test: add suite for utils/keyboard handlers (+4)

Covers onTabPress (Tab-only), preventScrollWithArrowKey (arrows-only),
onEnterOrSpace (Enter/Space gate the callback), and stopPropagation's
editable-element check (does not swallow keys when an input/textarea/
contenteditable is focused) via mock events + a document.activeElement stub.
Full suite now 133 tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/utils/keyboard.test.ts

@@ -0,0 +1,117 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { onTabPress, preventScrollWithArrowKey, onEnterOrSpace, stopPropagation } from './keyboard';
+
+type Evt = {
+  key: string;
+  which: number;
+  altKey: boolean;
+  ctrlKey: boolean;
+  metaKey: boolean;
+  shiftKey: boolean;
+  prevented: boolean;
+  preventDefault(): void;
+};
+const evt = (key: string, which: number): Evt => ({
+  key,
+  which,
+  altKey: false,
+  ctrlKey: false,
+  metaKey: false,
+  shiftKey: false,
+  prevented: false,
+  preventDefault() {
+    this.prevented = true;
+  },
+});
+
+test('onTabPress fires only on Tab', () => {
+  let called = 0;
+  const tab = evt('Tab', 9);
+  onTabPress(tab, () => {
+    called += 1;
+  });
+  assert.equal(called, 1);
+  assert.equal(tab.prevented, true);
+
+  const a = evt('a', 65);
+  onTabPress(a, () => {
+    called += 1;
+  });
+  assert.equal(called, 1); // unchanged
+  assert.equal(a.prevented, false);
+});
+
+test('preventScrollWithArrowKey prevents default only on arrows', () => {
+  const up = evt('ArrowUp', 38);
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  preventScrollWithArrowKey(up as any);
+  assert.equal(up.prevented, true);
+
+  const a = evt('a', 65);
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  preventScrollWithArrowKey(a as any);
+  assert.equal(a.prevented, false);
+});
+
+test('onEnterOrSpace fires on Enter or Space, not others', () => {
+  let count = 0;
+  const handler = onEnterOrSpace(() => {
+    count += 1;
+  });
+
+  const enter = evt('Enter', 13);
+  handler(enter);
+  assert.equal(count, 1);
+  assert.equal(enter.prevented, true);
+
+  const space = evt(' ', 32);
+  handler(space);
+  assert.equal(count, 2);
+  assert.equal(space.prevented, true);
+
+  const other = evt('a', 65);
+  handler(other);
+  assert.equal(count, 2); // unchanged
+  assert.equal(other.prevented, false);
+});
+
+test('stopPropagation: stops unless an editable element is focused', () => {
+  const makeKeyEvt = () => {
+    let stopped = false;
+    return {
+      ev: {
+        stopPropagation() {
+          stopped = true;
+        },
+      },
+      wasStopped: () => stopped,
+    };
+  };
+  const withActive = (activeElement: unknown) => {
+    (globalThis as { document?: unknown }).document = { activeElement };
+  };
+
+  // nothing focused → stops, returns true
+  withActive(null);
+  let k = makeKeyEvt();
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  assert.equal(stopPropagation(k.ev as any), true);
+  assert.equal(k.wasStopped(), true);
+
+  // input focused → does not stop, returns false
+  withActive({ nodeName: 'INPUT', getAttribute: () => null });
+  k = makeKeyEvt();
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  assert.equal(stopPropagation(k.ev as any), false);
+  assert.equal(k.wasStopped(), false);
+
+  // contenteditable focused → does not stop
+  withActive({
+    nodeName: 'DIV',
+    getAttribute: (a: string) => (a === 'contenteditable' ? 'true' : null),
+  });
+  k = makeKeyEvt();
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  assert.equal(stopPropagation(k.ev as any), false);
+});