Fix findUsages/undo/node-lookup bugs, split Viewport and Editor, share command and inspector helpers

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/editor/inspector/nodeSection.ts

@@ -2,12 +2,12 @@ import { RemoveNodeCommand, SetNodeParamCommand } from '../../core/commands/grap
 import { edgesInto, type GraphNode, inlineInputDef, inlineInputs, nodeDef } from '../../core/graph';
 import type { Asset } from '../../core/model/Asset';
 import { isPlaceableType } from '../../core/model/AssetTypes';
-import type { PropertyValue } from '../../core/model/Properties';
 import { findAsset, type Project } from '../../core/model/Project';
 import type { PropertyDef } from '../../core/properties/PropertySchema';
 import { Button, Label } from '../../ui';
 import { createFieldRow, type FieldHandlers } from './fieldFactory';
 import { addGap, addNote, addTitle, type InspectorHost } from './host';
+import { previewingHandlers } from './previewHandlers';
 
 /** Structure-defining facts of a node selection: type, connected inputs, declared variables. */
 export function nodeSignature(project: Project, assetId: string, nodeId: string): string {
@@ -83,30 +83,13 @@ function resolveParamDef(project: Project, param: PropertyDef, asset: Asset): Pr
 
 /** Previews straight into the node's params; the command records the value from before the preview. */
 function paramHandlers(host: InspectorHost, assetId: string, nodeId: string, key: string): FieldHandlers {
-  let original: PropertyValue | undefined;
-  let had = false;
-  return {
-    onInput: (value) => {
-      const target = currentNode(host.state.project, assetId, nodeId);
-      if (!target) return;
-      if (original === undefined) {
-        had = target.params[key] !== undefined;
-        original = target.params[key] ?? value;
-      }
-      target.params[key] = value;
-      host.state.preview();
-    },
-    onChange: (value) => {
-      const target = currentNode(host.state.project, assetId, nodeId);
-      if (!target) return;
-      if (original !== undefined) {
-        if (had) target.params[key] = original;
-        else delete target.params[key];
-      }
-      original = undefined;
-      host.state.execute(new SetNodeParamCommand(assetId, nodeId, key, value));
-    },
-  };
+  return previewingHandlers<GraphNode>(host, {
+    target: () => currentNode(host.state.project, assetId, nodeId),
+    read: (node) => node.params[key],
+    write: (node, value) => (node.params[key] = value),
+    remove: (node) => delete node.params[key],
+    commit: (value) => new SetNodeParamCommand(assetId, nodeId, key, value),
+  });
 }
 
 function currentNode(project: Project, assetId: string, nodeId: string): GraphNode | undefined {