Send students to a chosen page when registration succeeds

The Student Registration block's "After email confirmation" panel becomes
"After registration": the page it selects is now where a newly registered
student continues to, and a new autoRedirect toggle sends them there
instead of showing the link.

Only the two finished states qualify (RegistrationPage::isRegistrationComplete):
an invited student who is now logged in, and a self-signup back from the
emailed confirmation link. A validation error, an expired confirmation
link, and the intermediate "check your email" step all stay on the page so
their message is read.

The invited-student success previously had no link at all; it gains a
"Continue to your account" one. That path deliberately has no
WordPress-login-screen fallback — pointing someone already signed in at the
login screen helps nobody — so continueUrl() distinguishes "no page chosen"
from "page chosen", and the redirect does nothing until one is picked.

Closes #115

Co-Authored-By: Claude Opus 5 <[email protected]>

src/Auth/RegistrationPage.php

@@ -66,9 +66,20 @@ class RegistrationPage {
 
 		if ( is_user_logged_in() ) {
 			if ( self::RESULT_INVITE === $registered ) {
+				// An invited student is done the moment they land here logged in,
+				// so this is where their "continue" link belongs. The sign-in-page
+				// fallback is deliberately not used: pointing someone who is
+				// already signed in at the login screen helps nobody.
+				$continue = $this->continueUrl( $this->successPageId( $atts ) );
+				$link     = null === $continue
+					? ''
+					: '<p><a href="' . esc_url( $continue ) . '">'
+						. esc_html__( 'Continue to your account', 'unsupervised-schedular' )
+						. '</a></p>';
+
 				return '<div class="us-register-form"><p class="us-success">'
 					. esc_html__( 'Your account has been created and you are now logged in.', 'unsupervised-schedular' )
-					. '</p></div>';
+					. '</p>' . $link . '</div>';
 			}
 
 			return '<p>' . esc_html__( 'You already have an account and are logged in.', 'unsupervised-schedular' ) . '</p>';
@@ -98,7 +109,7 @@ class RegistrationPage {
 		$confirmResult = sanitize_key( Val::string( wp_unslash( $_GET['us_confirmed'] ?? '' ) ) );
 
 		// Where the post-confirmation prompt sends students to sign in.
-		$loginUrl = $this->loginUrl( Val::int( $atts['loginPageId'] ?? $atts['login_page_id'] ?? 0 ) );
+		$loginUrl = $this->loginUrl( $this->successPageId( $atts ) );
 
 		$policyForms       = $this->signupPolicies();
 		$accountQuestions  = $this->questions->findByScope( Question::SCOPE_ACCOUNT, activeOnly: true );
@@ -319,21 +330,68 @@ class RegistrationPage {
 		return $autoApprove ? self::RESULT_CONFIRM_GROUP : self::RESULT_CONFIRM;
 	}
 
+	/**
+	 * The page id chosen for the post-registration destination, from either the
+	 * block (`loginPageId`) or shortcode (`login_page_id`) attribute.
+	 *
+	 * @param array<int|string, mixed> $atts
+	 */
+	private function successPageId( array $atts ): int {
+		return Val::int( $atts['loginPageId'] ?? $atts['login_page_id'] ?? 0 );
+	}
+
 	/**
 	 * URL the post-confirmation sign-in link points to: the chosen login page
 	 * when one is configured (and still exists), otherwise the WordPress login
 	 * screen.
 	 */
 	private function loginUrl( int $loginPageId ): string {
-		if ( $loginPageId > 0 ) {
-			$url = get_permalink( $loginPageId );
+		return $this->continueUrl( $loginPageId ) ?? wp_login_url();
+	}
 
-			if ( is_string( $url ) ) {
-				return $url;
-			}
+	/**
+	 * The chosen post-registration page's URL, or null when none is configured
+	 * (or it has since been deleted). Unlike {@see loginUrl()} this has no
+	 * WordPress-login-screen fallback, so callers that need a page the student
+	 * was actually sent to — the invited-student link and the block's
+	 * auto-redirect — can tell "not configured" from "configured".
+	 */
+	public function continueUrl( int $pageId ): ?string {
+		if ( $pageId <= 0 ) {
+			return null;
 		}
 
-		return wp_login_url();
+		$url = get_permalink( $pageId );
+
+		return is_string( $url ) ? $url : null;
+	}
+
+	/**
+	 * Whether this request is a *finished* registration — the states the
+	 * block's auto-redirect may act on:
+	 *
+	 * - an invited student who just signed up and is now logged in, and
+	 * - a self-signup returning from the emailed confirmation link, whether
+	 *   their account is ready (`ready`) or awaiting studio approval (`1`).
+	 *
+	 * Deliberately excluded: the intermediate "check your email" step (the
+	 * student would never see the instruction) and every failure — a validation
+	 * error or an expired confirmation link (`expired`) — so the message always
+	 * gets shown. The `us_confirmed` values are set by
+	 * {@see EmailConfirmationHandler::maybeConfirm()}.
+	 */
+	public function isRegistrationComplete(): bool {
+		// phpcs:ignore WordPress.Security.NonceVerification.Recommended -- read-only display flag; the submit that set it was nonce-checked.
+		$registered = sanitize_key( Val::string( wp_unslash( $_GET['us_registered'] ?? '' ) ) );
+
+		if ( self::RESULT_INVITE === $registered ) {
+			return is_user_logged_in();
+		}
+
+		// phpcs:ignore WordPress.Security.NonceVerification.Recommended -- read-only display flag set by EmailConfirmationHandler's redirect.
+		$confirmed = sanitize_key( Val::string( wp_unslash( $_GET['us_confirmed'] ?? '' ) ) );
+
+		return in_array( $confirmed, [ '1', 'ready' ], true );
 	}
 
 	/**