chore: strengthen validation guidance in system prompt (#18544)

evals/validation_fidelity.eval.ts

@@ -0,0 +1,85 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, expect } from 'vitest';
+import { evalTest } from './test-helper.js';
+
+describe('validation_fidelity', () => {
+  evalTest('ALWAYS_PASSES', {
+    name: 'should perform exhaustive validation autonomously when guided by system instructions',
+    files: {
+      'src/types.ts': `
+export interface LogEntry {
+  level: 'info' | 'warn' | 'error';
+  message: string;
+}
+`,
+      'src/logger.ts': `
+import { LogEntry } from './types.js';
+
+export function formatLog(entry: LogEntry): string {
+  return \`[\${entry.level.toUpperCase()}] \${entry.message}\`;
+}
+`,
+      'src/logger.test.ts': `
+import { expect, test } from 'vitest';
+import { formatLog } from './logger.js';
+import { LogEntry } from './types.js';
+
+test('formats log correctly', () => {
+  const entry: LogEntry = { level: 'info', message: 'test message' };
+  expect(formatLog(entry)).toBe('[INFO] test message');
+});
+`,
+      'package.json': JSON.stringify({
+        name: 'test-project',
+        type: 'module',
+        scripts: {
+          test: 'vitest run',
+          build: 'tsc --noEmit',
+        },
+      }),
+      'tsconfig.json': JSON.stringify({
+        compilerOptions: {
+          target: 'ESNext',
+          module: 'ESNext',
+          moduleResolution: 'node',
+          strict: true,
+          esModuleInterop: true,
+          skipLibCheck: true,
+          forceConsistentCasingInFileNames: true,
+        },
+      }),
+    },
+    prompt:
+      "Refactor the 'LogEntry' interface in 'src/types.ts' to rename the 'message' field to 'payload'.",
+    timeout: 600000,
+    assert: async (rig) => {
+      // The goal of this eval is to see if the agent realizes it needs to update usages
+      // AND run 'npm run build' or 'tsc' autonomously to ensure project-wide structural integrity.
+
+      const toolLogs = rig.readToolLogs();
+      const shellCalls = toolLogs.filter(
+        (log) => log.toolRequest.name === 'run_shell_command',
+      );
+
+      const hasBuildOrTsc = shellCalls.some((log) => {
+        const cmd = JSON.parse(log.toolRequest.args).command.toLowerCase();
+        return (
+          cmd.includes('npm run build') ||
+          cmd.includes('tsc') ||
+          cmd.includes('typecheck') ||
+          cmd.includes('npm run verify')
+        );
+      });
+
+      expect(
+        hasBuildOrTsc,
+        'Expected the agent to autonomously run a build or type-check command to verify the refactoring',
+      ).toBe(true);
+    },
+  });
+});