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/variable/GetVariables.ts

@@ -0,0 +1,24 @@
+import type { NodeDef } from '../../NodeRegistry';
+import { GET_VARIABLES } from '../../nested';
+import type { Value } from '../../values';
+
+/**
+ * The plural of Get variable: one output per variable picked, so a graph reading a handful of them
+ * is one node instead of a column of five. The ports are declared on the node, the way Expand
+ * declares the fields of a struct.
+ */
+export const GetVariables: NodeDef = {
+  type: GET_VARIABLES,
+  label: 'Get variables',
+  category: 'variable',
+  description: "Reads several of this behavior's variables at once, one output per variable.",
+  inputs: [],
+  outputs: [],
+  params: [],
+  declaresPorts: 'outputs',
+  run: (ctx, _inputs, _params, def) => {
+    const outputs: Record<string, Value> = {};
+    for (const port of def.outputs) outputs[port.key] = ctx.variables[port.key] ?? null;
+    return { outputs };
+  },
+};

src/core/graph/nodes/variable/SetVariables.ts

@@ -0,0 +1,25 @@
+import type { NodeDef } from '../../NodeRegistry';
+import { SET_VARIABLES } from '../../nested';
+import { writeTyped } from '../../values';
+import { exec } from '../shared';
+
+/**
+ * The plural of Set variable: one input per variable picked. An input left unconnected writes the
+ * value typed on the node, exactly as it does on the singular node – the node writes every variable
+ * it lists, every time it runs.
+ */
+export const SetVariables: NodeDef = {
+  type: SET_VARIABLES,
+  label: 'Set variables',
+  category: 'variable',
+  description: "Writes several of this behavior's variables at once, one input per variable.",
+  inputs: [exec()],
+  outputs: [exec()],
+  params: [],
+  declaresPorts: 'inputs',
+  run: (ctx, inputs, _params, def) => {
+    for (const port of def.inputs)
+      if (port.type !== 'exec') writeTyped(ctx.variables, port.key, inputs[port.key]);
+    return { next: 'exec' };
+  },
+};