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/services/propagation_task_runner.py

@@ -83,6 +83,17 @@ def _polygon_bbox(polygon: list[list[float]]) -> list[float]:
     return [left, top, max(right - left, 0.0), max(bottom - top, 0.0)]
 
 
+def _polygons_bbox(polygons: list[list[list[float]]]) -> list[float]:
+    points = [point for polygon in polygons for point in polygon if len(point) >= 2]
+    if not points:
+        return [0.0, 0.0, 0.0, 0.0]
+    xs = [_clamp01(point[0]) for point in points]
+    ys = [_clamp01(point[1]) for point in points]
+    left, right = min(xs), max(xs)
+    top, bottom = min(ys), max(ys)
+    return [left, top, max(right - left, 0.0), max(bottom - top, 0.0)]
+
+
 def _normalize_polygon(polygon: list[list[float]]) -> list[list[float]]:
     return [[_clamp01(point[0]), _clamp01(point[1])] for point in polygon if len(point) >= 2]
 
@@ -520,36 +531,49 @@ def _save_propagated_annotations(
                 polygon=cleanup_polygon,
             )
             cleaned_frame_ids.add(int(frame.id))
+        polygons_to_save: list[list[list[float]]] = []
+        holes_to_save: list[list[list[list[float]]]] = []
+        score_values: list[float] = []
         for polygon_index, polygon in prepared_polygons:
             if len(polygon) < 3:
                 continue
+            polygons_to_save.append(polygon)
             hole_group = result_holes[polygon_index] if polygon_index < len(result_holes) and isinstance(result_holes[polygon_index], list) else []
-            annotation = Annotation(
-                project_id=int(payload["project_id"]),
-                frame_id=frame.id,
-                template_id=template_id,
-                mask_data={
-                    "polygons": [polygon],
-                    **({"holes": [hole_group], "hasHoles": True} if hole_group else {}),
-                    "label": label,
-                    "color": color,
-                    "source": f"{model_id}_propagation",
-                    "propagated_from_frame_id": source_frame.id,
-                    "propagated_from_frame_index": source_frame.frame_index,
-                    "propagation_seed_key": seed_key,
-                    "propagation_seed_signature": seed_signature,
-                    "propagation_direction": direction,
-                    "source_annotation_id": source_annotation_id,
-                    "source_mask_id": source_mask_id,
-                    "score": scores[polygon_index] if polygon_index < len(scores) else None,
-                    **({"geometry_smoothing": smoothing} if smoothing else {}),
-                    **({"class": class_metadata} if class_metadata else {}),
-                },
-                points=None,
-                bbox=_polygon_bbox(polygon),
-            )
-            db.add(annotation)
-            created.append(annotation)
+            holes_to_save.append(hole_group if isinstance(hole_group, list) else [])
+            if polygon_index < len(scores):
+                try:
+                    score_values.append(float(scores[polygon_index]))
+                except (TypeError, ValueError):
+                    pass
+        if not polygons_to_save:
+            continue
+        annotation = Annotation(
+            project_id=int(payload["project_id"]),
+            frame_id=frame.id,
+            template_id=template_id,
+            mask_data={
+                "polygons": polygons_to_save,
+                **({"holes": holes_to_save, "hasHoles": True} if any(holes_to_save) else {}),
+                "label": label,
+                "color": color,
+                "source": f"{model_id}_propagation",
+                "propagated_from_frame_id": source_frame.id,
+                "propagated_from_frame_index": source_frame.frame_index,
+                "propagation_seed_key": seed_key,
+                "propagation_seed_signature": seed_signature,
+                "propagation_direction": direction,
+                "source_annotation_id": source_annotation_id,
+                "source_mask_id": source_mask_id,
+                "score": max(score_values) if score_values else None,
+                **({"scores": score_values} if len(score_values) > 1 else {}),
+                **({"geometry_smoothing": smoothing} if smoothing else {}),
+                **({"class": class_metadata} if class_metadata else {}),
+            },
+            points=None,
+            bbox=_polygons_bbox(polygons_to_save),
+        )
+        db.add(annotation)
+        created.append(annotation)
 
     db.commit()
     for annotation in created: