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/Registration/Question.php

@@ -12,6 +12,9 @@ class Question {
 	public const FIELD_SELECT   = 'select';
 	public const FIELD_CHECKBOX = 'checkbox';
 
+	/** Maximum length of a question label, matching the `label` VARCHAR(255) column. */
+	public const MAX_LABEL_LENGTH = 255;
+
 	/** Question is scoped to a single offering, asked at booking/enrolment time. */
 	public const SCOPE_OFFERING = 'offering';
 

src/Registration/QuestionController.php

@@ -85,7 +85,7 @@ class QuestionController {
 		$label     = sanitize_text_field( Val::string( wp_unslash( $_POST['label'] ?? '' ) ) );
 		$fieldType = sanitize_key( Val::string( wp_unslash( $_POST['field_type'] ?? Question::FIELD_TEXT ) ) );
 
-		if ( '' === $label || ! in_array( $fieldType, Question::VALID_FIELD_TYPES, true ) ) {
+		if ( '' === $label || mb_strlen( $label ) > Question::MAX_LABEL_LENGTH || ! in_array( $fieldType, Question::VALID_FIELD_TYPES, true ) ) {
 			return;
 		}
 

src/Registration/QuestionEndpoint.php

@@ -79,6 +79,9 @@ class QuestionEndpoint {
 		if ( '' === $label ) {
 			return $this->invalid( __( 'A question label is required.', 'unsupervised-schedular' ) );
 		}
+		if ( mb_strlen( $label ) > Question::MAX_LABEL_LENGTH ) {
+			return $this->invalid( $this->tooLongMessage( __( 'question', 'unsupervised-schedular' ), Question::MAX_LABEL_LENGTH ) );
+		}
 
 		$fieldType = Val::string( $request->get_param( 'field_type' ) ?? Question::FIELD_TEXT );
 		if ( ! in_array( $fieldType, Question::VALID_FIELD_TYPES, true ) ) {
@@ -118,9 +121,17 @@ class QuestionEndpoint {
 			return $this->invalid( __( 'Invalid field type.', 'unsupervised-schedular' ) );
 		}
 
+		$label = $request->has_param( 'label' ) ? sanitize_text_field( Val::string( $request->get_param( 'label' ) ) ) : $existing->label;
+		if ( '' === $label ) {
+			return $this->invalid( __( 'A question label is required.', 'unsupervised-schedular' ) );
+		}
+		if ( mb_strlen( $label ) > Question::MAX_LABEL_LENGTH ) {
+			return $this->invalid( $this->tooLongMessage( __( 'question', 'unsupervised-schedular' ), Question::MAX_LABEL_LENGTH ) );
+		}
+
 		$question = new Question(
 			offeringId: $existing->offeringId,
-			label:      $request->has_param( 'label' ) ? sanitize_text_field( Val::string( $request->get_param( 'label' ) ) ) : $existing->label,
+			label:      $label,
 			fieldType:  $fieldType,
 			options:    $request->has_param( 'options' ) ? $this->sanitizeOptions( $request->get_param( 'options' ) ) : $existing->options,
 			isRequired: $request->has_param( 'is_required' ) ? (bool) $request->get_param( 'is_required' ) : $existing->isRequired,
@@ -217,4 +228,16 @@ class QuestionEndpoint {
 	private function invalid( string $message ): \WP_Error {
 		return new \WP_Error( 'invalid_question', $message, [ 'status' => 400 ] );
 	}
+
+	/**
+	 * Build a uniform "too long" validation message for a named field.
+	 */
+	private function tooLongMessage( string $field, int $max ): string {
+		return sprintf(
+			/* translators: 1: field name, 2: maximum character count. */
+			__( 'The %1$s must be %2$d characters or fewer.', 'unsupervised-schedular' ),
+			$field,
+			$max
+		);
+	}
 }