Fix field-length saves, student wp-admin access, and empty instructor picker

Three bug fixes for the 1.2.1 section:

- Fixed-size fields (question labels, offering titles/notes/e-transfer
  email, policy titles/slugs) no longer silently fail to save when the
  value exceeds its column length. The REST endpoints reject over-long
  values with a 400, the admin controllers refuse to insert them, and the
  form inputs carry a maxlength so the browser blocks over-long entry.
  Limits are MAX_* constants on the value objects, kept in lockstep with
  the schema columns.

- Students are kept out of wp-admin entirely. New StudentAdminGuard
  redirects front-end-only users (no back-office capability) away from the
  dashboard and hides the admin bar for them, while administrators, studio
  admins, and instructors keep full access.

- The Add/Edit Offering instructor picker now includes WordPress
  administrators when they act as instructors (the default single-account
  setup), so a solo studio owner is selectable instead of the dropdown
  being empty.

composer test (618), composer lint, composer cs all pass.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/Offering/OfferingEndpoint.php

@@ -148,6 +148,14 @@ class OfferingEndpoint {
 			return $this->invalid( __( 'Invalid billing mode.', 'unsupervised-schedular' ) );
 		}
 
+		$scheduleNote   = $this->nullableText( $request->get_param( 'schedule_note' ) );
+		$etransferEmail = $this->nullableEmail( $request->get_param( 'etransfer_email' ) );
+
+		$lengthError = $this->checkLengths( $title, $scheduleNote, $etransferEmail );
+		if ( $lengthError instanceof \WP_Error ) {
+			return $lengthError;
+		}
+
 		$offering = new Offering(
 			instructorId:    get_current_user_id(),
 			kind:            $kind,
@@ -162,8 +170,8 @@ class OfferingEndpoint {
 			termStart:       $this->nullableText( $request->get_param( 'term_start' ) ),
 			termEnd:         $this->nullableText( $request->get_param( 'term_end' ) ),
 			enrollmentDeadline: $this->nullableText( $request->get_param( 'enrollment_deadline' ) ),
-			scheduleNote:    $this->nullableText( $request->get_param( 'schedule_note' ) ),
-			etransferEmail:  $this->nullableEmail( $request->get_param( 'etransfer_email' ) ),
+			scheduleNote:    $scheduleNote,
+			etransferEmail:  $etransferEmail,
 			cancellationCutoffHours: $this->nullableInt( $request->get_param( 'cancellation_cutoff_hours' ) ),
 			accessMode:      $this->accessMode( $request->get_param( 'access_mode' ), Offering::ACCESS_PUBLIC ),
 			isActive:        null === $request->get_param( 'is_active' ) ? true : (bool) $request->get_param( 'is_active' ),
@@ -196,10 +204,19 @@ class OfferingEndpoint {
 			return $this->invalid( __( 'Invalid billing mode.', 'unsupervised-schedular' ) );
 		}
 
+		$title          = $request->has_param( 'title' ) ? sanitize_text_field( Val::string( $request->get_param( 'title' ) ) ) : $existing->title;
+		$scheduleNote   = $request->has_param( 'schedule_note' ) ? $this->nullableText( $request->get_param( 'schedule_note' ) ) : $existing->scheduleNote;
+		$etransferEmail = $request->has_param( 'etransfer_email' ) ? $this->nullableEmail( $request->get_param( 'etransfer_email' ) ) : $existing->etransferEmail;
+
+		$lengthError = $this->checkLengths( $title, $scheduleNote, $etransferEmail );
+		if ( $lengthError instanceof \WP_Error ) {
+			return $lengthError;
+		}
+
 		$offering = new Offering(
 			instructorId:    $existing->instructorId,
 			kind:            $kind,
-			title:           $request->has_param( 'title' ) ? sanitize_text_field( Val::string( $request->get_param( 'title' ) ) ) : $existing->title,
+			title:           $title,
 			price:           $request->has_param( 'price' ) ? $this->price( $request->get_param( 'price' ) ) : $existing->price,
 			currency:        $request->has_param( 'currency' ) ? sanitize_text_field( Val::string( $request->get_param( 'currency' ) ) ) : $existing->currency,
 			billingMode:     $billingMode,
@@ -210,8 +227,8 @@ class OfferingEndpoint {
 			termStart:       $request->has_param( 'term_start' ) ? $this->nullableText( $request->get_param( 'term_start' ) ) : $existing->termStart,
 			termEnd:         $request->has_param( 'term_end' ) ? $this->nullableText( $request->get_param( 'term_end' ) ) : $existing->termEnd,
 			enrollmentDeadline: $request->has_param( 'enrollment_deadline' ) ? $this->nullableText( $request->get_param( 'enrollment_deadline' ) ) : $existing->enrollmentDeadline,
-			scheduleNote:    $request->has_param( 'schedule_note' ) ? $this->nullableText( $request->get_param( 'schedule_note' ) ) : $existing->scheduleNote,
-			etransferEmail:  $request->has_param( 'etransfer_email' ) ? $this->nullableEmail( $request->get_param( 'etransfer_email' ) ) : $existing->etransferEmail,
+			scheduleNote:    $scheduleNote,
+			etransferEmail:  $etransferEmail,
 			cancellationCutoffHours: $request->has_param( 'cancellation_cutoff_hours' ) ? $this->nullableInt( $request->get_param( 'cancellation_cutoff_hours' ) ) : $existing->cancellationCutoffHours,
 			accessMode:      $request->has_param( 'access_mode' ) ? $this->accessMode( $request->get_param( 'access_mode' ), $existing->accessMode ) : $existing->accessMode,
 			isActive:        $request->has_param( 'is_active' ) ? (bool) $request->get_param( 'is_active' ) : $existing->isActive,
@@ -266,6 +283,34 @@ class OfferingEndpoint {
 		return new \WP_Error( 'invalid_offering', $message, [ 'status' => 400 ] );
 	}
 
+	/**
+	 * Reject any fixed-size field whose value exceeds its column length, so an
+	 * over-long value is refused with a clear 400 rather than silently dropped
+	 * by the database.
+	 */
+	private function checkLengths( string $title, ?string $scheduleNote, ?string $etransferEmail ): ?\WP_Error {
+		$fields = [
+			[ __( 'title', 'unsupervised-schedular' ), $title, Offering::MAX_TITLE_LENGTH ],
+			[ __( 'schedule note', 'unsupervised-schedular' ), $scheduleNote, Offering::MAX_SCHEDULE_NOTE_LENGTH ],
+			[ __( 'e-transfer email', 'unsupervised-schedular' ), $etransferEmail, Offering::MAX_ETRANSFER_EMAIL_LENGTH ],
+		];
+
+		foreach ( $fields as [ $name, $value, $max ] ) {
+			if ( null !== $value && mb_strlen( $value ) > $max ) {
+				return $this->invalid(
+					sprintf(
+						/* translators: 1: field name, 2: maximum character count. */
+						__( 'The %1$s must be %2$d characters or fewer.', 'unsupervised-schedular' ),
+						$name,
+						$max
+					)
+				);
+			}
+		}
+
+		return null;
+	}
+
 	private function price( mixed $value ): float {
 		return max( 0.0, Val::float( $value ) );
 	}