Let the studio register the students who cannot register themselves

The Book a lesson for a student panel built its picker from the us_student
role but vetted the submission with the book_lesson capability. ChildLoginGate
and RegistrationLoginGate withhold that capability from accounts that keep the
role, so the panel offered every guardian-managed child and every unapproved
signup and then refused them — with a message claiming no student had been
chosen, and a form cleared of all five fields.

Withholding book_lesson stops those accounts registering in their own name. It
was never meant to stop the studio acting for them, which is what the panel is
for, and for a child is the only route to a lesson besides their guardian.

Guard the student role instead, via a new RoleManager::isStudent() shared with
every picker and guard on the staff side so the two cannot drift apart again.
Group enrolment gets the same predicate: addDirect() and grantAccess() vetted
their posted ids not at all, and would enrol an instructor, an administrator,
or an account deleted since the page was drawn — raising a real payment against
them for a priced class.

Keep a refused booking's fields as submitted, reading the form through one
LessonController::submittedBooking() so what gets booked and what is shown
again cannot disagree about a field name. A booking that succeeds still leaves
an empty form, so the next one does not inherit it.

Closes #185

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01XunBYk2sFEc1oL14sUiuBU

tests/Unit/GroupClass/GroupClassControllerTest.php

@@ -7,6 +7,7 @@ use Brain\Monkey\Functions;
 use Mockery;
 use Unsupervised\Schedular\Auth\InviteRepository;
 use Unsupervised\Schedular\Auth\RegistrationMailer;
+use Unsupervised\Schedular\Auth\RoleManager;
 use Unsupervised\Schedular\GroupClass\Enrollment;
 use Unsupervised\Schedular\GroupClass\EnrollmentRepository;
 use Unsupervised\Schedular\GroupClass\GroupAccessRepository;
@@ -87,7 +88,8 @@ class GroupClassControllerTest extends TestCase
     {
         [$first, $last] = array_pad(explode(' ', $full, 2), 2, '');
 
-        $user = Mockery::mock(\WP_User::class);
+        $user               = Mockery::mock(\WP_User::class);
+        $user->roles        = [RoleManager::STUDENT];
         $user->first_name   = $first;
         $user->last_name    = $last;
         $user->nickname     = $full;
@@ -406,6 +408,8 @@ class GroupClassControllerTest extends TestCase
         Functions\when('wp_unslash')->returnArg();
         Functions\when('sanitize_email')->returnArg();
         Functions\when('absint')->alias(static fn ($v) => abs((int) $v));
+        // Every posted id is vetted as a student before it is enrolled or granted.
+        Functions\when('get_userdata')->justReturn($this->userNamed('Ada Lovelace'));
 
         // Render tail: no classes/enrolments to draw so the assertion targets the notice.
         $this->offerings->shouldReceive('findAll')->with(3, Offering::KIND_GROUP_CLASS)->andReturn([]);
@@ -544,6 +548,64 @@ class GroupClassControllerTest extends TestCase
         $this->audit->shouldReceive('acceptances')->with($enrollment)->andReturn([]);
     }
 
+    /**
+     * The multi-select is built from the studio's students, but a posted id is just
+     * a number: it could name an instructor, an administrator, or an account
+     * deleted since the page was drawn. Enrolling one would put a non-student on
+     * the roster and raise a payment against them.
+     */
+    public function testAddDirectIgnoresAnIdThatIsNotAStudent(): void
+    {
+        $_POST = ['usc_action' => 'add_direct', 'offering_id' => 8, 'student_ids' => [5]];
+        $this->stubActionContext();
+
+        $instructor        = Mockery::mock(\WP_User::class);
+        $instructor->roles = [RoleManager::INSTRUCTOR];
+        Functions\when('get_userdata')->justReturn($instructor);
+
+        $this->offerings->shouldReceive('findById')->with(8)->andReturn($this->inviteOnlyOffering(100.0));
+        $this->enrollments->shouldReceive('insert')->never();
+        $this->paymentService->shouldReceive('createForRegistration')->never();
+        $this->access->shouldReceive('markEnrolled')->never();
+
+        $html = $this->renderInstructor();
+
+        self::assertStringContainsString('0 student(s) added to the class.', $html);
+    }
+
+    public function testAddDirectIgnoresAnAccountThatNoLongerExists(): void
+    {
+        $_POST = ['usc_action' => 'add_direct', 'offering_id' => 8, 'student_ids' => [5]];
+        $this->stubActionContext();
+        Functions\when('get_userdata')->justReturn(false);
+
+        $this->offerings->shouldReceive('findById')->with(8)->andReturn($this->inviteOnlyOffering(100.0));
+        $this->enrollments->shouldReceive('insert')->never();
+        $this->paymentService->shouldReceive('createForRegistration')->never();
+
+        $html = $this->renderInstructor();
+
+        self::assertStringContainsString('0 student(s) added to the class.', $html);
+    }
+
+    public function testGrantAccessIgnoresAnIdThatIsNotAStudent(): void
+    {
+        $_POST = ['usc_action' => 'grant_access', 'offering_id' => 8, 'student_ids' => [5]];
+        $this->stubActionContext();
+
+        $instructor        = Mockery::mock(\WP_User::class);
+        $instructor->roles = [RoleManager::INSTRUCTOR];
+        Functions\when('get_userdata')->justReturn($instructor);
+
+        $this->offerings->shouldReceive('findById')->with(8)->andReturn($this->inviteOnlyOffering());
+        $this->access->shouldReceive('insert')->never();
+        $this->mailer->shouldReceive('sendClassAccessGranted')->never();
+
+        $html = $this->renderInstructor();
+
+        self::assertStringContainsString('0 student(s) granted access.', $html);
+    }
+
     public function testGrantAccessCreatesGrantAndEmailsStudent(): void
     {
         $_POST = ['usc_action' => 'grant_access', 'offering_id' => 8, 'student_ids' => [5]];
@@ -554,7 +616,8 @@ class GroupClassControllerTest extends TestCase
         $this->access->shouldReceive('hasGrant')->with(8, 5)->andReturn(false);
         $this->access->shouldReceive('insert')->once()->andReturn(1);
 
-        $user = Mockery::mock(\WP_User::class);
+        $user             = Mockery::mock(\WP_User::class);
+        $user->roles      = [RoleManager::STUDENT];
         $user->user_email = '[email protected]';
         Functions\when('get_userdata')->justReturn($user);
         $this->mailer->shouldReceive('sendClassAccessGranted')->once()->with($user, 'Private Choir')->andReturn(true);