fix(chat): enable in-place subtask navigation in embedded session-chat iframe (#2138)

packages/ui/src/components/chat/message/MessageBody.tsx

@@ -53,6 +53,7 @@ import {
     sendImplementationResponseToReviewer,
     sendReviewFeedbackToOriginal,
 } from '@/lib/reviewFlow';
+import { isEmbeddedSessionChat } from '@/components/layout/contextPanelEmbeddedChat';
 
 
 const CONTAIN_LAYOUT_STYLE = { contain: 'layout' as const, transform: 'translateZ(0)' };
@@ -252,7 +253,11 @@ const UserSubtaskPart: React.FC<{ part: SubtaskPartLike }> = ({ part }) => {
                         className="typography-meta text-muted-foreground hover:text-foreground transition-colors underline underline-offset-2"
                         onClick={() => {
                             if (!effectiveDirectory) return;
-                            if (isMobile || isVSCodeRuntime()) {
+                            // In contexts with no ContextPanel (embedded
+                            // session-chat iframe) or single-surface layouts
+                            // (mobile, VS Code), navigate in place. Otherwise
+                            // open a new side-panel tab.
+                            if (isEmbeddedSessionChat() || isMobile || isVSCodeRuntime()) {
                                 setCurrentSession(taskSessionID, effectiveDirectory);
                                 return;
                             }