保持传播多区域结果为单个遮罩

- 后端传播落库时将同一 seed 在同一目标帧的多个不连通 polygon 保存到同一 annotation
- 同步任务传播和兼容同步传播接口的多 polygon 保存逻辑
- 传播结果 bbox 改为覆盖全部不连通 polygon，并保留多 polygon scores 与 holes
- 前端回显单条多 polygon annotation 时使用组合 bbox 和真实 polygon 面积
- 补充后端传播 worker 回归测试，验证不连通结果只生成一个 annotation
- 补充前端 API 回归测试，验证多 polygon annotation 回显为一个 mask
- 更新项目指南和设计冻结文档

backend/tests/test_ai.py

@@ -582,6 +582,79 @@ def test_propagation_task_runner_saves_annotations_and_progress(client, db_sessi
     assert len(stored_polygon) > 3
 
 
+def test_propagation_task_runner_keeps_disconnected_result_polygons_in_one_annotation(client, db_session, monkeypatch):
+    project = client.post("/api/projects", json={"name": "Propagation Disconnected Mask"}).json()
+    frames = [
+        client.post(f"/api/projects/{project['id']}/frames", json={
+            "project_id": project["id"],
+            "frame_index": idx,
+            "image_url": f"frames/{idx}.jpg",
+            "width": 640,
+            "height": 360,
+        }).json()
+        for idx in range(2)
+    ]
+    first_piece = [[0.15, 0.15], [0.25, 0.15], [0.25, 0.25], [0.15, 0.25]]
+    second_piece = [[0.70, 0.70], [0.90, 0.70], [0.90, 0.90], [0.70, 0.90]]
+    second_hole = [[[0.76, 0.76], [0.82, 0.76], [0.82, 0.82], [0.76, 0.82]]]
+    task = ProcessingTask(
+        task_type="propagate_masks",
+        status="queued",
+        progress=0,
+        project_id=project["id"],
+        payload={
+            "project_id": project["id"],
+            "frame_id": frames[0]["id"],
+            "model": "sam2.1_hiera_tiny",
+            "include_source": False,
+            "save_annotations": True,
+            "steps": [{
+                "direction": "forward",
+                "max_frames": 2,
+                "seed": {
+                    "polygons": [
+                        [[0.1, 0.1], [0.2, 0.1], [0.2, 0.2]],
+                        [[0.6, 0.6], [0.8, 0.6], [0.8, 0.8]],
+                    ],
+                    "label": "多区域",
+                    "color": "#ff0000",
+                    "source_annotation_id": 7,
+                    "source_mask_id": "annotation-7",
+                },
+            }],
+        },
+    )
+    db_session.add(task)
+    db_session.commit()
+    db_session.refresh(task)
+
+    monkeypatch.setattr("services.propagation_task_runner.download_file", lambda object_name: b"jpeg")
+    monkeypatch.setattr("services.propagation_task_runner.publish_task_progress_event", lambda event_task: None)
+    monkeypatch.setattr("services.propagation_task_runner.sam_registry.propagate_video", lambda *args, **kwargs: [
+        {"frame_index": 0, "polygons": [], "scores": []},
+        {
+            "frame_index": 1,
+            "polygons": [first_piece, second_piece],
+            "holes": [[], second_hole],
+            "scores": [0.72, 0.93],
+        },
+    ])
+
+    result = run_propagate_project_task(db_session, task.id)
+
+    assert result["created_annotation_count"] == 1
+    annotations = db_session.query(Annotation).filter(Annotation.project_id == project["id"]).all()
+    assert len(annotations) == 1
+    annotation = annotations[0]
+    assert annotation.frame_id == frames[1]["id"]
+    assert annotation.bbox == [0.15, 0.15, 0.75, 0.75]
+    assert annotation.mask_data["polygons"] == [first_piece, second_piece]
+    assert annotation.mask_data["holes"] == [[], second_hole]
+    assert annotation.mask_data["hasHoles"] is True
+    assert annotation.mask_data["score"] == 0.93
+    assert annotation.mask_data["scores"] == [0.72, 0.93]
+
+
 def test_propagation_task_runner_skips_unchanged_seed_and_replaces_changed_seed(client, db_session, monkeypatch):
     project = client.post("/api/projects", json={"name": "Propagation Dedupe"}).json()
     frames = [