Add code quality gates

Add ESLint/quality gates, per-file ratchet budgets, and regression tests for code quality checks.

scripts/quality/code-quality.test.ts

@@ -0,0 +1,64 @@
+import { describe, expect, it } from 'vitest';
+
+import { analyzeCodeQuality, evaluateCodeQuality } from './code-quality.js';
+
+describe('code quality evaluator', () => {
+  it('measures line count and function metrics from TypeScript source', () => {
+    const metrics = analyzeCodeQuality(
+      'sample.ts',
+      [
+        'export function choose(value: number) {',
+        '  if (value > 10) {',
+        '    return value;',
+        '  }',
+        '  return value > 0 ? value : 0;',
+        '}',
+      ].join('\n'),
+    );
+
+    expect(metrics.lineCount).toBe(6);
+    expect(metrics.nonEmptyLineCount).toBe(6);
+    expect(metrics.maxFunctionLines).toBe(6);
+    expect(metrics.maxComplexity).toBeGreaterThanOrEqual(3);
+    expect(metrics.maxNesting).toBeGreaterThanOrEqual(1);
+  });
+
+  it('does not let nested functions inflate the parent function budget', () => {
+    const metrics = analyzeCodeQuality(
+      'nested.ts',
+      [
+        'export function outer() {',
+        '  const inner = () => {',
+        '    if (true) return 1;',
+        '    return 0;',
+        '  };',
+        '  return inner();',
+        '}',
+      ].join('\n'),
+    );
+
+    expect(metrics.maxComplexity).toBe(2);
+  });
+
+  it('returns budget findings for metrics over the configured limit', () => {
+    const metrics = analyzeCodeQuality(
+      'oversized.ts',
+      ['export function f() {', '  return 1;', '}'].join('\n'),
+    );
+
+    expect(
+      evaluateCodeQuality(metrics, {
+        maxComplexity: 1,
+        maxFunctionLines: 2,
+        maxLines: 2,
+        maxNesting: 0,
+        owner: 'test',
+      }),
+    ).toEqual(
+      expect.arrayContaining([
+        expect.objectContaining({ metric: 'lineCount' }),
+        expect.objectContaining({ metric: 'maxFunctionLines' }),
+      ]),
+    );
+  });
+});