[codex] Fix async conversation restore decoding and add targeted unit tests

Package.swift

@@ -40,6 +40,11 @@ let package = Package(
             exclude: [
                 "Yemma4.entitlements",
             ]
+        ),
+        .testTarget(
+            name: "Yemma4Tests",
+            dependencies: ["Yemma4"],
+            path: "Tests/Yemma4Tests"
         )
     ]
 )

Tests/Yemma4Tests/ConversationStoreTests.swift

@@ -0,0 +1,80 @@
+import Foundation
+import XCTest
+import ExyteChat
+@testable import Yemma4
+
+@MainActor
+final class ConversationStoreTests: XCTestCase {
+    func testAsyncRestoreDecodesIso8601DatesFromPersistedConversation() async throws {
+        let fileManager = FileManager.default
+        let storageRoot = fileManager.temporaryDirectory.appendingPathComponent(
+            "ConversationStoreTests-\(UUID().uuidString)",
+            isDirectory: true
+        )
+        let defaultsName = "ConversationStoreTests-\(UUID().uuidString)"
+        let defaults = UserDefaults(suiteName: defaultsName)
+        XCTAssertNotNil(defaults)
+
+        guard let defaults else {
+            return
+        }
+
+        defer {
+            defaults.removePersistentDomain(forName: defaultsName)
+            try? fileManager.removeItem(at: storageRoot)
+        }
+
+        let store = ConversationStore(
+            fileManager: fileManager,
+            defaults: defaults,
+            storageRootOverride: storageRoot
+        )
+
+        let createdAt = Date(timeIntervalSince1970: 1_700_000_000)
+        let message = ChatMessage(
+            id: "message-1",
+            user: .user,
+            status: .sent,
+            createdAt: createdAt,
+            text: "Hello",
+            attachments: []
+        )
+        let draftAttachment = Attachment(
+            id: "attachment-1",
+            url: storageRoot.appendingPathComponent("draft.png"),
+            type: .image
+        )
+
+        let conversationID = store.saveConversation(
+            id: nil,
+            messages: [message],
+            draftText: "Draft text",
+            draftAttachments: [draftAttachment]
+        )
+
+        let reloadedStore = ConversationStore(
+            fileManager: fileManager,
+            defaults: defaults,
+            storageRootOverride: storageRoot
+        )
+
+        await reloadedStore.loadIndexIfNeeded()
+
+        XCTAssertEqual(reloadedStore.conversations.count, 1)
+        XCTAssertEqual(reloadedStore.conversations.first?.id, conversationID)
+        XCTAssertEqual(reloadedStore.conversations.first?.messageCount, 1)
+        XCTAssertEqual(reloadedStore.conversations.first?.hasDraft, true)
+        XCTAssertEqual(reloadedStore.currentConversationID, conversationID)
+
+        let snapshot = await reloadedStore.loadConversationAsync(id: conversationID)
+
+        XCTAssertNotNil(snapshot)
+        XCTAssertEqual(snapshot?.id, conversationID)
+        XCTAssertEqual(snapshot?.title, "Hello")
+        XCTAssertEqual(snapshot?.draftText, "Draft text")
+        XCTAssertEqual(snapshot?.draftAttachments.count, 1)
+        XCTAssertEqual(snapshot?.messages.count, 1)
+        XCTAssertEqual(snapshot?.messages.first?.createdAt, createdAt)
+        XCTAssertEqual(snapshot?.messages.first?.text, "Hello")
+    }
+}

Tests/Yemma4Tests/StreamingRendererTests.swift

@@ -0,0 +1,16 @@
+import XCTest
+@testable import Yemma4
+
+final class StreamingRendererTests: XCTestCase {
+    func testSanitizeRemovesControlMarkersAndThinkingBlocks() {
+        let raw = "<start_of_turn>model\n<|channel>thinking<channel|>Hello<end_of_turn>user"
+
+        XCTAssertEqual(StreamingRenderer.sanitize(raw), "Hello")
+    }
+
+    func testStreamingVisibleTextAndStopDetection() {
+        XCTAssertEqual(StreamingRenderer.streamingVisibleText("Hello wor"), "Hello")
+        XCTAssertTrue(StreamingRenderer.shouldStopStreaming(tailOf: "prefix <|end_of_turn|>"))
+        XCTAssertFalse(StreamingRenderer.shouldStopStreaming(tailOf: "prefix Hello"))
+    }
+}

Yemma4/Appearance.swift

@@ -287,7 +287,7 @@ struct UtilityBackground: View {
 }
 
 private struct ProgressiveHeaderHeightKey: PreferenceKey {
-    static var defaultValue: CGFloat = 0
+    static let defaultValue: CGFloat = 0
 
     static func reduce(value: inout CGFloat, nextValue: () -> CGFloat) {
         value = nextValue()

Yemma4/Services/ConversationStore.swift

@@ -490,6 +490,7 @@ final class ConversationStore {
     private func loadIndexAsync() async {
         let decoded = await Task.detached(priority: .utility) { [indexURL] in
             let decoder = JSONDecoder()
+            decoder.dateDecodingStrategy = .iso8601
             guard let data = try? Data(contentsOf: indexURL) else {
                 return [ConversationMetadata]()
             }
@@ -638,6 +639,7 @@ final class ConversationStore {
         decoder.dateDecodingStrategy = .iso8601
         return decoder
     }()
+
 }
 
 private enum ConversationSnapshotLoader {
@@ -647,6 +649,7 @@ private enum ConversationSnapshotLoader {
         }
 
         let decoder = JSONDecoder()
+        decoder.dateDecodingStrategy = .iso8601
         guard let conversation = try? decoder.decode(PersistedConversation.self, from: data) else {
             return nil
         }

Yemma4/Views/ChatView.swift

@@ -2037,7 +2037,7 @@ private struct StartupLoadingAnimationView: View {
 }
 
 private struct ConversationBottomOffsetPreferenceKey: PreferenceKey {
-    static var defaultValue: CGFloat = 0
+    static let defaultValue: CGFloat = 0
 
     static func reduce(value: inout CGFloat, nextValue: () -> CGFloat) {
         value = nextValue()

docs/testing.md

@@ -0,0 +1,17 @@
+# Testing Notes
+
+The highest-value pure-Swift coverage added for this task lives under `Tests/Yemma4Tests/`:
+
+- `ConversationStoreTests.swift` exercises the async restore path against an ISO-8601 persisted conversation.
+- `StreamingRendererTests.swift` covers the sanitizer and stop-stream detection helpers.
+
+Run the package-backed XCTest target with:
+
+```bash
+xcodebuild test \
+  -workspace .swiftpm/xcode/package.xcworkspace \
+  -scheme Yemma4 \
+  -destination 'platform=iOS Simulator,name=Yemma Preview 17 Pro Max'
+```
+
+The app target can still be validated separately with the project build path when you want a simulator compile of the shipped shell.