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

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

tests/core/graph.test.ts

@@ -1,5 +1,6 @@
 import { describe, expect, it } from 'vitest';
-import { DisconnectCommand, RemoveNodeCommand, SetNodeParamCommand } from '../../src/core/commands/graphCommands';
+import { CommandError } from '../../src/core/commands/Command';
+import { AddNodeCommand, DisconnectCommand, RemoveNodeCommand, SetNodeParamCommand } from '../../src/core/commands/graphCommands';
 import { AddVariableCommand, RemoveVariableCommand, RenameVariableCommand } from '../../src/core/commands/variableCommands';
 import { GraphInterpreter, allNodeDefs, findNode, portsCompatible } from '../../src/core/graph';
 import type { BehaviorAsset } from '../../src/core/model/Asset';
@@ -296,3 +297,16 @@ describe('behavior serialization', () => {
     expect(cleaned.graph.edges.length).toBe(behavior.graph.edges.length);
   });
 });
+
+describe('unknown node types', () => {
+  it('are rejected as a CommandError by execute, not thrown from the constructor', () => {
+    const fixture = makeProject();
+    const behavior = makeBehavior(fixture, 'B');
+    // Building the command must not throw: callers construct it outside the editor's
+    // error handling (`state.execute(new AddNodeCommand(…))`), so a throw here would crash.
+    const command = new AddNodeCommand(behavior.id, 'DoesNotExist', 0, 0);
+    expect(command.label).toBe('Add DoesNotExist');
+    expect(() => command.execute(fixture.project)).toThrow(CommandError);
+    expect(behavior.graph.nodes).toHaveLength(0);
+  });
+});