improve signup experience

apps/frontend/app/(public)/auth/login/page.tsx

@@ -7,6 +7,7 @@ import { Button } from '@/components/ui/button';
 import { Card, CardContent, CardDescription, CardHeader, CardTitle } from '@/components/ui/card';
 import { Input } from '@/components/ui/input';
 import { useLoginForm } from '@/features/public/auth/login/hooks';
+import { appendCallbackUrl, normalizeCallbackUrl } from '@/lib/auth/callback-url';
 
 export default function LoginPage() {
   return (
@@ -19,7 +20,8 @@ export default function LoginPage() {
 function LoginPageContent() {
   const router = useRouter();
   const searchParams = useSearchParams();
-  const callbackUrl = searchParams.get('callbackUrl') ?? '/dashboard';
+  const callbackUrl = normalizeCallbackUrl(searchParams.get('callbackUrl'));
+  const registerHref = appendCallbackUrl('/auth/register', callbackUrl);
   const { form, error, validators } = useLoginForm(() => {
     router.push(callbackUrl);
   });
@@ -90,7 +92,7 @@ function LoginPageContent() {
           </p>
           <p className='text-sm text-center text-muted-foreground mt-4'>
             アカウントをお持ちでない方は{' '}
-            <Link href='/auth/register' className='text-primary hover:underline'>
+            <Link href={registerHref} className='text-primary hover:underline'>
               新規登録
             </Link>
           </p>

apps/frontend/app/(public)/auth/register/page.tsx

@@ -1,19 +1,36 @@
 'use client';
 
 import Link from 'next/link';
-import { useRouter } from 'next/navigation';
-import { useState } from 'react';
+import { useRouter, useSearchParams } from 'next/navigation';
+import { Suspense, useState } from 'react';
 import { Button } from '@/components/ui/button';
 import { Card, CardContent, CardDescription, CardHeader, CardTitle } from '@/components/ui/card';
 import { Input } from '@/components/ui/input';
 import { useRegisterForm } from '@/features/public/auth/register/hooks';
+import { appendCallbackUrl, normalizeCallbackUrl } from '@/lib/auth/callback-url';
 
 export default function RegisterPage() {
+  return (
+    <Suspense fallback={null}>
+      <RegisterPageContent />
+    </Suspense>
+  );
+}
+
+function RegisterPageContent() {
   const router = useRouter();
+  const searchParams = useSearchParams();
+  const rawCallbackUrl = searchParams.get('callbackUrl');
+  const callbackUrl = normalizeCallbackUrl(rawCallbackUrl);
+  const hasCallbackUrl = rawCallbackUrl !== null;
+  const loginHref = hasCallbackUrl ? appendCallbackUrl('/auth/login', callbackUrl) : '/auth/login';
   const [registeredEmail, setRegisteredEmail] = useState<string | null>(null);
-  const { form, error, validators } = useRegisterForm((email) => {
-    setRegisteredEmail(email);
-  });
+  const { form, error, validators } = useRegisterForm(
+    (email) => {
+      setRegisteredEmail(email);
+    },
+    hasCallbackUrl ? callbackUrl : undefined,
+  );
 
   if (registeredEmail) {
     return (
@@ -27,7 +44,7 @@ export default function RegisterPage() {
             <p className='text-sm text-muted-foreground'>
               メール内のリンクを開くとアカウント作成が完了します。
             </p>
-            <Button type='button' className='w-full' onClick={() => router.push('/auth/login')}>
+            <Button type='button' className='w-full' onClick={() => router.push(loginHref)}>
               ログインへ
             </Button>
           </CardContent>
@@ -146,7 +163,7 @@ export default function RegisterPage() {
           </form>
           <p className='text-sm text-center text-muted-foreground mt-4'>
             すでにアカウントをお持ちの方は{' '}
-            <Link href='/auth/login' className='text-primary hover:underline'>
+            <Link href={loginHref} className='text-primary hover:underline'>
               ログイン
             </Link>
           </p>

apps/frontend/app/(public)/invite/[invitationId]/page.tsx

@@ -15,6 +15,9 @@ export default function InvitePage({ params }: { params: Promise<{ invitationId:
   const router = useRouter();
   const [status, setStatus] = useState<'idle' | 'loading' | 'error'>('idle');
   const [errorMessage, setErrorMessage] = useState<string | null>(null);
+  const inviteCallbackUrl = `/invite/${encodeURIComponent(invitationId)}`;
+  const loginHref = `/auth/login?callbackUrl=${encodeURIComponent(inviteCallbackUrl)}`;
+  const registerHref = `/auth/register?callbackUrl=${encodeURIComponent(inviteCallbackUrl)}`;
 
   const handleAccept = async () => {
     setStatus('loading');
@@ -55,13 +58,8 @@ export default function InvitePage({ params }: { params: Promise<{ invitationId:
             <CardDescription>ログインまたはアカウントを作成してから承認できます</CardDescription>
           </CardHeader>
           <CardContent className='flex flex-col gap-3'>
-            <Button render={<Link href={`/auth/login?callbackUrl=/invite/${invitationId}`} />}>
-              ログイン
-            </Button>
-            <Button
-              variant='outline'
-              render={<Link href={`/auth/register?callbackUrl=/invite/${invitationId}`} />}
-            >
+            <Button render={<Link href={loginHref} />}>ログイン</Button>
+            <Button variant='outline' render={<Link href={registerHref} />}>
               アカウントを作成
             </Button>
           </CardContent>

apps/frontend/features/public/auth/register/hooks.ts

@@ -4,7 +4,10 @@ import { z } from 'zod';
 import { useInvalidateMe } from '@/contexts/AuthContext';
 import { authClient } from '@/lib/auth/client';
 
-export function useRegisterForm(onSuccess: (email: string) => void) {
+export function useRegisterForm(
+  onSuccess: (email: string) => void,
+  verificationCallbackUrl?: string,
+) {
   const invalidateMe = useInvalidateMe();
   const [error, setError] = useState<string | null>(null);
 
@@ -16,7 +19,9 @@ export function useRegisterForm(onSuccess: (email: string) => void) {
         name: value.name,
         email: value.email,
         password: value.password,
-        callbackURL: `${window.location.origin}/auth/verify-email`,
+        callbackURL: verificationCallbackUrl
+          ? new URL(verificationCallbackUrl, window.location.origin).toString()
+          : `${window.location.origin}/auth/verify-email`,
       });
 
       if (result.error) {

apps/frontend/lib/auth/callback-url.ts

@@ -0,0 +1,15 @@
+const DEFAULT_CALLBACK_URL = '/dashboard';
+
+export function normalizeCallbackUrl(callbackUrl: string | null): string {
+  if (!callbackUrl) return DEFAULT_CALLBACK_URL;
+  if (!callbackUrl.startsWith('/') || callbackUrl.startsWith('//')) {
+    return DEFAULT_CALLBACK_URL;
+  }
+
+  return callbackUrl;
+}
+
+export function appendCallbackUrl(path: string, callbackUrl: string): string {
+  const params = new URLSearchParams({ callbackUrl });
+  return `${path}?${params.toString()}`;
+}