feat(test-utils): add CPU performance integration test harness (#24951)

perf-tests/vitest.config.ts

@@ -0,0 +1,27 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { defineConfig } from 'vitest/config';
+
+export default defineConfig({
+  test: {
+    testTimeout: 600000, // 10 minutes — performance profiling needs time for multiple samples
+    globalSetup: './globalSetup.ts',
+    reporters: ['default'],
+    include: ['**/*.test.ts'],
+    retry: 0, // No retries — noise is handled by IQR filtering and tolerance
+    fileParallelism: false, // Must run serially to avoid CPU contention
+    pool: 'forks',
+    poolOptions: {
+      forks: {
+        singleFork: true, // Single process for accurate per-test CPU readings
+      },
+    },
+    env: {
+      GEMINI_TEST_TYPE: 'perf',
+    },
+  },
+});