Fix review cycle 2 findings

- thread-sidebar: use callback-based modify+delete in handleDeleteFolder
  to properly clear folderId (Dexie ignores undefined in object-form modify)
- chat-page: clear artifact store on compare enter/exit/new transitions
- artifact-panel: remove redundant viewedContent from useEffect deps to
  prevent unnecessary re-syncs during store updates
- db.ts: use toArray()+sort() instead of sortBy() inside upgrade transaction
  for better Dexie compatibility
- thread-export: prefer modelType over modelId for compare-export filename
  suffix to differentiate LoRA compare pairs

studio/frontend/src/features/chat/chat-page.tsx

@@ -537,6 +537,7 @@ export function ChatPage(): ReactElement {
   );
   const handleNewCompare = useCallback(
     () => {
+      useArtifactStore.getState().clearArtifacts();
       setView({ mode: "compare", pairId: crypto.randomUUID() });
       useChatRuntimeStore.getState().setContextUsage(null);
     },
@@ -565,6 +566,7 @@ export function ChatPage(): ReactElement {
   const openSidebar = useCallback(() => setSidebarOpen(true), []);
 
   const enterCompare = useCallback(() => {
+    useArtifactStore.getState().clearArtifacts();
     setViewBeforeCompare((prev) => prev ?? view);
     setView({ mode: "compare", pairId: crypto.randomUUID() });
     useChatRuntimeStore.getState().setContextUsage(null);
@@ -572,6 +574,7 @@ export function ChatPage(): ReactElement {
 
   const exitCompare = useCallback(() => {
     if (!viewBeforeCompare) return;
+    useArtifactStore.getState().clearArtifacts();
     setView(viewBeforeCompare);
     setViewBeforeCompare(null);
     // Restore context usage from the active thread's last assistant message

studio/frontend/src/features/chat/components/artifact-panel.tsx

@@ -74,8 +74,10 @@ export const ArtifactPanel: FC = () => {
 
   // Sync local editor value when switching artifacts or versions
   useEffect(() => {
-    if (active) setLocalValue(viewedContent);
-  }, [active?.id, active?.activeVersion, viewedContent]);
+    if (!active) return;
+    setLocalValue(active.history[active.activeVersion] ?? active.content);
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [active?.id, active?.activeVersion]);
 
   // Cleanup copy timer on unmount
   useEffect(() => {

studio/frontend/src/features/chat/db.ts

@@ -62,7 +62,8 @@ db.version(4)
         .table("messages")
         .where("threadId")
         .equals(thread.id)
-        .sortBy("createdAt");
+        .toArray();
+      msgs.sort((a: MessageRecord, b: MessageRecord) => a.createdAt - b.createdAt);
       const firstUser = msgs.find(
         (m: MessageRecord) => m.role === "user",
       );

studio/frontend/src/features/chat/lib/thread-export.ts

@@ -102,7 +102,7 @@ function buildExportFilename(
 ): string {
   const base = sanitizeFilename(thread.title);
   const suffix = thread.pairId
-    ? `_${sanitizeFilename(thread.modelId || thread.modelType || "compare")}`
+    ? `_${sanitizeFilename(thread.modelType || thread.modelId || "compare")}`
     : "";
   return `${base}${suffix}.${ext}`;
 }

studio/frontend/src/features/chat/thread-sidebar.tsx

@@ -245,7 +245,9 @@ export function ThreadSidebar({
 
   const handleDeleteFolder = useCallback(async (folderId: string) => {
     await db.transaction("rw", db.threads, db.folders, async () => {
-      await db.threads.where("folderId").equals(folderId).modify({ folderId: undefined });
+      await db.threads.where("folderId").equals(folderId).modify((thread) => {
+        delete thread.folderId;
+      });
       await db.folders.delete(folderId);
     });
   }, []);