fix(auth): preserve MFA continuation through field hydration

packages/auth/test/mfa-runtime.test.ts

@@ -0,0 +1,53 @@
+import { expect, test } from "bun:test";
+import { readFileSync } from "node:fs";
+import { Window } from "happy-dom";
+
+test("MFA uses the nested Select and restores continuation after hydration without reviving expired challenges", async () => {
+  const window = new Window({ url: "https://sso.example.test/mfa" });
+  try {
+    window.sessionStorage.setItem(
+      "wrnexus.auth.mfa",
+      JSON.stringify({
+        mfaToken: "synthetic-test-challenge",
+        requires: { mfa: ["totp"] },
+      }),
+    );
+    window.document.body.innerHTML = `<section data-auth-mfa-challenge data-mfa-initial-method="totp">
+      <form data-auth-mfa-form>
+        <input type="hidden" name="mfaToken">
+        <input type="hidden" name="challengeId">
+        <div data-auth-mfa-method><select name="method"><option value="totp">Authenticator app</option><option value="email-otp">Email</option></select></div>
+        <input name="code"><p data-auth-mfa-status></p><button type="submit">Verify</button>
+      </form><a data-auth-mfa-restart hidden href="/login">Back to sign in</a>
+    </section>`;
+    window.eval(readFileSync(new URL("../assets/client/auth.js", import.meta.url), "utf8"));
+    (window as any).WRNexusAuth.mount(window.document);
+    const form = window.document.querySelector("form")!;
+    const token = form.querySelector<HTMLInputElement>('[name="mfaToken"]')!;
+    expect(token.value).toBe("synthetic-test-challenge");
+    expect(form.querySelector<HTMLOptionElement>('option[value="email-otp"]')!.disabled).toBe(true);
+    token.value = ""; // Hydration reapplies the component's initial empty prop.
+    form.dispatchEvent(new window.Event("submit", { bubbles: true, cancelable: true }));
+    expect(token.value).toBe("synthetic-test-challenge");
+    form.dispatchEvent(
+      new window.CustomEvent("wrn:error", { bubbles: true, detail: { code: "mfa-invalid" } }),
+    );
+    expect(token.value).toBe("synthetic-test-challenge");
+    form.dispatchEvent(
+      new window.CustomEvent("wrn:error", {
+        bubbles: true,
+        detail: { code: "mfa-transaction-expired" },
+      }),
+    );
+    expect(window.sessionStorage.getItem("wrnexus.auth.mfa")).toBeNull();
+    expect(window.document.querySelector<HTMLElement>("[data-auth-mfa-restart]")!.hidden).toBe(
+      false,
+    );
+    const retry = new window.Event("submit", { bubbles: true, cancelable: true });
+    form.dispatchEvent(retry);
+    expect(retry.defaultPrevented).toBe(true);
+    expect(token.value).toBe("");
+  } finally {
+    await window.happyDOM.close();
+  }
+});