Let a value be a bundle of named fields

PropertyValue was number | string | boolean | list. A struct joins it, which
costs two things the typechecker found rather than I did.

An object on a data edge used to mean a live entity, so asEntity would have
taken a struct for one and asString would have read .name off it. EntityHandle
now carries a symbol brand – a symbol so no field name can impersonate it, and
it never serializes, which suits a thing that exists only while the game runs.
It is built in exactly one place.

String(value) would have written a struct as [object Object] at 39 call sites.
They go through textOf(), which is identical for primitives.

normalizeGraph dropped everything but primitives from node params, so the List
node lost its value on every save ([3,1,4] round-tripped to undefined).
Variables were spared: they have a schema, params have none.

src/editor/graph/GraphCanvas.ts

@@ -1,4 +1,5 @@
 import { Container, type FederatedPointerEvent, type FederatedWheelEvent, Graphics, Text } from 'pixi.js';
+import { textOf } from '../../core/model/Properties';
 import type { Command } from '../../core/commands/Command';
 import { CompoundCommand } from '../../core/commands/CompoundCommand';
 import {
@@ -380,7 +381,7 @@ export class GraphCanvas extends Widget {
   /** Selecting the asset is what opens it: the graph tab follows the selection. */
   private openCalledBehavior(node: GraphNode): boolean {
     if (node.type !== RUN_BEHAVIOR) return false;
-    const id = String(node.params[BEHAVIOR_PARAM] ?? '');
+    const id = textOf(node.params[BEHAVIOR_PARAM] ?? '');
     const asset = id ? findAsset(this.state.project, id) : undefined;
     if (asset?.type !== 'behavior') return false;
     this.state.select({ kind: 'asset', assetId: id });

src/editor/graph/NodeView.ts

@@ -14,7 +14,7 @@ import {
 } from '../../core/graph';
 import type { BehaviorAsset } from '../../core/model/Asset';
 import type { Project } from '../../core/model/Project';
-import { isList, type PropertyValue } from '../../core/model/Properties';
+import { isList, type PropertyValue, textOf } from '../../core/model/Properties';
 import { assetRefLabel } from '../../core/properties/assetRef';
 import type { PropertyDef } from '../../core/properties/PropertySchema';
 import { formatNumber, Theme, textStyle, type TextStyleToken, truncate, Widget } from '../../ui';
@@ -60,6 +60,8 @@ export function portColor(type: PortType): number {
       return c.portObject;
     case 'list':
       return c.portList;
+    case 'struct':
+      return c.portStruct;
     case 'any':
       return c.portAny;
   }
@@ -296,8 +298,8 @@ function formatParam(
   project: Project | null,
 ): string {
   if (value === undefined || value === '') return '—';
-  if (param.kind === 'key') return keyLabel(String(value));
-  if (param.kind === 'asset') return assetRefLabel(project, String(value));
+  if (param.kind === 'key') return keyLabel(textOf(value));
+  if (param.kind === 'asset') return assetRefLabel(project, textOf(value));
   if (
     param.kind === 'enum' &&
     param.key === 'variable' &&