diff --git a/frontend-web/src/roundtable-planning/components/ArtifactPreviewModal.tsx b/frontend-web/src/roundtable-planning/components/ArtifactPreviewModal.tsx
index 1073a515..04beb374 100644
--- a/frontend-web/src/roundtable-planning/components/ArtifactPreviewModal.tsx
+++ b/frontend-web/src/roundtable-planning/components/ArtifactPreviewModal.tsx
@@ -1,4 +1,5 @@
 import React, { useCallback, useEffect, useMemo, useState } from "react";
+import { createPortal } from "react-dom";
 import type { ReactNode } from "react";
 import ReactMarkdown from "react-markdown";
 import remarkGfm from "remark-gfm";
@@ -214,7 +215,9 @@ export const ArtifactPreviewModal: React.FC<ArtifactPreviewModalProps> = ({
     [content],
   );
 
-  return (
+  // 经 portal 挂到 body：脱离会商页 <main>(`relative z-0`) 的层叠上下文，
+  // 否则 fixed 弹窗会被会商页头(z-40)/全局顶栏(z-45)盖住顶部。
+  return createPortal(
     <div
       className="fixed inset-0 z-[100] flex items-center justify-center bg-slate-900/40 backdrop-blur-sm p-6"
       onMouseDown={(e) => {
@@ -287,6 +290,7 @@ export const ArtifactPreviewModal: React.FC<ArtifactPreviewModalProps> = ({
           )}
         </div>
       </div>
-    </div>
+    </div>,
+    document.body,
   );
 };
diff --git a/frontend-web/src/roundtable-planning/components/Step3SummaryMode.tsx b/frontend-web/src/roundtable-planning/components/Step3SummaryMode.tsx
index b6a900f3..e16151cf 100644
--- a/frontend-web/src/roundtable-planning/components/Step3SummaryMode.tsx
+++ b/frontend-web/src/roundtable-planning/components/Step3SummaryMode.tsx
@@ -10,6 +10,7 @@
  * 互不影响（report 画 HTML 看板，summary 写 Markdown 报告 + 问答）。
  */
 import { useEffect, useMemo, useRef, useState, type FormEvent } from "react";
+import { createPortal } from "react-dom";
 import ReactMarkdown from "react-markdown";
 import remarkGfm from "remark-gfm";
 import {
@@ -1005,7 +1006,10 @@ function ContentModal({
   onClose: () => void;
   headerAction?: React.ReactNode;
 }) {
-  return (
+  // 经 portal 挂到 body：页面 <main> 是 `relative z-0`（浅蓝主题层叠基线），会把
+  // 内部 fixed 弹窗困在 z-0 层叠上下文里，被会商页头(z-40)/全局顶栏(z-45)盖住顶部。
+  // 挂到 body 后脱离该上下文，z-50 才真正盖在顶栏之上，弹窗标题栏正常显示。
+  return createPortal(
     <div
       className="fixed inset-0 z-50 flex items-center justify-center bg-black/40 backdrop-blur-[1px] p-4"
       onClick={onClose}
@@ -1029,7 +1033,8 @@ function ContentModal({
         </div>
         <div className="flex-1 overflow-y-auto p-5">{children}</div>
       </div>
-    </div>
+    </div>,
+    document.body,
   );
 }