Book title

A title is not a String that any caller may invent. BookTitle.parse is the only constructor that produces one. The private constructor means a test, a use case, and a mapper cannot build an empty title by calling BookTitle('').

This file imports the domain exception and nothing else. It does not import Serverpod. It is not a spy enum and it is not a column.

Create lib/src/domain/book/value_objects/book_title.dart:

import '../../shared/exceptions/validation_failure.dart';

/// A book title the shelf will store. Construct it only through [parse].
class BookTitle {
  const BookTitle._(this.value);

  final String value;

  static const maxLength = 200;

  static BookTitle parse(String raw) {
    final trimmed = raw.trim();
    if (trimmed.isEmpty) {
      throw const ValidationFailure('Title is required');
    }
    if (trimmed.length > maxLength) {
      throw const ValidationFailure('Title is too long');
    }
    return BookTitle._(trimmed);
  }
}

maxLength is a real limit a caller needs. Two hundred characters is enough for a title and short enough that a pasted page does not become one. The entity will store value, the checked string, so the rest of the server does not unwrap a BookTitle on every read. The value object still owns the rule.

Next: reading status.