fix(ui): expand session dialogs and repeat confirmation actions

frontend/src/shell/AppShell.tsx

@@ -117,8 +117,7 @@ export function AppShell({ canLogout }: AppShellProps) {
     resizing: sessionResizing,
     separatorProps: sessionSeparatorProps,
   } = useSessionPanelResize(containerRef, panelSession !== null);
-  // Publish the app area's horizontal geometry so viewport-fixed dialogs center on
-  // the application area rather than the whole browser window.
+  // Publish the visible app bounds for dialogs, including embedded portal layouts.
   useEffect(() => {
     const el = containerRef.current;
     if (!el) return;
@@ -127,16 +126,23 @@ export function AppShell({ canLogout }: AppShellProps) {
       const r = el.getBoundingClientRect();
       doc.style.setProperty("--app-area-left", `${r.left}px`);
       doc.style.setProperty("--app-area-width", `${r.width}px`);
+      const top = Math.max(0, r.top);
+      doc.style.setProperty("--app-area-top", `${top}px`);
+      doc.style.setProperty("--app-area-height", `${Math.max(0, Math.min(window.innerHeight, r.bottom) - top)}px`);
     };
     publish();
     const observer = typeof ResizeObserver === "undefined" ? null : new ResizeObserver(publish);
     observer?.observe(el);
     window.addEventListener("resize", publish);
+    window.addEventListener("scroll", publish, true);
     return () => {
       observer?.disconnect();
       window.removeEventListener("resize", publish);
+      window.removeEventListener("scroll", publish, true);
       doc.style.removeProperty("--app-area-left");
       doc.style.removeProperty("--app-area-width");
+      doc.style.removeProperty("--app-area-top");
+      doc.style.removeProperty("--app-area-height");
     };
   }, [containerRef]);
   const panelWidthsStyle = {