fix: isolate startup tools and preview dialogs

frontend/src/components/client-message-dialog.tsx

@@ -120,7 +120,15 @@ function actionVariant(style: MessageActionStyle) {
  * Renders messages requested by the agent through the generic Client Tool
  * channel. The tool result is held until the user chooses an action.
  */
-export function ClientMessageDialog({ preview }: { preview: VoicePreview }) {
+export function ClientMessageDialog({
+  preview,
+  container,
+  contained = false,
+}: {
+  preview: VoicePreview;
+  container?: HTMLElement | null;
+  contained?: boolean;
+}) {
   const { registerClientTool, status } = preview;
   const [message, setMessage] = useState<MessageState | null>(null);
   const pendingRef = useRef<PendingMessage | null>(null);
@@ -163,6 +171,7 @@ export function ClientMessageDialog({ preview }: { preview: VoicePreview }) {
 
   return (
     <Dialog
+      modal={!contained}
       open={message !== null}
       onOpenChange={(open) => {
         if (!open && message?.dismissible) complete("dismissed");
@@ -170,6 +179,8 @@ export function ClientMessageDialog({ preview }: { preview: VoicePreview }) {
     >
       <DialogContent
         className="gap-5 sm:max-w-md"
+        portalContainer={container}
+        contained={contained}
         showCloseButton={message?.dismissible ?? true}
         onEscapeKeyDown={(event) => {
           if (!message?.dismissible) event.preventDefault();