Let a list hold structs, and read or write variables in bundles

A list item may now be a struct. The depth is bounded in the declaration
rather than by a comment: FieldKind (number|text|boolean|color) says what a
struct field holds, ListItemKind adds struct on top and says what a list
holds, so list -> struct -> primitive is the deepest storable shape and
sameValue stays finite. A struct item renders inline in the List tab, which
is why it needs no path in the slot address.

Four paths silently assumed a list item was a primitive: sameValue compared
items with ===, textOf would have printed [object Object], asListItem turned
a struct into text on Set item and Fill, and Index of used indexOf, which is
reference equality and could never have found a struct.

Tetris now runs on bundles. shapes is 112 {x, y} structs instead of 224 loose
numbers, piece and the candidate are structs, so Next move hands back a whole
candidate and each strand packs only the field it changes, since mergeStruct
leaves the rest standing. Declared behavior ports drop 49 -> 35, the master's
variables 18 -> 13, its graph 84/94 -> 69/76 nodes/edges.

Get variables and Set variables declare their ports from a list of variable
names, the way Pack and Expand already do, so one node can read or write
several at once. Renaming a variable rewires them, because there the port key
is the variable name.

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

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

@@ -1,3 +1,4 @@
+import { sameValue } from '../../../model/Properties';
 import type { NodeDef } from '../../NodeRegistry';
 import { asList, asListItem } from '../../values';
 import { any, list, num } from '../shared';
@@ -10,7 +11,9 @@ export const IndexOf: NodeDef = {
   inputs: [list('list'), any('value')],
   outputs: [num('index')],
   params: [],
-  run: (_ctx, inputs) => ({
-    outputs: { index: asList(inputs.list).indexOf(asListItem(inputs.value)) },
-  }),
+  // Compared by content, not by identity: two equal structs are never the same object.
+  run: (_ctx, inputs) => {
+    const wanted = asListItem(inputs.value);
+    return { outputs: { index: asList(inputs.list).findIndex((item) => sameValue(item, wanted)) } };
+  },
 };