diff --git a/editor/src/messages/portfolio/document/utility_types/network_interface.rs b/editor/src/messages/portfolio/document/utility_types/network_interface.rs
index 2ea051fb46..c452de2a31 100644
--- a/editor/src/messages/portfolio/document/utility_types/network_interface.rs
+++ b/editor/src/messages/portfolio/document/utility_types/network_interface.rs
@@ -1,7 +1,11 @@
+#[cfg(test)]
+mod characterization_tests;
 mod deserialization;
 mod memo_network;
 mod resolved_types;
 pub mod storage_metadata;
+#[cfg(test)]
+mod validation;
 
 use super::document_metadata::{DocumentMetadata, LayerNodeIdentifier, NodeRelations};
 use super::misc::PTZ;
diff --git a/editor/src/messages/portfolio/document/utility_types/network_interface/characterization_tests.rs b/editor/src/messages/portfolio/document/utility_types/network_interface/characterization_tests.rs
new file mode 100644
index 0000000000..40ef78ad4f
--- /dev/null
+++ b/editor/src/messages/portfolio/document/utility_types/network_interface/characterization_tests.rs
@@ -0,0 +1,343 @@
+use super::{InputConnector, OutputConnector, Previewing, RootNode, TransactionStatus};
+use crate::test_utils::test_prelude::*;
+use graph_craft::document::NodeInput;
+use graph_craft::document::value::TaggedValue;
+use graphene_std::uuid::NodeId;
+
+fn assert_invariants(editor: &EditorTestUtils, context: &str) {
+	let violations = editor.active_document().network_interface.validate_invariants();
+	assert!(violations.is_empty(), "Invariant violations {context}:\n{}", violations.join("\n"));
+}
+
+fn rectangle_definition() -> DefinitionIdentifier {
+	DefinitionIdentifier::ProtoNode(graphene_std::vector::generator_nodes::rectangle::IDENTIFIER)
+}
+
+fn new_artboard_message(id: NodeId) -> GraphOperationMessage {
+	GraphOperationMessage::NewArtboard {
+		id,
+		location: DVec2::ZERO,
+		dimensions: DVec2::new(400., 300.),
+		background: Color::WHITE,
+		clip: false,
+	}
+}
+
+#[tokio::test]
+async fn invariants_hold_through_basic_editing_flow() {
+	let mut editor = EditorTestUtils::create();
+
+	// This test covers the interface's structural invariants. The storage dual-write is out of its scope and asserted by the storage round-trip tests.
+	editor.editor.handle_message(PreferencesMessage::ValidateStorageRoundTrip { enabled: false });
+
+	editor.new_document().await;
+	assert_invariants(&editor, "after opening a new document");
+
+	editor.handle_message(new_artboard_message(NodeId::new())).await;
+	assert_invariants(&editor, "after creating an artboard");
+
+	let rectangle = editor.create_node_by_name(rectangle_definition()).await;
+	assert_invariants(&editor, "after creating a node");
+
+	editor.handle_message(NodeGraphMessage::SelectedNodesSet { nodes: vec![rectangle] }).await;
+	editor.handle_message(NodeGraphMessage::DeleteSelectedNodes { delete_children: true }).await;
+	assert_invariants(&editor, "after deleting the node");
+
+	editor.handle_message(DocumentMessage::Undo).await;
+	assert_invariants(&editor, "after undo");
+
+	editor.handle_message(DocumentMessage::Redo).await;
+	assert_invariants(&editor, "after redo");
+}
+
+#[tokio::test]
+async fn deleting_a_node_with_children_prunes_them_from_the_selection() {
+	let mut editor = EditorTestUtils::create();
+	editor.new_document().await;
+
+	let parent = editor.create_node_by_name(rectangle_definition()).await;
+	let child = editor.create_node_by_name(rectangle_definition()).await;
+
+	let network_interface = &mut editor.active_document_mut().network_interface;
+	assert!(network_interface.number_of_inputs(&parent, &[]) >= 2, "Test needs a secondary input to wire the child into");
+
+	// Wire the child into the parent's secondary input so it is a sole dependent, then select both and delete only the parent
+	network_interface.set_input(&InputConnector::node(parent, 1), NodeInput::node(child, 0), &[]);
+	network_interface.selected_nodes_mut(&[]).unwrap().set_selected_nodes(vec![parent, child]);
+	network_interface.delete_nodes(vec![parent], true, &[]);
+
+	assert!(network_interface.document_network().nodes.is_empty(), "Both the parent and its sole-dependent child should be deleted");
+	let remaining_selection = network_interface.selected_nodes_mut(&[]).unwrap().selected_nodes().copied().collect::<Vec<_>>();
+	assert!(remaining_selection.is_empty(), "Deleted children should be pruned from the selection, found {remaining_selection:?}");
+
+	assert_invariants(&editor, "after deleting a node with children");
+}
+
+#[tokio::test]
+async fn cyclic_connection_is_rejected_without_side_effects() {
+	let mut editor = EditorTestUtils::create();
+	editor.new_document().await;
+
+	let a = editor.create_node_by_name(rectangle_definition()).await;
+	let b = editor.create_node_by_name(rectangle_definition()).await;
+
+	let network_interface = &mut editor.active_document_mut().network_interface;
+	network_interface.set_input(&InputConnector::node(a, 1), NodeInput::node(b, 0), &[]);
+
+	// Attempt to complete a cycle inside a transaction: the edit must be rejected without marking the transaction as modified
+	network_interface.start_transaction();
+	let input_before = network_interface.input_from_connector(&InputConnector::node(b, 1), &[]).cloned();
+	network_interface.set_input(&InputConnector::node(b, 1), NodeInput::node(a, 0), &[]);
+
+	let input_after = network_interface.input_from_connector(&InputConnector::node(b, 1), &[]).cloned();
+	assert_eq!(input_before, input_after, "A rejected cyclic connection should leave the input unchanged");
+	assert_eq!(
+		network_interface.transaction_status(),
+		TransactionStatus::Started,
+		"A rejected cyclic connection should not mark the transaction as modified"
+	);
+	network_interface.finish_transaction();
+
+	assert_invariants(&editor, "after rejecting a cyclic connection");
+}
+
+#[tokio::test]
+async fn toggling_preview_on_a_disconnected_export() {
+	let mut editor = EditorTestUtils::create();
+	editor.new_document().await;
+
+	let node = editor.create_node_by_name(rectangle_definition()).await;
+
+	let network_interface = &mut editor.active_document_mut().network_interface;
+	network_interface.disconnect_input(&InputConnector::Export(0), &[]);
+
+	// Previewing a node while the export is disconnected is a preview with nothing to restore
+	network_interface.toggle_preview(node, &[]);
+	assert_eq!(network_interface.previewing(&[]), Previewing::Yes { root_node_to_restore: None });
+	let export = network_interface.input_from_connector(&InputConnector::Export(0), &[]);
+	assert_eq!(export.and_then(|input| input.as_node()), Some(node), "The previewed node should be wired to the export");
+
+	// Ending the preview restores the disconnected export
+	network_interface.toggle_preview(node, &[]);
+	assert_eq!(network_interface.previewing(&[]), Previewing::No);
+	let export = network_interface.input_from_connector(&InputConnector::Export(0), &[]);
+	assert!(export.is_some_and(|input| input.as_node().is_none()), "Ending the preview should disconnect the export again");
+
+	assert_invariants(&editor, "after toggling preview twice");
+}
+
+#[tokio::test]
+async fn artboard_identity_is_independent_of_scene_connectivity() {
+	let mut editor = EditorTestUtils::create();
+	editor.new_document().await;
+
+	let artboard = NodeId::new();
+	editor.handle_message(new_artboard_message(artboard)).await;
+
+	let network_interface = &mut editor.active_document_mut().network_interface;
+	assert!(network_interface.is_artboard(&artboard, &[]));
+	assert!(!network_interface.all_artboards().is_empty());
+
+	// Disconnecting the artboard from the export keeps its identity but removes it from the scene's artboards
+	network_interface.disconnect_input(&InputConnector::Export(0), &[]);
+	assert!(network_interface.is_artboard(&artboard, &[]), "Artboard identity should survive disconnection");
+	assert!(network_interface.all_artboards().is_empty(), "Disconnected artboards should not count as scene artboards");
+
+	assert_invariants(&editor, "after disconnecting an artboard");
+}
+
+#[tokio::test]
+async fn selection_history_is_not_serialized() {
+	let mut editor = EditorTestUtils::create();
+	editor.new_document().await;
+
+	let node = editor.create_node_by_name(rectangle_definition()).await;
+	editor.handle_message(NodeGraphMessage::SelectedNodesSet { nodes: vec![node] }).await;
+
+	let serialized = editor.active_document().serialize_document();
+	assert!(!serialized.contains("selection_undo_history"), "Selection history should not be persisted into saved documents");
+	assert!(!serialized.contains("selection_redo_history"), "Selection history should not be persisted into saved documents");
+}
+
+fn merge_definition() -> DefinitionIdentifier {
+	DefinitionIdentifier::Network("Merge".to_string())
+}
+
+async fn create_node_at(editor: &mut EditorTestUtils, node_type: DefinitionIdentifier, x: i32, y: i32) -> NodeId {
+	let node_id = NodeId::new();
+	editor
+		.handle_message(NodeGraphMessage::CreateNodeFromContextMenu {
+			node_id: Some(node_id),
+			node_type,
+			xy: Some((x, y)),
+			add_transaction: true,
+		})
+		.await;
+	node_id
+}
+
+#[tokio::test]
+async fn layer_stacking_follows_wiring() {
+	let mut editor = EditorTestUtils::create();
+	editor.new_document().await;
+
+	let upper = create_node_at(&mut editor, merge_definition(), 20, 10).await;
+	let lower = create_node_at(&mut editor, merge_definition(), 20, 16).await;
+
+	let network_interface = &mut editor.active_document_mut().network_interface;
+	network_interface.set_to_node_or_layer(&upper, &[], true);
+	network_interface.set_to_node_or_layer(&lower, &[], true);
+	assert!(network_interface.is_layer(&upper, &[]) && network_interface.is_layer(&lower, &[]));
+	assert!(network_interface.is_absolute(&lower, &[]));
+
+	// Wiring a layer into the bottom input of another layer converts it to stack positioning at its current visual spot
+	let lower_position_before = network_interface.position(&lower, &[]).expect("Lower layer should have a position");
+	network_interface.create_wire(&OutputConnector::node(lower, 0), &InputConnector::node(upper, 0), &[]);
+	assert!(network_interface.is_stack(&lower, &[]), "A layer feeding the bottom of a layer should be stack positioned");
+	let stacked_position = network_interface.position(&lower, &[]).expect("Stacked layer should have a position");
+	assert_eq!(stacked_position.y, lower_position_before.y, "Stacking should preserve the layer's vertical position");
+
+	// Disconnecting converts the layer back to absolute positioning without moving it
+	network_interface.disconnect_input(&InputConnector::node(upper, 0), &[]);
+	assert!(network_interface.is_absolute(&lower, &[]), "A disconnected stack layer should return to absolute positioning");
+	assert_eq!(network_interface.position(&lower, &[]), Some(stacked_position), "Unstacking should not move the layer");
+
+	assert_invariants(&editor, "after stacking and unstacking a layer");
+}
+
+#[tokio::test]
+async fn chain_membership_follows_wiring() {
+	let mut editor = EditorTestUtils::create();
+	editor.new_document().await;
+
+	let layer = create_node_at(&mut editor, merge_definition(), 20, 10).await;
+	let node = create_node_at(&mut editor, rectangle_definition(), 15, 10).await;
+
+	let network_interface = &mut editor.active_document_mut().network_interface;
+	network_interface.set_to_node_or_layer(&layer, &[], true);
+
+	// A node wired into a layer's secondary input from the same row, within chain distance, joins the chain
+	network_interface.create_wire(&OutputConnector::node(node, 0), &InputConnector::node(layer, 1), &[]);
+	assert!(
+		network_interface.is_chain(&node, &[]),
+		"A node feeding a layer's secondary input from chain range should become a chain node"
+	);
+
+	// Disconnecting breaks the chain and the node becomes absolute at its chain spot
+	let chained_y = network_interface.position(&node, &[]).expect("Chained node should have a position").y;
+	network_interface.disconnect_input(&InputConnector::node(layer, 1), &[]);
+	assert!(!network_interface.is_chain(&node, &[]), "Disconnecting should break the chain");
+	assert!(network_interface.is_absolute(&node, &[]));
+	assert_eq!(network_interface.position(&node, &[]).map(|position| position.y), Some(chained_y));
+
+	assert_invariants(&editor, "after forming and breaking a chain");
+}
+
+#[tokio::test]
+async fn move_layer_to_stack_builds_the_layer_stack() {
+	let mut editor = EditorTestUtils::create();
+	editor.new_document().await;
+
+	let artboard = NodeId::new();
+	editor.handle_message(new_artboard_message(artboard)).await;
+
+	let first = create_node_at(&mut editor, merge_definition(), 0, 30).await;
+	let second = create_node_at(&mut editor, merge_definition(), 0, 40).await;
+
+	let network_interface = &mut editor.active_document_mut().network_interface;
+	network_interface.set_to_node_or_layer(&first, &[], true);
+	network_interface.set_to_node_or_layer(&second, &[], true);
+
+	let artboard_layer = LayerNodeIdentifier::new(artboard, network_interface);
+	let first_layer = LayerNodeIdentifier::new(first, network_interface);
+	let second_layer = LayerNodeIdentifier::new(second, network_interface);
+
+	network_interface.move_layer_to_stack(first_layer, artboard_layer, 0, &[]);
+	let children = artboard_layer.children(network_interface.document_metadata()).collect::<Vec<_>>();
+	assert_eq!(children, vec![first_layer], "The first moved layer should become the artboard's only child");
+
+	network_interface.move_layer_to_stack(second_layer, artboard_layer, 1, &[]);
+	let children = artboard_layer.children(network_interface.document_metadata()).collect::<Vec<_>>();
+	assert_eq!(children, vec![first_layer, second_layer], "The second layer should be inserted below the first");
+	assert!(network_interface.is_stack(&second, &[]), "A layer below a sibling should be stack positioned");
+
+	assert_invariants(&editor, "after moving two layers into an artboard");
+}
+
+#[tokio::test]
+async fn signature_edits_keep_parallel_metadata_in_sync() {
+	let mut editor = EditorTestUtils::create();
+	editor.new_document().await;
+
+	let merge = create_node_at(&mut editor, merge_definition(), 0, 0).await;
+	let path = vec![merge];
+
+	let network_interface = &mut editor.active_document_mut().network_interface;
+	let initial_imports = network_interface.number_of_imports(&path);
+	let initial_exports = network_interface.number_of_exports(&path);
+
+	network_interface.add_import(TaggedValue::None, true, -1, "Extra import", "", &path);
+	assert_eq!(network_interface.number_of_imports(&path), initial_imports + 1);
+	assert_invariants(&editor, "after adding an import");
+
+	let network_interface = &mut editor.active_document_mut().network_interface;
+	network_interface.add_export(TaggedValue::None, -1, "Extra export", &path);
+	assert_eq!(network_interface.number_of_exports(&path), initial_exports + 1);
+	assert_invariants(&editor, "after adding an export");
+
+	let network_interface = &mut editor.active_document_mut().network_interface;
+	network_interface.reorder_import(initial_imports, 0, &path);
+	assert_invariants(&editor, "after reordering an import to the front");
+
+	let network_interface = &mut editor.active_document_mut().network_interface;
+	network_interface.remove_import(0, &path);
+	assert_eq!(network_interface.number_of_imports(&path), initial_imports);
+	assert_invariants(&editor, "after removing the reordered import");
+
+	let network_interface = &mut editor.active_document_mut().network_interface;
+	network_interface.remove_export(initial_exports, &path);
+	assert_eq!(network_interface.number_of_exports(&path), initial_exports);
+	assert_invariants(&editor, "after removing the added export");
+}
+
+#[tokio::test]
+async fn toggle_preview_transitions_with_a_connected_export() {
+	let mut editor = EditorTestUtils::create();
+	editor.new_document().await;
+
+	let artboard = NodeId::new();
+	editor.handle_message(new_artboard_message(artboard)).await;
+	let node = create_node_at(&mut editor, rectangle_definition(), 0, 20).await;
+
+	let network_interface = &mut editor.active_document_mut().network_interface;
+	let export_node = |network_interface: &super::NodeNetworkInterface| network_interface.input_from_connector(&InputConnector::Export(0), &[]).and_then(|input| input.as_node());
+	assert_eq!(export_node(network_interface), Some(artboard));
+
+	// Previewing a node remembers the artboard as the connection to restore
+	network_interface.toggle_preview(node, &[]);
+	assert_eq!(export_node(network_interface), Some(node));
+	assert_eq!(
+		network_interface.previewing(&[]),
+		Previewing::Yes {
+			root_node_to_restore: Some(RootNode { node_id: artboard, output_index: 0 })
+		}
+	);
+
+	// Toggling the previewed node again restores the artboard connection
+	network_interface.toggle_preview(node, &[]);
+	assert_eq!(export_node(network_interface), Some(artboard));
+	assert_eq!(network_interface.previewing(&[]), Previewing::No);
+
+	// Toggling the restore node while previewing promotes it to the export with nothing left to restore
+	network_interface.toggle_preview(node, &[]);
+	network_interface.toggle_preview(artboard, &[]);
+	assert_eq!(export_node(network_interface), Some(artboard));
+	assert_eq!(network_interface.previewing(&[]), Previewing::Yes { root_node_to_restore: None });
+
+	// Toggling it once more ends the preview by disconnecting the export entirely
+	network_interface.toggle_preview(artboard, &[]);
+	assert_eq!(export_node(network_interface), None);
+	assert_eq!(network_interface.previewing(&[]), Previewing::No);
+
+	assert_invariants(&editor, "after cycling through the preview states");
+}
diff --git a/editor/src/messages/portfolio/document/utility_types/network_interface/validation.rs b/editor/src/messages/portfolio/document/utility_types/network_interface/validation.rs
new file mode 100644
index 0000000000..60d03969d9
--- /dev/null
+++ b/editor/src/messages/portfolio/document/utility_types/network_interface/validation.rs
@@ -0,0 +1,96 @@
+use super::{NodeNetworkInterface, NodeNetworkMetadata};
+use graph_craft::document::{DocumentNodeImplementation, NodeId, NodeInput, NodeNetwork};
+
+impl NodeNetworkInterface {
+	/// Checks the structural invariants between the document network and its parallel metadata tree at every nesting level.
+	/// Returns a description of each violation found, or an empty list if the interface is internally consistent.
+	/// Intended for tests and debugging; violations indicate a desync bug in the mutation methods, not a user error.
+	// O(nodes + wires) summed across all nesting levels, plus an acyclicity walk per network
+	pub fn validate_invariants(&self) -> Vec<String> {
+		let mut violations = Vec::new();
+		validate_network(self.document_network(), &self.network_metadata, &mut Vec::new(), 0, &mut violations);
+		violations
+	}
+}
+
+fn validate_network(network: &NodeNetwork, network_metadata: &NodeNetworkMetadata, path: &mut Vec<NodeId>, import_count: usize, violations: &mut Vec<String>) {
+	let node_metadata = &network_metadata.persistent_metadata.node_metadata;
+
+	// The network and its metadata tree must contain exactly the same set of nodes
+	for node_id in network.nodes.keys() {
+		if !node_metadata.contains_key(node_id) {
+			violations.push(format!("Node {node_id} in network {path:?} has no metadata entry"));
+		}
+	}
+	for node_id in node_metadata.keys() {
+		if !network.nodes.contains_key(node_id) {
+			violations.push(format!("Metadata entry {node_id} in network {path:?} has no corresponding node"));
+		}
+	}
+
+	// Every wire must reference an existing endpoint within this network
+	let validate_input = |input: &NodeInput, location: &str, violations: &mut Vec<String>| match input {
+		NodeInput::Node { node_id, output_index, .. } => match network.nodes.get(node_id) {
+			None => violations.push(format!("{location} in network {path:?} references nonexistent node {node_id}")),
+			Some(target) if *output_index >= target.implementation.output_count() => {
+				violations.push(format!("{location} in network {path:?} references nonexistent output {output_index} of node {node_id}"));
+			}
+			_ => {}
+		},
+		NodeInput::Import { import_index, .. } if *import_index >= import_count => {
+			violations.push(format!("{location} in network {path:?} references nonexistent import {import_index} of {import_count}"));
+		}
+		_ => {}
+	};
+
+	for (node_id, node) in &network.nodes {
+		for input in &node.inputs {
+			validate_input(input, &format!("Input of node {node_id}"), violations);
+		}
+	}
+	for (export_index, export) in network.exports.iter().enumerate() {
+		validate_input(export, &format!("Export {export_index}"), violations);
+	}
+
+	if !network.is_acyclic() {
+		violations.push(format!("Network {path:?} contains a cycle"));
+	}
+
+	for (node_id, node) in &network.nodes {
+		let Some(metadata) = node_metadata.get(node_id) else { continue };
+		let persistent = &metadata.persistent_metadata;
+
+		// Input metadata is a parallel array to the node's inputs and the lengths must stay in sync
+		if persistent.input_metadata.len() != node.inputs.len() {
+			violations.push(format!(
+				"Node {node_id} in network {path:?} has {} inputs but {} input metadata entries",
+				node.inputs.len(),
+				persistent.input_metadata.len()
+			));
+		}
+
+		// Nested network metadata must exist exactly for nodes implemented as networks
+		match (&node.implementation, &persistent.network_metadata) {
+			(DocumentNodeImplementation::Network(nested_network), Some(nested_metadata)) => {
+				if persistent.output_names.len() != nested_network.exports.len() {
+					violations.push(format!(
+						"Node {node_id} in network {path:?} has {} exports but {} output names",
+						nested_network.exports.len(),
+						persistent.output_names.len()
+					));
+				}
+
+				path.push(*node_id);
+				validate_network(nested_network, nested_metadata, path, node.inputs.len(), violations);
+				path.pop();
+			}
+			(DocumentNodeImplementation::Network(_), None) => {
+				violations.push(format!("Network node {node_id} in network {path:?} is missing its nested network metadata"));
+			}
+			(_, Some(_)) => {
+				violations.push(format!("Non-network node {node_id} in network {path:?} has nested network metadata"));
+			}
+			(_, None) => {}
+		}
+	}
+}
diff --git a/editor/src/test_utils.rs b/editor/src/test_utils.rs
index 84f67f0418..12bcfe45bd 100644
--- a/editor/src/test_utils.rs
+++ b/editor/src/test_utils.rs
@@ -77,6 +77,10 @@ impl EditorTestUtils {
 			panic!("Failed to evaluate graph: {e}");
 		}
 
+		// Sweep the network interface's structural invariants so any desync fails at the message that caused it
+		let violations = self.active_document().network_interface.validate_invariants();
+		assert!(violations.is_empty(), "Network interface invariant violations:\n{}", violations.join("\n"));
+
 		frontend_messages_from_msg
 	}