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/nested.ts

@@ -6,9 +6,20 @@ import { nodeDef, type NodeDef, type PortDef } from './NodeRegistry';
 export const BEHAVIOR_START = 'BehaviorStart';
 export const BEHAVIOR_END = 'BehaviorEnd';
 export const RUN_BEHAVIOR = 'RunBehavior';
+export const GET_VARIABLES = 'GetVariables';
+export const SET_VARIABLES = 'SetVariables';
 
 export const BEHAVIOR_PARAM = 'behavior';
 
+/**
+ * Nodes whose declared ports are not names of their own but variables of the behavior around them.
+ * Renaming a variable therefore has to reach them, and the inspector picks their ports from a list
+ * instead of letting them be typed.
+ */
+export function declaresVariablePorts(type: string): boolean {
+  return type === GET_VARIABLES || type === SET_VARIABLES;
+}
+
 /** Identifier-like, and not `exec`: that key belongs to the fixed flow port of every terminal node. */
 export function isValidPortName(name: string): boolean {
   return /^[A-Za-z_][A-Za-z0-9_]*$/.test(name) && name !== 'exec';