iMessage extension runs old compiled code on device instead of new code in debug mode in Xcode

Why is it that when I change to code in MessagesViewController in an iMessage extension the old compiled code runs instead on my connected iPhone device?

I have tried to fix the problem by deleting the DerivedData folder in the Xcode folder on my Mac mini that runs Xcode. I have run Option + Product->Clean Build Folder in the Xcode menu. I have completely removed the containing app on the iPhone device, which also removes the iMessage extension. I have done all of those things combined, and it doesn't fix the problem.

This is the old compiled code that the device actually runs:

        guard let conversation = activeConversation else { fatalError("Expected a conversation") }
        
        // Create a new message with the same session as any currently selected message.
        let message = composeMessage(with: sticker, caption: "messageCaption", session: conversation.selectedMessage?.session)
        
        // Add the message to the conversation.
        conversation.insert(message) { error in
            if let error = error {
                print(error)
            }
        }

This is the new code that the device is supposed to run in debug mode in Xcode:

        guard let conversation = activeConversation else { fatalError("Expected a conversation") }
        
        conversation.insertText("Hello there!") {
            (error: Error?) in
            print("completionHandler insert(text:_:)")
        }