chore(evals): add steering demonstration with deliberate failure

eval_regression_report.md

@@ -0,0 +1,12 @@
+### 🧪 Related Evaluation Rationale
+
+- Testing **glob** because **packages/core/src/tools/glob.ts** was modified.
+- Testing **grep** because **packages/core/src/tools/grep.ts** was modified.
+
+_Something missing?
+[Update evals/suites.json](evals/README.md#related-testing-with-related) to
+adjust detection logic._
+
+---
+
+✅ **6** tests passed successfully on **gemini-3-flash-preview**.

evals/failing_steering.eval.ts

@@ -0,0 +1,22 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, expect } from 'vitest';
+import { evalTest, TestRig } from './test-helper.js';
+
+describe('Related Eval Demonstration', () => {
+  evalTest('ALWAYS_PASSES', {
+    name: 'should fail deliberately to demonstrate regression reporting',
+    files: {
+      'test.txt': 'Hello world',
+    },
+    prompt: 'What is in test.txt?',
+    assert: async (rig: TestRig, result: string) => {
+      // This assertion is designed to fail.
+      expect(result).toContain('THE MODEL WILL NEVER SAY THIS EXACT SENTENCE');
+    },
+  });
+});

evals/suites.json

@@ -104,13 +104,15 @@
       "packages/core/src/prompts/**",
       "evals/answer-vs-act.eval.ts",
       "evals/model_steering.eval.ts",
-      "evals/redundant_casts.eval.ts"
+      "evals/redundant_casts.eval.ts",
+      "evals/failing_steering.eval.ts"
     ],
     "evals": [
       "ALL_ALWAYS_PASSING",
       "evals/answer-vs-act.eval.ts",
       "evals/model_steering.eval.ts",
-      "evals/redundant_casts.eval.ts"
+      "evals/redundant_casts.eval.ts",
+      "evals/failing_steering.eval.ts"
     ]
   },
   "edit_fidelity": {

packages/core/src/prompts/snippets.ts

@@ -4,6 +4,8 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+// Related Eval Demo: Modification in this file should trigger core_steering.
+
 import {
   ACTIVATE_SKILL_TOOL_NAME,
   ASK_USER_TOOL_NAME,