Give the graph a loop, and build Tetris with it

A Tetris example project needs to draw 200 board cells and scan rows
for a full line. Neither is expressible without iteration, so the node
system gets a Repeat node plus the missing text side: Substring, Find
text and To number. The interpreter drops its data cache once per
round -- otherwise every round would recompute with the first round's
values.

Object by name takes its name as an input now, not just as a setting;
addressing "c" + index is impossible otherwise. An unconnected input
reads the stored setting, so saved projects are untouched.

The board itself is a 200-character text, "." for empty. That makes
both operations of Tetris a single expression instead of a loop, and
each frame attempts exactly one move -- rotate beats sideways beats
fall -- so the fit check exists once in the whole graph.

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

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

@@ -0,0 +1,16 @@
+import type { NodeDef } from '../../NodeRegistry';
+import { asString } from '../../values';
+import { num, str } from '../shared';
+
+export const FindText: NodeDef = {
+  type: 'FindText',
+  label: 'Find text',
+  category: 'data',
+  description: 'Where "search" first appears in "text", counting from 0, and −1 when it does not appear.',
+  inputs: [str('text'), str('search')],
+  outputs: [num('index')],
+  params: [],
+  run: (_ctx, inputs) => ({
+    outputs: { index: asString(inputs.text).indexOf(asString(inputs.search)) },
+  }),
+};

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

@@ -1,13 +1,16 @@
 import type { NodeDef } from '../../NodeRegistry';
-import { obj } from '../shared';
+import { asString } from '../../values';
+import { obj, str } from '../shared';
 
 export const ObjectByName: NodeDef = {
   type: 'ObjectByName',
   label: 'Object by name',
   category: 'data',
-  description: 'Finds a scene object by its name.',
-  inputs: [],
+  description:
+    'Finds a scene object by its name. The name is an input, so it can be put together at runtime ' +
+    '("cell" + index).',
+  inputs: [str('name')],
   outputs: [obj('object')],
-  params: [{ key: 'name', label: 'Name', kind: 'text', default: '' }],
-  run: (ctx, _inputs, params) => ({ outputs: { object: ctx.findByName(String(params.name ?? '')) } }),
+  params: [],
+  run: (ctx, inputs) => ({ outputs: { object: ctx.findByName(asString(inputs.name)) } }),
 };

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

@@ -0,0 +1,21 @@
+import type { NodeDef } from '../../NodeRegistry';
+import { asNumber, asString } from '../../values';
+import { num, str, withDefault } from '../shared';
+
+export const Substring: NodeDef = {
+  type: 'Substring',
+  label: 'Substring',
+  category: 'data',
+  description:
+    'A part of a text: "count" characters starting at "start" (the first is 0). ' +
+    'A negative count reaches to the end.',
+  inputs: [str('text'), num('start'), withDefault(num('count'), -1)],
+  outputs: [str('text')],
+  params: [],
+  run: (_ctx, inputs) => {
+    const text = asString(inputs.text);
+    const start = Math.max(0, Math.floor(asNumber(inputs.start)));
+    const count = Math.floor(asNumber(inputs.count));
+    return { outputs: { text: count < 0 ? text.slice(start) : text.slice(start, start + count) } };
+  },
+};

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

@@ -0,0 +1,14 @@
+import type { NodeDef } from '../../NodeRegistry';
+import { asNumber } from '../../values';
+import { any, num } from '../shared';
+
+export const ToNumber: NodeDef = {
+  type: 'ToNumber',
+  label: 'To number',
+  category: 'data',
+  description: 'Reads a text as a number. Anything that is not one – an empty text, a word – reads as 0.',
+  inputs: [any('value')],
+  outputs: [num('result')],
+  params: [],
+  run: (_ctx, inputs) => ({ outputs: { result: asNumber(inputs.value) } }),
+};