diff --git a/src/components/flows/flow-builder.tsx b/src/components/flows/flow-builder.tsx
index d644d76..ae459da 100644
--- a/src/components/flows/flow-builder.tsx
+++ b/src/components/flows/flow-builder.tsx
@@ -17,7 +17,7 @@
  * are list-only and have no canvas analogue.
  */
 
-import { useCallback, useEffect, useMemo, useRef, useState } from 'react';
+import { Fragment, useCallback, useEffect, useMemo, useRef, useState } from 'react';
 import {
   CircleAlert,
   Plus,
@@ -39,6 +39,7 @@ import {
 import {
   DropdownMenu,
   DropdownMenuContent,
+  DropdownMenuGroup,
   DropdownMenuItem,
   DropdownMenuLabel,
   DropdownMenuSeparator,
@@ -589,21 +590,27 @@ function AddNodeButton({ onAdd }: { onAdd: (type: NodeType) => void }) {
       </DropdownMenuTrigger>
       <DropdownMenuContent align="end" className="border-border bg-popover">
         {groupNodeTypesByCategory(types).map((group, i) => (
-          <div key={group.id}>
+          // A DropdownMenuGroup (base-ui Menu.Group) is REQUIRED here:
+          // DropdownMenuLabel is base-ui's Menu.GroupLabel, which throws
+          // at render if it can't find a Menu.Group ancestor context. A
+          // plain <div> wrapper made opening this menu crash the page.
+          <Fragment key={group.id}>
             {i > 0 && <DropdownMenuSeparator />}
-            <DropdownMenuLabel className="text-muted-foreground text-[11px] font-semibold tracking-wider uppercase">
-              {group.label}
-            </DropdownMenuLabel>
-            {group.types.map((t) => {
-              const meta = NODE_META[t];
-              return (
-                <DropdownMenuItem key={t} onClick={() => onAdd(t)}>
-                  <meta.icon className={cn('h-3.5 w-3.5', meta.color)} />
-                  {meta.label}
-                </DropdownMenuItem>
-              );
-            })}
-          </div>
+            <DropdownMenuGroup>
+              <DropdownMenuLabel className="text-muted-foreground text-[11px] font-semibold tracking-wider uppercase">
+                {group.label}
+              </DropdownMenuLabel>
+              {group.types.map((t) => {
+                const meta = NODE_META[t];
+                return (
+                  <DropdownMenuItem key={t} onClick={() => onAdd(t)}>
+                    <meta.icon className={cn('h-3.5 w-3.5', meta.color)} />
+                    {meta.label}
+                  </DropdownMenuItem>
+                );
+              })}
+            </DropdownMenuGroup>
+          </Fragment>
         ))}
       </DropdownMenuContent>
     </DropdownMenu>
diff --git a/src/components/flows/flow-canvas.tsx b/src/components/flows/flow-canvas.tsx
index 29bea17..10e668b 100644
--- a/src/components/flows/flow-canvas.tsx
+++ b/src/components/flows/flow-canvas.tsx
@@ -36,7 +36,7 @@
  * list view reads.
  */
 
-import { useCallback, useEffect, useMemo, useRef, useState } from 'react';
+import { Fragment, useCallback, useEffect, useMemo, useRef, useState } from 'react';
 import {
   applyNodeChanges,
   Background,
@@ -87,6 +87,7 @@ import {
 import {
   DropdownMenu,
   DropdownMenuContent,
+  DropdownMenuGroup,
   DropdownMenuItem,
   DropdownMenuLabel,
   DropdownMenuSeparator,
@@ -737,37 +738,43 @@ function CanvasAddNodeButton() {
         className="border-border bg-popover w-[268px] p-1.5"
       >
         {groupNodeTypesByCategory(ADD_NODE_TYPES).map((group, i) => (
-          <div key={group.id}>
+          // DropdownMenuGroup (base-ui Menu.Group) is REQUIRED: the
+          // DropdownMenuLabel below is base-ui's Menu.GroupLabel, which
+          // throws at render without a Menu.Group ancestor. A plain <div>
+          // here crashed the page when this menu opened (issue #336).
+          <Fragment key={group.id}>
             {i > 0 && <DropdownMenuSeparator />}
-            <DropdownMenuLabel className="text-muted-foreground px-2 py-1.5 text-[11px] font-semibold tracking-wider uppercase">
-              {group.label}
-            </DropdownMenuLabel>
-            {group.types.map((t) => {
-              const meta = NODE_META[t];
-              return (
-                <DropdownMenuItem
-                  key={t}
-                  onClick={() => handleAdd(t)}
-                  className="gap-3 py-2"
-                >
-                  <NodeIconChip
-                    type={t}
-                    size={28}
-                    iconSize={16}
-                    className="rounded-md"
-                  />
-                  <span className="flex flex-col">
-                    <span className="text-popover-foreground text-[13px] font-semibold">
-                      {meta.label}
+            <DropdownMenuGroup>
+              <DropdownMenuLabel className="text-muted-foreground px-2 py-1.5 text-[11px] font-semibold tracking-wider uppercase">
+                {group.label}
+              </DropdownMenuLabel>
+              {group.types.map((t) => {
+                const meta = NODE_META[t];
+                return (
+                  <DropdownMenuItem
+                    key={t}
+                    onClick={() => handleAdd(t)}
+                    className="gap-3 py-2"
+                  >
+                    <NodeIconChip
+                      type={t}
+                      size={28}
+                      iconSize={16}
+                      className="rounded-md"
+                    />
+                    <span className="flex flex-col">
+                      <span className="text-popover-foreground text-[13px] font-semibold">
+                        {meta.label}
+                      </span>
+                      <span className="text-muted-foreground text-[11.5px]">
+                        {meta.blurb}
+                      </span>
                     </span>
-                    <span className="text-muted-foreground text-[11.5px]">
-                      {meta.blurb}
-                    </span>
-                  </span>
-                </DropdownMenuItem>
-              );
-            })}
-          </div>
+                  </DropdownMenuItem>
+                );
+              })}
+            </DropdownMenuGroup>
+          </Fragment>
         ))}
       </DropdownMenuContent>
     </DropdownMenu>
diff --git a/src/components/ui/dropdown-menu-group-label.test.tsx b/src/components/ui/dropdown-menu-group-label.test.tsx
new file mode 100644
index 0000000..998c366
--- /dev/null
+++ b/src/components/ui/dropdown-menu-group-label.test.tsx
@@ -0,0 +1,36 @@
+import { describe, it, expect } from 'vitest'
+import React from 'react'
+import { renderToStaticMarkup } from 'react-dom/server'
+
+import { DropdownMenuGroup, DropdownMenuLabel } from './dropdown-menu'
+
+/**
+ * Regression for issue #336 — "clicking Add node reloads the page".
+ *
+ * DropdownMenuLabel is base-ui's Menu.GroupLabel, which reads a required
+ * Menu.Group context and THROWS at render when it's missing. The flow
+ * builder's add-node menu wrapped its labels in a plain <div> instead of
+ * a DropdownMenuGroup, so opening the menu crashed the whole page. These
+ * tests pin the contract so the div-wrapper regression can't come back.
+ */
+describe('DropdownMenuLabel requires a DropdownMenuGroup ancestor', () => {
+  it('throws when rendered without a group (the #336 crash)', () => {
+    expect(() =>
+      renderToStaticMarkup(
+        React.createElement(DropdownMenuLabel, null, 'Messaging'),
+      ),
+    ).toThrow()
+  })
+
+  it('renders when wrapped in a DropdownMenuGroup (the fix)', () => {
+    expect(() =>
+      renderToStaticMarkup(
+        React.createElement(
+          DropdownMenuGroup,
+          null,
+          React.createElement(DropdownMenuLabel, null, 'Messaging'),
+        ),
+      ),
+    ).not.toThrow()
+  })
+})