Let a variable hold a list

A variable could only be a number, a text or a yes/no, so every set of values had
to be smuggled through a string - which is where Tetris got its unreadable
"03066326048763714" colours from. A list is now a value of its own, with an item
kind (number, text, yes/no, colour) that decides how the inspector reads the one
comma-separated line it is typed as, and eight nodes to work with: List, Fill,
Count, Item at, Set item, Sub list, Join lists, Index of.

Two traps came with it. An array is typeof 'object', so every place that told a
value from an entity had to learn the difference, or a list would have been
passed around as a game object. And a value was compared by identity in three
places - with lists that marks everything as an overridden property after each
reload, so those comparisons now compare contents.

There is no list of objects: a list is written to the project file and an object
is a live handle that no reload survives. A set of objects stays a list of names.

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

src/core/graph/nodes/data/ItemAt.ts

@@ -0,0 +1,18 @@
+import type { NodeDef } from '../../NodeRegistry';
+import { asList, asNumber } from '../../values';
+import { any, list, num } from '../shared';
+
+export const ItemAt: NodeDef = {
+  type: 'ItemAt',
+  label: 'Item at',
+  category: 'data',
+  description: 'The item at an index, counting from 0. Out of range gives 0.',
+  inputs: [list('list'), num('index')],
+  outputs: [any('item')],
+  run: (_ctx, inputs) => {
+    const items = asList(inputs.list);
+    const i = Math.floor(asNumber(inputs.index));
+    return { outputs: { item: items[i] ?? 0 } };
+  },
+  params: [],
+};