feat(optimization): consolidate extraction pipeline and metrics

- Flatten directory structure by moving masking and evals to scripts root.
- Merge evaluation metrics into scripts/optimization/evals.
- Restore and verify extraction tests for the new structure.

scripts/optimization/masking.test.ts

@@ -0,0 +1,41 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect } from 'vitest';
+import { maskVariables, unmaskVariables } from './masking.js';
+
+describe('optimization masking utility', () => {
+  it('should mask unique template variables with indexed tokens', () => {
+    const input = 'Use ${TOOL_A} to read ${FILE_PATH}. ${TOOL_A} is efficient.';
+    const { maskedText, maskMap } = maskVariables(input);
+
+    expect(maskedText).toContain('[[GCLI_VAR_0]]');
+    expect(maskedText).toContain('[[GCLI_VAR_1]]');
+    // Ensure all occurrences of the same variable are replaced with the same token
+    const toolAToken = Object.keys(maskMap).find(
+      (key) => maskMap[key] === '${TOOL_A}',
+    )!;
+    const count = maskedText.split(toolAToken).length - 1;
+    expect(count).toBe(2);
+    expect(maskedText).not.toContain('${TOOL_A}');
+  });
+
+  it('should perfectly restore original text during unmasking', () => {
+    const original = 'Update ${OLD_STR} with ${NEW_STR} in ${FILE_PATH}.';
+    const { maskedText, maskMap } = maskVariables(original);
+    const restored = unmaskVariables(maskedText, maskMap);
+
+    expect(restored).toBe(original);
+  });
+
+  it('should handle text with no variables', () => {
+    const input = 'Static text with no placeholders.';
+    const { maskedText, maskMap } = maskVariables(input);
+
+    expect(maskedText).toBe(input);
+    expect(Object.keys(maskMap).length).toBe(0);
+  });
+});