How do I write this #Predicate?

I have two Models which are defined (simplified) as follows:

@Model final class Book {
    var id: UUID = UUID()
    var title: String = ""
    var authors: [Author]? = []
}

@Model final class Author {
    var id: UUID = UUID()
    var name: String ""
    @Relationship(inverse: \Book.authors) var books: [Book]? = []
}

Both Book.authors and Author.books are defined as optionals to satisfy the requirements of CloudKit, although it is clear from the above that neither is ever actually nil.

I am trying to write a #Predicate that finds objects of type Book with a title that matches a specified title and with an author that matches a specified author. The function I'd like to write looks something like this:

func find(title: String, author: Author, 
          with context: ModelContext) -> Book? {
    let same = ComparisonResult.orderedSame
    let predicate = #Predicate<Book> { book in 
        book.title.caseInsensitiveCompare(title) == same &&
        book.authors!.contains(where: { $0.id == author.id })
    }
    let descriptor = FetchDescriptor<Book>(predicate: predicate)
    return try? context.fetch(descriptor).first
}

This function fails to compile inside the expansion of the #Predicate macro with a very long error message:

Cannot convert value of type 
(a long 'PredicateExpresions....')
(aka
(another log 'PredicateExpressions....'))
to closure result type 'any StandardPredicateExpression<Bool>'

I don't understand. How can I write this predicate so that it will both compile and work? I know how to work around this problem, but would like to both deepen my understanding of Swift and SwiftData and to avoid the (inelegant) workaround.