Notify instructors on new bookings and enrolments

Add an opt-in, per-instructor email notice sent when someone books one of
their lessons or enrols in one of their group classes. Off by default and
set from My Availability → Notifications; covers both the student/guardian
REST flows and the studio's wp-admin "book/add for a student" forms.

The opt-in check lives in InstructorNotificationMailer so no booking path
can drift on who is mailed; lessons fire from LessonBooker::settle (the one
step both booking paths reach), enrolments from EnrollmentEndpoint::enroll
and GroupClassController::addDirect. The notice is a courtesy and never
fails a booking or enrolment that otherwise succeeded.

Co-authored-by: anthropic/claude-opus-4-8

tests/Unit/GroupClass/EnrollmentEndpointTest.php

@@ -5,6 +5,7 @@ namespace Unsupervised\Schedular\Tests\Unit\GroupClass;
 
 use Brain\Monkey\Functions;
 use Mockery;
+use Unsupervised\Schedular\Auth\InstructorNotificationMailer;
 use Unsupervised\Schedular\GroupClass\Enrollment;
 use Unsupervised\Schedular\GroupClass\EnrollmentEndpoint;
 use Unsupervised\Schedular\GroupClass\EnrollmentRepository;
@@ -26,6 +27,7 @@ class EnrollmentEndpointTest extends TestCase
     private RegistrationGate $gate;
     private PaymentService $payments;
     private GroupAccessRepository $access;
+    private InstructorNotificationMailer&Mockery\MockInterface $instructorMailer;
     private EnrollmentEndpoint $endpoint;
 
     protected function setUp(): void
@@ -37,6 +39,9 @@ class EnrollmentEndpointTest extends TestCase
         Functions\when('sanitize_text_field')->returnArg();
         Functions\when('get_current_user_id')->justReturn(5);
         Functions\when('current_time')->justReturn('2026-07-24');
+        // The enrolment notice resolves the student's name before handing off to the
+        // (mocked) mailer; a bare false is enough since the name falls back to the id.
+        Functions\when('get_userdata')->justReturn(false);
 
         $this->enrollments = Mockery::mock(EnrollmentRepository::class);
         $this->offerings   = Mockery::mock(OfferingRepository::class);
@@ -44,6 +49,11 @@ class EnrollmentEndpointTest extends TestCase
         $this->payments    = Mockery::mock(PaymentService::class);
         $this->access      = Mockery::mock(GroupAccessRepository::class);
 
+        // The opt-in instructor notice is exercised on its own; here it is a mock
+        // that ignores whatever it is handed, so enrolment tests stay about enrolment.
+        $this->instructorMailer = Mockery::mock(InstructorNotificationMailer::class);
+        $this->instructorMailer->shouldReceive('notifyEnrollment')->andReturn(true)->byDefault();
+
         $this->guardians = Mockery::mock(GuardianService::class);
         $this->guardians->shouldReceive('canActFor')
             ->andReturnUsing(static fn (int $actor, int $student): bool => $actor === $student)->byDefault();
@@ -57,6 +67,7 @@ class EnrollmentEndpointTest extends TestCase
             $this->payments,
             $this->access,
             $this->guardians,
+            $this->instructorMailer,
         );
     }
 
@@ -93,6 +104,19 @@ class EnrollmentEndpointTest extends TestCase
         self::assertNull($result->get_data()['payment']);
     }
 
+    public function testASuccessfulEnrolmentNotifiesTheClassInstructor(): void
+    {
+        $this->offerings->shouldReceive('findById')->with(8)->andReturn($this->offering(0.0));
+        $this->expectSuccessfulEnrollment();
+        $this->payments->shouldNotReceive('createForRegistration');
+
+        // The class is taught by instructor 3; the enrolling student falls back to
+        // their id for a name (get_userdata is stubbed false in setUp).
+        $this->instructorMailer->shouldReceive('notifyEnrollment')->once()->with(3, '5', 'Choir')->andReturn(true);
+
+        $this->endpoint->enroll(new \WP_REST_Request(['offering_id' => 8]));
+    }
+
     public function testEnrollInPricedClassReturnsPaymentSummary(): void
     {
         $this->offerings->shouldReceive('findById')->with(8)->andReturn($this->offering(120.0));

tests/Unit/GroupClass/GroupClassControllerTest.php

@@ -5,6 +5,7 @@ namespace Unsupervised\Schedular\Tests\Unit\GroupClass;
 
 use Brain\Monkey\Functions;
 use Mockery;
+use Unsupervised\Schedular\Auth\InstructorNotificationMailer;
 use Unsupervised\Schedular\Auth\InviteRepository;
 use Unsupervised\Schedular\Auth\RegistrationMailer;
 use Unsupervised\Schedular\Auth\RoleManager;
@@ -32,6 +33,7 @@ class GroupClassControllerTest extends TestCase
     private RegistrationMailer&Mockery\MockInterface $mailer;
     private IntakeAudit&Mockery\MockInterface $audit;
     private IntakeRecording&Mockery\MockInterface $intake;
+    private InstructorNotificationMailer&Mockery\MockInterface $instructorMailer;
     private GroupClassController $controller;
 
     protected function setUp(): void
@@ -47,6 +49,10 @@ class GroupClassControllerTest extends TestCase
         $this->mailer         = Mockery::mock(RegistrationMailer::class);
         $this->audit          = Mockery::mock(IntakeAudit::class);
         $this->intake         = Mockery::mock(IntakeRecording::class);
+        // The opt-in instructor notice is tested on its own; a mock keeps these
+        // tests about enrolment, not about who gets emailed.
+        $this->instructorMailer = Mockery::mock(InstructorNotificationMailer::class);
+        $this->instructorMailer->shouldReceive('notifyEnrollment')->andReturn(true)->byDefault();
         $this->controller     = new GroupClassController(
             $this->enrollments,
             $this->offerings,
@@ -57,6 +63,7 @@ class GroupClassControllerTest extends TestCase
             $this->mailer,
             $this->audit,
             $this->intake,
+            $this->instructorMailer,
         );
 
         Functions\when('current_user_can')->justReturn(true);