Feature Chat Module

// Factory method with dependency injection
public func makeChatViewModel(conversationID: UUID) -> ChatViewModel {
    ChatViewModel(
        conversationID: conversationID,
        messageRepository: messageRepository,  // SwiftData repositories
        llmClient: llmClient                     // Proxy or Echo client
    )
}

// Create dual-style chat view (both UIs with switcher)
public func makeDualStyleChatView(
    conversationID: UUID,
    onRequireSubscription: (() -> Void)? = nil
) -> DualStyleChatView {
    let viewModel = makeChatViewModel(conversationID: conversationID)
    
    return DualStyleChatView(
        viewModel: viewModel,
        onRequireSubscription: onRequireSubscription
    )
}

@MainActor
@Observable
class ChatHistoryViewModel {
    var conversations: [ConversationDTO]
    var searchText: String
    var filteredConversations: [ConversationDTO]
    
    func createConversation() async -> UUID
    func renameConversation(id: UUID, title: String) async
    func deleteConversation(id: UUID) async
}

// In ChatViewModel
for try await chunk in llmClient.streamResponse(messages: messages) {
    currentResponse += chunk
    // UI updates automatically via @Observable
}

// InfinitePaginator handles:
// - Cursor-based pagination
// - Reverse chronological order
// - No duplicate messages
// - Smooth scrolling

class InfinitePaginator<Item, Cursor> {
    func loadNextPage() async throws -> [Item]
    var hasMore: Bool
    var isLoading: Bool
}

// In DesignSystemColors.xcassets:
// - BubbleUser.colorset (user message color)
// - BubbleAssistant.colorset (AI message color)

// All chat styles update automatically!

// Add to ChatView:
.contextMenu {
    Button("Copy", systemImage: "doc.on.doc") {
        UIPasteboard.general.string = message.text
    }
    Button("Regenerate", systemImage: "arrow.clockwise") {
        await viewModel.regenerateResponse(messageID: message.id)
    }
    Button("Delete", systemImage: "trash", role: .destructive) {
        await viewModel.deleteMessage(id: message.id)
    }
}

// In ChatViewModel
let systemPrompt = LLMMessage(
    role: .system,
    content: """
    You are a Swift expert.
    Provide clear answers with code examples.
    """
)

let messages = [systemPrompt] + history + [userMessage]

// In ChatHistoryViewModel
func searchMessages(query: String) async -> [MessageDTO] {
    try await messageRepository.search(
        query: query,
        limit: 50
    )
}

struct TypingIndicatorView: View {
  @State private var isVisible = false
  var body: some View { /* minimal dots animation */ }
}
// TODO: wire to ChatViewModel.isTyping (throttle: 600ms)