webapp: route new Google SSO users to the welcome page (once)

After Google sign-in, brand-new accounts now land on /welcome instead of
the set-password page; returning users go to their normal destination.

"New user" is detected via the SSO response's username_not_yet_customized
(forced to false by the backend for returning Google logins, so repeat
logins never re-trigger it). A per-user-token localStorage marker guards
against the rare email→Google-link edge case so welcome shows at most
once per account.

- session.ts: add consumeNewUserWelcome(isNewUser) helper
- login / signup-form / signup-cta-modal: route via the helper

frontend/apps/artcraft-webapp/src/components/auth/signup-form.tsx

@@ -15,7 +15,7 @@ import {
   getReferralUsername,
   getReferrer,
 } from "@storyteller/common";
-import { refreshSession, useSessionStore } from "../../lib/session";
+import { consumeNewUserWelcome, refreshSession } from "../../lib/session";
 import { GoogleLoginButton } from "./GoogleLoginButton";
 
 interface SignupFormProps {
@@ -85,13 +85,13 @@ export const SignupForm = ({
     }
   };
 
-  const handleGoogleSuccess = async () => {
-    // Refresh so the session reflects the new cookie (and whether the account
-    // still needs a password), then route accordingly. New SSO users skip
-    // setting a password and go straight to pricing; everyone else goes home.
+  const handleGoogleSuccess = async (isNewUser: boolean) => {
+    // Refresh so the session reflects the new cookie, then route accordingly.
+    // Brand-new accounts see the welcome page once (mirrors the signup flow);
+    // returning users go home.
     await refreshSession(true);
-    if (useSessionStore.getState().passwordNotSet) {
-      navigate("/pricing");
+    if (consumeNewUserWelcome(isNewUser)) {
+      navigate("/welcome");
     } else {
       navigate("/");
     }

frontend/apps/artcraft-webapp/src/components/signup-cta-modal.tsx

@@ -6,7 +6,7 @@ import { faCheck } from "@fortawesome/pro-solid-svg-icons";
 import { Modal } from "@storyteller/ui-modal";
 import { Button } from "@storyteller/ui-button";
 import { GoogleLoginButton } from "./auth";
-import { refreshSession, useSession, useSessionStore } from "../lib/session";
+import { consumeNewUserWelcome, refreshSession, useSession } from "../lib/session";
 
 interface SignupCtaState {
   isOpen: boolean;
@@ -51,13 +51,13 @@ export function SignupCtaModal() {
   const [error, setError] = useState<string | null>(null);
 
   // Mirror the login/signup pages: refresh the session so it reflects the new
-  // cookie, then send brand-new SSO users straight to pricing. Everyone else
-  // just closes the modal and stays on the page they were on.
-  const handleGoogleSuccess = async () => {
+  // cookie, then send brand-new accounts to the welcome page (once). Everyone
+  // else just closes the modal and stays on the page they were on.
+  const handleGoogleSuccess = async (isNewUser: boolean) => {
     await refreshSession(true);
     close();
-    if (useSessionStore.getState().passwordNotSet) {
-      navigate("/pricing");
+    if (consumeNewUserWelcome(isNewUser)) {
+      navigate("/welcome");
     }
   };
 

frontend/apps/artcraft-webapp/src/lib/session.ts

@@ -81,6 +81,34 @@ export function updateSessionUser(partial: Partial<UserInfo>): void {
   invalidateSession();
 }
 
+// Decide whether a just-authenticated user should see the one-time post-signup
+// welcome page, and record that they have. Call once after `refreshSession`.
+//
+// `isNewUser` comes from the SSO response (`username_not_yet_customized`), which
+// the backend forces to false for returning Google logins — so it never re-fires
+// for normal repeat logins regardless of whether the user customized their
+// username. As a belt-and-suspenders guard (e.g. the email→Google-link case where
+// the flag can read true on an existing account), we also persist a per-user-token
+// marker so the welcome page shows at most once per account on this device.
+const WELCOME_SHOWN_KEY_PREFIX = "artcraft.welcomeShown.";
+
+export function consumeNewUserWelcome(isNewUser: boolean): boolean {
+  if (!isNewUser) return false;
+  if (typeof window === "undefined") return true;
+
+  const userToken = useSessionStore.getState().user?.user_token;
+  if (!userToken) return true;
+
+  const key = `${WELCOME_SHOWN_KEY_PREFIX}${userToken}`;
+  try {
+    if (window.localStorage.getItem(key)) return false;
+    window.localStorage.setItem(key, "1");
+  } catch {
+    // localStorage blocked (e.g. privacy mode) — fall through and just show it.
+  }
+  return true;
+}
+
 // Attach the auth-change listener exactly once per page load. Login/logout/
 // password-reset flows dispatch this event; every consumer shares the resulting
 // store update instead of each re-running its own effect.

frontend/apps/artcraft-webapp/src/pages/login/login.tsx

@@ -11,7 +11,7 @@ import { Link, useNavigate, useSearchParams } from "react-router-dom";
 import { UsersApi } from "@storyteller/api";
 import { AuthHeader, AuthFooter, GoogleLoginButton } from "../../components/auth";
 import Seo from "../../components/seo";
-import { refreshSession, useSessionStore } from "../../lib/session";
+import { consumeNewUserWelcome, refreshSession } from "../../lib/session";
 
 const Login = () => {
   const navigate = useNavigate();
@@ -48,13 +48,13 @@ const Login = () => {
     }
   };
 
-  const handleGoogleSuccess = async () => {
-    // Refresh so the session store reflects the new cookie (and whether the
-    // account still needs a password) before deciding where to send them.
+  const handleGoogleSuccess = async (isNewUser: boolean) => {
+    // Refresh so the session store reflects the new cookie before navigating.
     await refreshSession(true);
-    if (useSessionStore.getState().passwordNotSet) {
-      // New SSO users skip setting a password and go straight to pricing.
-      navigate("/pricing");
+    if (consumeNewUserWelcome(isNewUser)) {
+      // Brand-new accounts see the welcome page once (mirrors the signup flow);
+      // returning users go wherever they were headed.
+      navigate("/welcome");
     } else {
       navigate(redirectTo);
     }