fix(settings): fix signup email redirection loop and add functional tests

Because:
- Navigating directly to /signup?email=... caused a redirect loop
- The useEffect in SignupContainer had no dependency array, re-running every render
- After account creation, accountStatusByEmail returned exists: true and
  redirected to /signin instead of allowing navigation to /confirm_signup_code

This commit:
- Adds a useRef guard and empty dependency array in SignupContainer to ensure
  the email status check runs only once on mount
- Passes service param to accountStatusByEmail for correct passwordless eligibility
- Adds functional tests for password signup via Sync OAuth RP navigating
  directly to /signup?email=... and passwordless redirect behavior

Fixes FXA-13309

Author: vbudhram

packages/functional-tests/tests/passwordless/signinPasswordless.spec.ts

@@ -994,6 +994,32 @@ test.describe('severity-2', () => {
       await page.waitForURL(/signin_passwordless_code/);
       await expect(signinPasswordlessCode.heading).toBeVisible();
     });
+
+    test('direct /signup URL with email param redirects to passwordless code when enabled', async ({
+      target,
+      page,
+      pages: { settings, signinPasswordlessCode },
+      testAccountTracker,
+    }) => {
+      const { email } = testAccountTracker.generatePasswordlessAccountDetails();
+
+      // Navigate directly to /signup with email, without force_passwordless=false
+      // so the passwordlessEnabled config flag takes effect
+      await page.goto(
+        `${target.contentServerUrl}/signup?showReactApp=true&email=${encodeURIComponent(email)}&forceExperiment=generalizedReactApp&forceExperimentGroup=react`
+      );
+
+      // Should redirect to passwordless code page
+      await page.waitForURL(/signin_passwordless_code/);
+      await expect(signinPasswordlessCode.heading).toBeVisible();
+
+      const code = await target.emailClient.getPasswordlessSignupCode(email);
+      await signinPasswordlessCode.fillOutCodeForm(code);
+
+      await page.waitForURL(/settings/);
+
+      await settings.signOut();
+    });
   });
 
   test.describe('Passwordless authentication - Sync flows', () => {

packages/functional-tests/tests/react-conversion/signup.spec.ts

@@ -4,7 +4,10 @@
 
 import { FirefoxCommand, LinkAccountResponse } from '../../lib/channels';
 import { expect, test } from '../../lib/fixtures/standard';
-import { syncDesktopV3QueryParams } from '../../lib/query-params';
+import {
+  syncDesktopOAuthQueryParams,
+  syncDesktopV3QueryParams,
+} from '../../lib/query-params';
 
 const eventDetailLinkAccount: LinkAccountResponse = {
   id: 'account_updates',
@@ -41,6 +44,38 @@ test.describe('severity-1 #smoke', () => {
       await settings.signOut();
     });
 
+    test('signup with email query param navigates to confirm page', async ({
+      target,
+      syncOAuthBrowserPages: {
+        confirmSignupCode,
+        page,
+        signup,
+        signupConfirmedSync,
+      },
+      testAccountTracker,
+    }) => {
+      const { email, password } =
+        testAccountTracker.generateSignupAccountDetails();
+
+      // Navigate directly to /signup with email in query params using Sync OAuth RP,
+      // bypassing the email-first page (no emailStatusChecked flag).
+      // Sync requires keys, so passwordless never applies.
+      const params = new URLSearchParams(syncDesktopOAuthQueryParams);
+      params.set('email', email);
+      await signup.goto('/signup', params);
+
+      await signup.fillOutSyncSignupForm(password);
+
+      // Should navigate to confirm_signup_code, not redirect to signin
+      await page.waitForURL(/confirm_signup_code/);
+
+      const code = await target.emailClient.getVerifyShortCode(email);
+      await confirmSignupCode.fillOutCodeForm(code);
+
+      await page.waitForURL(/signup_confirmed_sync/);
+      await expect(signupConfirmedSync.bannerConfirmed).toBeVisible();
+    });
+
     test('signup sync desktop v3, verify account', async ({
       target,
       syncBrowserPages: {

packages/fxa-settings/src/pages/Signup/container.tsx

@@ -9,7 +9,7 @@ import { Signup } from '.';
 import { useValidatedQueryParams } from '../../lib/hooks/useValidate';
 import { SignupQueryParams } from '../../models/pages/signup';
 import { BeginSignupHandler, SignupIntegration } from './interfaces';
-import { useCallback, useEffect } from 'react';
+import { useCallback, useEffect, useRef } from 'react';
 import { handleAuthClientError } from './utils';
 import {
   getCredentials,
@@ -87,13 +87,21 @@ const SignupContainer = ({
 
   const wantsKeys = integration.wantsKeys();
 
+  const attemptedEmailStatusCheck = useRef(false);
+
   useEffect(() => {
     (async () => {
-      if (!validationError && !emailStatusChecked) {
+      if (
+        !validationError &&
+        !emailStatusChecked &&
+        !attemptedEmailStatusCheck.current
+      ) {
+        attemptedEmailStatusCheck.current = true;
         const { exists, hasLinkedAccount, hasPassword, passwordlessSupported } =
           await authClient.accountStatusByEmail(queryParamModel.email, {
             thirdPartyAuthStatus: true,
             clientId: integration.getClientId(),
+            service: integration.getService(),
           });
         if (exists) {
           const signInPath = location.pathname.startsWith('/oauth')
@@ -120,7 +128,8 @@ const SignupContainer = ({
         }
       }
     })();
-  });
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, []);
 
   const beginSignupHandler: BeginSignupHandler = useCallback(
     async (email, password) => {
@@ -145,11 +154,11 @@ const SignupContainer = ({
         let credentialsV2 = undefined;
         let v2Payload:
           | {
-            wrapKb: string;
-            authPWVersion2: string;
-            wrapKbVersion2: string;
-            clientSalt: string;
-          }
+              wrapKb: string;
+              authPWVersion2: string;
+              wrapKbVersion2: string;
+              clientSalt: string;
+            }
           | {} = {};
 
         if (keyStretchExp.queryParamModel.isV2(config)) {