// ==============================================================
        // NATIVE SAVE FUNCTION (With Array/String Fixes)
        // ==============================================================
        public function ajax_save_user_interaction() {
            check_ajax_referer('dd_app_auth_nonce', 'security');
            if (!is_user_logged_in()) wp_send_json_error();

            $user_id = get_current_user_id();
            $type = sanitize_text_field($_POST['interaction_type']);
            $ref = sanitize_text_field(wp_unslash($_POST['reference']));
            $meta_key = '_dd_user_' . $type . 's';
            
            // 1. Force clean unserialization in case of old DB artifacts
            $raw_data = get_user_meta($user_id, $meta_key, true);
            if (is_string($raw_data)) {
                $raw_data = maybe_unserialize($raw_data);
            }
            $existing_data = is_array($raw_data) ? $raw_data : array();

            if ($type === 'note') {
                $text = isset($_POST['note_text']) ? wp_kses_post(wp_unslash($_POST['note_text'])) : '';
                $tags = isset($_POST['note_tags']) ? sanitize_text_field(wp_unslash($_POST['note_tags'])) : '[]';
                $existing_data[$ref] = array(
                    'timestamp' => current_time('mysql'),
                    'text'      => $text,
                    'tags'      => json_decode($tags, true)
                );
            } elseif ($type === 'highlight') {
                $style = isset($_POST['highlight_style']) ? sanitize_text_field($_POST['highlight_style']) : '';
                // THE FIX: Save as a flat string, NOT an array, so class-dd-app-formatters.php can read it!
                $existing_data[$ref] = $style;
            } elseif ($type === 'bookmark') {
                 $title = isset($_POST['bookmark_title']) ? sanitize_text_field($_POST['bookmark_title']) : 'Bookmark';
                 $existing_data[$ref] = array('title' => $title, 'timestamp' => current_time('mysql'));
            }

            // Actively hunt and destroy any ghost notes in the entire array before saving
            if ($type === 'note') {
                foreach ($existing_data as $k => $v) {
                    if (is_array($v) && isset($v['text'])) {
                        $raw_test = strip_tags(html_entity_decode($v['text'], ENT_QUOTES | ENT_HTML5, 'UTF-8'));
                        $nuked_test = preg_replace('/[^a-zA-Z0-9]/', '', $raw_test);
                        $has_tags = !empty($v['tags']);
                        
                        if (empty($nuked_test) && !$has_tags) {
                            unset($existing_data[$k]);
                        }
                    }
                }
            }

            update_user_meta($user_id, $meta_key, $existing_data);
            wp_send_json_success();
        }

        // ==============================================================
        // NATIVE DELETE FUNCTION (With Array/String Fixes)
        // ==============================================================
        public function ajax_delete_user_interaction() {
            check_ajax_referer('dd_app_auth_nonce', 'security');
            if (!is_user_logged_in()) wp_send_json_error();

            $user_id = get_current_user_id();
            $type = sanitize_text_field($_POST['interaction_type']);
            $ref = sanitize_text_field(wp_unslash($_POST['reference']));
            $meta_key = '_dd_user_' . $type . 's';

            // 1. Force clean unserialization in case of old DB artifacts
            $raw_data = get_user_meta($user_id, $meta_key, true);
            if (is_string($raw_data)) {
                $raw_data = maybe_unserialize($raw_data);
            }
            $existing_data = is_array($raw_data) ? $raw_data : array();

            $normalized_ref = preg_replace('/[^a-z0-9]/', '', strtolower($ref));
            
            foreach ($existing_data as $k => $v) {
                if (preg_replace('/[^a-z0-9]/', '', strtolower($k)) === $normalized_ref) {
                    unset($existing_data[$k]);
                }
            }
            
            // Clean ghost notes safely
            if ($type === 'note') {
                foreach ($existing_data as $k => $v) {
                    if (is_array($v) && isset($v['text'])) {
                        $raw_test = strip_tags(html_entity_decode($v['text'], ENT_QUOTES | ENT_HTML5, 'UTF-8'));
                        $nuked_test = preg_replace('/[^a-zA-Z0-9]/', '', $raw_test);
                        if (empty($nuked_test) && empty($v['tags'])) {
                            unset($existing_data[$k]);
                        }
                    }
                }
            }

            // THE FIX: If the array is entirely empty, literally delete the meta row so no empty arrays get cached
            if (empty($existing_data)) {
                delete_user_meta($user_id, $meta_key);
            } else {
                update_user_meta($user_id, $meta_key, $existing_data);
            }
            
            wp_send_json_success();
        }