge(clips)
+        assert result.total_duration == 9.0
+
+    def test_merge_text_concatenation(self):
+        clips = [
+            FakeClip(id="c1", order=0, text_content="第一句"),
+            FakeClip(id="c2", order=1, text_content="第二句"),
+        ]
+        result = calculate_merge(clips)
+        assert result.merged_text == "第一句\n第二句"
+
+    def test_merge_empty_text_skipped(self):
+        clips = [
+            FakeClip(id="c1", order=0, text_content="hello"),
+            FakeClip(id="c2", order=1, text_content=""),
+            FakeClip(id="c3", order=2, text_content="world"),
+        ]
+        result = calculate_merge(clips)
+        assert result.merged_text == "hello\nworld"
+
+    def test_merge_whitespace_text_skipped(self):
+        clips = [
+            FakeClip(id="c1", order=0, text_content="a"),
+            FakeClip(id="c2", order=1, text_content="   "),
+            FakeClip(id="c3", order=2, text_content="b"),
+        ]
+        result = calculate_merge(clips)
+        assert result.merged_text == "a\nb"
+
+    def test_merge_all_empty_text(self):
+        clips = [
+            FakeClip(id="c1", order=0, text_content=""),
+            FakeClip(id="c2", order=1, text_content=""),
+        ]
+        result = calculate_merge(clips)
+        assert result.merged_text == ""
+
+    def test_merge_config_later_overrides(self):
+        clips = [
+            FakeClip(id="c1", order=0, config={"font_size": 20, "color": "red"}),
+            FakeClip(id="c2", order=1, config={"font_size": 24, "bold": True}),
+        ]
+        result = calculate_merge(clips)
+        assert result.merged_config["font_size"] == 24  # 后面的覆盖
+        assert result.merged_config["color"] == "red"
+        assert result.merged_config["bold"] is True
+
+    def test_merge_config_removes_trim_fields(self):
+        clips = [
+            FakeClip(id="c1", order=0, config={"trim_start": 1.0, "a": 1}),
+            FakeClip(id="c2", order=1, config={"trim_end": 2.0, "b": 2}),
+        ]
+        result = calculate_merge(clips)
+        assert "trim_start" not in result.merged_config
+        assert "trim_end" not in result.merged_config
+        assert result.merged_config["a"] == 1
+        assert result.merged_config["b"] == 2
+
+    def test_merge_none_config_handled(self):
+        clips = [
+            FakeClip(id="c1", order=0, config=None),
+            FakeClip(id="c2", order=1, config={"key": "val"}),
+        ]
+        result = calculate_merge(clips)
+        assert result.merged_config == {"key": "val"}
+
+    def test_merge_first_order_and_shift(self):
+        clips = [
+            FakeClip(id="c1", order=5),
+            FakeClip(id="c2", order=6),
+            FakeClip(id="c3", order=7),
+        ]
+        result = calculate_merge(clips)
+        assert result.first_order == 5
+        assert result.shift_amount == 2  # 3个合并成1个，前移2位
+
+    def test_merge_two_clips_shift(self):
+        clips = [FakeClip(id="c1", order=0), FakeClip(id="c2", order=1)]
+        result = calculate_merge(clips)
+        assert result.shift_amount == 1
+
+    def test_merge_unordered_input(self):
+        """输入乱序也能正确处理（内部排序）."""
+        clips = [
+            FakeClip(id="c3", order=2, duration=4.0, text_content="C"),
+            FakeClip(id="c1", order=0, duration=2.0, text_content="A"),
+            FakeClip(id="c2", order=1, duration=3.0, text_content="B"),
+        ]
+        result = calculate_merge(clips)
+        assert result.total_duration == 9.0
+        assert result.merged_text == "A\nB\nC"
+        assert result.first_order == 0
+
+    def test_merge_precision(self):
+        clips = [
+            FakeClip(id="c1", order=0, duration=1 / 3),
+            FakeClip(id="c2", order=1, duration=1 / 3),
+        ]
+        result = calculate_merge(clips, precision=3)
+        assert result.total_duration == round(2 / 3, 3)
+
+    def test_merge_empty_list_raises(self):
+        try:
+            calculate_merge([])
+        except ValueError as e:
+            assert "不能为空" in str(e)
+        else:
+            raise AssertionError("expected ValueError")
+
+    def test_merge_result_is_frozen(self):
+        clips = [FakeClip(id="c1", order=0), FakeClip(id="c2", order=1)]
+        result = calculate_merge(clips)
+        try:
+            result.total_duration = 10.0  # type: ignore
+        except AttributeError:
+            pass
+        else:
+            raise AssertionError("MergeResult should be frozen")
+
+
+@dataclass
+class FakeItem:
+    id: str
+    order: int = 0
+
+
+class TestCalculateReorderNewOrders:
+    def test_basic_reorder(self):
+        items = [
+            FakeItem(id="a", order=0),
+            FakeItem(id="b", order=1),
+            FakeItem(id="c", order=2),
+        ]
+        new_order = ["c", "a", "b"]
+        result = calculate_reorder_new_orders(new_order, items)
+        assert result == {"c": 0, "a": 1, "b": 2}
+
+    def test_reverse_order(self):
+        items = [FakeItem(id="a"), FakeItem(id="b"), FakeItem(id="c")]
+        new_order = ["c", "b", "a"]
+        result = calculate_reorder_new_orders(new_order, items)
+        assert result["c"] == 0
+        assert result["b"] == 1
+        assert result["a"] == 2
+
+    def test_same_order(self):
+        items = [FakeItem(id="a"), FakeItem(id="b")]
+        new_order = ["a", "b"]
+        result = calculate_reorder_new_orders(new_order, items)
+        assert result == {"a": 0, "b": 1}
+
+    def test_mismatched_ids_raises(self):
+        items = [FakeItem(id="a"), FakeItem(id="b")]
+        try:
+            calculate_reorder_new_orders(["a", "c"], items)
+        except ValueError as e:
+            assert "不匹配" in str(e)
+        else:
+            raise AssertionError("expected ValueError")
+
+    def test_extra_id_in_list_raises(self):
+        items = [FakeItem(id="a")]
+        try:
+            calculate_reorder_new_orders(["a", "b"], items)
+        except ValueError:
+            pass
+        else:
+            raise AssertionError("expected ValueError")
+
+    def test_missing_id_raises(self):
+        items = [FakeItem(id="a"), FakeItem(id="b")]
+        try:
+            calculate_reorder_new_orders(["a"], items)
+        except ValueError:
+            pass
+        else:
+            raise AssertionError("expected ValueError")
+
+    def test_custom_id_attr(self):
+        @dataclass
+        class CustomItem:
+            key: str
+            order: int = 0
+
+        items = [CustomItem(key="x"), CustomItem(key="y")]
+        result = calculate_reorder_new_orders(["y", "x"], items, id_attr="key")
+        assert result == {"y": 0, "x": 1}
+
+    def test_custom_order_attr_does_not_affect_return(self):
+        """order_attr不影响返回值（返回的是索引），只影响参数校验的ID提取."""
+        items = [FakeItem(id="a", order=10), FakeItem(id="b", order=20)]
+        result = calculate_reorder_new_orders(["b", "a"], items)
+        assert result == {"b": 0, "a": 1}  # 新order是索引，不是原值
+
+
+class TestCalculateShiftOrders:
+    def test_shift_positive(self):
+        items = [
+            FakeItem(id="a", order=0),
+            FakeItem(id="b", order=1),
+            FakeItem(id="c", order=2),
+        ]
+        result = calculate_shift_orders(items, threshold_order=0, shift=5)
+        # order > 0 的是 b(1) 和 c(2)
+        shifted = {item.id: new_order for item, new_order in result}
+        assert len(result) == 2
+        assert shifted["b"] == 6
+        assert shifted["c"] == 7
+
+    def test_shift_negative(self):
+        items = [
+            FakeItem(id="a", order=0),
+            FakeItem(id="b", order=1),
+            FakeItem(id="c", order=2),
+        ]
+        result = calculate_shift_orders(items, threshold_order=0, shift=-1)
+        shifted = {item.id: new_order for item, new_order in result}
+        assert shifted["b"] == 0
+        assert shifted["c"] == 1
+
+    def test_threshold_not_included(self):
+        """threshold_order本身不包含在内（严格大于）."""
+        items = [FakeItem(id="a", order=5)]
+        result = calculate_shift_orders(items, threshold_order=5, shift=1)
+        assert len(result) == 0
+
+    def test_excluded_ids_skipped(self):
+        items = [
+            FakeItem(id="a", order=1),
+            FakeItem(id="b", order=2),
+            FakeItem(id="c", order=3),
+        ]
+        result = calculate_shift_orders(items, threshold_order=0, shift=10, excluded_ids={"b"})
+        shifted = {item.id: new_order for item, new_order in result}
+        assert "b" not in shifted
+        assert shifted["a"] == 11
+        assert shifted["c"] == 13
+
+    def test_none_excluded_ids(self):
+        items = [FakeItem(id="a", order=1)]
+        result = calculate_shift_orders(items, threshold_order=0, shift=1, excluded_ids=None)
+        assert len(result) == 1
+
+    def test_empty_excluded_ids(self):
+        items = [FakeItem(id="a", order=1)]
+        result = calculate_shift_orders(items, threshold_order=0, shift=1, excluded_ids=set())
+        assert len(result) == 1
+
+    def test_no_items_above_threshold(self):
+        items = [
+            FakeItem(id="a", order=0),
+            FakeItem(id="b", order=1),
+        ]
+        result = calculate_shift_orders(items, threshold_order=10, shift=5)
+        assert len(result) == 0
+
+    def test_custom_id_attr(self):
+        @dataclass
+        class CustomItem:
+            key: str
+            pos: int = 0
+
+        items = [CustomItem(key="x", pos=1), CustomItem(key="y", pos=2)]
+        result = calculate_shift_orders(
+            items,
+            threshold_order=0,
+            shift=3,
+            id_attr="key",
+            order_attr="pos",
+        )
+        assert len(result) == 2
+        assert result[0][1] == 4
+        assert result[1][1] == 5
+
+    def test_preserves_item_reference(self):
+        item = FakeItem(id="a", order=5)
+        items = [item]
+        result = calculate_shift_orders(items, threshold_order=3, shift=2)
+        assert len(result) == 1
+        assert result[0][0] is item  # 是同一个对象引用
+        assert result[0][1] == 7