fix(tools): enforce string schema lengths by Unicode code point

src/tools/tool-schema-codepoints.test.mjs

@@ -0,0 +1,20 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { validateValue } from './schema.js';
+test('tool string schemas count Unicode characters rather than UTF-16 units', () => {
+  const value = '𠮷野家😀';
+  assert.deepEqual(validateValue({ type: 'string', maxLength: 4 }, value), []);
+  assert.equal(
+    validateValue({ type: 'string', minLength: 5 }, value).length,
+    1,
+  );
+  assert.equal(
+    validateValue({ type: 'string', maxLength: 3 }, value).length,
+    1,
+  );
+  assert.deepEqual(
+    validateValue({ type: 'string', minLength: 4, maxLength: 4 }, 'abcd'),
+    [],
+  );
+  assert.equal(validateValue({ type: 'string', minLength: 2 }, '𠮷').length, 1);
+});