Persist map selections as derived datasets

backend/README.md

@@ -580,12 +580,19 @@ builder, live provider fetching or new analysis behavior.
 read-only EPSG:4326 bbox query against persisted PostGIS `vector_features` and
 returns a canonical-envelope GeoJSON FeatureCollection. It is intended for the
 Map workspace area-extract flow and does not create derived datasets or export
-records.
+records by itself.
+
+`POST /api/v1/projects/{project_id}/datasets/{dataset_id}/vector/select/derive`
+uses the same persisted `vector_features` selection but writes the result as a
+new derived vector dataset. The created dataset uses
+`source="operation:selection"`, `source_name="map_selection"` and
+`derived_from_dataset_id` for source provenance, stores a GeoJSON artifact and
+indexes its features back into `vector_features` for later QA/QC and analysis.
 
 `POST /api/v1/exports/geojson` with `export_kind="vector_selection"` persists
 the same bbox-selected FeatureCollection as a normal export record with
 `export_type="vector_selection_geojson"`. This creates a handoff artifact only;
-it does not create a derived dataset or mutate `vector_features`.
+it does not create a derived dataset.
 
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