added reference png export

python_app/storage/npz/store.py

@@ -411,5 +411,15 @@ class NpzStore(StoreApi):
         """Return directory for set kind and radar key."""
         return self._root_dir / kind / radar_key
 
+    def preview_png_dir(self, kind: str, set_name: str, radar_key: str) -> Path:
+        """Return directory for preview PNGs of one set/radar variant.
+
+        Lives under ``preview_png/`` inside the store so saved graphs sit next to
+        the data they describe, grouped by set name then radar variant. The set
+        name is operator-supplied, so it is sanitized; ``radar_key`` is already
+        filesystem-safe by construction.
+        """
+        return self._root_dir / "preview_png" / kind / sanitize_path_component(set_name) / radar_key
+
 
 __all__ = ["NpzStore", "radar_key_from_config"]