fix(settings): cached passwordless Sync signin on mobile stuck on sign-in page

For passwordless Sync accounts on mobile (Firefox iOS), the cached
signin page was stuck after clicking "Sign in" because performNavigation
was false and no webchannel messages were sent. Allow in-webview
navigation to the set-password page for these accounts.

Author: vbudhram

packages/fxa-settings/src/pages/Signin/index.test.tsx

@@ -1182,6 +1182,41 @@ describe('Signin component', () => {
           handleNavigationSpy.mockRestore();
         });
 
+        it('allows navigation for cached Sync passwordless user on mobile', async () => {
+          const ensureCanLinkSpy = jest.spyOn(
+            SigninUtils,
+            'ensureCanLinkAcountOrRedirect'
+          ).mockResolvedValue(true);
+          const handleNavigationSpy = jest.spyOn(
+            SigninUtils,
+            'handleNavigation'
+          );
+          const cachedSigninHandler = jest
+            .fn()
+            .mockReturnValueOnce(CACHED_SIGNIN_HANDLER_RESPONSE);
+          const integration = createMockSigninOAuthNativeSyncIntegration({
+            isMobile: true,
+          });
+          render({
+            integration,
+            sessionToken: MOCK_SESSION_TOKEN,
+            hasPassword: false,
+            hasLinkedAccount: false,
+            cachedSigninHandler,
+          });
+
+          await submit();
+          await waitFor(() => {
+            expect(handleNavigationSpy).toHaveBeenCalledWith(
+              expect.objectContaining({
+                performNavigation: true,
+              })
+            );
+          });
+          ensureCanLinkSpy.mockRestore();
+          handleNavigationSpy.mockRestore();
+        });
+
         it('shows merge warning for cached Sync passwordless signin when user accepts', async () => {
           const ensureCanLinkSpy = jest.spyOn(
             SigninUtils,

packages/fxa-settings/src/pages/Signin/index.tsx

@@ -199,9 +199,13 @@ const Signin = ({
               : '',
           finishOAuthFlowHandler,
           queryParams: location.search,
-          performNavigation: !integration.isFirefoxMobileClient(),
+          // Passwordless Sync accounts (OTP or third-party auth) need to navigate
+          // to set_password within the webview, even on mobile clients. No webchannel
+          // messages are sent (deferred until after password creation), so the webview
+          // must handle navigation internally.
+          performNavigation: (isSync && !hasPassword) || !integration.isFirefoxMobileClient(),
           isServiceWithEmailVerification,
-          // Sync users in the cached path are passwordless (third-party auth);
+          // Sync users in the cached path are passwordless (third-party auth or OTP);
           // defer web channel messages until after password creation.
           handleFxaLogin: !isSync,
           handleFxaOAuthLogin: !isSync,