feat: per-class exemplar preview, class hide toggle, container NMS flag (REQ-182, REQ-183, REQ-184)

backend/preview.py

@@ -72,6 +72,10 @@ def preview_frame(
     allowed_classes_set = {c.strip().lower() for c in target_class_names} if target_class_names else None
     per_class = _parse_class_params(class_params)
     predict_conf = min([threshold] + [v["threshold"] for v in per_class.values() if "threshold" in v])
+    # REQ-184: classes marked container keep boxes that sit inside them. The
+    # prompt pass below still sees prompt-index ids, so it gets the index-aligned set.
+    container_ids = {c["class_id"] for c in project["classes"] if c.get("container")}
+    prompt_container_ids = {i for i, c in enumerate(sam3_target_classes) if c.get("container")}
 
     all_raw_detections = []
 
@@ -153,6 +157,7 @@ def preview_frame(
             thresholds=thr_list,
             iou_by_class=dict(enumerate(iou_list)) if iou_list else None,
             min_box_fracs=mb_list,
+            container_ids=prompt_container_ids,
         )
         if not res.error and res.detections:
             for det in res.detections:
@@ -169,7 +174,8 @@ def preview_frame(
         and "iou_threshold" in per_class[c["name"].strip().lower()]
     }
     kept = labeling.deduplicate(all_raw_detections, iou_threshold=iou_threshold,
-                                iou_by_class=iou_by_class_proj or None)
+                                iou_by_class=iou_by_class_proj or None,
+                                container_ids=container_ids)
     items = []
     for det in kept:
         if project["label_type"] == "bbox" or det.mask is None: