fix: use crypto.getRandomValues in randId and stub it in tests for determinism

apps/web/src/core/utils/randId.test.ts

@@ -1,44 +1,53 @@
-import { beforeEach, describe, expect, it, vi } from "vitest";
+import { afterEach, describe, expect, it, vi } from "vitest";
 import { randId } from "./randId.ts";
 
 describe("randId", () => {
-  beforeEach(() => {
+  afterEach(() => {
     vi.restoreAllMocks();
   });
 
-  it("returns a number", () => {
-    const result = randId();
-    expect(typeof result).toBe("number");
-  });
-
   it("returns an integer", () => {
     const result = randId();
+    expect(typeof result).toBe("number");
     expect(Number.isInteger(result)).toBe(true);
   });
 
-  it("uses Math.random to generate the number", () => {
-    const mockRandom = vi.spyOn(Math, "random").mockReturnValue(0.5);
+  it("uses crypto.getRandomValues to generate the number", () => {
+    const mockGetRandomValues = vi
+      .spyOn(crypto, "getRandomValues")
+      .mockImplementation((array) => {
+        if (array instanceof Uint32Array) {
+          array[0] = 42;
+        }
+        return array;
+      });
+
     const result = randId();
 
-    expect(mockRandom).toHaveBeenCalled();
-    expect(result).toBe(Math.floor(0.5 * 1e9));
+    expect(mockGetRandomValues).toHaveBeenCalled();
+    expect(result).toBe(42);
   });
 
-  it("returns a value between 0 and 1e9 (exclusive)", () => {
+  it("returns a value within the uint32 range", () => {
     const result = randId();
     expect(result).toBeGreaterThanOrEqual(0);
-    expect(result).toBeLessThan(1e9);
+    expect(result).toBeLessThanOrEqual(0xffffffff);
   });
 
-  it("returns different values on subsequent calls", () => {
-    vi.spyOn(Math, "random").mockRestore();
+  it("returns unique values across many calls", () => {
+    let counter = 0;
+    vi.spyOn(crypto, "getRandomValues").mockImplementation((array) => {
+      if (array instanceof Uint32Array) {
+        array[0] = counter++;
+      }
+      return array;
+    });
 
-    const results = new Set();
-
-    for (let i = 0; i < 100; i++) {
+    const results = new Set<number>();
+    for (let i = 0; i < 1000; i++) {
       results.add(randId());
     }
 
-    expect(results.size).toBeGreaterThan(95);
+    expect(results.size).toBe(1000);
   });
 });

apps/web/src/core/utils/randId.ts

@@ -1,3 +1,5 @@
-export const randId = () => {
-  return Math.floor(Math.random() * 1e9);
+export const randId = (): number => {
+  const buf = new Uint32Array(1);
+  crypto.getRandomValues(buf);
+  return buf[0];
 };