ios: add chat fork actions

ios/Packages/Sybil/Tests/SybilTests/SybilTests.swift

@@ -13,6 +13,9 @@ private struct MockClientCallSnapshot: Sendable {
     var listSearches = 0
     var createChat = 0
     var getChat = 0
+    var forkChat = 0
+    var lastForkChatID: String?
+    var lastForkMessageID: String?
     var updateChatTitle = 0
     var suggestChatTitle = 0
     var updateChatStar = 0
@@ -43,6 +46,7 @@ private actor MockSybilClient: SybilAPIClienting {
     private let chatDetails: [String: ChatDetail]
     private let searchDetails: [String: SearchDetail]
     private let createChatResponse: ChatSummary?
+    private let forkChatResponse: ChatSummary?
     private let updateChatTitleResponses: [String: ChatSummary]
     private let suggestChatTitleResponses: [String: ChatSummary]
     private let updateChatStarResponses: [String: ChatSummary]
@@ -74,6 +78,7 @@ private actor MockSybilClient: SybilAPIClienting {
         chatDetails: [String: ChatDetail] = [:],
         searchDetails: [String: SearchDetail] = [:],
         createChatResponse: ChatSummary? = nil,
+        forkChatResponse: ChatSummary? = nil,
         updateChatTitleResponses: [String: ChatSummary] = [:],
         suggestChatTitleResponses: [String: ChatSummary] = [:],
         updateChatStarResponses: [String: ChatSummary] = [:],
@@ -87,6 +92,7 @@ private actor MockSybilClient: SybilAPIClienting {
         self.chatDetails = chatDetails
         self.searchDetails = searchDetails
         self.createChatResponse = createChatResponse
+        self.forkChatResponse = forkChatResponse
         self.updateChatTitleResponses = updateChatTitleResponses
         self.suggestChatTitleResponses = suggestChatTitleResponses
         self.updateChatStarResponses = updateChatStarResponses
@@ -220,6 +226,16 @@ private actor MockSybilClient: SybilAPIClienting {
         return detail
     }
 
+    func forkChat(chatID: String, messageID: String?) async throws -> ChatSummary {
+        snapshot.forkChat += 1
+        snapshot.lastForkChatID = chatID
+        snapshot.lastForkMessageID = messageID
+        guard let forkChatResponse else {
+            throw UnexpectedClientCall()
+        }
+        return forkChatResponse
+    }
+
     func updateChatTitle(chatID: String, title: String) async throws -> ChatSummary {
         snapshot.updateChatTitle += 1
         guard let summary = updateChatTitleResponses[chatID] else {
@@ -775,6 +791,63 @@ private func makeCompletionToolCall(
     #expect(viewModel.errorMessage == nil)
 }
 
+@MainActor
+@Test func wholeChatForkAddsReturnedChatToWorkspace() async throws {
+    let date = Date(timeIntervalSince1970: 1_700_000_160)
+    let source = makeChatSummary(id: "chat-source", date: date)
+    var forked = makeChatSummary(id: "chat-fork", date: date.addingTimeInterval(10))
+    forked.title = "Fork of Chat chat-source"
+    forked.parentChatId = source.id
+    forked.titleGenerationPending = true
+    let client = MockSybilClient(forkChatResponse: forked)
+    let viewModel = SybilViewModel(settings: testSettings(named: #function)) { _ in client }
+    viewModel.isAuthenticated = true
+    viewModel.isCheckingSession = false
+    viewModel.chats = [source]
+    viewModel.workspaceItems = [WorkspaceItem(chat: source)]
+    viewModel.selectedItem = .chat(source.id)
+
+    let result = await viewModel.forkChat(chatID: source.id)
+
+    let snapshot = await client.currentSnapshot()
+    #expect(snapshot.forkChat == 1)
+    #expect(snapshot.lastForkChatID == source.id)
+    #expect(snapshot.lastForkMessageID == nil)
+    #expect(result == forked)
+    #expect(viewModel.chats.first == forked)
+    #expect(viewModel.workspaceItems.first == WorkspaceItem(chat: forked))
+    #expect(viewModel.selectedItem == .chat(source.id))
+    #expect(!viewModel.isForkingChat)
+    #expect(viewModel.errorMessage == nil)
+}
+
+@MainActor
+@Test func responseForkPassesAssistantMessageID() async throws {
+    let date = Date(timeIntervalSince1970: 1_700_000_165)
+    let source = makeChatSummary(id: "chat-source", date: date)
+    var forked = makeChatSummary(id: "response-fork", date: date.addingTimeInterval(10))
+    forked.title = "Fork of 'A useful response'"
+    forked.parentChatId = source.id
+    forked.titleGenerationPending = true
+    let client = MockSybilClient(forkChatResponse: forked)
+    let viewModel = SybilViewModel(settings: testSettings(named: #function)) { _ in client }
+    viewModel.isAuthenticated = true
+    viewModel.isCheckingSession = false
+    viewModel.chats = [source]
+    viewModel.workspaceItems = [WorkspaceItem(chat: source)]
+
+    let result = await viewModel.forkChat(chatID: source.id, messageID: "assistant-message")
+
+    let snapshot = await client.currentSnapshot()
+    #expect(snapshot.forkChat == 1)
+    #expect(snapshot.lastForkChatID == source.id)
+    #expect(snapshot.lastForkMessageID == "assistant-message")
+    #expect(result == forked)
+    #expect(viewModel.sidebarItems.contains(where: { $0.selection == .chat(forked.id) }))
+    #expect(!viewModel.isForkingChat)
+    #expect(viewModel.errorMessage == nil)
+}
+
 @MainActor
 @Test func starringItemsUpdatesSidebarState() async throws {
     let date = Date(timeIntervalSince1970: 1_700_000_175)