Cover the stored modification format with the demo artwork that leans on it

Author: Keavon

editor/src/messages/portfolio/document/storage_tests/round_trip_tests.rs

@@ -716,6 +716,57 @@ async fn demo_artwork_edit_autosaves_and_round_trips() {
 	editor.active_document_mut().commit_storage_snapshot(&byte_store, true);
 }
 
+/// Manual edits ride a saved document as a folded `VectorModification`, so opening the artworks carrying the most
+/// of them is what proves the stored format still reads and applies. Their Path nodes sit on pen-drawn layers, so
+/// each layer's geometry, curves included, comes from its stored modification alone.
+#[tokio::test]
+async fn demo_artwork_vector_modifications_still_apply() {
+	use graph_craft::document::value::TaggedValue;
+
+	for name in ["red-dress", "isometric-fountain", "valley-of-spires"] {
+		let mut editor = EditorTestUtils::create();
+
+		let data = std::fs::read(format!("../demo-artwork/{name}.graphite")).expect("read demo artwork");
+		editor
+			.handle_message(IngestMessage::Ingest {
+				data,
+				action: IngestAction::Open,
+				mime_type: String::new(),
+				path: Some(format!("{name}.graphite").into()),
+			})
+			.await;
+
+		let document = editor.active_document();
+		let network = &document.network_interface;
+		let path_definition = DefinitionIdentifier::Network("Path".into());
+		let mut path_layers = 0;
+		let mut any_curve = false;
+
+		for layer in document.metadata().all_layers() {
+			let Some(path_node) = NodeGraphLayer::new(layer, network).upstream_visible_node_id_from_name_in_layer(&path_definition) else {
+				continue;
+			};
+			path_layers += 1;
+
+			let stored = network.document_network().nodes.get(&path_node).and_then(|node| node.inputs.get(1)).and_then(|input| input.as_value());
+			let Some(TaggedValue::VectorModification(modification)) = stored else {
+				panic!("{name} layer {layer:?} has a Path node without a stored modification");
+			};
+			assert!(!modification.is_empty(), "{name} layer {layer:?} stored a modification that changes nothing");
+
+			let upstream = document.metadata().vector_modify.get(&path_node).expect("the graph run should capture what reaches the Path node");
+			assert!(upstream.anchor_points().next().is_none(), "{name} layer {layer:?} has geometry upstream of its Path node");
+
+			let geometry = network.compute_modified_vector(layer).expect("a layer with a Path node should have a vector");
+			assert!(geometry.anchor_points().next().is_some(), "{name} layer {layer:?} surfaced no anchors from its stored modification");
+			any_curve |= geometry.segment_iter().any(|(_, segment, ..)| !matches!(segment, kurbo::PathSeg::Line(_)));
+		}
+
+		assert!(path_layers > 0, "{name} has no layers edited through a Path node");
+		assert!(any_curve, "{name} drew no curves from its stored modifications");
+	}
+}
+
 /// The document's single Fill node, as `(network_path, node_id)`.
 fn find_fill_node(document: &DocumentMessageHandler) -> (Vec<graph_craft::document::NodeId>, graph_craft::document::NodeId) {
 	node_paths(&document.network_interface)