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/routers/ai.py

@@ -196,6 +196,17 @@ 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 _polygon_area(polygon: list[list[float]]) -> float:
     if len(polygon) < 3:
         return 0.0
@@ -805,32 +816,44 @@ def propagate(
             result_polygons = frame_result.get("polygons") or []
             result_holes = frame_result.get("holes") or []
             scores = frame_result.get("scores") or []
+            polygons_to_save: list[list[list[float]]] = []
+            holes_to_save: list[list[list[list[float]]]] = []
+            score_values: list[float] = []
             for polygon_index, polygon in enumerate(result_polygons):
                 if len(polygon) < 3:
                     continue
-                polygon_to_save = _smooth_polygon(polygon, smoothing) if smoothing else polygon
+                polygons_to_save.append(_smooth_polygon(polygon, smoothing) if smoothing else 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=payload.project_id,
-                    frame_id=frame.id,
-                    template_id=template_id,
-                    mask_data={
-                        "polygons": [polygon_to_save],
-                        **({"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,
-                        "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_to_save),
-                )
-                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=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,
+                    "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: