fix: Task2 质量修复（TS2774/降级分支测试/跨平台checksize/显式lib）

Co-Authored-By: Claude Code <noreply@anthropic.com>

sdk/test/util.test.ts

@@ -1,4 +1,4 @@
-import { describe, it, expect } from "vitest";
+import { describe, it, expect, vi } from "vitest";
 import { uuid } from "../src/util";
 describe("uuid", () => {
   it("生成 36 位且不重复", () => {
@@ -6,4 +6,11 @@ describe("uuid", () => {
     expect(a).toMatch(/^[0-9a-f-]{36}$/);
     expect(a).not.toBe(b);
   });
+  it("Math.random 降级分支：格式正确且唯一", () => {
+    vi.stubGlobal("crypto", {});
+    const a = uuid(), b = uuid();
+    expect(a).toMatch(/^[0-9a-f-]{36}$/);
+    expect(a).not.toBe(b);
+    vi.unstubAllGlobals();
+  });
 });