Loop over a list and stop at the first match with For each (#249)

Finding the first item that matches took Count, Repeat, Item at and a
Branch, and the loop could not stop once it had found something. A graph
has no lambdas, so the predicate is an input that is read every round.

- For each runs body once per element, with item and index set, and
  goes on at done.
- Its break input is read anew before every round, after item is set.
  Once it is true the loop ends there and that round's body does not
  run.
- done sees the matching item and index with stopped true. Without a
  match it sees no item, index -1 and stopped false, the OrDefault.
- RepeatResult has optional items, stopWhen, stopped and exhausted.
  GraphInterpreter.loop reads them, Repeat runs as before.

Tests:
- ./check.sh: 180 files, 2623 tests, CHECK EXIT 0
- e2e GM_STEPS=1-6: ALL PASSED, 269 checks
- 5 interpreter tests in graph.test.ts, 2 catalog cases
- e2e 6z-iv: the palette creates the node, and a search for
  Name == "Gold" in Axe, Gold, Bow, Gold logs "1true"
- Counter-checks: without the break check 2 unit tests fail, and with
  break not read over its edge 6z-iv fails
- This commit alone: tsc and the three touched unit files pass
  (349 tests)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/core/graph/nodes/flow/ForEach.ts

@@ -0,0 +1,36 @@
+import type { NodeDef } from '../../NodeRegistry';
+import { asList } from '../../values';
+import { any, bool, exec, list, num, withDefault } from '../shared';
+
+/** What `item`, `index` and `stopped` say when no round stopped the loop – or there was none. */
+const NOTHING = { item: null, index: -1, stopped: false };
+
+export const ForEach: NodeDef = {
+  type: 'ForEach',
+  label: 'For each',
+  category: 'flow',
+  description:
+    'Runs "body" once per element of the list, "item" and "index" telling which one, and continues at ' +
+    '"done" afterwards. "break" is read before every round: once it is true, the loop ends there – ' +
+    'that round\'s body does not run, and "done" sees its item with "stopped" set. Without a break, ' +
+    '"done" sees no item, index -1. "break" built on "item" finds the first element that matches.',
+  inputs: [exec(), list('list'), withDefault(bool('break'), false)],
+  outputs: [exec('body', 'body'), any('item'), num('index'), bool('stopped'), exec('done', 'done')],
+  params: [],
+  run: (_ctx, inputs) => {
+    const values = asList(inputs.list);
+    return {
+      outputs: { ...NOTHING },
+      repeat: {
+        port: 'body',
+        index: 'index',
+        times: values.length,
+        items: { port: 'item', values },
+        stopWhen: 'break',
+        stopped: 'stopped',
+        exhausted: NOTHING,
+      },
+      next: 'done',
+    };
+  },
+};

src/core/graph/nodes/index.ts

@@ -113,6 +113,7 @@ import { OnUpdate } from './events/OnUpdate';
 import { BehaviorEnd } from './flow/BehaviorEnd';
 import { BehaviorStart } from './flow/BehaviorStart';
 import { Branch } from './flow/Branch';
+import { ForEach } from './flow/ForEach';
 import { Repeat } from './flow/Repeat';
 import { RunBehavior } from './flow/RunBehavior';
 import { Sequence } from './flow/Sequence';
@@ -150,6 +151,7 @@ export const BUILT_IN_NODES: readonly NodeDef[] = [
   Branch,
   Sequence,
   Repeat,
+  ForEach,
   RunBehavior,
   StateBranch,
   SetState,