Sync strict polygon dataset importer

README.md

@@ -78,6 +78,19 @@ satellites, sensors, resolutions, and fusion states.
 
 See [docs/dataset_standard.md](docs/dataset_standard.md).
 
+For the SAMPoly-style polygon head, the dataset gate is stricter: only real
+mask or polygon annotations enter the main polygon training set. Bbox-only
+labels are rejected because rectangles cannot supervise true boundaries,
+vertices, or polygon ordering. The polygon-ready layout is:
+
+```text
+images/{train,val,test}
+masks/{train,val,test}
+manifests/accepted_polygon_samples.jsonl
+manifests/rejected_polygon_samples.jsonl
+dataset_card.json
+```
+
 ## Key Scripts
 
 - `scripts/build_marine_feature_dataset.py`: scan local or server-side data roots
@@ -86,6 +99,8 @@ See [docs/dataset_standard.md](docs/dataset_standard.md).
   normalized `hf://` manifest references without downloading full repositories.
 - `scripts/import_quality_gated_hf_dataset.py`: import only HF samples that pass
   explicit quality adapters; unverified samples stay in review/reject manifests.
+- `scripts/prepare_polygon_dataset.py`: build the strict mask/polygon dataset
+  for SAMPoly-style training and reject bbox-only samples.
 - `scripts/compose_task_profile.py`: compose Markdown capability cards into a
   JSON task profile.
 - `scripts/infer_whole_scene.py`: sliding-window whole-scene inference with