Protocols and Associated Existential Types - Compiler and/or user problem?

Why is this ok …

        let noCrash = controller.composer

        let noCrashExtraStep = noCrash.document.title

But this is not?  (Causes compiler crash — nonzero exit)

        let crash = controller.composer.document.title

Is this a bug in the compiler or am I missing some logic about protocols and associated types?

Many thanks for any advice and also to the people who work on the Swift compiler.  

Cheers

Ventura / Xcode 14.1 beta 2

import SwiftUI

// VIEWS
@main
struct CrashingApp: App {
@StateObject var controller = ComposerController(composer: ConcreteComposer())
    var body: some Scene {
        WindowGroup {
            ContentView()
                .environmentObject(controller)
        }
    }  
}


struct ContentView: View {
    @EnvironmentObject var controller: ComposerController

    var body: some View {


        //  This line cannot be built without a crash
        let crash = controller.composer.document.title

        
        //  If it's broken in two it works fine
        let noCrash = controller.composer
        let noCrashExtraStep = noCrash.document.title

        Text(noCrashExtraStep)
    }
}


// CONTROLLER
class ComposerController: ObservableObject {   
    var composer: any ComposerProtocol
    init(composer: any ComposerProtocol) {self.composer = composer }
}


// PROTOCOLS
protocol ComposerProtocol {
    associatedtype DocumentType: DocumentProtocol
    var document: DocumentType {get set}
}


protocol DocumentProtocol {
    var title: String { get set }
}


// CONCRETE TYPES
struct ConcreteComposer: ComposerProtocol {
    init() {document = ConcreteDocument()}
    var document: ConcreteDocument
}

struct ConcreteDocument: DocumentProtocol {
    var title: String = "Title"
}