feat: add tag functionality to Asset

- domain: Asset.tags field with add_tag/remove_tag methods
- validation: no empty tags, auto deduplication
- tests: 5 integration tests (add/remove/duplicate/empty/idempotent)
- all 13 tests passing

packages/domain/entities.py

@@ -95,6 +95,7 @@ class Asset:
     storage_key: str
     mime_type: str
     metadata: dict[str, Any] = field(default_factory=dict)
+    tags: list[str] = field(default_factory=list)
     created_at: datetime = field(default_factory=lambda: datetime.now(timezone.utc))
 
     @classmethod
@@ -124,8 +125,23 @@ class Asset:
             storage_key=storage_key.strip(),
             mime_type=mime_type.strip(),
             metadata=metadata or {},
+            tags=[],
         )
 
+    def add_tag(self, tag: str) -> None:
+        """添加标签。空标签会被忽略，自动去重。"""
+        clean_tag = tag.strip()
+        if not clean_tag:
+            raise ValueError("标签不能为空")
+        if clean_tag not in self.tags:
+            self.tags.append(clean_tag)
+
+    def remove_tag(self, tag: str) -> None:
+        """删除标签。如果标签不存在，不报错（幂等性）。"""
+        clean_tag = tag.strip()
+        if clean_tag in self.tags:
+            self.tags.remove(clean_tag)
+
 
 @dataclass(slots=True)
 class IngestJob:

tests/integration/test_asset_tags.py

@@ -0,0 +1,99 @@
+import pytest
+
+from packages.domain import Asset
+
+
+def test_add_tag_to_asset():
+    """测试添加标签到 Asset。"""
+    asset = Asset.create(
+        workspace_id="ws-1",
+        project_id="proj-1",
+        library_id="lib-1",
+        name="video.mp4",
+        storage_key="uploads/abc/video.mp4",
+        mime_type="video/mp4",
+    )
+    
+    asset.add_tag("风景")
+    asset.add_tag("自然")
+    
+    assert len(asset.tags) == 2
+    assert "风景" in asset.tags
+    assert "自然" in asset.tags
+
+
+def test_add_duplicate_tag_should_ignore():
+    """测试添加重复标签应自动去重。"""
+    asset = Asset.create(
+        workspace_id="ws-1",
+        project_id="proj-1",
+        library_id="lib-1",
+        name="video.mp4",
+        storage_key="uploads/abc/video.mp4",
+        mime_type="video/mp4",
+    )
+    
+    asset.add_tag("风景")
+    asset.add_tag("风景")  # 重复
+    
+    assert len(asset.tags) == 1
+    assert asset.tags.count("风景") == 1
+
+
+def test_add_empty_tag_should_fail():
+    """测试添加空标签应失败。"""
+    asset = Asset.create(
+        workspace_id="ws-1",
+        project_id="proj-1",
+        library_id="lib-1",
+        name="video.mp4",
+        storage_key="uploads/abc/video.mp4",
+        mime_type="video/mp4",
+    )
+    
+    with pytest.raises(ValueError, match="标签不能为空"):
+        asset.add_tag("")
+    
+    with pytest.raises(ValueError, match="标签不能为空"):
+        asset.add_tag("   ")  # 仅空格
+
+
+def test_remove_tag_from_asset():
+    """测试从 Asset 删除标签。"""
+    asset = Asset.create(
+        workspace_id="ws-1",
+        project_id="proj-1",
+        library_id="lib-1",
+        name="video.mp4",
+        storage_key="uploads/abc/video.mp4",
+        mime_type="video/mp4",
+    )
+    
+    asset.add_tag("风景")
+    asset.add_tag("自然")
+    
+    asset.remove_tag("风景")
+    
+    assert len(asset.tags) == 1
+    assert "风景" not in asset.tags
+    assert "自然" in asset.tags
+
+
+def test_remove_nonexistent_tag_should_be_idempotent():
+    """测试删除不存在的标签应幂等（不报错）。"""
+    asset = Asset.create(
+        workspace_id="ws-1",
+        project_id="proj-1",
+        library_id="lib-1",
+        name="video.mp4",
+        storage_key="uploads/abc/video.mp4",
+        mime_type="video/mp4",
+    )
+    
+    asset.add_tag("风景")
+    
+    # 删除不存在的标签，不应报错
+    asset.remove_tag("不存在的标签")
+    
+    assert len(asset.tags) == 1
+    assert "风景" in asset.tags