fix: show cron validation field errors

test/front/http-error.test.cjs

@@ -0,0 +1,29 @@
+const assert = require('node:assert/strict');
+const test = require('node:test');
+
+const { getErrorDetails } = require('../../src/utils/httpError');
+
+test('validation errors include the failing field names', () => {
+  const details = getErrorDetails({
+    message: 'Validation failed',
+    validation: {
+      body: {
+        source: 'body',
+        keys: ['labels', 'allow_multiple_instances'],
+        message: 'request body contains invalid values',
+      },
+    },
+  });
+
+  assert.deepEqual(details, [
+    'labels: request body contains invalid values',
+    'allow_multiple_instances: request body contains invalid values',
+  ]);
+});
+
+test('existing API error details remain visible', () => {
+  assert.deepEqual(
+    getErrorDetails({ errors: [{ message: 'duplicate value', value: 'foo' }] }),
+    ['duplicate value (foo)'],
+  );
+});