Persist draft attachments across navigation

Wisp/Models/Local/SpriteChat.swift

@@ -15,6 +15,7 @@ final class SpriteChat {
     var messagesData: Data?
     var streamEventUUIDsData: Data?
     var draftInputText: String?
+    var draftAttachmentPaths: [String]?
     var isClosed: Bool
     var spriteCreatedAt: Date?
     var firstMessagePreview: String?

Wisp/ViewModels/ChatViewModel.swift

@@ -193,6 +193,12 @@ final class ChatViewModel {
             inputText = draft
         }
 
+        if attachedFiles.isEmpty, let paths = chat.draftAttachmentPaths, !paths.isEmpty {
+            attachedFiles = paths.map { path in
+                AttachedFile(name: (path as NSString).lastPathComponent, path: path)
+            }
+        }
+
         if let context = chat.forkContext, !context.isEmpty {
             let notice = ChatMessage(role: .system, content: [.text("Forked from a previous chat")])
             messages.insert(notice, at: 0)
@@ -203,6 +209,8 @@ final class ChatViewModel {
     func saveDraft(modelContext: ModelContext) {
         guard let chat = fetchChat(modelContext: modelContext) else { return }
         chat.draftInputText = inputText.isEmpty ? nil : inputText
+        let paths = attachedFiles.map(\.path)
+        chat.draftAttachmentPaths = paths.isEmpty ? nil : paths
         try? modelContext.save()
     }
 

Wisp/Views/SpriteDetail/Chat/ChatView.swift

@@ -121,6 +121,9 @@ struct ChatView: View {
         .onChange(of: viewModel.inputText) {
             viewModel.saveDraft(modelContext: modelContext)
         }
+        .onChange(of: viewModel.attachedFiles.count) {
+            viewModel.saveDraft(modelContext: modelContext)
+        }
         .onDisappear {
             viewModel.saveDraft(modelContext: modelContext)
         }

WispTests/ChatViewModelTests.swift

@@ -703,4 +703,64 @@ struct ChatViewModelTests {
         #expect(vm.inputText == "long prompt I want to come back to")
         #expect(vm.stashedDraft == nil)
     }
+
+    // MARK: - Draft attachment persistence
+
+    @Test func saveDraft_persistsAttachmentPaths() throws {
+        let ctx = try makeModelContext()
+        let (vm, chat) = makeChatViewModel(modelContext: ctx)
+
+        vm.attachedFiles = [
+            AttachedFile(name: "main.py", path: "/home/sprite/project/main.py"),
+            AttachedFile(name: "README.md", path: "/home/sprite/project/README.md"),
+        ]
+        vm.saveDraft(modelContext: ctx)
+
+        #expect(chat.draftAttachmentPaths == [
+            "/home/sprite/project/main.py",
+            "/home/sprite/project/README.md",
+        ])
+    }
+
+    @Test func saveDraft_clearsAttachmentPathsWhenEmpty() throws {
+        let ctx = try makeModelContext()
+        let (vm, chat) = makeChatViewModel(modelContext: ctx)
+
+        chat.draftAttachmentPaths = ["/home/sprite/project/old.py"]
+        vm.attachedFiles = []
+        vm.saveDraft(modelContext: ctx)
+
+        #expect(chat.draftAttachmentPaths == nil)
+    }
+
+    @Test func loadSession_restoresDraftAttachments() throws {
+        let ctx = try makeModelContext()
+        let (vm, chat) = makeChatViewModel(modelContext: ctx)
+
+        chat.draftAttachmentPaths = [
+            "/home/sprite/project/main.py",
+            "/home/sprite/project/photo.png",
+        ]
+
+        vm.loadSession(apiClient: SpritesAPIClient(), modelContext: ctx)
+
+        #expect(vm.attachedFiles.count == 2)
+        #expect(vm.attachedFiles[0].name == "main.py")
+        #expect(vm.attachedFiles[0].path == "/home/sprite/project/main.py")
+        #expect(vm.attachedFiles[1].name == "photo.png")
+        #expect(vm.attachedFiles[1].path == "/home/sprite/project/photo.png")
+    }
+
+    @Test func loadSession_doesNotOverwriteExistingAttachments() throws {
+        let ctx = try makeModelContext()
+        let (vm, chat) = makeChatViewModel(modelContext: ctx)
+
+        chat.draftAttachmentPaths = ["/home/sprite/project/persisted.py"]
+        vm.attachedFiles = [AttachedFile(name: "live.py", path: "/home/sprite/project/live.py")]
+
+        vm.loadSession(apiClient: SpritesAPIClient(), modelContext: ctx)
+
+        #expect(vm.attachedFiles.count == 1)
+        #expect(vm.attachedFiles[0].name == "live.py")
+    }
 }