perf: enforce journey budgets and reference traces

tests/performance/aggregation.test.ts

@@ -0,0 +1,30 @@
+import { describe, expect, it } from 'vitest';
+import { aggregateFiveDriveTraces } from '../../scripts/lib/performance-aggregation.mjs';
+
+const run = (lcp: number, tbt: number, gatingReferenceResult = true) => ({
+  schema: 'drive-trace.v1',
+  profile: 'desktop-high',
+  gatingReferenceResult,
+  validReferenceCadence: true,
+  metrics: { lcp, tbt },
+  budgetResults: { cls: true, scene: true },
+});
+
+describe('five-run drive trace aggregation', () => {
+  it('uses worst and median gates across exactly five reference runs', () => {
+    expect(aggregateFiveDriveTraces([
+      run(2_000, 100), run(2_100, 110), run(2_500, 200), run(2_900, 250), run(3_000, 300),
+    ])).toMatchObject({
+      runCount: 5,
+      passes: true,
+      summary: { lcpWorst: 3_000, lcpMedian: 2_500, tbtWorst: 300, tbtMedian: 200 },
+    });
+  });
+
+  it('rejects non-reference developer evidence and wrong run counts', () => {
+    expect(aggregateFiveDriveTraces([
+      run(2_000, 100, false), run(2_000, 100), run(2_000, 100), run(2_000, 100), run(2_000, 100),
+    ]).passes).toBe(false);
+    expect(() => aggregateFiveDriveTraces([run(2_000, 100)])).toThrow(/five/u);
+  });
+});